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1
Chen, Hua, Tian Yu Zhang, X. Y. Lu, Su Qiu Jia, and Zhi Long Chai. "A Study on Characteristics of TiH2-Al-Nb Alloyed Powder During High Energy Ball Milling." Materials Science Forum 688 (June 2011): 1–5. http://dx.doi.org/10.4028/www.scientific.net/msf.688.1.
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In this paper, TiH2-47Al-5Nb (at.%) and TiH2-47Al-7Nb(at.%) alloys were mixed and synthesized using TiH2, Al and Nb powders. The composition and morphology evolution of the mixed powder were systematically investigated during high energy ball milling. The results show obvious that structure change of the particle during milling, and amorphous, TiAl, Ti3Al and Ti2Al phases at nanoscale are formed. The addition of Nb shows an active influence on the decomposition of TiH2and formation of TiAl-intermetallics. Compare with Ti-Al system alloy, the forming process of TiAl-intermetallics for TiH2-Al-Nb system alloy is different and slower. Ti2Al metastable phase formed after ball milling for 15 h in our experiments.
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Jia, Lei, and Long Fan. "Effects of Hydrogen on Diffusion Bonding of TiAl-Based Intermetallics with Hydrogenated Ti6AI4V Alloy Interlayer Containing 0.5wt% Hydrogen." Advanced Materials Research 750-752 (August 2013): 624–29. http://dx.doi.org/10.4028/www.scientific.net/amr.750-752.624.
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The direct diffusion bonding of TiAl-based intermetallics and the diffusion bonding of TiAl-based intermetallics with hydrogenated Ti6Al4V alloys interlayer containing 0.5wt% hydrogen were carried out. The effects of hydrogen on diffusion bonding were investigated by SEM, EPMA, XRD, TEM and TG/DSC. The good joint was formed at 850°C for 15 min under a pressure of 15MPa at the diffusion bonding of TiAl-based intermetallics with hydrogenated Ti6Al4V alloy interlayer containing 0.5wt% hydrogen, and the room temperature shear strength was up to 290MPa. Relatived to direct diffusion bonding of TiAl-based intermetallic, the bonding parameters decreased prodigiously. According to the experimental observations, the Ti6Al4V alloy hydrogenated 0.5 wt% consisted of close-packed hexagonal structure α′ martensite phase, face-centered cubic structure of δ-phase, α and βH structure. The lamellar δ hydride and βH phase disappeared after bonding, and the lamellar (α+β) structure were formed. Because of the dehydrogenation during bonding, metastable hydride containing low hydrogen appeared. The remaining hydrogen in Ti6Al4V alloy at high temperatures enhanced the capacity of the plastic deformation and the diffusion ability of the alloy elements, which helped to improve the spread of the atom.
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Góral, Marek, Tadeusz Kubaszek, Marcin Kobylarz, Marcin Drajewicz, and Maciej Pytel. "Thermal Barrier Coating Deposited Using the PS-PVD Method on TiAl-Nb-Mo Intermetallic Alloy with Different Types of Bond Coats." Solid State Phenomena 320 (June 30, 2021): 60–65. http://dx.doi.org/10.4028/www.scientific.net/ssp.320.60.
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TiAl intermetallics can be considered an alternative for conventional nickel superalloys in the high-temperature application. A TBC (Thermal Barrier Coatings) with ceramic topcoat with columnar structure obtained using EB-PVD (electron beam physical vapour deposition) is currently used to protect TiAl intermetallics. This article presents the new concept and technology of TBC for TiAl intermetallic alloys. Bond coats produced using the slurry method were obtained. Si and Al nanopowders (70 nm) were used for water-based slurry preparation with different composition of solid fraction: 100 wt.% of Al, 50 wt.% Al + 50 wt.% Si and pure Si. Samples of TNM-B1 (TiAl-Nb-Mo) TiAl intermetallic alloy were used as a base material. The samples were immersed in slurries and dried. The samples were heat treated in Ar atmosphere at 1000 °C for 4 h. The outer ceramic layer was produced using the new plasma spray physical vapour deposition (PS-PVD) method. The approximately 110 μm thick outer ceramic layers contained yttria-stabilised zirconium oxide. It was characterised by a columnar structure. Differences in phase composition and structures were observed in bond coats. The coatings obtained from Al-contained slurry were approximately 30 μm thick and consisted of two zones: the outer contained the TiAl3 phase and the inner zone consisted of the TiAl2 phase. The second bond coat produced from 50 wt.% Al + 50 wt.% Si slurry was characterised by a similar thickness and contained the TiAl2 phase, as well as titanium silicides. The bond coat formed from pure-Si slurry had a thickness < 10 μm and contained up to 20 at % of Si. This suggests the formation of different types of titanium silicides and Ti-Al phases. The obtained results showed that PS-PVD method can be considered as an alternative to the EB-PVD method, which is currently applied for deposition a columnar structure ceramic layer. On the other hand, the use of nanopowder for slurry production is problematic due to the smaller thickness of the produced coating in comparison with conventional micro-sized slurries.
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Jang, Ok Jun, Cheol-Woong Yang, and Dong Bok Lee. "Transmission Electron Microscopy Characterization of Thermomechanically Treated Al3Ti–(8, 10, 15)% Cr Intermetallics." Microscopy and Microanalysis 19, S5 (August 2013): 89–94. http://dx.doi.org/10.1017/s1431927613012403.
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AbstractThe ordered L12-type Al3Ti–(8, 10, 15)% Cr intermetallic compounds, namely, Al67Ti25Cr8, Al66Ti24Cr10, and Al59Ti26Cr15, were prepared by induction melting followed by thermomechanical treatment. Their microstructure, compositional variation, and crystal structure were characterized using X-ray diffraction, optical microscopy, and scanning and transmission electron microscopy equipped with energy-dispersive spectroscopy. The Al67Ti25Cr8 alloy consisted of the L12-Al3Ti matrix and precipitates of α2-Ti3Al, D022-Al3Ti, and γ-TiAl. The Al66Ti24Cr10 and Al59Ti26Cr15 alloys consisted of the L12-Al3Ti matrix and grains of α-TiAl and β-Cr.
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Chen, Wen Zhe, Kai Ping Peng, Kuang Wu Qian, and Hai Cheng Gu. "Effects of Forming Processing on Mechanical Properties of Ti-48Al-2Mn-2Nb Intermetallics." Key Engineering Materials 297-300 (November 2005): 471–76. http://dx.doi.org/10.4028/www.scientific.net/kem.297-300.471.
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Ti-48Al-2Mn-2Nb alloy was produced by “centrifugal spray deposition” (CSD), and then hot isostatic pressing (HIP) was employed to remove the porosity formed by CSD. The effects of CSD and HIP processing on the mechanical properties and microstructure of the TiAl alloy were investigated. The results show that the CSD and HIP processing can both improve the strength, plasticity of the TiAl alloy, and the tensile elongation values of the CSD or HIP samples are around 3%, which are better than those of as-cast TiAl alloys in room temperature. Especially, they show more excellent compressive properties at ambient temperature with a compressive ratio of 33.8% and compressive strength of 2210MPa for the CSD samples, and a compressive ratio of 37.8% and compressive strength of 2348MPa for the HIP samples. The CSD processing also improves the fracture toughness of TiAl alloy, which is much higher than that of the HIP processing, while the HIP processing seems to be beneficial the ductility and plasticity as having a duplex structure. The effects of CSD and HIP processing on microstructure and properties of TiAl alloys are discussed to understand the deformation and fracture process of the alloy.
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Ramos, Ana Sofia, M. Teresa Vieira, Sonia Simões, Filomena Viana, and Manuel F. Vieira. "Joining of Superalloys to Intermetallics Using Nanolayers." Advanced Materials Research 59 (December 2008): 225–29. http://dx.doi.org/10.4028/www.scientific.net/amr.59.225.
