Journal articles: 'Martensitic transformations'

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Nagy, Erzsebet, Márton Benke, Árpád Kovács, and Valéria Mertinger. "Orientation Relations of Martensitic Transformations in FeMnCr Steels." Materials Science Forum 885 (February 2017): 165–70. http://dx.doi.org/10.4028/www.scientific.net/msf.885.165.

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The crystallographic orientation relations of phases forming during the martensitic transformation determine the properties of alloys. In TRIP/TWIP steels, the circumstances of thermomechanical treatment (e.g. temperature, deformation) define the forming of martensites of different origins. Due to the thermomechanical treatment, thermally induced martensite (εTH), strain induced martensite (εD) and α’ martensite phases are present in the samples besides the austenite. The proportion of martensites in the sample is defined by the parameters of treatment. The thermally and strain induced martensites which are simultaneously present in the alloy at room temperature can be differentiated by the orientation relations.The martensitic transformations were followed by different methods in FeMn alloys with different Cr content. The macroscopic crystallographic anisotropy was measured by X-ray diffraction method; the microscopic one was examined by EBSD. The cognition of phenomenon observed in the texture image in different scales helps determine the possible origin of martensites.

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Adiguzel, Osman. "Martensitic Transformation and Microstructural Characteristics in Copper Based Shape Memory Alloys." Key Engineering Materials 510-511 (May 2012): 105–10. http://dx.doi.org/10.4028/www.scientific.net/kem.510-511.105.

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Martensitic transformations are first order solid state phase transitions and occur in the materials on cooling from high temperature. Shape memory effect is an unusual property exhibited by certain alloy systems, and based on martensitic transformation. The shape memory property is characterized by the recoverability of previously defined shape or dimension when they are subjected to variation of temperature. The shape memory effect is facilitated by martensitic transformation, and shape memory properties are intimately related to the microstructures of the materials. Martensitic transformations occur as martensite variant with the cooperative movement of atoms on {110}β - type plane of austenite matrix. Martensitic transformations have diffusionless character, and the atomic movement is confined to interatomic lengths in the materials. The basic factors which govern the martensitic transformation are Bain distortion and homogeneous shears. Copper based alloys exhibit this property in metastable β-phase field.

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Waitz, T., K. Tsuchiya, T. Antretter, and F. D. Fischer. "Phase Transformations of Nanocrystalline Martensitic Materials." MRS Bulletin 34, no. 11 (November 2009): 814–21. http://dx.doi.org/10.1557/mrs2009.231.

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AbstractThe physical phenomena and engineering applications of martensitic phase transformations are the focus of intense ongoing research. The martensitic phase transformation and functional properties such as the shape-memory effect and superelasticity are strongly affected by the crystal size at the nanoscale. The current state of research on the impact of crystal size on the phase stability of the martensite is reviewed summarizing experimental results of various nanostructured martensitic materials and discussing the corresponding theoretical approaches. The review outlines the effects of crystal size on the complex morphology of the martensite, leading to interface structures not encountered in coarse-grained bulk materials. The unique shape-memory properties of martensitic materials can persist even at the nanoscale. Nanocrystalline martensitic materials can be processed to obtain tailored functional properties in combination with enhanced strength. Structural changes of metallic nanowires are similar to those arising by martensitic phase transformations and also can lead to shape-memory effects, as predicted by atomistic simulations.

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Meng, Q. P., and N. Chen. "Interfacial Structural Modification of Martensitic Transformations." Materials Science Forum 561-565 (October 2007): 2309–12. http://dx.doi.org/10.4028/www.scientific.net/msf.561-565.2309.

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The free energy function of martensitic transformation is established using Landau polynomial. According to the free energy function, the interfacial structural modification of austenite-martensite with the chemical driving force of martensitic transformation and elastic constants of materials is discussed. Some characteristics of martensitic transformation, such as the difference between thermoelastic and nonthermoelastic martensitic transformation, martensitic growth, are explained.

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Song, Ren Bo, Yu Pei, Yi Su Jia, Zhe Gao, Yang Xu, and Peng Deng. "Effect of Different Deformation on Microstructures and Properties in 304HC Austenitic Stainless Steel Wire." Materials Science Forum 788 (April 2014): 323–28. http://dx.doi.org/10.4028/www.scientific.net/msf.788.323.

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Two different components of Φ5.5mm 304HC stainless steel wires were drawn at room temperature. After the drawing tests, hard wires of Φ4.5mm, Φ3.8mm and Φ3.45mm were obtained. During the process of drawing, the stacking fault energy of the metastable austenitic stainless steel was low, which have caused strain-induced martensitic transformation. By XRD, TEM, martensitic volume fraction measurement, etc., the results show that the strain-induced martensitic transformations of the two different components were different significantly. When the deformation amount was controlled at 33% or less, a small amount of γ → α ' martensitic transformations of two steels has occurred. While the deformation arrived at 52% or more, a large amount of γ → α ' martensitic transformation has occurred. The stainless steel which has a higher Cu content will have a lower martensite content, which results from the reason that Cu has a strong inhibitory effect on the martensitic formation. In addition, the martensitic transformation can also influence properties. With the accumulation of strain, deformation mainly occurs in martensitic structure, which reduces the plasticity.

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Vermaut, Philippe, Anna Manzoni, Anne Denquin, Frédéric Prima, and Richard Portier. "Unexpected Constrained Twin Hierarchy in Equiatomic Ru-Based High Temperature Shape Memory Alloy Martensite." Materials Science Forum 738-739 (January 2013): 195–99. http://dx.doi.org/10.4028/www.scientific.net/msf.738-739.195.

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Among the different systems for high temperature shape memory alloys (SMA’s), equiatomic RuNb and RuTa alloys demonstrate both shape memory effect (SME) and MT temperatures above 800°C. Equiatomic compounds undergo two successive martensitic transformations, β (B2) → β’ (tetragonal) → β’’ (monoclinic), whereas out of stoechiometry alloys exhibit a single transition from cubic to tetragonal. In the case of two successive martensitic transformations, we expect to have a finer microstructure of the second martensite because it is supposed to develop inside the smallest twin elements of the former one. In equiatomic Ru-based alloys, if the first martensitic transformation is “normal”, the second one gives different unexpected microstructures with, for instance, twins with a thickness which is larger than the smallest spacing between twin variants of the first martensite. In fact, the reason for this unexpected hierarchy of the twins size is that the second martensitic transformation takes place in special conditions: geometrically, elastically and crystallographically constrained.

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Hsu, T. Y., Q. P. Meng, Yong Hua Rong, and Xue Jun Jin. "Perspective in Application of the Phase Field Theory to Smart Materials Performance." Materials Science Forum 475-479 (January 2005): 1909–14. http://dx.doi.org/10.4028/www.scientific.net/msf.475-479.1909.

