Academic literature on the topic 'Avrami exponent'
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Journal articles on the topic "Avrami exponent"
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Luo, Hai Wen, Lian Zi An, and Hong Wei Ni. "A New Approach to Model Heterogonous Recrystallization Kinetics Based on the Natural Inhomogeneity of Deformation." Materials Science Forum 558-559 (October 2007): 1139–44. http://dx.doi.org/10.4028/www.scientific.net/msf.558-559.1139.
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The classical JMAK equation was modified by combination with distribution density of the rate parameter k, which was deduced from a normal distribution of local strain. The modified equation is able to calculate the JMAK plots and the average Avrami exponent to characterize the entire heterogeneous recrystallization process. This new extension can successfully describe the relevant experimental observations, such as a smaller exponent than the basic JMAK theory predicts, and a decreasing slope of JMAK plots with the proceeding recrystallization. Moreover, it reveals that the Avrami exponent observed experimentally should significantly decrease with the increasing standard deviation of local strain distribution. In addition, it has a great potential to explain why most of experimentally observed values of Avrami exponents are less than 2 and why the Avrami exponent is insensitive to temperature and deformation conditions when the real standard deviation of local strain distribution in deformed metals is known.
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Fjeldberg, E., and Knut Marthinsen. "On the Recrystallization Kinetics of 3D Potts Monte Carlo Simulations." Materials Science Forum 715-716 (April 2012): 959–64. http://dx.doi.org/10.4028/www.scientific.net/msf.715-716.959.
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The present simulations have clearly demonstrated that the kinetics, as derived directly from the 3D Potts Monte Carlo simulations, deviate strongly from the classical JMAK theory. The Avrami plots exhibit a strong initial transient and the Avrami exponents are far from constant and generally much lower than predicted by the classical JMAK theory. However, by introducing a suitable time delay,t0, due to a non-zero volume fraction of recrystallized grains at the start-up of the simulations, this initial transient can be removed and the Avrami plots are made close to linear at the same time as the Avrami exponent is in better agreement with theory.
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Rezaei-Shahreza, Parisa, Amir Seifoddini, Saeed Hasani, Zahra Jaafari, Agata Śliwa, and Marcin Nabiałek. "Isokinetic Analysis of Fe41Co7Cr15Mo14Y2C15B6 Bulk Metallic Glass: Effect of Minor Copper Addition." Materials 13, no. 17 (2020): 3704. http://dx.doi.org/10.3390/ma13173704.
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In the present study, (Fe41Co7Cr15Mo14Y2C15B6)100−xCux (x = 0, 0.25 and 0.5 at.%) amorphous alloys were prepared by copper-mold casting. To clarify the effect of the minor addition of copper on the mechanism of nucleation and growth during the crystallization process, an isokinetic analysis was performed. The activation energies (E) of the various crystallization stages were calculated by using theoretical models including Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO), Augis–Bennett and Gao–Wang methods. In addition, Augis–Bennett, Gao–Wang and Matusita methods were used to investigate the nucleation and growth mechanisms and to determine other kinetic parameters including Avrami exponent (n), the rate constant (Kp) and dimensionality of growth (m). The obtained results revealed that the activation energy—as well as thermal stability—was changed with minor addition of copper. In addition, the obtained Avrami exponent values were confirmed by Johnson–Mehl–Avrami–Kolmogorov (JMAK) method. The research findings demonstrated that the value of Avrami exponent is changed with minor addition of copper, so that the Avrami exponents of all crystallization stages, except the second peak for copper-free amorphous alloy, were equal to integer values ranging from two to four, indicating that the growth mechanisms were controlled by interface. Moreover, the kinetic parameters of n and b for all peaks were increased by an increase in crystallization temperature, which can be attributed to the increase in the nucleation rate.
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Wang, Yan. "A fractal model for the crystallization kinetics." Thermal Science 25, no. 2 Part B (2021): 1313–15. http://dx.doi.org/10.2298/tsci191212027w.