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Joining nickel based superalloys to gamma-TiAl intermetallic alloys will contribute to a more efficient application of these advanced materials, particularly in extreme environments. In this study, Inconel alloy and gamma-TiAl are joined using as filler alternated nanolayer thin films deposited onto each base material. The nanolayers consisted in Ni/Al exothermic reactive multilayer thin films with periods of 5 and 14 nm deposited by d.c. magnetron sputtering in order to improve the adhesion to the substrates and to avoid the reaction between Ni and Al. Diffusion bonding experiments with multilayer coated alloys were performed under vacuum at 800°C by applying 50 MPa during 1h. Bonding was achieved in large areas of the centre of the joints where regions without cracks or pores were produced, especially when using multilayer thin films with a 14 nm modulation period.
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Beretta, Stefano, Mauro Filippini, Luca Patriarca, and Silvia Sabbadini. "Analysis of Fatigue Damage Accumulation in TiAl Intermetallics." Key Engineering Materials 592-593 (November 2013): 30–35. http://dx.doi.org/10.4028/www.scientific.net/kem.592-593.30.
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In this work, a Ti-48Al-2Cr-2Nb alloy obtained with a additive manufacturing technique by electron beam melting (EBM) has been examined by conducting high cycle fatigue tests both with plain specimens and with specimens with artificially introduced defects with the objective of studying the growth behavior of small cracks. A consistent model for predicting the fatigue endurance strength of specimens with artificial defects is proposed, based on the Kitagawa diagram and taking into account of the presence of inherent microstructural features of the studied intermetallic alloy. Thus, the origin of fatigue failures due to intermetallic phases and orientation of lamellar colonies was investigated by means of micromechanical analysis through the use of high-resolution Digital Image Correlation (DIC). The local strain heterogeneities were measured out of the load frame by means of an optical microscope at high magnifications. The strain maps were then overlaid with the images of the microstructure and detailed analyses were performed to investigate the features of the microstructure where high local strain heterogeneities arise. High local residual plastic strains were measured inside lamellar colonies, which are detected as the precursor to fatigue crack initiation. The measure of the residual strains also provides further information on the role of the intermetallic phases on the fatigue behaviour of γ-TiAl alloys.
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Zhang, Kai Feng, Shao Song Jiang, Zhen Lu, Guo Feng Wang, Chun Ping Zhang, and Ji Liang Yu. "Superplasticity of Nb-Si-Fe and TiAl Intermetallics Synthesized by Powder Metallurgy." Materials Science Forum 735 (December 2012): 113–19. http://dx.doi.org/10.4028/www.scientific.net/msf.735.113.
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Nb-16Si-2Fe alloy were processed by mechanical alloying (MA) and hot pressing sintering (HPS). Microstructure analysis revealed the presence of four phases: Nb solid solution (Nbss), three kinds of intermetallics Nb3Si, Nb5Si3 and Nb4Fe3Si5. The maximum elongation over 500% was obtained at 1450°C and strain rate of 2.31×10-4s-1. TiAl powder pre-alloyed was carried out on pulse current sintering equipment (PCS) with high heating rate. The effect of heating rate on microstructures and high temperature ductility was investigated. The results show that relatively high heating rate is beneficial for obtaining fine grained microstructures. And the resultant intermetallic alloy with equiaxed near gamma structures exhibits superplasticity at relatively low temperature.
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Simas, Pablo, Thomas Schmoelzer, Svea Mayer, Maria L. Nó, Helmut Clemens, and Jose San Juan. "Relaxation Processes at High Temperature in TiAl-Nb-Mo Intermetallics." MRS Proceedings 1516 (2012): 41–46. http://dx.doi.org/10.1557/opl.2012.1576.
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ABSTRACTIn the last decades there was a growing interest in developing new light-weight intermetallic alloys, which are able to substitute the heavy superalloys at a certain temperature range. At present a new Ti-Al-Nb-Mo family, called TNM™ alloys, is being optimized to fulfill the challenging requirements. The aim of the present work was to study the microscopic mechanisms of defect mobility at high temperature in TNM alloys in order to contribute to the understanding of their influence on the mechanical properties and hence to promote the further optimization of these alloys. Mechanical spectroscopy has been used to study the internal friction and the dynamic modulus up to 1460 K of a TNM alloy under different thermal treatments. These measurements allow to follow the microstructural evolution during in-situ thermal treatments. A relaxation process has been observed at about 1050 K and was characterized as a function of temperature and frequency in order to obtain the activation parameters of the responsible mechanism. In particular, the activation enthalpy has been determined to be H= 3 eV. The results are discussed and an atomic mechanism is proposed to explain the observed relaxation process.
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Song, X. G., J. Cao, H. Y. Chen, Y. F. Wang, and J. C. Feng. "Brazing TiAl intermetallics using TiNi–V eutectic brazing alloy." Materials Science and Engineering: A 551 (August 2012): 133–39. http://dx.doi.org/10.1016/j.msea.2012.05.002.
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Henriques, V. A. R., A. C. S. M. Dutra, and C. A. A. Cairo. "Production of Aerospace Tial Intermetallics for High Temperature Applications by Powder Metallurgy." Materials Science Forum 727-728 (August 2012): 44–49. http://dx.doi.org/10.4028/www.scientific.net/msf.727-728.44.
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During the recent years, alloys based on the intermetallic compound TiAl have attracted a considerable interest as potential competitors to steels and superalloys. Gamma-TiAl alloys are potential replacements for nickel and conventional titanium alloys in hot sections of turbine engines, as well as in orbital platform vehicles. The alloy design and efficient routes of TiAl processing are important technological challenges. Powder metallurgy is a near net shape process that allows the parts production with complex geometry at low costs. In this work, samples of Ti-48Al-2Cr-2Nb (at.%) were prepared from elemental and pre-alloyed powders mixed for 2 h, followed by cold uniaxial and isostatic pressing and sintered between 800 up to 1400°C, for 1 h, under vacuum. After metallographic preparation, sintered samples were characterized by SEM (Scanning Electron Microscopy), density analyses and Vickers microhardness measurements. The results indicated the viability of the pre-alloyed route and the tendency of a full lamellar microstructure of alternating gamma and α2 phases in high sintering temperatures.
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Góral, Marek, Andrzej Gradzik, Jan Sieniawski, Ryszard Filip, Jan Sieniawski, and Małgorzata Wierzbinska. "The Influence of Activator on Vapour Phase Aluminizing of TiAl Intermetallics." Solid State Phenomena 227 (January 2015): 357–60. http://dx.doi.org/10.4028/www.scientific.net/ssp.227.357.
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The paper presents results of research into the aluminizing process of TiAl intermetallics. The substrate was Ti48Al2Cr2Nb intermetallic alloy. The BPX Pro 325S CVD system was used for aluminizing process. Used in the experimental were four types of activators: AlCl3, AlF3, ZrCl4and HfCl4. During the aluminizing process 2 kg of Al-Cr granules were put in a container. The deposition process was carried out in argon atmosphere for a duration of 4 hours at the temperature of 1000°C. The XRD and chemical analysis were conducted. The results showed than aluminide coatings contained TiAl2and TiAl2phases were formed using an AlF3activator. In other processes the amount of Al in the coatings was smaller than in the substrate. The obtained results showed that for the aluminizing process use of aluminum fluorides is necessary.
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Sequeiros, Elsa W., Anibal Guedes, Ana Maria Pires Pinto, Manuel F. Vieira, and Filomena Viana. "Microstructure and Strength of γ-TiAl Alloy/Inconel 718 Brazed Joints." Materials Science Forum 730-732 (November 2012): 835–40. http://dx.doi.org/10.4028/www.scientific.net/msf.730-732.835.