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Previous works on the kinetics of martensitic transformation in shape memory materials through Landau theory and the application of the phase field theory to study phase transformations in alloys are briefly reviewed. Based on field model to improper martensitic transformation proposed by Wang and Khachaturyan in 1997, a simpler model is suggested. Using this model, the motion speed and shape of parent/martensite and martensite-martensite interface are quantitatively described, which are important factors to be considered in design of smart device using shape memory materials as a main element.

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de Bortoli, Daniel, Fauzan Adziman, Eduardo A. de Souza Neto, and Francisco M. Andrade Pires. "Constitutive modelling of mechanically induced martensitic transformations." Engineering Computations 35, no. 2 (April 16, 2018): 772–99. http://dx.doi.org/10.1108/ec-03-2017-0087.

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Purpose The purpose of this work is to apply a recently proposed constitutive model for mechanically induced martensitic transformations to the prediction of transformation loci. Additionally, this study aims to elucidate if a stress-assisted criterion can account for transformations in the so-called strain-induced regime. Design/methodology/approach The model is derived by generalising the stress-based criterion of Patel and Cohen (1953), relying on lattice information obtained using the Phenomenological Theory of Martensite Crystallography. Transformation multipliers (cf. plastic multipliers) are introduced, from which the martensite volume fraction evolution ensues. The associated transformation functions provide a variant selection mechanism. Austenite plasticity follows a classical single crystal formulation, to account for transformations in the strain-induced regime. The resulting model is incorporated into a fully implicit RVE-based computational homogenisation finite element code. Findings Results show good agreement with experimental data for a meta-stable austenitic stainless steel. In particular, the transformation locus is well reproduced, even in a material with considerable slip plasticity at the martensite onset, corroborating the hypothesis that an energy-based criterion can account for transformations in both stress-assisted and strain-induced regimes. Originality/value A recently developed constitutive model for mechanically induced martensitic transformations is further assessed and validated. Its formulation is fundamentally based on a physical metallurgical mechanism and derived in a thermodynamically consistent way, inheriting a consistent mechanical dissipation. This model draws on a reduced number of phenomenological elements and is a step towards the fully predictive modelling of materials that exhibit such phenomena.

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Guo, Zheng Hong, Yong Hua Rong, S. Y. Gu, and Ji Hua Zhang. "The Investigation of Internal Friction on Antiferromagnetic Transition and Martensitic Transformation in Mn-Fe(Cu) Alloys." Solid State Phenomena 184 (January 2012): 378–83. http://dx.doi.org/10.4028/www.scientific.net/ssp.184.378.

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The internal friction and elastic modulus variations caused by the structural rearrangement fcc↔fct in Mn-Fe (Cu) antiferromagnetic alloys were studied in this paper. Antiferromagnetic transition exhibits weak first-order features due to the formation of microtwins by modulus softening mechanism. Antiferromagnetic transition also assists subsequent transformation to form twinned martensite. The small hysteresis between direct and reveres martensitic transformations indicates the thermoelastic feature. Both the martensitic and its reverse transformations also depend on the modulus softening mechanism.

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Basak, Anup, and Valery I. Levitas. "An exact formulation for exponential-logarithmic transformation stretches in a multiphase phase field approach to martensitic transformations." Mathematics and Mechanics of Solids 25, no. 6 (February 14, 2020): 1219–46. http://dx.doi.org/10.1177/1081286520905352.

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A general theoretical and computational procedure for dealing with an exponential-logarithmic kinematic model for transformation stretch tensor in a multiphase phase field approach to stress- and temperature-induced martensitic transformations with N martensitic variants is developed for transformations between all possible crystal lattices. This kinematic model, where the natural logarithm of transformation stretch tensor is a linear combination of natural logarithm of the Bain tensors, yields isochoric variant–variant transformations for the entire transformation path. Such a condition is plausible and cannot be satisfied by the widely used kinematic model where the transformation stretch tensor is linear in Bain tensors. Earlier general multiphase phase field studies can handle commutative Bain tensors only. In the present treatment, the exact expressions for the first and second derivatives of the transformation stretch tensor with respect to the order parameters are obtained. Using these relations, the transformation work for austenite ↔ martensite and variant ↔ variant transformations is analyzed and the thermodynamic instability criteria for all homogeneous phases are expressed explicitly. The finite element procedure with an emphasis on the derivation of the tangent matrix for the phase field equations, which involves second derivatives of the transformation deformation gradients with respect to the order parameters, is developed. Change in anisotropic elastic properties during austenite–martensitic variants and variant–variant transformations is taken into account. The numerical results exhibiting twinned microstructures for cubic to orthorhombic and cubic to monoclinic-I transformations are presented.

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Wang, Lei, He Li, Yong Huang, Kehong Wang, and Ming Zhou. "Effect of Preheating on Martensitic Transformation in the Laser Beam Welded AH36 Steel Joint: A Numerical Study." Metals 12, no. 1 (January 9, 2022): 127. http://dx.doi.org/10.3390/met12010127.

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In this work, the effects of preheating temperatures on martensitic transformations in a laser beam-welded AH36 steel joint were observed using a numerical study. In the same weld, the martensitic contents increased slightly from the upper area, the middle area to the lower area, and simulated martensite contents in the fusion zone were slightly lower than that in the HAZ (Heat Affected Zone). Under different preheating temperatures, simulated martensitic contents decrease with the increase of the preheating temperature. According to the simulated results, the average cooling rate and the CCT (Continuous Cooling Transformation) diagram were drawn to analyze the relationships between preheating temperatures and martensitic transformations. Simulated martensitic contents agreed well with the experimental metallographic microstructures. Moreover, the measured microhardness was reduced with the increasing preheating temperature, and measured microhardness in HAZ was higher than that in the fusion zone. The accuracy of the simulation results was further confirmed. The main significance of this work is to provide a numerical model to design martensitic contents in order to control the performances of the weld, avoiding many tests.

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Beke, Dezső, Lajos Daróczi, László Tóth, Melinda Bolgár, Nora Samy, and Anikó Hudák. "Acoustic Emissions during Structural Changes in Shape Memory Alloys." Metals 9, no. 1 (January 9, 2019): 58. http://dx.doi.org/10.3390/met9010058.