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The Kolmogorov-Johnson-Mehl-Avrami equation is wildly applied in the crystallization kinetics, and Avrami exponent involved in the equation plays an important role in crystallization process. Here we show that the Kolmogorov-Johnson-Mehl-Avrami equation can be obtained by a fractal crystallization model, and the exponent is explained as the fractal dimension in time, which depends upon the chain length and molecule weight.
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Luo, Haiwen, Jilt Sietsma, and Sybrand van der Zwaag. "Characteristics of the Static Recrystallization Kinetics of an Intercritically Deformed C-Mn Steel." Materials Science Forum 467-470 (October 2004): 293–98. http://dx.doi.org/10.4028/www.scientific.net/msf.467-470.293.
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The austenite recrystallization kinetics in the intercritical region of a C-Mn steel is investigated by means of stress relaxation tests. It is found that the Avrami exponent, n, decreases significantly with decreasing temperature, i.e. with increasing ferrite fraction. This behaviour deviates from that of austenite recrystallization in the purely austenitic state, in which case the Avrami exponent is constant and independent of temperature and deformation. To interpret this, the influence of spatial variation of the plastic strain in the intercritical austenite grains on recrystallization kinetics is modelled quantitatively. The modelling results seem to indicate that the strain heterogeneity is responsible for the decreasing Avrami exponent with decreasing intercritical temperature.
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Gu, Xiao Hua, Peng Zeng, Xi Wei Zhang, and Xue Song. "Nonisothermal Crystallization Kinetics of Poly(m-xylylene adipamide)." Advanced Materials Research 971-973 (June 2014): 103–6. http://dx.doi.org/10.4028/www.scientific.net/amr.971-973.103.
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Abstract.In this paper, the nonisothermal crystallization kinetics was investigated by differential scanning calorimetry for the poly(m-xylylene adipamide) (MXD6) which were prepared by polymerization in reactor. The Avrami theory modified by Jeziorny and Z.S. Mo equation were used to describe the nonisothermal crystallization kinetics. The analysis based on the Avrami theory modified by Jeziorny shows that the Avrami exponent n of MXD6 ranges from 2.3 to 3.3, Moreover, both Avrami exponent (n) were around 3.0, which probably suggests a thermal nucleation and a three-dimensional crystal growth. The good linearity of the plots indicates the successful application of Z.S. Mo method in this case.
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Lelito, Janusz. "Crystallization Kinetics Analysis of the Amorphouse Mg72Zn24Ca4 Alloy at the Isothermal Annealing Temperature of 507 K." Materials 13, no. 12 (2020): 2815. http://dx.doi.org/10.3390/ma13122815.
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This paper presents tests of metallic glass based on Mg72Zn24Ca4 alloy. Metallic glass was made using induction melting and further injection on a rotating copper wheel. A differential scanning calorimeter (DSC) was used to investigate the phase transformation of an amorphous ribbon. The tests were carried out at an isothermal annealing temperature of 507 K. The Kolmogorov-Johnson-Mahl-Avrami-Evans model was used to analyze the crystallization kinetics of the amorphous Mg72Zn24Ca4 alloy. In this model, both Avrami’s exponent n and transformation rate constant K were analyzed. Both of these kinetic parameters were examined as a function of time and the solid fraction. The Avrami exponent n value at the beginning of the crystallization process has value n = 1.9 and at the end of the crystallization process has value n = 3.6. The kinetic constant K values change in the opposite way as the exponent n. At the beginning of the crystallization process the constant K has value K = 9.19 × 10−7 s−n (ln(K) = −13.9) and at the end of the crystallization process has the value K = 6.19 × 10−9 s−n (ln(K) = −18.9). These parameters behave similarly, analyzing them as a function of the duration of the isothermal transformation. The exponent n increases and the constant K decreases with the duration of the crystallization process. With such a change of the Avrami exponent n and the transformation rate constant K, the crystallization process is controlled by the 3D growth on predetermined nuclei. Because each metallic glass has a place for heterogeneous nucleation, so called pre-existing nuclei, in which nucleation is strengthened and the energy barrier is lowered. These nuclei along with possible surface-induced crystallization, lead to rapid nucleation at the beginning of the process, and therefore a larger transformed fraction than expected for purely uniform nucleation. These sites are used and saturated with time, followed mainly by homogeneous nucleation. In addition, such a high value of the Avrami exponent n at the end of the crystallization process can cause the impingement effect, heterogeneous distribution of nuclei and the diffusion-controlled grain growth in the Mg72Zn24Ca4 metallic glassy alloy.