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Intermetallics and superalloys brazing development is a current topic owing the extending use of these alloys in industrial applications. In this work a γ-TiAl alloy was joined to Inconel 718 by active metal brazing, using Incusil-ABA as filler. Joining was performed at 730 °C, 830 °C and 930 °C, with a 10 min dwelling time. The interfaces were characterized by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and Electron Backscatter Diffraction (EBSD). For all processing conditions, the reaction between the base materials and the braze alloy produced multilayered interfaces. For all processing temperatures tested (Ag), (Cu), AlNi2Ti and AlCu2Ti were identified at the interface. Raising the brazing temperature increased the thickness of the interface and coarsened its microstructure. The increase of the extension of the interface was essentially due to the growth of the reaction layers formed near each base material, which were found to be mainly composed of intermetallic compounds. The mechanical behavior of the joints, at room temperature, was assessed by microhardness and shear tests. For all processing conditions the hardness decreases from periphery towards the Ag-rich centre of the joints. Brazing at 730 °C for 10 min produced the joints with the highest average shear strength (228±83 MPa). SEM and EDS analysis of the fracture surfaces revealed that fracture of joints always occurred across the interface, preferentially through the hard layer, essentially composed of AlNi2Ti, resulting from the reaction between Inconel 718 and the braze alloy.
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Kartavykh, A. V., S. Ganina, Dieter Grothe, Fabienne Lemoisson, and W. Herfs. "Numerical Simulation of TiAl-Nb Alloy Solidification Experiment in TEM 01-3M Facility Aboard MAXUS 8." Materials Science Forum 649 (May 2010): 223–28. http://dx.doi.org/10.4028/www.scientific.net/msf.649.223.
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The problem of numerical modeling of directional solidification of TiAl refractory intermetallics aboard the MAXUS 8 sounding rocket is considered. The research is of relevance to the FP6 Integrated project IMPRESS (Intermetallic Materials Processing in Relation to Earth and Space Solidification). Attention is paid to columnar-to-equiaxed microstructure transition (CET) phenomenon and mushy zone evolution in Ti-45.9Al-8Nb (at %) alloy being processed in TEM 01-3M high-temperature (up to 17000C) furnace. In this three-zone resistive furnace the “bent” temperature profile is applied with two strongly different axial thermal gradients, presumably allowing the achieving of CET conditions along the sample of 160 mm length. Temperature profile evolution is defined by power-down furnace operation. 2D-numerical study of heat transfer and realtime-scale solidification dynamics of TiAl-Nb under zero gravity approximation is performed. The approaches used for solution of Navier-Stokes equations and phase transition (Stefan) problem are briefly described. The solidification time is shown to be satisfying the 12-minute microgravity limit aboard a MAXUS. The position and the time at which CET may be triggered are predicted and confirmed in line with the Hunt diagram. The comparison is performed of model predictions with the real microstructure of TiAl-Nb reference sample solidified on-ground in TEM 01-3M facility.
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Hashimoto, Keizo. "Role of Ti/Al Ratio of Ti-Al-X (X=Cr, Nb, Ta and W) Intermetallics on High Temperature Tensile Properties." Materials Science Forum 783-786 (May 2014): 1136–41. http://dx.doi.org/10.4028/www.scientific.net/msf.783-786.1136.
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The mechanical properties of g-TiAl at elevated temperatures have been investigated extensively over the last 30 years. Designed alloys have been proposed from the first generation alloy (Ti-48Al-2Cr-2Nb) to the second, the third and the fourth generations. However, a decisive chemical composition of g-TiAl has not been agreed among researchers yet. The main reasons for this situation are difficulties in compositional control of Ti-Al-X-Y. In this paper, the high temperature tensile properties of g-TiAl alloy with lots of different composition have been examined from the room temperature to 1200C and the tensile strength data of those specimens have been summarized. It is clear that Ti/Al atomic ratio plays an important role on the behaviors of the high temperature strength since the Ti/Al atomic ratio is strongly related to the phase stabilities between g and a2phases in the binary Ti-Al phase diagram. A very narrow confine of a/a2atomic ratio exists in the specimens having the comparatively high tensile strength at the elevated temperatures. Moreover, additions of the third elements such as Cr, Nb, Ta and W to g-TiAl contribute on the increase of the tensile strength and the shift of the phase stability among a2, b and g phases. In order to utilize g-TiAl alloys in the various machine components at high temperatures, the severe process controls of melting, casting, thermo-mechanical treatments and heat treatments are indispensable.
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Simões, Sónia, Carlos Tavares, and Aníbal Guedes. "Joining of γ-TiAl Alloy to Ni-Based Superalloy Using Ag-Cu Sputtered Coated Ti Brazing Filler Foil." Metals 8, no. 9 (September 14, 2018): 723. http://dx.doi.org/10.3390/met8090723.
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Joining γ-TiAl alloy to Ni-based superalloy Hastelloy using Ag-Cu sputtered coated Ti foil as brazing filler was investigated in this study. Brazing experiments were performed at 900, 950, and 980 °C with a dwelling stage of 10 min in vacuum. The microstructure and the chemical composition of the resulting interfaces were analyzed by scanning electron microscopy (SEM) and by energy dispersive X-ray spectroscopy (EDS), respectively. Sound joints were produced after brazing at 980 °C, presenting a multilayered interface, consisting mainly of Ti-Al and Ti-Ni-Al intermetallics close to the γ-TiAl alloy, and of Ti-rich, Ti-Ni, and Cr-Ni-Mo rich phases near Hastelloy. The hardness of the interface, ranging from around 300 to 1100 HV0.01, is higher than both base materials, but no segregation of either Ag solid solution or coarse intermetallic particles was observed. Therefore, the developed brazing filler also avoids the need to perform post-brazing heat treatments that aim to eliminate detrimental extensive segregation of either soft phases or of hard and brittle compounds.
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Matsuura, Kiyotaka, Naoki Mizuta, Soshu Kirihara, Yoshinari Miyamoto, and Atsushi Yumoto. "Intermetallic Coating Using a 3-Dimensional Micro Welder." Materials Science Forum 631-632 (October 2009): 259–64. http://dx.doi.org/10.4028/www.scientific.net/msf.631-632.259.
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The authors have studied a new method of intermetallic coating using a small TIG welder. This method is based on a reaction between small liquid beads produced from very thin metal wire and the substrate metal surface. The authors designed a computer-aided 3-dimensional micro welder (3DMW) for a previous study on freeform fabrication of intermetallics, and have applied it to this study on intermetallic coating. In this study, a predetermined length of thin aluminum wire was fed onto the titanium substrate surface, and a spark was stricken from a thin electrode of a W-Ce2O3 alloy to make a small aluminum liquid bead on the titanium substrate surface and to simultaneously melt a small area of the substrate surface beneath the liquid bead. All process conditions had been programmed beforehand, including the length of the wire feeding per spark, the position of the electrode, electric power, movement of the stage holding the substrate, etc. The liquid bead containing aluminum and titanium rapidly solidified on the titanium substrate surface producing titanium aluminides on it. Repetition of the aluminum wire feeding, the electrode positioning and the spark striking produced a coating layer consisting of sub-layers of TiAl3, TiAl and Ti3Al from the surface side to the substrate side. Vickers hardness and wear resistance of the coated sample were remarkably improved.
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Akhonin, S. V., V. A. Berezos, and A. Yu Severyn. "ELECTRON-BEAM MELTING OF INGOTS OF TiAl SYSTEM INTERMETALLICS." MATEC Web of Conferences 321 (2020): 10004. http://dx.doi.org/10.1051/matecconf/202032110004.
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Performance of scientific-technical researches at the E. O. Paton Electric Welding Institute of the NAS of Ukraine have been directed on development of technology for manufacture of titanium aluminide –based alloys using the method of electron-beam melting (EBM). The mathematical models of heat state and evaporation of alloying elements in EBM were developed. The results of calculations of heat state using the mathematical model allowed determining a dependence of depth of liquid pool on different melting rates. The mathematical models of processes of evaporation in EBM of titanium aluminide ingots were used for plotting the nomograms, which help to determine the necessary content of alloying element of the alloy in the initial charge for acquiring the necessary concentration of this element in ingot at set technological parameters of melting. In scopes of designed mathematical models there were investigated different technological modes of electron-beam melting of ingots based on titanium aluminide. The optimum EBM modes, at which a solidification front approaches to flat, were determined. At that, more uniform distribution of the additives on ingot section and volume is provided as well as level of stressed state is reduced. The works were carried out on manufacture of titanium aluminide based-ingots with addition of refractory as well as volatile alloying elements. Composition and structure of produced ingots were examined. It is shown that electron-beam melting allows getting chemically homogeneous ingots based on titanium aluminide and is a perspective method for production of such class materials.