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Structural changes (martensitic transformation, rearrangements of martensitic variants) in shape memory alloys have an intermittent character that is accompanied by the emission of different (thermal, acoustic, and magnetic) noises, which are fingerprints of the driven criticality, resulting in a damped power-law behaviour. We will illustrate what kinds of important information can be obtained on the structural changes in shape memory alloys. It was established that the power exponents of distributions of acoustic emission (AE) parameters (energy, amplitude, etc.), belonging to martensitic transformations, show quite a universal character and depend only on the symmetry of the martensite. However, we have shown that the asymmetry of the transformation (the exponents are different for the forward and reverse transformations) results in as large differences as those due to the martensite symmetry. We will also demonstrate how the recently introduced AE clustering method can help to identify the different contributions responsible for the asymmetry. The usefulness of the investigations of time correlations between the subsequent events and correlations between acoustic and magnetic noise events in ferromagnetic shape memory alloys will be demonstrated too. Finally, examples of acoustic and magnetic emissions during variant rearrangements (superplastic or superelastic behaviour) in the martensitic state will be described.

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Borowski, Tomasz, Maciej Kowalczyk, and Jerzy Jeleńkowski. "Thermal Stability of Athermal and Deformation Martensite in Ni27Ti2AlMoNb Steel." Solid State Phenomena 172-174 (June 2011): 585–90. http://dx.doi.org/10.4028/www.scientific.net/ssp.172-174.585.

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The study was devoted to the thermal stability of the phases present in chromium-less and practically carbon-less Ni27Ti2AlMoNb steel. Steel with an austenitic structure was subjected to martensitic transformations using a thermal treatment, namely cooling to below the temperature Ms (beginning of the martensitic transformation), or by plastic deformation using the TRIP effect. The cooling in liquid nitrogen gave a martensitic-austenitic structure with athermal martensite α’a. The martensite had a lenticular morphology, and its volumetric share was 51%, which is typical of duplex type steels. The 50% squeeze of the austenitic steel resulted in the formation of deformation martensite α’d with a lamellar structure (this transformation is only possible below a certain temperature Md). During the experiments, the thermal stability of the two phases, α’a and α’d, at temperatures of 450°C and 550°C was examined. The changes taking place in the steel structure when the athermal martensite and deformation martensite were annealed below and above the temperature As (beginning of the austenitic transformation) were observed using a vibrating sample magnetometer and an optical microscope.

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Litovchenko, Igor, Alexander Tyumentsev, and Alexander V. Korznikov. "Reversible Martensitic Transformation Produced by Severe Plastic Deformation of Metastable Austenitic Steel." Materials Science Forum 738-739 (January 2013): 491–95. http://dx.doi.org/10.4028/www.scientific.net/msf.738-739.491.

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The peculiarities of martensitic transformations and formation of nanostructured states in metastable austenitic steel (Fe-18Cr-8Ni-Ti) after severe plastic deformation by high pressure torsion are investigated. It is shown that during severe plastic deformation with increased strain rate not only direct (γ→α΄) but also reverse (α΄→γ) martensitic transformations occur, which is revealed by the changes in the volume content of α΄ - martensite during deformation. The fragments thought to be formed by direct and reverse martensitic transformations and those of dynamic recrystallization of austenite are observed.

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Otsuka, Kazuhiro. "Martensitic Transformations." Materia Japan 36, no. 9 (1997): 858–61. http://dx.doi.org/10.2320/materia.36.858.

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Hassan, Najam ul, Mohsan Jelani, Ishfaq Ahmad Shah, Khalil Ur Rehman, Abdul Qayyum Khan, Shania Rehman, Muhammad Jamil, Deok-kee Kim, and Muhammad Farooq Khan. "Tunable Martensitic Transformation and Magnetic Properties of Sm-Doped NiMnSn Ferromagnetic Shape Memory Alloys." Crystals 11, no. 9 (September 13, 2021): 1115. http://dx.doi.org/10.3390/cryst11091115.

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NiMnSn ferromagnetic shape memory alloys exhibit martensitic transformation at low temperatures, restricting their applications. Therefore, this is a key factor in improving the martensitic transformation temperature, which is effectively carried out by proper element doping. In this research, we investigated the martensitic transformation and magnetic properties of Ni43Mn46-x SmxSn11 (x = 0, 1, 2, 3) alloys on the basis of structural and magnetic measurements. X-ray diffraction showed that the crystal structure transforms from the cubic L21 to the orthorhombic martensite and gamma (γ) phases. The reverse martensitic and martensitic transformations were indicated by exothermic and endothermic peaks in differential scanning calorimetry. The martensitic transformation temperature increased considerably with Sm doping and exceeded room temperature for Sm = 3 at. %. The Ni43Mn45SmSn11 alloy exhibited magnetostructural transformation, leading to a large magnetocaloric effect near room temperature. The existence of thermal hysteresis and the metamagnetic behavior of Ni43Mn45SmSn11 confirm the first-order magnetostructural transition. The magnetic entropy change reached 20 J·kg−1·K−1 at 266 K, and the refrigeration capacity reached ~162 J·Kg−1, for Ni43Mn45SmSn11 under a magnetic field variation of 0–5 T.

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Adiguzel, Osman. "The Role of Twinned and Detwinned Structures on Memory Behaviour of Shape Memory Alloys." Advanced Materials Research 1105 (May 2015): 78–82. http://dx.doi.org/10.4028/www.scientific.net/amr.1105.78.

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Shape memory alloys have a peculiar property to return to a previously defined shape or dimension when they are subjected to variation of temperature. Shape memory effect is facilitated by martensitic transformation governed by changes in the crystalline structure of the material. Martensitic transformations are first order lattice-distorting phase transformations and occur with the cooperative movement of atoms by means of lattice invariant shears in the materials on cooling from high temperature parent phase region. The material cycles between the deformed and original shapes on cooling and heating in reversible shape memory effect. Thermal induced martensite occurs as twinned martensite, and the twinned martensite structures turn into detwinned structures by deforming the material in the martensitic condition. Deformation of shape memory alloys in martensitic state proceeds through a martensite variant reorientation. The deformed material recovers the original shape on first heating over the austenite finish temperature in reversible and irreversible shape memory cases. Meanwhile, the parent phase structure returns to the twinned structure in irreversible shape memory effect on cooling below to martensite finish temperature and to the detwinned structure in reversible shape memory effect. Therefore, the twinning and detwinning processes have great importance in the shape memory behaviour of the materials. Copper based alloys exhibit this property in metastable β-phase region, which has bcc-based structures at high temperature parent phase field, and these structures martensitically turn into layered complex structures with lattice twinning following two ordered reactions on cooling.

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Paúl, A., A. Beirante, Nuno Franco, Eduardo Alves, and José Antonio Odriozola. "Phase Transformation and Structural Studies of EUROFER RAFM Alloy." Materials Science Forum 514-516 (May 2006): 500–504. http://dx.doi.org/10.4028/www.scientific.net/msf.514-516.500.