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Ji, Mo, Martin Strangwood, and Claire Davis. "Effect of Strain-Induced Precipitation on the Recrystallization Kinetics in a Model Alloy." Metallurgical and Materials Transactions A 52, no. 5 (2021): 1963–75. http://dx.doi.org/10.1007/s11661-021-06206-8.
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AbstractThe effects of Nb addition on the recrystallization kinetics and the recrystallized grain size distribution after cold deformation were investigated by using Fe-30Ni and Fe-30Ni-0.044 wt pct Nb steel with comparable starting grain size distributions. The samples were deformed to 0.3 strain at room temperature followed by annealing at 950 °C to 850 °C for various times; the microstructural evolution and the grain size distribution of non- and fully recrystallized samples were characterized, along with the strain-induced precipitates (SIPs) and their size and volume fraction evolution. It was found that Nb addition has little effect on recrystallized grain size distribution, whereas Nb precipitation kinetics (SIP size and number density) affects the recrystallization Avrami exponent depending on the annealing temperature. Faster precipitation coarsening rates at high temperature (950 °C to 900 °C) led to slower recrystallization kinetics but no change on Avrami exponent, despite precipitation occurring before recrystallization. Whereas a slower precipitation coarsening rate at 850 °C gave fine-sized strain-induced precipitates that were effective in reducing the recrystallization Avrami exponent after 50 pct of recrystallization. Both solute drag and precipitation pinning effects have been added onto the JMAK model to account the effect of Nb content on recrystallization Avrami exponent for samples with large grain size distributions.
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Sidel, S. M., F. A. Santos, V. O. Gordo, et al. "Avrami exponent of crystallization in tellurite glasses." Journal of Thermal Analysis and Calorimetry 106, no. 2 (2011): 613–18. http://dx.doi.org/10.1007/s10973-011-1312-4.
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Sun, N. X., X. D. Liu, and K. Lu. "An explanation to the anomalous avrami exponent." Scripta Materialia 34, no. 8 (1996): 1201–7. http://dx.doi.org/10.1016/1359-6462(95)00657-5.
Full textDissertations / Theses on the topic "Avrami exponent"
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Sidel, Salmo Moreira [UNESP]. "Síntese e caracterização de vidros teluritos." Universidade Estadual Paulista (UNESP), 2011. http://hdl.handle.net/11449/100885.