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Ghadyani, Mohammad, Claire Utton, and Panos Tsakiropoulos. "Microstructures and Isothermal Oxidation of the Alumina Scale Forming Nb1.45Si2.7Ti2.25Al3.25Hf0.35 and Nb1.35Si2.3Ti2.3Al3.7Hf0.35 Alloys." Materials 12, no. 5 (March 5, 2019): 759. http://dx.doi.org/10.3390/ma12050759.
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Coating system(s) will be required for Nb-silicide based alloys. Alumina forming alloys that are chemically compatible with the Nb-silicide based alloy substrate could be components of such systems. The intermetallic alloys Nb1.45Si2.7Ti2.25Al3.25Hf0.35 (MG5) and Nb1.35Si2.3Ti2.3Al3.7Hf0.35 (MG6) were studied in the cast, heat treated and isothermally oxidised conditions at 800 and 1200 °C to find out if they are αAl2O3 scale formers. A (Al/Si)alloy versus Nb/(Ti + Hf)alloy map, which can be considered to be a map for Multi-Principle Element or Complex Concentrated Nb-Ti-Si-Al-Hf alloys, and a [Nb/(Ti + Hf)]Nb5Si3 versus [Nb/(Ti + Hf)]alloy map were constructed making use of the alloy design methodology NICE and data from a previously studied alloy, and were used to select the alloys MG5 and MG6 that were expected (i) not to pest, (ii) to form αAl2O3 scale at 1200 °C, (iii) to have no solid solution, (iv) to form only hexagonal Nb5Si3 and (v) to have microstructures consisting of hexagonal Nb5Si3, Ti5Si3, Ti5Si4, TiSi silicides, and tri-aluminides and Al rich TiAl. Both alloys met the requirements (i) to (v). The alumina scale was able to self-heal at 1200 °C. Liquation in the alloy MG6 at 1200 °C was linked with the formation of a eutectic like structure and the TiAl aluminide in the cast alloy. Key to the oxidation of the alloys was the formation (i) of “composite” silicide grains in which the Nb5Si3 core was surrounded by the Ti5Si4 and TiSi silicides, and (ii) of tri-aluminides with high Al/Si ratio, particularly at 1200 °C and very low Nb/Ti ratio forming in-between the “composite” silicide grains. Both alloys met the “standard definition” of high entropy alloys (HEAs). Compared with HEAs with bcc solid solution and intermetallics, the VEC values of both the alloys were outside the range of reported values. The parameters VEC, and of Nb-Ti-Si-Al-Hf coating alloys and non-pesting Nb-silicide based alloys were compared and trends were established. Selection of coating alloys with possible “layered” structures was discussed and alloy compositions were proposed.
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Cai, Y. S., R. C. Liu, H. B. Ji, Y. Y. Cui, and R. Yang. "Vacuum brazing TiAl-based intermetallics using novel Ti–Fe–Mn eutectic brazing alloy." Intermetallics 136 (September 2021): 107274. http://dx.doi.org/10.1016/j.intermet.2021.107274.
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Xue, Zi Gong, Yuan Xun Huang, Yong Tian Wang, and Xiao Jing Hai. "Laser Remelting Effect on the Joint Property of Diffusion Bonding of TiAl Intermetallics and TC4 Alloy." Materials Science Forum 747-748 (February 2013): 77–84. http://dx.doi.org/10.4028/www.scientific.net/msf.747-748.77.
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The influence of laser remelting on the mechanical property and fracture behavior of the superplastic diffusion bonding between TiAl intermetallics and TC4 alloy was investigated. The joint bonded by the pre-remelted samples displayed well diffusion, but the mechanical properties of the joint should be further enhanced. The mechanical properties of the joint pre-remelted under the diffusion bonding conditions of 915/80MPa/1h are lower than that of the joint without remelting. After the heat treatment on pre-remelted joint sample at 860, the mechanical properties have been enhanced greatly.
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Ren, H. S., H. P. Xiong, B. Chen, S. J. Pang, X. Wu, Y. Y. Cheng, and B. Q. Chen. "Transient liquid phase diffusion bonding of Ti–24Al–15Nb–1Mo alloy to TiAl intermetallics." Materials Science and Engineering: A 651 (January 2016): 45–54. http://dx.doi.org/10.1016/j.msea.2015.10.075.
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Guedes, Anibal, Filomena Viana, Ana Maria Pires Pinto, and Manuel F. Vieira. "Diffusion Brazing of a γ-TiAl Alloy Using Tini 67: Microstructural Evolution of the Interface." Materials Science Forum 587-588 (June 2008): 425–29. http://dx.doi.org/10.4028/www.scientific.net/msf.587-588.425.
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A detail study focussing the microstructural evolution of the interfacial zone in the course of the processing of Ti-47Al-2Cr-2Nb joints using Tini 67 as filler alloy was carried out in this investigation. Experiments, aiming the understanding of the mechanisms that promote the melting of the braze alloy, were performed below the solidus temperature of the filler, at 750 and 900°C. Diffusion brazed samples were joined at 1000 and 1100°C, with no dwelling stage and subsequently quenched in water in order to frozen the microstructure formed at the bonding temperature. The interfaces were analysed by scanning electron microscopy (SEM) and by energy dispersive X-ray spectroscopy (EDS), respectively. In the course of the heating stage, several single phase layers were formed within the filler alloy due to the solid state interdiffusion of Ti and Ni atoms. At 900°C, the microstructure of the filler evolved form the initial Ti (α)/(Ni)/Ti/ (α) layers to a Ti (β)/Ti2Ni/TiNi/TiNi3/TiNi/Ti2Ni/Ti (β) layered microstructure. The filler alloy begun to melt due to the eutectic reaction between the contiguous layers composed of Ti (β) and Ti2Ni. After joining, the main phases detected at the interfaces were α2-Ti3Al, Ti-Ni-Al and Ti-Ni intermetallics. For joining at 1000°C, a substantial amount of residual filler (Ti2Ni and Ti (α) particles) was also detected at the central zone of the interface. No marked evidences of residual filler zones were noticed for joining at 1100°C; instead, a mixture α2-Ti3Al with Ti-Ni-Al or Ti2Ni intermetallics was detected at the centre of the interface.
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Sienkiewicz, Judyta, Seiji Kuroda, Hideyuki Murakami, Hiroshi Araki, Maciej Giżyński, and Krzysztof J. Kurzydłowski. "Fabrication and Oxidation Resistance of TiAl Matrix Coatings Reinforced with Silicide Precipitates Produced by Heat Treatment of Warm Sprayed Coatings." Journal of Thermal Spray Technology 27, no. 7 (September 5, 2018): 1165–76. http://dx.doi.org/10.1007/s11666-018-0751-x.
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Abstract Ti-Al-based intermetallics are promising candidates as coating materials for thermal protection systems in aerospace vehicles; they can operate just below the temperatures where ceramics are commonly used, and their main advantage is the fact that they are lighter than most other alloys, such as MCrAlY. Therefore, Ti-Al-Si alloy coatings with five compositions were manufactured by spraying pure Ti and Al-12 wt.% Si powders using warm spray process. Two-stage hot pressing at 600 and 1000 °C was applied to the deposits in order to obtain titanium aluminide intermetallic phases. The microstructure, chemical composition, and phase composition of the as-deposited and hot-pressed coatings were investigated using SEM, EDS, and XRD. Applying of hot pressing enabled the formation of dense coatings with porosity around 0.5% and hard Ti5(Si,Al)3 silicide precipitates. It was found that the Ti5(Si,Al)3 silicides existed in two types of morphologies, i.e., as large particles connected together and as small isolated particles dispersed in the matrix. Furthermore, the produced coatings exhibited good isothermal and cyclic oxidation resistance at a temperature of 750 °C for 100 h.