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High temperature phase transformations in EUROFER reduced activation ferritic martensitic (RAFM) steel were studied in-situ by means of X-ray diffraction. Results show that, during slow cooling, the austenite to ferrite transformation takes place around 755 oC. Full transformation of the austenitic phase into pure martensite is observed for cooling above 5 oC/min. This transformation was found in samples annealed at 950 oC for 3 h and quenched in liquid nitrogen. TEM analyses reveal a high concentration of carbides along the grain boundaries of the martensitic structure. The thermal expansion coefficient derived from the measurements was 12.7x10-6 K-1.

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Mertinger, Valeria, Erzsebet Nagy, Márton Benke, and Ferenc Tranta. "Characteristics of Martensitic Transformations Induced by Uni-Axial Tensile Tests in a FeMnCr Steel." Materials Science Forum 812 (February 2015): 161–66. http://dx.doi.org/10.4028/www.scientific.net/msf.812.161.

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Austenitic FeMnCr steels have high strength, high toughness and formability because of the stress-and strain-induced γ→α and γ→ε martensitic phase transformations. These are the so-called TRIP (Transformation Induced Plasticity) and TWIP (Twining induced Plasticity) effects. TWIP steels deform by both glide of individual dislocations and mechanical twinning [1]. The type and mechanism of the austenite→martensite transformation depends on the composition, deformation rate and temperature. The ratio and quantity of the resulting phases determine the properties of the product. It is known that austenitic steels can transform into α and/or ε martensite phases during plastic deformation The characteristics of the martensitic transformations induced by uni-axial tensile tests between room temperature and 200°C in a FeMnCr steel with 2,26 w% Cr content were examined. Mechanical properties as, yield stress were determined from tensile tests. Metallographic examinations, quantitative and qualitative phase analysis by X-ray diffraction were carried out on the uniformly elongated part of the samples (cross, longitudinal sections).

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Song, Gen Zong, and Duo Zhang. "Study of Martensitic Transformation Temperatures of Ferromagnetic Shape Memory NiMnGa Alloys." Applied Mechanics and Materials 364 (August 2013): 537–41. http://dx.doi.org/10.4028/www.scientific.net/amm.364.537.

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As a new class of shape memory alloy, Ni2MnGa ferromagnetic shape memory alloy (FSMA) has both large reversible strain and higher response frequency, which has attracted considerable attention and has been widely investigated.The martensitic transformations temperatures of the as-cast Ni2MnGa alloys are investigated by differential scanning calorimeter (DSC). Following conclusions were obtained from experimental results: By using DSC measurement, martensite transformation temperatures (including Ms, Mf, As and Af) were obtained in two alloy series of Ni51.5+xMn23.5Ga25-x and Ni51.5Mn23.5+yGa25-y. Results showed that: martensite transformation temperatures enhanced with the Ni and Mn increasing respectively, and the effect is stronger for Ni than Mn. After 600°C vacuum annealing 6h using powder samples, the martensitic transformation temperature was slight lower than as-cast state.

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Benke, Márton, and Valéria Mertinger. "In Situ Optical Microscopic Examination Techniques of Thermally Induced Displacive Transformations." Materials Science Forum 812 (February 2015): 279–84. http://dx.doi.org/10.4028/www.scientific.net/msf.812.279.

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The mechanical (reversible deformation, stress-strain diagrams, etc.) and thermal (transformation temperatures, hysteresis) characteristics of the thermoelastic martensitic transformations are in the focus of many manuscripts, however, other aspects of the transformations are given less attention. The relief formation accompanied with displacive transformations ensures the possibility of the direct observation of the mechanism and physical metallurgical characteristics of the martensite↔austenite transformations. The authors of the present manuscript applied the in situ optical microscopy method successfully using self-developed examination techniques and self-made heating stages to characterize the thermally induced displacive transformations in shape memory alloys (SMAs) and TWIP steels.

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Lee, Seok Jae, and Young Kook Lee. "Effect of Austenite Grain Size on Martensitic Transformation of a Low Alloy Steel." Materials Science Forum 475-479 (January 2005): 3169–72. http://dx.doi.org/10.4028/www.scientific.net/msf.475-479.3169.

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There are many empirical equations for predicting martensite start temperature (Ms) and the kinetics models of martensitic transformation of plain carbon and low alloy steels. The Ms temperature equations are only dependent upon the chemistry, while the martensite transformation kinetics models are based on the degree of undercooling below Ms temperature. However, the prior austenite grain size (AGS) is also expected to influence both Ms temperature and martensite transformation kinetics as it does in diffusive transformations. In this study, herefore, both Ms temperature and martensite transformation kinetics of a low alloy steel with different austenite grain sizes were investigated using a dilatometer. The new Ms equation and martensite transformation kinetics model including the AGS effect are proposed.

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Karlsson, A. M. "On the Mechanical Response in a Thermal Barrier System Due to Martensitic Phase Transformation in the Bond Coat." Journal of Engineering Materials and Technology 125, no. 4 (September 22, 2003): 346–52. http://dx.doi.org/10.1115/1.1605107.

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Recent studies have shown that Pt-aluminide—a common bond coat material in thermal barrier coatings—undergoes martensitic transformations during thermal cycling. The transformations are associated with both large transformation strain and a strain hysteresis, leading to accumulation of a mismatch strain. Thermal barrier systems based on Pt-aluminide bond coats are susceptible to interfacial morphological instabilities. In this study, we investigate how the cyclic martensitic transformation influences the morphology. Two key results are: (i) the morphological instabilities are highly sensitive to the thermo-mechanical properties of the substrate due to the martensitic transformation; (ii) the hysteresis associated with cyclic martensitic transformation cannot drive the morphological instabilities; the strains associated with the formation of the thermally grown oxide do.

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Seguí, Concepcio, Eduard Cesari, and Jaume Pons. "Intermartensitic Transformations in Ni-Mn-Ga Alloys: A General View." Advanced Materials Research 52 (June 2008): 47–55. http://dx.doi.org/10.4028/www.scientific.net/amr.52.47.

