Kinetics Of Martensitic Transformation Research Articles

Thermo-magneto-mechanical coupling dynamics of magnetic shape memory alloys

This paper is to improve our previous phase-transformable material constitutive model (Chen et al., 2014) and implement it in a mass-spring configuration to study the recently discovered dynamic phenomena in (Zhang et al., 2018a, 2018b): the harmonic oscillator of the cyclic magnetic-field-induced deformation in Magnetic Shape Memory Alloys (MSMA) is modulated by a thermo-magneto-mechanical coupling feedback loop where the cyclic field-induced Martensite Reorientation (MR) provides cyclic dissipative deformation whose dissipation heat influencing the material temperature modifies the temperature-dependent MR process and/or triggers the martensite-to-austenite Phase Transformation (PT) to modify the martensite volume fraction so as to change the deformation oscillation amplitude. Such a feedback loop causing the amplitude modulation was ignored in the existing models. This paper develops a dynamic model to include the feedback loop by considering the heat balance (i.e. the interactions among heat generation due to MR, the latent heat release/absorption of PT and the heat transferred to the ambient), by introducing proper kinetics of the temperature–dependent MR and PT processes, and by taking into account the inertial dynamic effect with a simple mass-spring configuration. The simulation based on the model captures all the main features of the experimental phenomena and provides the relations between the macroscopic responses (the deformation amplitude and temperature evolution) and the microscopic physical mechanisms (the kinetics of MR and PT). The study reveals that, with the coupling effects, the MSMA system can be smart to keep its temperature constant by self-organized microstructures under varying external thermo-magneto-mechanical boundary conditions. Moreover, the forward and reverse martensitic phase transformations influenced by the coupling dynamics show little hysteresis, contrasting to the usual hysteretic kinetics of the quasi-static martensitic phase transformation.

Probing martensitic transformation, kinetics, elastic and magnetic properties of Ni2-xMn1.5In0.5Cox alloys

The martensitic transformation, kinetics, elastic and magnetic properties of the Ni2-xMn1.5In0.5Cox (x = 0-0.33) ferromagnetic shape memory alloys were investigated experimentally and theoretically by first-principles calculations. First-principles calculations show that Co directly occupies the site of Ni sublattice, and Co atoms prefer to distribute evenly in the structure. The optimized lattice constants are consistent with the experimental results. The martensitic transformation paths are as follows: PA ↔ FA ↔ 6 MFIM ↔ NMFIM when 0 ≤ x < 0.25; PA ↔ FA ↔ 6 MFM ↔ NMFIM with 0.25 ≤ x < 0.3 and PA ↔ FA ↔ NMFM with 0.3 ≤ x ≤ 0.33 for Ni2-xMn1.5In0.5Cox (x = 0-0.33) alloys. The fundamental reasons for the decrease of TM with increasing Co content are explained from the aspects of first-principles calculations and martensitic transformation kinetics. The component interval of the magnetostructural coupling is determined as 0 ≤ x ≤ 0.25 by first-principles calculations. Furthermore, the origin of the demagnetization effect during martensitic transformation is attributed to the shortening of the nearest neighboring distances for Ni-Ni (Co) and Mn-Mn. Combining the theoretical calculations with experimental results, it is verified that the TM of the Co6 alloy is near room temperature and its magnetization difference ΔM is 94.6 emu/g. Therefore, magnetic materials with high performance can be obtained, which may be useful for new magnetic applications.

Molecular dynamics simulation of migration behavior of FCC-BCC atomic terrace-step phase boundary in iron-based alloy

The martensitic transformation between the high-temperature face-centered cubic (FCC) phase and the low-temperature body-centered cubic (BCC) phase in iron-based alloys has been studied for years, which plays a critical role in controlling microstructures and hence properties of the alloys. Generally, the BCC structure martensitic phase forms from the FCC parent phase, involving a collective motions of atoms over a distance less than the interatomic distance in the vicinity of the interphase boundary. Thus the structure of interphase boundary separating the FCC and BCC phases is the key characteristics to quantitatively understanding the mechanism and kinetics of martensitic transformation. Due to the difficulty in observing the atomic motions taking place at a velocity as high as the speed of sound, the experimental investigation on the migration of FCC/BCC interphase boundary during the transformation is as yet limited. Noteworthily, molecular dynamics (MD) simulation has been applied to studying the martensitic transformation, in particular for investigating the mobility of the FCC/BCC interphase boundary in iron. However, in most of the MD studies the atomistically planar interfaces of {111}&lt;sub&gt;FCC&lt;/sub&gt; // {110}&lt;sub&gt;BCC&lt;/sub&gt; are considered as the initial configuration of the interphase boundary between FCC and BCC phases, which is in contradiction to the high-resolution TEM observations. In fact, the FCC/BCC interphase boundary, which is known as the macroscopic habit plane, is a semi-coherent interface consisting of several steps and terrace planes on an atomic scale. In the present work, the atomic configuration of a terrace-step FCC/BCC interphase boundary of iron is built in terms of the topological model. The MD simulation is conducted to clarify the mechanism of interphase boundary migration in the FCC-to-BCC transformation. The results show that the FCC/BCC boundary migrates along its normal at the expense of FCC phase as a result of the lateral motions of the transformation dislocations. Meanwhile, the interphase boundary maintains the stable terrace-step structure during the transformation. Further examinations reveal that the transformation dislocations move steadily at a velocity as high as (2.8 ± 0.2) × 10&lt;sup&gt;3&lt;/sup&gt; m/s, affecting the migration of the interphase boundary with a constant velocity of about (4.4 ± 0.3) × 10&lt;sup&gt;2&lt;/sup&gt; m/s. The effective migration velocity of FCC/BCC interface exhibits dynamic properties consistent with the characteristic features commonly observed in a displacive martensitic transformation. Additionally, the motion of transformation dislocations gives rise to the macroscopic shape strain composed of a shear component &lt;inline-formula&gt;&lt;tex-math id="M3"&gt;\begin{document}$ {\varGamma _{{\rm{yz}}}} = 0.349$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20191903_M3.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20191903_M3.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; parallel to the boundary and a dilatation &lt;inline-formula&gt;&lt;tex-math id="M4"&gt;\begin{document}$ {\varGamma _{{\rm{zz}}}} = 0.053$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20191903_M4.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="13-20191903_M4.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; normal to the boundary in the MD simulation, which is close to the crystallographic calculations by the topological model.