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Li, Shuai, Zhongying Liu, Yueqing Xia, Xingxing Wang, Peng He, Yongtao Jiu, Lianhui Jia, and Weimin Long. "Vacuum brazing TiAl intermetallics to GH3030 alloy with a multi-component Ti-based filler metal." Journal of Manufacturing Processes 70 (October 2021): 484–93. http://dx.doi.org/10.1016/j.jmapro.2021.09.001.
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Gil, A., E. Wallura, H. Grübmeier, and W. J. Quadakkers. "The influence of cooling rate during alloy casting on the oxidation behaviour of TiAl-based intermetallics." Journal of Materials Science 28, no. 21 (November 1993): 5869–74. http://dx.doi.org/10.1007/bf00365194.
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Doorbar, Phill, Mark Dixon, and Amit Chatterjee. "Aero-Engine Titanium from Alloys to Composites." Materials Science Forum 618-619 (April 2009): 127–34. http://dx.doi.org/10.4028/www.scientific.net/msf.618-619.127.
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The aero-engine has provided the major drive for the development of new improved titanium alloys in recent years. This paper covers these developments from the workhorse alloy Titanium 6/4 and it’s higher temperature stable mates through to the more exotic intermetallic materials and on to their reinforcement with ceramics. The use of Ti6/4 alloy is now widespread throughout the aero space industry providing a good combination of strength at moderate temperatures (~300°C) a relatively low density and a wide range of processing options ranging from castings to forgings to powder HIP and diffusion bonding. Alloy development for the aero-engine essentially concentrated on either increasing the temperature capability and creep resistance or increasing the strength at intermediate temperatures. Alloys such as Ti 6242 and IMI 834 were aimed at compressor disc applications with operation up to around 600°C. Improvements resulted from compositional control and thermal processing to optimize the microstructure for creep and fatigue. High strength intermediate temperature capability (~500°C) alloys were also developed (Ti6246) where higher levels of molybdenum balance the alpha strengthening additions. The drive for lighter weight led to the development of titanium intermetallic systems. Alloys such as 45-2-2XD and Alloy 7 have been the subject of much research and manufacturing development over the last 20 years, demonstrating that they are capable of operating at temperatures well above those of conventional titanium. More recently, alloys with higher additions of Nb and Ta have shown improved mechanical properties and offer promise to extend the application of TiAl above 700°C. In parallel with intermetallic developments combining titanium alloys with the extreme high strength of ceramic fibres has proved irresistible and many ways to produce titanium composites have been developed. The majority of application development has focused on Ti6/4 alloy as the matrix although other matrix alloys have been investigated and tested in U.S. engine demonstrators. Recently a combination of Ti-22Al-26Nb disks reinforced with orthorhombic MMC ran for over 100 hours in an engine test. However, none of these niche composite systems has yet made the transition into large volume production and the fibre reinforced Ti6/4 system probably offers the greatest potential for implementation. The main barrier to the take up of both advanced intermetallics and titanium composites is the cost of raw materials and processing. The challenge still exists to produce net shape components and provide weight savings at an acceptable cost. This will be the key to future exploitation.
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Sasaki, Tomohiro, Takahiro Yagi, Takehiko Watanabe, and Atsushi Yanagisawa. "Effect of Diffusion Condition for Aluminizing on TiAl Based Alloy." Materials Science Forum 706-709 (January 2012): 2571–76. http://dx.doi.org/10.4028/www.scientific.net/msf.706-709.2571.
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Diffusion treatments of TiAl-based alloys (49.1 at% Al) aluminum coated by thermal spray were carried out at the temperature range of 700°C-1100°C. The influence of the diffusion condition for the formation of intermetallic phases in the coating has been investigated. In the initial stage of diffusion treatment, TiAl3 was formed on the outermost surface by the diffusion between liquid aluminum and the substrate. In addition, an intermediate layer comprised of Ti2Al5 (at 1100°C), TiAl2 and Al diffused layer (Al-rich TiAl) was confirmed under the outermost layer. The maximum thickness of TiAl3 during the initial stage increases as the diffusion temperature decreases. In addition, the shape of TiAl3 layer was dependent on the diffusion temperature; the outermost layer without pores was confirmed at the temperature of 700°C. TiAl2 and Al-rich TiAl developed by solid-state diffusion from TiAl3 layer following a parabolic low. The activation energies for growth have been calculated to be 194 kJ/mol for TiAl2 and 292 kJ/mol for Al-rich TiAl.
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Li, Xiaoqiang, Li Li, Ke Hu, and Shengguan Qu. "Vacuum brazing of TiAl-based intermetallics with Ti–Zr–Cu–Ni–Co amorphous alloy as filler metal." Intermetallics 57 (February 2015): 7–16. http://dx.doi.org/10.1016/j.intermet.2014.09.010.
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Kommel, Lembit A. "Diffusion in the Interface Region of Ti/TiAl-Nb Bonding." Defect and Diffusion Forum 249 (January 2006): 193–200. http://dx.doi.org/10.4028/www.scientific.net/ddf.249.193.
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Diffusion in the interface regions of lightweight heatproof quality titanium and titanium/aluminum alloys was investigated. We studied the diffusion of aluminum from intermetallide to titanium alloy. The concentration of other chemical elements and microhardness has been measured in diffusion region formed in the solid titanium alloy. The interface region includes a transition zone from the initially solid Ti-alloy and the molten TiAl-Nb intermetallic substrate. The width of the interface region after diffusion bonding is 45-60 µm. The titanium content decreases and aluminum content increases starting from surface up to 120-150 µm in depth in solid titanium alloy. As a result of diffusion, the intermetallic Ti3Al thin layer was formed in the transition zone in the Ti-alloy substrate. The microporosity was also formed in the interface region.
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Pelic, B., D. Rafaja, Patrick J. Masset, H. J. Seifert, L. Bortolotto, Michael Schütze, G. Wolf, and I. Loeh. "Corrosion Behaviour of Ti-48Al-2Nb-2Cr Alloys." Defect and Diffusion Forum 323-325 (April 2012): 301–7. http://dx.doi.org/10.4028/www.scientific.net/ddf.323-325.301.
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γ-TiAl intermetallics are attractive materials for high-temperature structural applications in the aerospace and automobile industries. However, they show environmental embrittlement at elevated temperatures that is mainly related to their low high-temperature corrosion resistance. One way how to improve the high-temperature corrosion resistance is the deposition of protective coatings on the surface of the base material. In this study, samples of a Ti-Al alloy with the chemical composition Ti-48Al-2Cr-2Nb (at.%) were covered by physically vapour deposited (PVD), by metalorganic chemically vapour deposited (MOCVD) and by high-velocity oxy-fuel (HVOF) sprayed coatings. All coatings were based on the Ti-Al alloys and contained different amounts of alloying elements. The corrosion experiments were performed in molten salts containing 75 wt.% Na2SO4and 25 wt.% NaCl at 850°C up to 336 h. Both, PVD and CVD protected coatings reduced the changes in the mass of the samples over the corrosion time. Still, the formation of TiO2could not be avoided, as it was confirmed by glancing-angle X-ray diffraction experiments.
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Góral, Marek, Andrzej Nowotnik, and Jan Sieniawski. "The CVD Aluminizing of TiAl Intermetallics." Solid State Phenomena 203-204 (June 2013): 327–30. http://dx.doi.org/10.4028/www.scientific.net/ssp.203-204.327.
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The article presents the first attempt to CVD-aluminise alloys based on an intermetallic phase Ti48Al2Cr2Nb. Moreover, it includes initial results of producing VPA-deposited aluminide coating in industrial environment. Microstructure and phase analyses of the obtained coatings have been conducted. The chemical and phase composition analyses have revealed that the CVD-deposited coating was roughly 8 m thick, and composed of aluminium-rich TiAl phase, whereas the application of VPA method results in a coating which is approximately 18 m thick and consists of three layers made up of TiAl3, TiAl2 i TiAl phases. Both deposition processes were conducted with industrial equipment.