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Off-stoichiometric Ni2MnGa ferromagnetic shape memory alloys undergo a martensitic transformation (MT) from the L21 cubic phase to a martensitic crystal lattice consisting, in the majority of cases, of a periodic stacking sequence of nearly closed-packed planes with periodicity of 5, 7 or 2 planes, denoted as 10M (five layered tetragonal), 14M (seven layered orthorhombic) and 2M (non-modulated tetragonal). In addition to the parent to martensite transformation, Ni-Mn-Ga alloys tend to show stress or temperature induced intermartensitic transformations (IMTs) towards the most stable 2M phase, through the sequences 10M→14M→2M or 14M→2M depending on the first formed martensite. The IMTs reported in the literature show a variety of characteristics such as reversibility, completeness, hysteresis and temperature of occurrence, but, as a general trend, the role of internal stresses in favouring the occurrence of IMTs is recognised. Recently it has been shown that the L21 order degree favours the occurrence of the intermartensitic transformation from 14M to 2M martensite, stabilising the non modulated martensite through a decrease of its free energy with respect to the layered martensite. From this point of view, the occurrence of intermartensitic transformations in Ni-Mn-Ga alloys appears as a “chemical“ free energy effect. Aiming to go deeply into this aspect, in this work the occurrence of IMTs and their properties have been examined for an extensive set of off-stoichiometric Ni2MnGa. The results show the existence of a relationship between the IMTs temperatures and the alloys composition, as well as the dependence of all observed IMTs (i.e., 10M→14M, 14M→2M and their corresponding reverse transformations) on the L21 order degree.

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Wozniak, T. Z., Z. Ranachowski, P. Ranachowski, W. Ozgowicz, and A. Trafarski. "The Application of Neural Networks for Studying Phase Transformation by the Method of Acoustic Emission in Bearing Steel/ Zastosowanie Sieci Neuronowych Do Badania Przemian Fazowych W Stali Łożyskowej Metodą Emisji Akustycznej." Archives of Metallurgy and Materials 59, no. 4 (December 1, 2014): 1705–12. http://dx.doi.org/10.2478/amm-2014-0288.

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Abstract The research was carried out on steel 100CrMnSi6-4 under isothermal austempering resulting in forming the duplex structure: martensitic and bainitic. The kinetics of transformation was controlled by the acoustic emission method. Complex phase transformations caused by segregation and carbide banding occur at the low-temperature heat treatment of bearing steel. At the temperature close to MS, a certain temperature range occurs where an effect of the first product of prior athermal martensite on the bainitic transformation can be observed. In the registered signal about 15 million various events were registered. There were considered three types of acoustic emission events (of high, medium and low energy), with relatively wide sections and with different spectral characteristics. It was found that the method of acoustic emission complemented by the application of neural networks is a sensitive tool to identify the kinetics of bainitic transformation and to show the interaction between martensitic and bainitic transformations.

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Lobodyuk, Valentin A., and Emmanuil I. Estrin. "Isothermal martensitic transformations." Physics-Uspekhi 48, no. 7 (July 31, 2005): 713–32. http://dx.doi.org/10.1070/pu2005v048n07abeh002005.

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Lobodyuk, Valentin A., and Emmanuil I. Estrin. "Isothermal martensitic transformations." Uspekhi Fizicheskih Nauk 175, no. 7 (2005): 745. http://dx.doi.org/10.3367/ufnr.0175.200507d.0745.

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Pazooki, A. M. Akbari, M. J. M. Hermans, and I. M. Richardson. "Numerical Investigation of the Influence of Microstructure on the Residual Stress Distribution and Distortion in DP600 Welds." Materials Science Forum 681 (March 2011): 79–84. http://dx.doi.org/10.4028/www.scientific.net/msf.681.79.

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Dual phase steel consists of martensite embedded in a ferrite matrix. The material experiences high heating and cooling rates during welding, which alter the microstructure significantly. In this work the effects of solid state phase transformations on the prediction of residual stresses and distortion during welding of DP600 steel is investigated. Phase fractions have been calculated implicitly using continuous cooling time (CCT) diagrams. The results of the model are compared with experimental measurements for bead-on-plate welds made on DP600 sheets. It is found that the volume changes and the increase of the strength due to the martensitic transformation have both a significant effect on the residual stress and distortion level although in opposite directions. Martensitic phase transformations in DP600 steel tend to reduce tensile residual stresses in the weld metal.

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Bazaleeva, Kseniya, Alexander Golubnichiy, Anton Chernov, Andrey Ni, and Ruslan Mendagaliyev. "The Features of Martensitic Transformation in 12% Chromium Ferritic–Martensitic Steels." Materials 14, no. 16 (August 11, 2021): 4503. http://dx.doi.org/10.3390/ma14164503.

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An anomaly in martensitic transformation (the effect of martensitic two-peak splitting in the temperature-dependent thermal expansion coefficient) in complex alloyed 12% chromium steels Fe-12%Cr-Ni-Mo-W-Nb-V-B (ChS-139), Fe-12%Cr-Mo-W-Si-Nb-V (EP-823) and Fe-12%Cr-2%W-V-Ta-B (EK-181) was investigated in this study. This effect is manifested in steels with a higher degree of alloying (ChS-139). During varying temperature regimes in dilatometric analysis, it was found that the splitting of the martensitic peak was associated with the superposition of two martensitic transformations of austenite depleted and enriched with alloying elements. The anomaly was subsequently eliminated by homogenization of the steel composition due to high-temperature aging in the γ-region. It was shown that if steel is heated to 900 °C, which lies in the (α + γ) phase region or slightly higher during cooling, then the decomposition of austenite proceeds in two stages: during the first stage, austenite is diffused into ferrite with carbides; during the second stage, shear transformation of austenite to martensite occurs.

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30

de Mendonça, Renato, José D. Ardisson, Mirian De Lourdes Noronha Motta Melo, and Neide A. Mariano. "Study of the Tempering Effect in Phase Transformations of 13Cr1Ni0.15C and 13Cr2Ni0.1C Steels." Materials Science Forum 775-776 (January 2014): 130–35. http://dx.doi.org/10.4028/www.scientific.net/msf.775-776.130.

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The martensitic stainless steels are applied in specific conditions due to theirs corrosion and mechanical resistance. The study of these steels after heat treatment is relevant because it may involve the production and development of new steels with better properties for several applications. This study investigates the effect of heat treatment of quenching and tempering in two martensitic steels - 13Cr2Ni0.1C and 13Cr1Ni0.15C (% weight). Dilatometric tests were performed in the samples after melting process in order to obtain the initial and final temperatures of formation of austenite and martensite. The results showed that the quenched samples have the highest hardness and a martensitic microstructure with delta ferrite presence. On the other hand, the samples after tempering showed different matrix suggesting that the martensite decomposition with no change of the delta ferrite.

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31

Liu, S., C. B. Ke, S. Cao, X. Ma, Y. F. Xu, and X. P. Zhang. "A study of grain boundary effects on the stress-induced martensitic transformation and superelasticity in NiTi alloy via atomistic simulation." Journal of Applied Physics 133, no. 8 (February 28, 2023): 085106. http://dx.doi.org/10.1063/5.0134274.