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sidel_sm_dr_ilha.pdf: 916747 bytes, checksum: 29e258472ed07d7364e52a3b2739b834 (MD5)<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)<br>O desenvolvimento de sistemas e dispositivos ópticos deu origem à área hoje conhecida como fotônica. A busca por novas aplicações ou aprimoramento de sistemas optoeletrônicos tem levado à obtenção de novos materiais vítreos, os quais exigem minuciosa investigação com relação às suas propriedades físicas. Entre os vários sistemas vítreos estudados, os vidros teluritos destacam-se como um dos mais promissores vidros óxidos já desenvolvidos quando comparados com outros vidros clássicos, como os vidros silicatos, fosfatos e boratos. Desta forma, neste trabalho foram preparados vidros com diferentes composições para o sistema Li2O-TeO2-R (R: WO3 e Nb2O5), e caracterizados usando técnicas de análises térmicas, estruturais e ópticas. O estudo das propriedades térmicas é importante na determinação e entendimento do mecanismo de nucleação e crescimento de cristais, sendo, essencial este conhecimento quando o intuito for preparar vidros de alta qualidade exigidos para aplicações tecnológicas. O desenvolvimento tecnológico destes vidros requer que a nucleação intrínseca e o crescimento de cristais sejam suficientemente reduzidos para evitar perdas ópticas. O estudo estrutural destes vidros também é importante para determinação das unidades estruturais constituintes dos vidros. Sabe-se que a adição de metais de transição na matriz telurito provoca a diminuição das unidades TeO3 e aumenta as TeO4, assim, causando aumento da densidade do vidro e, conseqüentemente, aumento no índice de refração. As técnicas utilizadas foram as de análise térmica (DSC), FTIR, XRD, lente térmica (LT) e método de ângulo de Brewster para a obtenção do índice de refração<br>The development of optical systems and devices is the area known as photonics. The search for new applications or improvements of optoelectronic systems has led to the obtaining of new glassy materials, which require thorough investigation with respect to their physical properties. Among the various glass systems studied, the tellurite glasses are presented as one of the most promising oxide glasses that have been developed, when compared with other classics glasses like silicates, phosphates and borates. Thus, in this work were prepared with different glass compositions for the system Li2O-TeO2-R (R: WO3 and Nb2O5) and characterized using techniques of thermal analysis, structural and optical properties. The study of thermal properties is important in determining and understanding the mechanism of nucleation and crystal growth and this knowledge is essential when the purpose is to prepare high-quality glasses required for technological applications. The technological development of these glasses demands sufficiently low intrinsic nucleation and crystal growth to avoid optics losses. The structural study of these glasses is also important for determining the structural units constituting the glass. It is known that the addition of transition metals in the tellurite glass matrix causes a decrease in the TeO3 and increases the TeO4 units and thus causing the increased of density of the glass and, consequently, increasing the refractive index. The techniques used were differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD) and thermal lens (TL) and Brewster angle method for obtaining the refractive index
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Sidel, Salmo Moreira. "Síntese e caracterização de vidros teluritos /." Ilha Solteira: [s.n.], 2011. http://hdl.handle.net/11449/100885.
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Orientador: Keizo Yukimitu<br>Banca:João Carlos Silos Moraes<br>Banca: Valmor Roberto Mastelaro<br>Banca: Mauro Luciano Baesso<br>Banca: Tomaz Catunda<br>Resumo: O desenvolvimento de sistemas e dispositivos ópticos deu origem à área hoje conhecida como fotônica. A busca por novas aplicações ou aprimoramento de sistemas optoeletrônicos tem levado à obtenção de novos materiais vítreos, os quais exigem minuciosa investigação com relação às suas propriedades físicas. Entre os vários sistemas vítreos estudados, os vidros teluritos destacam-se como um dos mais promissores vidros óxidos já desenvolvidos quando comparados com outros vidros clássicos, como os vidros silicatos, fosfatos e boratos. Desta forma, neste trabalho foram preparados vidros com diferentes composições para o sistema Li2O-TeO2-R (R: WO3 e Nb2O5), e caracterizados usando técnicas de análises térmicas, estruturais e ópticas. O estudo das propriedades térmicas é importante na determinação e entendimento do mecanismo de nucleação e crescimento de cristais, sendo, essencial