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Knaislová, Anna, Pavel Novák, Marcello Cabibbo, Lucyna Jaworska, and Dalibor Vojtěch. "Development of TiAl–Si Alloys—A Review." Materials 14, no. 4 (February 22, 2021): 1030. http://dx.doi.org/10.3390/ma14041030.
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This paper describes the effect of silicon on the manufacturing process, structure, phase composition, and selected properties of titanium aluminide alloys. The experimental generation of TiAl–Si alloys is composed of titanium aluminide (TiAl, Ti3Al or TiAl3) matrix reinforced by hard and heat-resistant titanium silicides (especially Ti5Si3). The alloys are characterized by wear resistance comparable with tool steels, high hardness, and very good resistance to oxidation at high temperatures (up to 1000 °C), but also low room-temperature ductility, as is typical also for other intermetallic materials. These alloys had been successfully prepared by the means of powder metallurgical routes and melting metallurgy methods.
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Staron, Peter, Andreas Stark, Norbert Schell, Petra Spoerk-Erdely, and Helmut Clemens. "Thermal Expansion of a Multiphase Intermetallic Ti-Al-Nb-Mo Alloy Studied by High-Energy X-ray Diffraction." Materials 14, no. 4 (February 4, 2021): 727. http://dx.doi.org/10.3390/ma14040727.
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Intermetallic γ-TiAl-based alloys are lightweight materials for high-temperature applications, e.g., in the aerospace and automotive industries. They can replace much heavier Ni-based alloys at operating temperatures up to 750 °C. Advanced variants of this alloy class enable processing routes that include hot forming. These alloys consist of three relevant crystallographic phases (γ-TiAl, α2-Ti3Al, βo-TiAl) that transform into each other at different temperatures. For thermo-mechanical treatments as well as for adjusting alloy properties required under service conditions, the knowledge of the thermal expansion behavior of these phases is important. Therefore, thermal expansion coefficients were determined for the relevant phases in a Ti-Al-Nb-Mo alloy for temperatures up to 1100 °C using high-energy X-ray diffraction.
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Emadinia, Omid, Aníbal Guedes, Carlos José Tavares, and Sónia Simões. "Joining Alumina to Titanium Alloys Using Ag-Cu Sputter-Coated Ti Brazing Filler." Materials 13, no. 21 (October 28, 2020): 4802. http://dx.doi.org/10.3390/ma13214802.
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The joining of alumina (Al2O3) to γ-TiAl and Ti6Al4V alloys, using Ag-Cu sputter-coated Ti brazing filler foil, was investigated. Brazing experiments were performed at 980 °C for 30 min in vacuum. The microstructure and chemical composition of the brazed interfaces were analyzed by scanning electron microscopy and by energy dispersive X-ray spectroscopy, respectively. A microstructural characterization of joints revealed that sound multilayered interfaces were produced using this novel brazing filler. Both interfaces are composed mainly of α-Ti, along with Ti2(Ag,Cu) and TiAg intermetallics. In the case of the brazing of γ-TiAl alloys, α2-Ti3Al and γ-TiAl intermetallics are also detected at the interface. Bonding to Al2O3 is promoted by the formation of a quite hard Ti-rich layer, which may reach a hardness up to 1872 HV 0.01 and is possibly composed of a mixture of α-Ti and Ti oxides. Hardness distribution maps indicate that no segregation of either soft or brittle phases occurs at the central regions of the interfaces or near the base Ti alloys. In addition, a smooth hardness transition was established between the interface of Al2O3 to either γ-TiAl or Ti6Al4V alloys.
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Dong, Jiawei, Kemin Zhang, Yang Cai, Zhimin Zhang, Yuan Lei, and Tao Zhang. "Formation of Ultrafine-Grained Ti3Al on a Ti48Al2Cr2Nb Intermetallic Alloy Induced by Pulsed Electron Beam Treatment." Journal of Nanomaterials 2015 (2015): 1–7. http://dx.doi.org/10.1155/2015/389594.
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The microstructure modifications, phase, and texture formations encountered in a TiAl based Ti48Al2Cr2Nb intermetallic alloy induced by the high current pulsed electron beam (HCPEB) treatment were carefully investigated using scanning electron microscope (SEM), X-ray diffraction (XRD), and electron backscattered diffraction (EBSD) techniques. The initial material contains the majorityγ-TiAl phase and the minorityα-Ti3Al phase. After the HCPEB treatment, the initialα-Ti3Al was dissolved into the melted layer and the very top surface is covered by ultrafine-grainedα-Ti3Al phase having thermal stress induced cracks. EBSD analyses showed thatα-Ti3Al phase on the very top surface has a001//ND fiber texture and its texture intensity increases with the number of pulses. The superfast thermal stress cycles and the selective evaporation induced by the HCPEB treatment account for the microstructure modifications and formations of ultrafineα-Ti3Al in the TiAl based intermetallic alloy.
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Basuki, Eddy, Fadhli Mohammad, Ahmad Fauzi, and Djoko Prajitno. "Hot Corrosion of Aluminide Coated Ti-Al-Cr-Nb-Zr-Y Intermetallic Alloys." Advanced Materials Research 1112 (July 2015): 363–66. http://dx.doi.org/10.4028/www.scientific.net/amr.1112.363.
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Pack aluminide coatings were performed on a Ti-Al-Cr-Nb alloy doped with zirconium and yttrium having two phase of a2-Ti3Al and g-TiAl microstructure. The high activity TiAl3-based coating was developed from aluminizing process carried out at 850°C for 25 hours in a pack containing 20%-wt Al, 2%wt NH4Cl, and 78%wt Al2O3. During applications at high temperatures, the coating can degrade due to the interaction between the coated system and the environment exhibit high corrosion potentials. This study investigates the hot corrosion behavior of high-activity aluminide coated Zr-Y doped a2-Ti3Al/g-TiAlCrNb intermetallic alloy at 700°C, 800°C, and 900°C in a mixture of 90% Na2SO4 and 10% NaCl. The experimental results showed that the addition of Zr and Y in the alloy reduces significantly the hot corrosion rate of the coating as resulted from the interdiffusion of these elements from the alloy to the coatings and influence the behavior of the TiAl3-based coatings.
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Sun, Yan Bo, Mao Wen Liu, Su Jing Ge, Feng Mei Ma, and Chao Li Ma. "Preparation of Multilayered Ti-Al Alloys by Solid Reaction." Materials Science Forum 747-748 (February 2013): 1–8. http://dx.doi.org/10.4028/www.scientific.net/msf.747-748.1.
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The multilayered materials with different combinations of Ti, Al and Ti-Al intermetallics were prepared by heat treatment and hot pressing (HP) with elemental foils. The microstructures and phase formation of the obtained samples were detected by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), energy dispersive spectroscopy (EDS) and X-ray diffractometer (XRD). When the HP is applied under the melt point of aluminum, aluminum is the only diffusive element across the oxide films on the surface of the initial foils; however, some unusual TiAl3 particles are found in the multilayered structure due to the broken of oxide films; after hot pressing for 4 hours, all the aluminum was consumed; many voids exist at the centerline of TiAl3 layers, which are mainly caused by Kirkendall effect and the difference of molar volumes between reactants and products; before the aluminum is completely consumed, TiAl3 is the only product in the solid reaction under the melting temperature of aluminum; however, other Ti-Al intermetallics like Ti3Al and TiAl are formed in the updated temperature diffusion after aluminum is consumed.
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Zhang, Yuan Bin, Huai Xue Li, and Kai Zhang. "Investigation of the Laser Melting Deposited TiAl Intermetallic Alloy on Titanium Alloy." Advanced Materials Research 146-147 (October 2010): 1638–41. http://dx.doi.org/10.4028/www.scientific.net/amr.146-147.1638.
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To improve the wear resistance of Titanium alloy, TiAl intermetallic claddings were fabricated on TC4 substrate using laser melting deposition technology. Optical microscope, scan electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction meter were applied to investigate the deposited TiAl layer and their interface with substrate. Using hardness tester and M-2000 wear testing machine, hardness, frictional coefficient and wear resistance of the TiAl layers and TC4 alloy were tested. It was indicated that the deposited TiAl layers were well integrated with TC4 substrate, γ-TiAl and Ti3Al dual phase microstructure was formed in the deposited layer. With higher hardness and lower friction coefficient, the deposited TiAl layer improved the wear resistance obviously comparing to TC4 titanium alloy substrate.