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The stress-induced martensitic transformations and superelasticity behavior in the NiTi alloy with a single crystal model and a twist grain boundary bicrystal model at different temperatures are studied using molecular dynamics simulations. An atomic tracing method is proposed to identify specific numbers of B19′ martensite variants. Under uniaxial compressive loading, the stress-induced martensitic transformation takes place accompanied by the formation of <011>M type II twins, and the deformation process can be divided into three distinct stages based on microstructure evolution and average atomic total energy. It is found that the twist grain boundary induces an increase in the martensite start temperature, which is consistent with the experimental results. There is no residual B19′ martensite at the end of the unloading process, and the irrecoverable strain mainly results from plastic deformation at the grain boundary through the analysis of atomic local shear strains and has hardly changed with increasing deformation temperature. Remarkably, the grain boundary brings about the acceleration of martensite nucleation and an earlier occurrence of stress plateau. Further simulation results manifest that the presence of the twist grain boundary leads to weakened temperature dependence of martensitic transformation stress and a reduction in the hysteresis loop area.

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32

Weidner, Anja, Harry Berek, Christian Segel, Christos G. Aneziris, and Horst Biermann. "In Situ Tensile Deformation of TRIP Steel / Mg-PSZ Composites." Materials Science Forum 738-739 (January 2013): 77–81. http://dx.doi.org/10.4028/www.scientific.net/msf.738-739.77.

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Composite material on the basis of a TRIP (transformation induced plasticity) steel with zirconia particles as reinforcement was produced by powder metallurgical technology and conventional sinter process. The goal of such type of material is to obtain exceptional mechanical properties like high deformation energy absorption due to the combination of martensitic phase transformations both in steel and ceramic. The steel matrix was made of the commercial steel AISI 304, which shows a deformation-induced martensitic phase transformation from the austenitic phase (fcc) into the α’-martensite (bcc). The zirconia particles were partially stabilized with MgO and show a stress-assisted martensitic phase transformation from the tetragonal to the monocline phase. Flat specimens were tensile deformed in-situ in a scanning electron microscope in order to follow the damage behaviour of the material. Some zirconia particles were characterized before and after tensile testing both by backscattered electron contrast as well as by electron backscatter diffraction (EBSD) in combination with energy dispersive X-ray spectroscopy (EDS).

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33

Jin, Hyeong Min, Xiao Li, James A. Dolan, R. Joseph Kline, José A. Martínez-González, Jiaxing Ren, Chun Zhou, Juan J. de Pablo, and Paul F. Nealey. "Soft crystal martensites: An in situ resonant soft x-ray scattering study of a liquid crystal martensitic transformation." Science Advances 6, no. 13 (March 2020): eaay5986. http://dx.doi.org/10.1126/sciadv.aay5986.

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Liquid crystal blue phases (BPs) are three-dimensional soft crystals with unit cell sizes orders of magnitude larger than those of classic, atomic crystals. The directed self-assembly of BPs on chemically patterned surfaces uniquely enables detailed in situ resonant soft x-ray scattering measurements of martensitic phase transformations in these systems. The formation of twin lamellae is explicitly identified during the BPII-to-BPI transformation, further corroborating the martensitic nature of this transformation and broadening the analogy between soft and atomic crystal diffusionless phase transformations to include their strain-release mechanisms.

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34

Kakeshita, Tomoyuki, Takashi Fukuda, and Yong-Hee Lee. "An Interpretation on Kinetics of Martensitic Transformation." Solid State Phenomena 172-174 (June 2011): 90–98. http://dx.doi.org/10.4028/www.scientific.net/ssp.172-174.90.

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We have investigated athermal and isothermal martensitic transformations (typical displacive transformations) in Fe–Ni, Fe–Ni–Cr, and Ni-Co-Mn-In alloys under magnetic fields and hydrostatic pressures in order to understand the time-dependent nature of martensitic transformation, that is, the kinetics of martensitic transformation. We have confirmed that the two transformation processes are closely related to each other, that is, the athermal process changes to the isothermal process and the isothermal process changes to the athermal one under a hydrostatic pressure or a magnetic field. These findings can be explained by the phenomenological theory, which gives a unified explanation for the two transformation processes previously proposed by our group.

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35

Jeong, Hi Won, Seung Eon Kim, Chang Yong Jo, Yong Tae Lee, and Joong Kuen Park. "Analysis on the Martensitic Transformation in the Ti-xNb Alloys Using a Phenomenological Theory." Solid State Phenomena 124-126 (June 2007): 1669–72. http://dx.doi.org/10.4028/www.scientific.net/ssp.124-126.1669.

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The titanium alloys containing the Nb transition elements have been investigated as the Ni-free shape memory and the biomedical alloys with a low elastic modulus. The mechanical properties of the alloys depended upon the meta-stable phases like the α`, α``, ω. To study the martensitic transformations from the β to α`` or α` the Ti-xNb (x=0 to 40 wt%) alloys were melted into the button type ingots using a VAR, and followed by the water-quenching after the soaking at 1000oC for 2hrs. The crystallography of the martensitic phases in the water-quenched alloys was analyzed using a XRD. The diffraction peaks of the orthorhombic martensites were identified by the crystallographic relationship with the bcc matrix. The lattice parameters of the orthorhombic martensites were varied continuously with the contents of the Nb elements. The martensitic transformations of the alloys were studied using the phenomenological theory of Bowles and Mackenzie.

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36

Cheng, Wei Chun, Kun Hsien Lee, Shu Mao Lin, and Shao Yu Chien. "The Observation of Austenite to Ferrite Martensitic Transformation in an Fe-Mn-Al Austenitic Steel after Cooling from High Temperature." Materials Science Forum 879 (November 2016): 335–38. http://dx.doi.org/10.4028/www.scientific.net/msf.879.335.

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Fe-Mn-Al steels with low density have the potential to substitute for TRIP (transformation induced plasticity) steels. For the development of Fe-Mn-Al TRIP steels, phase transformations play an important role. Our methods of studying the phase transformations of the Fe-16.7 Mn-3.4 Al (wt%) austenitic steel include heating and cooling. We have studied the martensitic transformation of the ternary Fe-Mn-Al steel. Single austenite phase is the equilibrium phase at 1373 K, and dual phases of ferrite and austenite are stable at low temperatures. It is noteworthy that lath martensite forms in the prior austenite grains after cooling from 1373 K via quenching, air-cooling, and/or furnace-cooling. The crystal structure of the martensite belongs to body-centered cubic. The formation mechanism of the ferritic martensite is different from the traditional martensite in steels. Ferrite is the stable phase at low temperature.