este conhecimento quando o intuito for preparar vidros de alta qualidade exigidos para aplicações tecnológicas. O desenvolvimento tecnológico destes vidros requer que a nucleação intrínseca e o crescimento de cristais sejam suficientemente reduzidos para evitar perdas ópticas. O estudo estrutural destes vidros também é importante para determinação das unidades estruturais constituintes dos vidros. Sabe-se que a adição de metais de transição na matriz telurito provoca a diminuição das unidades TeO3 e aumenta as TeO4, assim, causando aumento da densidade do vidro e, conseqüentemente, aumento no índice de refração. As técnicas utilizadas foram as de análise térmica (DSC), FTIR, XRD, lente térmica (LT) e método de ângulo de Brewster para a obtenção do índice de refração<br>Abstract: The development of optical systems and devices is the area known as photonics. The search for new applications or improvements of optoelectronic systems has led to the obtaining of new glassy materials, which require thorough investigation with respect to their physical properties. Among the various glass systems studied, the tellurite glasses are presented as one of the most promising oxide glasses that have been developed, when compared with other classics glasses like silicates, phosphates and borates. Thus, in this work were prepared with different glass compositions for the system Li2O-TeO2-R (R: WO3 and Nb2O5) and characterized using techniques of thermal analysis, structural and optical properties. The study of thermal properties is important in determining and understanding the mechanism of nucleation and crystal growth and this knowledge is essential when the purpose is to prepare high-quality glasses required for technological applications. The technological development of these glasses demands sufficiently low intrinsic nucleation and crystal growth to avoid optics losses. The structural study of these glasses is also important for determining the structural units constituting the glass. It is known that the addition of transition metals in the tellurite glass matrix causes a decrease in the TeO3 and increases the TeO4 units and thus causing the increased of density of the glass and, consequently, increasing the refractive index. The techniques used were differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD) and thermal lens (TL) and Brewster angle method for obtaining the refractive index<br>Doutor
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Siyasiya, Charles Witness. "Effect of sulphur content on the recrystallisation behaviour of cold worked low carbon aluminium-killed strip steels." Thesis, 2007. http://hdl.handle.net/2263/24240.
Full textBook chapters on the topic "Avrami exponent"
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Low, I. M., and W. K. Pang. "Decomposition Kinetics of MAX Phases in Extreme Environments." In MAX Phases and Ultra-High Temperature Ceramics for Extreme Environments. IGI Global, 2013. http://dx.doi.org/10.4018/978-1-4666-4066-5.ch002.
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MAX phases are remarkable materials but they become unstable at elevated temperatures and decompose into binary carbides or nitrides in inert atmospheres. The susceptibility of MAX phases to thermal dissociation at 1300-1550 °C in high vacuum has been studied using in-situ neutron diffraction. Above 1400 °C, MAX phases decomposed to binary carbide (e.g., TiCx) or binary nitride (e.g., TiNx), primarily through the sublimation of A-elements such as Al or Si, which results in a porous surface layer of MXx being formed Positive activation energies were determined for decomposed MAX phases with coarse pores but a negative activation energy when the pore size was less than 1.0 µm. The kinetics of isothermal phase decomposition at 1550 °C was modelled using a modified Avrami equation. An Avrami exponent (n) of < 1.0 was determined, indicative of the highly restricted diffusion of Al or Si between the channels of M6X octahedra. The role of pore microstructures on the decomposition kinetics is discussed.
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CALKA, A., and A. P. RADLINSKI. "The Local Value of the Avrami Exponent: a New Approach to Devitrification of Glassy Metallic Ribbons." In Rapidly Quenched Metals 6. Elsevier, 1988. http://dx.doi.org/10.1016/b978-1-85166-971-4.50052-9.
Full textConference papers on the topic "Avrami exponent"
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Waryoba, D. R., and P. N. Kalu. "Quantification of Recrystallization Kinetics in Heavily Drawn OFHC Copper Wires by Microhardness Technique." In ASME 2003 International Mechanical Engineering Congress and Exposition. ASMEDC, 2003. http://dx.doi.org/10.1115/imece2003-42251.