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Cho, Gue Serb, Kang Rae Lee, Kyeong Hwan Choe, and Kyong Whoan Lee. "In Situ Combustion Synthesis of Ti-Al Intermetallic Compounds in Al Alloy Casting Process." Advanced Materials Research 26-28 (October 2007): 527–30. http://dx.doi.org/10.4028/www.scientific.net/amr.26-28.527.
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Ti-Al intermetallic compounds are regarded as promising materials for the hightemperature structural and coating applications. We focused on the joining of Al casting alloy with Ti-Al intermetallic compounds by in-situ combustion synthesis to improve the surface properties of Al casting components. Microstructures and phase formation behavior of Ti-Al based intermetallic compounds synthesized by combustion reaction were analyzed using scanning electron microscope(SEM) equipped with energy dispersive x-ray spectroscopy (EDS) and x-ray diffractometer(XRD) in Ti-Al intermetallic compounds. Three kinds of titanium aluminides of Ti3Al, TiAl and TiAl3 were synthesized by the heat from the Al molten metal and a coating layer of intermetallic phase were formed simultaneously on solidifed Al alloy surface. The shapes and microstructures of reacted compacts were varied by mixing ratio of elemental powders. The TiAl3 intermetallic compound was observed in the compacts regardless of the mixing ratio of elemental powders. And the unreacted Ti powders were remained in the reacted compacts due to the big size of Ti powder and low exothermic heat of reaction between Ti and Al powders. The zone that poured Al alloy diffused into the reacted Ti-25at.%Al compact of about 200 μm thickness was formed at the interface by the reaction between liquid molten Al alloy and solid Ti powders in green compact.
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Moskal, G., M. Góral, Lucjan Swadźba, B. Mendala, and G. Jarczyk. "Characterization of TiAlSi Coating Deposited by Arc-PVD Method on TiAlCrNb Intermetallic Base Alloy." Defect and Diffusion Forum 237-240 (April 2005): 1153–56. http://dx.doi.org/10.4028/www.scientific.net/ddf.237-240.1153.
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Results of microstructural investigations of aluminide coatings modified by Si are presented in this work. Protective coating (TiAlSi type) was deposited by Arc-PVD. Thickness of the outside layer of deposited coating was 35µm and it contained TiAl3 phase modified by Si as a main component. The second layer was found as a transition area between the TiAl3 outside layer and the surface of TiAlCrNb substrate. Thickness of the inside sublayer was 5 µm. The diffusion treatment caused the progress of coating homogenisation from the point of view of phase and chemical composition. It was found that the coating consisted of the dominant TiAl3 phase and Ti5Si3 in thick outer sublayer and only TiAl2 phase in transition thin sublayer. Below the transition area, on the surface of TiAlCrNb substrate alloy, the layer of g−TiAl was found. The amount of silicides was increased in comparison with the coating only after the Arc-PVD process and the area of its presence had been removed in the outside direction of the coating.
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Dzogbewu, Thywill Cephas, and Willie Bouwer du Preez. "Additive Manufacturing of Ti-Based Intermetallic Alloys: A Review and Conceptualization of a Next-Generation Machine." Materials 14, no. 15 (August 2, 2021): 4317. http://dx.doi.org/10.3390/ma14154317.
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TiAl-based intermetallic alloys have come to the fore as the preferred alloys for high-temperature applications. Conventional methods (casting, forging, sheet forming, extrusion, etc.) have been applied to produce TiAl intermetallic alloys. However, the inherent limitations of conventional methods do not permit the production of the TiAl alloys with intricate geometries. Additive manufacturing technologies such as electron beam melting (EBM) and laser powder bed fusion (LPBF), were used to produce TiAl alloys with complex geometries. EBM technology can produce crack-free TiAl components but lacks geometrical accuracy. LPBF technology has great geometrical precision that could be used to produce TiAl alloys with tailored complex geometries, but cannot produce crack-free TiAl components. To satisfy the current industrial requirement of producing crack-free TiAl alloys with tailored geometries, the paper proposes a new heating model for the LPBF manufacturing process. The model could maintain even temperature between the solidified and subsequent layers, reducing temperature gradients (residual stress), which could eliminate crack formation. The new conceptualized model also opens a window for in situ heat treatment of the built samples to obtain the desired TiAl (γ-phase) and Ti3Al (α2-phase) intermetallic phases for high-temperature operations. In situ heat treatment would also improve the homogeneity of the microstructure of LPBF manufactured samples.
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Sasaki, Tomohiro, Takahiro Yagi, and Takehiko Watanabe. "Aluminizing of TiAl-Based Alloy Using Thermal Spray Coating." Materials Science Forum 654-656 (June 2010): 1884–87. http://dx.doi.org/10.4028/www.scientific.net/msf.654-656.1884.
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Aluminizing the surface of a TiAl-based alloy (49.1 at% Al) was carried out by thermally spraying a pure aluminum coating and subsequent diffusion treatment at 1100°C. The influence of the diffusion time for the formation of Ti-Al intermetallic phases in the coating layers and the oxidation resistance of the aluminized TiAl-based alloys were investigated. The layer formed on the outermost surface was comprised of the Al-rich intermetallic T2iAl5 and contained pores. On the other hand, an intermediate layer consisting of TiAl2 and TiAl was formed between the outermost layer and the substrate. The thickness of the outermost layer decreased as the diffusion time increased, while the thickness of the intermediate layer increased. In addition, the coating/substrate interface changed from a wavy to a linear form with the growth of the intermediate layer. The aluminized coating showed good oxidation resistance at 900°C for all diffusion times.
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Nakamura, Morihiko. "Fundamental Properties of Intermetallic Compounds." MRS Bulletin 20, no. 8 (August 1995): 33–39. http://dx.doi.org/10.1557/s0883769400045085.
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More than 25 years have passed since Intermetallic Compounds, edited by Westbrook, was published. Since that time, enormous advances have been made in the understanding and usage of intermetallic compounds. It is known that intermetallic compounds are generally brittle. Thus, alloys that contain intermetallics may also be brittle. However, many intermetallic compounds are known to have extraordinary functions and characteristics that are not observed in ordinary metals and alloys. Thus, they function as magnetic materials, superconductors, semiconductors, hydrogen absorbing alloys, shape memory alloys, and so on.Many high-strength structural alloys like maraging steels and duralumins are strengthened by fine precipitates of intermetallic phases. Nickel-based superalloys, which are used for airplane-engine parts, contain 60-70% of Ni3Al-based intermetallics by volume fraction and exhibit high strength at high temperatures. Hard metals, which are used for cutting tools, are composed of a large amount of hard but brittle intermetallics like WC and a small amount of ductile cobalt. Intermetallic compounds like TiAl are also investigated for their applications as structural materials where high strength at high temperatures is required.In a strict sense, intermetallic compounds are composed of two or more metallic elements. In a wider sense, they are composed of metallic and/or semimetallic elements. Each is characterized by an ordered arrangement of two or more kinds of atoms, that is, the formation of a superlattice, and have various kinds of interatomic bonding, ranging from metallic to covalent or ionic bonding. The ordering of atoms and the strong interatomic bonding result in many attractive properties for intermetallic compounds.
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Donchev, Alexander, Mathias Galetz, Svea Mayer, Helmut Clemens, and Michael Schütze. "The Use of Fluorine to Protect β-Solidifying γ-TiAl-Based Alloys against High-Temperature Oxidation." MRS Advances 2, no. 25 (2017): 1361–67. http://dx.doi.org/10.1557/adv.2017.170.