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37

Seguí, Concepcio, Jaume Pons, and Eduard Cesari. "Effect of L2₁ Ordering on the Martensitic and Intermartensitic Transformations in a Ni-Mn-Ga Shape Memory Alloy." Solid State Phenomena 130 (December 2007): 127–34. http://dx.doi.org/10.4028/www.scientific.net/ssp.130.127.

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The present work analyses the influence of austenite ordering on a single crystal Ni-Mn- Ga alloy which displays, on cooling, a sequence of martensitic (MT) and intermartensitic (IMT) transformations. The MT and IMT show distinct behaviour after ageing in austenite: while the MT temperatures are not affected by the performed heat treatments, the IMT shifts toward lower temperatures after quenching from increasing temperatures, progressive recovery occurring upon ageing in parent phase. Such evolution can be related to changes in the L21 order degree, in the sense that ordering favours the occurrence of the intermartensitic transformation, while it does not affect noticeably the forward and reverse martensitic transformation temperatures. The closeness of the free energies of the different martensite structures allows to explain this behaviour.

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38

Nó, M. L., L. Dirand, A. Denquin, and J. San Juan. "Internal Friction and Dynamic Modulus in Ultra-High Temperature Ru-Nb Functional Intermetallics / Tarcie Wewnętrzne I Moduł Dynamiczny W Bardzo Wysoko Temperaturowych Funkcjonalnych Związkach Międzymetalicznych Z Układu Ru-Nb." Archives of Metallurgy and Materials 60, no. 4 (December 1, 2015): 3069–72. http://dx.doi.org/10.1515/amm-2015-0490.

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In the present work we have studied the high-temperature shape memory alloys based on the Ru-Nb system by using two mechanical spectrometers working in temperature ranges from 200 to 1450ºC and -150 to 900ºC. We have studied internal friction peaks linked to the martensitic transformations in the range from 300 to 1200ºC. In addition, we have evidenced another internal friction peak at lower temperature than the transformations peaks, which apparently exhibits the behaviour of a thermally activated relaxation peak, but in fact is a strongly time-dependent peak. We have carefully studied this peak and discussed its microscopic origin, concluding that it is related to the interaction of some structural defects with martensite interfaces. Finally, we perform a complete analysis of the whole internal friction spectrum, taking into account the possible relationship between the time-dependent peak and the martensitic transformation behaviour.

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39

Glavatska, Nadiya, G. Mogylnyy, S. Danilkin, and D. Hohlwein. "Temperature Dependence of Lattice Parameters in Martensite and Effect of the External Magnetic Field on Martensite Structure in Ni₂MnGa Studied In-Situ with Neutron Diffraction." Materials Science Forum 443-444 (January 2004): 397–400. http://dx.doi.org/10.4028/www.scientific.net/msf.443-444.397.

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The crystal structure of Ni1.99Mn1.14Ga0.87 single-crystal that exhibits large magnetic field induced strain in the martensitic phase is studied by neutron diffraction within temperature range 300K-4K. The 5-layered modulated structure is observed within the whole temperature interval and no another martensitic transformations occur. The anisotropic change of the martensite lattice parameters during cooling from 300K down to 4K is found. The combined change in the a- and c-lattice parameters affects change of the (c/a) ratio in martensite with cooling down by 2.32%. Redistribution of twin martensitic variants in the external magnetic field is studied in-situ at temperatures 98K-296K.

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40

Tolea, Felicia, Bogdan Popescu, Cristina Bartha, Monica Enculescu, Mugurel Tolea, and Mihaela Sofronie. "Kinetics and the Effect of Thermal Treatments on the Martensitic Transformation and Magnetic Properties in Ni49Mn32Ga19 Ferromagnetic Shape Memory Ribbons." Magnetochemistry 9, no. 1 (December 25, 2022): 7. http://dx.doi.org/10.3390/magnetochemistry9010007.

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In our work, the kinetics of martensitic transformations and the influence of thermal treatments on martensitic transformations, as well as the related magnetic properties of the Ni49Mn32Ga19 ferromagnetic shape memory melt-spun ribbons, have been investigated. Thermal treatments at 673 K for 1, 4 and 8 h can be considered an instrument for fine-tuning the performance parameters of alloys. One-hour thermal treatments promote an improvement in the crystallinity of these otherwise highly textured ribbons, reducing internal defects and stress induced by the melt-spinning technique. Longer thermal treatments induce an important magnetization rise concomitantly with a slight and continuous increase in martensitic temperatures and transformation enthalpy. The activation energy, evaluated from differential scanning calorimeter experimental data with a Friedman model, significantly increases after thermal treatments as a result of the multi-phase coexistence and stabilization of the non-modulated martensitic phase, which increases the reverse martensitic transformation hindrance.

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41

Spiridonova, K. V., I. Yu Litovchenko, N. A. Polekhina, V. V. Linnik, T. A. Borisenko, V. M. Chernov, and M. V. Leont’eva-Smirnova. "Structural-phase transformations of 12% chromium ferritic-martensitic steel EP-823." Izvestiya. Ferrous Metallurgy 66, no. 6 (December 29, 2023): 725–32. http://dx.doi.org/10.17073/0368-0797-2023-6-725-732.

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The features of phase transformations of 12 % chromium ferritic-martensitic steel EP-823 under heating and cooling conditions in the temperature range from 30 to 1100 ℃ were studied by the methods of high-temperature X-ray diffraction analysis (XRD) in situ and differential scanning calorimetry (DSC). According to XRD in situ data, upon heating, the temperatures of the beginning and end of the (α → γ) transformation of ferrite (martensite – austenite) are Ac1 ≈ 880 °C, Ac3 ≈ 1000 °C, respectively. Upon cooling, a diffusion (γ → α) transformation occurs with critical points – Аr1 ≈ 860°С (beginning temperature) and Аr3 ≈ 840 °С (end temperature). According to DSC data, during heating, the critical points of the (α → γ) transformation are Ac1 ≈ 840 °C and Ac3 ≈ 900 °C. During cooling, a martensitic (γ → α) transformation is realized with critical points of the beginning of Ms = 344 ℃ and the end of Mf = 212 ℃ of this transformation. The XRD in situ analysis revealed no precipitation of carbide phases under heating and cooling conditions of steel EP-823. Position of the critical points of phase transformations depends on the research method (XRD in situ or DSC), which is determined by the difference in effective (taking into account the time for shooting in the XRD method) heating-cooling rate. The effect of elemental composition on the position of critical points of phase transformations and the formation of structural-phase states of ferritic-martensitic steels is discussed. It is shown that the increased content of ferrite-stabilizing elements (Cr, Mo, Nb) in composition of EP-823 steel, compared with other steels of the same class, expands the region of existence of the ferrite phase, which can contribute to an increase in the temperature of Ac1 .