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Mechanical properties of materials are inherently dependent on the microstructures that evolve during processing. The microstruture of heavily drawn and annealed OFHC copper is inhomogeneous, and as such it is difficult to assess its recrystallization kinetics by conventional methods. In this article, restoration kinetics of static recrystallization of heavily drawn oxygen free high conducting (OFHC) copper wires has been investigated by microhardness technique. The investigation was carried out on two cold drawn wires deformed to a true strain of 2.31 and 3.10 and annealed at 250°C for annealing times ranging from 10 s to 1 hr. The physical phenomena during annealing were characterized and analyzed using optical microscopy and measurement of microhardness. A unified approach, through the use of microhardness data, for the analysis of the restoration kinetics of recovery, recrystallization, and grain growth has been proposed. In this approach, a JMAK (Johnson-Mehl-Avrami-Kolmogrov) model was expressed in terms of microhardness data, and the results showed that the modified model linked the different restoration kinetics and provided the critical time for the transition from recovery to recrystallization, and to grain growth. The model compared favorably with conventional models, which treat the different restoration kinetics separately. Exponents of about 0.4 for recovery, 4.0 for recrystallization, and 0.5 for grain growth, were obtained. The results also showed that the JMAK exponent, n, is of the same order of magnitude as the grain growth exponent, 1/p.
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PRADELL, T., D. CRESPO, N. CLAVAGUERA, and M. T. CLAVAGUERA-MORA. "AVRAMI EXPONENTS VERSUS CRYSTALLIZATION MECHANISMS." In Proceedings of the Fifth International Workshop on Non-Crystalline Solids. WORLD SCIENTIFIC, 1998. http://dx.doi.org/10.1142/9789814447225_0046.
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Luo, Min, Chun Xu, Bing Zhou, Yan-hui Guo, and Rong-bin Li. "Static Recrystallization Behavior of a Nitrogen Controlled Z2CN19-10 Austenitic Stainless Steel." In ASME 2017 12th International Manufacturing Science and Engineering Conference collocated with the JSME/ASME 2017 6th International Conference on Materials and Processing. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/msec2017-2746.
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In order to increase the hot workability and provide proper hot forming parameters for nitrogen controlled Z2CN19-10 austenitic stainless steel, the static recrystallization behavior was investigated by double-pass hot compression tests in the temperature range of 950–1100°C, initial grain size of 72μm–152μm, and the strain rates of 0.01, 0.1, 1, and 5 s−1. The tests were conducted with inter-pass times varying between 1 and 100 s after achieving a pass strain of 0.05, 0.1, 0.15 and 0.2 in the first pass on a Gleeble-1500 thermo-mechanical simulator. The static recrystallization fraction has been predicted by the 2 % offset stress method and verified by metallographic observations. The metallographic results indicate the crystallized grains generate at the cross of the prior austenite grain boundary and grow up. Also the kinetics of static recrystallization behavior for Z2CN19-10 steel are proposed. Experimental results show that the volume fraction of static recrystallization increases with the increase of deformation temperature, strain rates, pass strain and interval time, while it decreases with the increase of initial grain size. According to the present experimental results, the activation energy (Q) and Avrami exponent (n) was determined as 199.02kJ/mol and 0.69. The established equations can give a reasonable estimate of the static recrystallization behavior for Z2CN19-10 steel.
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Wu, Yujie, Qiang Yu, and Sven K. Esche. "Static Recrystallization Modeling With a Cellular Automata Algorithm." In ASME 2005 International Mechanical Engineering Congress and Exposition. ASMEDC, 2005. http://dx.doi.org/10.1115/imece2005-82840.
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This paper reports on one part of a research project supported by NSF, which aims at developing a multi-scale methodology for systematic microstructure prediction in thermo-mechanical processing of metals. Based on combining mesoscopic microstructure models with macroscopic process formulations, the methodology is expected to provide universally applicable and accurate microstructure prediction capabilities. Cellular Automata (CA) models have been widely used in scientific studies of various microstructural phenomena. This paper discusses the modeling of the static recrystallization phenomenon by employing a regular CA algorithm. The recrystallization processes of single-phase systems under different nucleation conditions are simulated followed by the recrystallization kinetics analysis for 200 × 200 two-dimensional lattice. The performed simulations of static recrystallization confirm that the recrystallized volume fractions are time dependent. Furthermore, the simulated microstructures validate the following Johnson-Mehl-Avrami-Kolmogorov (JMAK) model according to which the recrystallized volume fraction is a sigmoidal function of time, and their evolution matches the JMAK equation with the expected exponents.