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ABSTRACTLight-weight alloys based on intermetallic titanium aluminides (TiAl) are structural materials considered for high-temperature applications, e.g. in aero engines or automotive engines. TiAl alloys of engineering interest consist of two phases, the γ-TiAl and the α2-Ti3Al-phase. Recent developments have led to the so-called TNM alloys (T = TiAl; N = Nb; M = Mo) with an Al-content of 43.5 at.%. These alloys also possess the disordered body centered cubic β-Ti(Al)-phase at elevated temperatures, which ensures a better hot-workability compared to conventional two-phase alloys. However, the relatively low Al content (< 45 at.%) limits the high-temperature capability due to reduced oxidation resistance. This impedes their application in a temperature range above 800°C. The present work shows how the fluorine effect counteracts this disadvantage due to the formation of a protective alumina layer. The performance of the TNM alloy with the nominal composition of Ti-43.5Al-4Nb-1Mo-0.1B (at.%) is compared with another TNM alloy variant containing additional elements, such as Si and C, and the so-called GE alloy (Ti-48Al-2Cr-2Nb; at.%), which is already in use for turbine blades. The results of isothermal and thermocyclic high-temperature exposure tests of untreated and fluorine treated specimens will be compared. The effect of composition and microstructure of the alloys on the oxidation behavior with and without fluorine treatment are discussed.
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Stark, A., Frank Peter Schimansky, and Helmut Clemens. "Texture Formation during Hot-Deformation of High-Nb Containing γ-TiAl Based Alloys." Solid State Phenomena 160 (February 2010): 301–6. http://dx.doi.org/10.4028/www.scientific.net/ssp.160.301.
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In this study texture and microstructure formation in high-Nb containing TiAl alloys during lab-scale compression experiments and “near conventional” forging on an industrial scale are investigated. The deformation temperatures range from 700 °C up to temperatures close to the α transus temperature (Tα = 1295 °C). Depending on the deformation conditions, the texture of the tetragonal γ-TiAl phase is formed by pure deformation components, components related to dynamic recrystallization, or transformation components. This changing corresponds with microstructural observations. The hexagonal phases α2-Ti3Al and α-Ti(Al) show a similar texture as it is known for Ti and Ti-base alloys after compressive deformation at elevated temperatures. In contrast to the γ texture, no significant change of the α/α2 texture was observed in the investigated temperature range. In the alloy with a composition of Ti-45Al-10Nb (in at.%) even deformation textures of ternary intermetallic phases, as the hexagonal ωo-Ti4Al3Nb and the cubic βo-TiAl(Nb) phase, respectively, were measured and analyzed.
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Clemens, Helmut, and Svea Mayer. "Advanced Intermetallic TiAl Alloys." Materials Science Forum 879 (November 2016): 113–18. http://dx.doi.org/10.4028/www.scientific.net/msf.879.113.
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Challenging issues concerning energy efficiency and environmental politics require novel approaches to materials design. A recent example with regard to structural materials is the emergence of lightweight intermetallic TiAl alloys. Their excellent high-temperature mechanical properties, low density, and high stiffness constitute a profile perfectly suitable for their application as advanced aero-engine turbine blades or as turbocharger turbine wheels in next-generation automotive engines. Advanced so-called 3rd generation TiAl alloys, such as the TNM alloy described in this paper, are complex multi-phase alloys which can be processed by ingot or powder metallurgy as well as precision casting methods. Each process leads to specific microstructures which can be altered and optimized by thermo-mechanical processing and/or subsequent heat treatments.
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Werner, Robert, Martin Schloffer, Emanuel Schwaighofer, Helmut Clemens, and Svea Mayer. "Thermodynamic Calculations of Phase Equilibria and Phase Fractions of a β-Solidifying TiAl Alloy using the CALPHAD Approach." MRS Proceedings 1516 (2012): 59–64. http://dx.doi.org/10.1557/opl.2012.1680.
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ABSTRACTThe CALPHAD (CALculation of PHAse Diagrams) method is widely recognized as a powerful tool in both scientific and industrial development of new materials and processes. For the implementation of consistent databases, where each phase is described separately, models are used which are based on physical principles and parameters assessed from experimental data. Such a database makes it possible to perform realistic calculations of thermodynamic properties of multi-component systems. However, a commercial available TiAl database can be applied for thermodynamic calculations to both conventional Ti-base alloys and complex intermetallic TiAl alloys to describe experimentally evaluated phase fractions as a function of temperature. In the present study calculations were done for a β-solidifying TiAl alloy with a nominal composition of Ti-43.5Al-4Nb-1Mo-0.1B (in at. %), termed TNMTM alloy. At room temperature this alloy consists of ordered γ-TiAl, α2-Ti3Al and β0-TiAl phases. At a certain temperature α2 and β0 disorder to α and β, respectively. Using the commercial database the thermodynamic calculations reflect only qualitative trends of phase fractions as a function of temperature. For more exact quantitative calculations the commercial available thermodynamic database had to be improved for TiAl alloys with high Nb (and Mo) contents, as recently reported for Nb-rich γ-TiAl alloys. Therefore, the database was modified by experimentally evaluated phase fractions obtained from quantitative microstructure analysis of light-optical and scanning electron micrographs as well as conventional X-ray diffraction after long-term heat treatments and by means of in-situ highenergy X-ray diffraction experiments. Based on the CALPHAD-conform thermodynamic assessment, the optimized database can now be used to correctly predict the phase equilibria of this multi-component alloying system, which is of interest for applications in automotive and aircraft engine industry.
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Basuki, Eddy, Djoko Prajitno, and Pawawoi. "Oxidation Behavior of Aluminide Coated Ti-Al-Cr-Nb-Zr-Y Alloys at High Temperatures." Solid State Phenomena 227 (January 2015): 345–48. http://dx.doi.org/10.4028/www.scientific.net/ssp.227.345.
Full textAbstract:
In this study the oxidation behavior of diffusion aluminide coating containing layers of TiAl3 and TiAl2, develop on a substrate of Zr-Y doped α2-Ti3Al/γ-TiAlCrNb intermetallic alloy using pack aluminizing method, was investigated isothermally at 800°C, 900°C, and 1000°C under atmospheric air pressure. The pack cementation was carried out at 850°C for 25 hours in a pack containing 20%-wt Al, 2%-wt NH4Cl, and 78%-wt Al2O3.The phases in the coatings and oxide layers were examined by optical and scanning electron microscopy as well as X-ray diffraction method, while chemical composition of the oxides and phases were examined with EDS attached on the SEM. The experimental results showed that the addition of Zr and Y increases the oxidation resistance of the coating by formation of complex oxides mainly of Al2O3 at the coating surfaces and sub-surface. Combination of oxidation and interdiffusion process cause transformation of TiAl3 layer to TiAl2 that decrease the oxidation resistance through the formation of TiO2 rod crystals on the junction between TiAl2 and Al2O3 in the outer layer.
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Ramos, Ana Sofia, M. Teresa Vieira, Sonia Simões, Filomena Viana, and Manuel F. Vieira. "Reaction-Assisted Diffusion Bonding of Advanced Materials." Defect and Diffusion Forum 297-301 (April 2010): 972–77. http://dx.doi.org/10.4028/www.scientific.net/ddf.297-301.972.
Full textAbstract:
The aim of this work is to join -TiAl intermetallics to Ni based superalloys by solid state diffusion bonding. The surface of the -TiAl alloys and Ni superalloys to be joined was prepared by magnetron sputtering with a few microns thick Ni/Al reactive multilayer thin films with nanometric modulation periods. Sound joining without cracks or pores is achieved along the central region of the bond, especially at 800°C and when a 14 nm period Ni/Al film is used as filler material. During the diffusion bonding experiments interdiffusion and reaction inside the Ni/Al multilayer thin film and between the interlayer film and the base materials is promoted with the formation of intermetallic phases. The final reaction product in the multilayer films is the B2-NiAl intermetallic phase. The interfacial diffusion layers between the base materials and the multilayer films should correspond to: 3-NiTiAl and 4-Ni2TiAl phases from the -TiAl side; Ni-rich aluminide and -phase from the Inconel side. These intermetallic phases are responsible for the hardness increase observed on the diffusion layers.