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42

Laptev, I. N., O. O. Parkhomenko, and V. I. Tkachenko. "THE DUALISM OF THE VACANCIES NATURE IN NONEQUILIBRIUM SYSTEMS." East European Journal of Physics 3, no. 1 (April 23, 2016): 41–48. http://dx.doi.org/10.26565/2312-4334-2016-1-04.

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Based on the method of phase diagrams martensitic transformations, the analysis of conditions of occurrence of martensitic transformations (MP) at different temperatures with the participation of vacancies in pure iron. Built versus temperature MT values of the normal stress of the MP and the concentration of vacancies in a wide range of temperatures (up to 900°С). Sharp the fracture shows the change of mechanisms of accumulation of vacancies in iron, required for MP: how do point defects at temperatures below 547°C, and as the strains of the lattice in the form of free volume at higher temperatures (dualism). At the atomic level the mechanism of occurrence of vacancies during reverse martensitic transformation. The quantum-mechanical interpretation of the nonequilibrium martensitic transformations associated with localization (vacancy-point defect) – delocalization (as the longitudinal waves of elastic deformation).

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43

Kashchenko, Mikhail P., and Vera G. Chashchina. "Fundamental Achievements of the Dynamic Theory of Reconstructive Martensitic Transformations." Materials Science Forum 738-739 (January 2013): 3–9. http://dx.doi.org/10.4028/www.scientific.net/msf.738-739.3.

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Basic directions in the theory of martensitic transformations are briefly listed. Solutions of several important problems in the context of dynamic theory of reconstructive martensitic transformations are reviewed. The FCC-BCC (BCT) transformation in iron alloys is used as an example. Main attention is paid to concept links. In particular, the key role of the concept of initial exited state for realization of transformations with crystal growth at supersonic speed is shown. The leading value of this concept both for calculation of critical rates of austenite cooling and for estimation of scales of incubatory times at bainitic transformation is marked as well.

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Murakami, Y., D. Shindo, T. Oikawa, and M. Kersker. "Martensitic Transformation in a Ti50ni48fe2 Alloy Studied by Eels." Microscopy and Microanalysis 3, S2 (August 1997): 991–92. http://dx.doi.org/10.1017/s1431927600011843.

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Martensitic transformation is the first-order diffusionless phase transformation in solids, and is responsible for unique phenomena such as shape memory effect and superelasticity. Recently, many researchers tried to explain the origin of martensitic transformations from a viewpoint of electronic structure. It is strongly required to investigate electronic state changes associated with a martensitic transformation by an accurate experiment. EELS (Electron Energy-Loss Spectroscopy) was successfully applied to study electronic state in several alloys and oxides, e.g. a composition dependence of density-of-state (DOS) in Cu-3d band was clearly observed for Cu1-xAlx alloys by a core-loss measurement. However, this method has been less applied to studies of phase transformations to date. The purpose of the present work is to investigate electronic state changes associated with a martensitic transformation in a Ti50Ni48Fe2 alloy by EELS.A Ti50Ni48Fe2 alloy was prepared by induction-melting method. Thin-foiled specimens were solution-treated in Ar atmosphere at 1173K for 1hr.,

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45

Yoshida, Kenichi, T. Yasuda, D. Tani, and H. Nishino. "Dynamic Behavior of Two Types of Martensitic Transformations in Cu-Al-Ni Shape Memory Alloy Single Crystal by Acoustic Emission Method." Advanced Materials Research 13-14 (February 2006): 305–12. http://dx.doi.org/10.4028/www.scientific.net/amr.13-14.305.

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Dynamic behavior of two types of martensitic transformations during tensile deformation of Cu-Al-Ni shape memory alloy single crystal has been investigated using an acoustic emission waveform analysis. Two kinds of martensitic transformations consist of β1 ⇔ β1′ (structural change of DO3 to 18R) and β1 ⇒ γ1′ (structural change of DO3 to 2H), each of which is called super-elastic and thermo-elastic martensitic transformations, respectively. These two types of martensitic transformations could be obtained during tensile deformation because of different heat treatment. The rise time at the source (the source rise time) in finite elastic solid by the modified Takashima’s method was analyzed using the acoustic emission waveform detected during the martensitic transformation. The mean source rise time to the γ1′ phase was smaller than that to the β1′ phase before yielding and became the same after yielding. The former result means that the nucleation of the γ1′ phase is faster than that of the β1′ phase because of different crystallographic structure. The latter result is that the growth rate of the γ1′ phase is the same as that of the β1′ phase.

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46

Adiguzel, Osman. "Phase Transitions and Elementary Processes in Shape Memory Alloys." Advanced Materials Research 1101 (April 2015): 124–28. http://dx.doi.org/10.4028/www.scientific.net/amr.1101.124.

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Shape memory effect is a peculiar property exhibited by certain alloy systems, and shape memory alloys are recognized to be smart materials. These alloys have important ability to recover the original shape of material after deformation, and they are used as shape memory elements in devices due to this property. The shape memory effect is facilitated by a displacive transformation known as martensitic transformation. Shape memory effect refers to the shape recovery of materials resulting from martensite to austenite transformation when heated above reverse transformation temperature after deforming in the martensitic phase. These alloys also cycle between two certain shapes with changing temperature.Martensitic transformations occur with cooperative movement of atoms by means of lattice invariant shears on a {110} - type plane of austenite matrix which is basal plane of martensite.Copper based alloys exhibit this property in metastable β-phase field. High temperature β-phase bcc-structures martensiticaly undergo the non-conventional structures following two ordered reactions on cooling, and structural changes in nanoscale level govern this transition cooling. Atomic movements are also confined to interatomic lengths due to the diffusionless character of martensitic transformation.

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47

Estrin, E. I. "Martensitic and “normal” transformations." Bulletin of the Russian Academy of Sciences: Physics 73, no. 9 (September 2009): 1173–81. http://dx.doi.org/10.3103/s1062873809090019.

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48

Krishnan, R. V. "Stress Induced Martensitic Transformations." Materials Science Forum 3 (January 1985): 387–98. http://dx.doi.org/10.4028/www.scientific.net/msf.3.387.

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49

Kelly, P. M. "Martensitic Transformations in Ceramics." Materials Science Forum 56-58 (January 1991): 335–46. http://dx.doi.org/10.4028/www.scientific.net/msf.56-58.335.

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50

Kriven, W. M. "Martensitic Transformations in Ceramics." Materials Science Forum 56-58 (January 1991): 347. http://dx.doi.org/10.4028/www.scientific.net/msf.56-58.347.

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Journal articles on the topic 'Martensitic transformations'

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