Modeling the Residual Stresses Induced in the Metastable Austenitic Stainless Steel Disc Springs manufactured by Incremental Sheet Forming by a Combined Hardening Model with Phase Transformation

A numerical model for predicting the beneficial residual stress induced in metastable austenitic stainless steel (MASS) disc springs through incremental sheet forming (ISF) is developed. An important input for the numerical model is the phase-specific flow curves of the MASS constituents, i.e., austenite γ and martensite α phase. These curves are determined by using an available CP-FEM framework. The cyclic plasticity effects introduced by the bending/unbending deformation mechanism of the ISF are modeled by using a combined non-linear isotropic/kinematic hardening model. The kinetics of the strain-induced martensite transformation is modeled by using the Olson-Cohen model, whereas the stresses in the whole material are approximated by a mixture rule. The combined non-linear isotropic/kinematic hardening along with Olson-Cohen model and the mixture rule is integrated as a user-material routine (UMAT). The model parameters are calibrated by tensile tests with online Feritscope measurements and tension-compression tests. Afterward, the incremental forming simulations of disc spring manufacturing are performed and the numerically determined residual stress values are compared to the experimental values. The comparison indicates a good match. Hence, the developed numerical strategy provides accurate residual stresses prediction and can be utilized to design the disc spring properties through adjusting residual stresses, which is possible by varying process parameters of the ISF process.

Simulation of isothermal kinetics of martensitic transformation in the Ti40.7Hf9.5Ni44.8Cu5 alloy

Simulation of isothermal kinetics of martensitic transformation in the Ti40.7Hf9.5Ni44.8Cu5 alloy

Austenitizing Temperature and Cooling Rate Effects on the Martensitic Transformation in a Microalloyed-Steel

Abstract The effects of the austenitizing temperature and the cooling rate upon the kinetic of athermal martensitic transformation in a microalloyed steel were evaluated. Considering the studied steel, the knowledge about these effects on the martensitic transformation has a great relevance for naval manufacturers and steel researchers. In this study, computational simulation was performed aiming to evaluate the phase’s stability. Specimens were submitted to quenching simulations in a dilatometer, considering four different austenitizing temperatures and four cooling rates. The results shown that the austenite chemical composition was not significantly affected by the austenitizing temperatures. Both the austenitic grain size and the cooling rate affected the martensitic transformation kinetics. The larger the austenitic grain size, the higher the Ms. The austenitic grain growth promoted a decrease in the required chemical energy to compensate the free energy increase associated with the lattice strain and the creation of new interfaces, leading to a lower austenite undercooling. An extrinsic effect of the cooling rate on the Ms was observed. For lower cooling rates, the carbide precipitation modified que austenite chemical composition, changing its stability and increasing Ms. A predictability equation, correlating the MS with the austenite grain size and the steel cooling rate, was proposed.

Experiment research on the transformation plasticity by tensile/compressive stress and transformation kinetics during the martensitic transformation of 30Cr2Ni4MoV steel

The martensitic transformation plasticity and martensitic transformation kinetics in 30Cr2Ni4MoV steel were studied under different tensile/compressive stress conditions using the Gleeble-3500 thermal simulation machine. Elastic strain, thermal strain and transformation strain were separated out from the total strain, and the transformation strain under different loads was finally obtained. The transformation plasticity coefficient K in the Greenwood-Johnson’s mechanism, the coefficients α and Ms in the Koistinen-Marburg equation and the applied stress were particularly studied. The results provide the necessary coefficients for the numerical simulation during quenching process of the 30Cr2Ni4MoV steel.

Deformation mechanisms and ductile fracture characteristics of a friction stir processed transformative high entropy alloy

Deformation mechanisms of a friction stir processed Fe40Mn20Co20Cr15Si5 transformative high entropy alloy using three different process parameters were studied to explain the microstructural dependence of tensile response in these specimens. The relative strain hardening contribution due to transformation and twinning effects was different for the three different microstructural conditions and thus resulted in different magnitude of work hardening. Crystal plasticity simulations confirmed that synergistic activity of face centered cubic and hexagonal close packed slip and twin mechanisms resulted in sustained work hardening and enhanced uniform elongation. The non-uniform ductility and extent of void nucleation and growth in these specimens were limited. Nevertheless, fractography and X-ray microscopy of fractured tensile specimens verified that microstructural flexibility induced different propensities for void growth and ductile fracture mode. Thus, alloy design induced phase stability, adaptive phase evolution due to friction stir processing, extent and kinetics of martensitic transformation and related work hardening capability of the individual phases combined together to determine the overall tensile response. The crystallographic orientation dependence of deformation induced phase transformation was also thoroughly studied. This study included quantitative determination of the crystallographic orientation where resolved shear stress on leading and trailing partial dislocations favored separation of the partials to cause transformation at a critical value of applied stress.

Kinetics of Thermoelastic Martensitic Transformation in TiNi

The kinetics of the thermoelastic martensitic transformations of types В2 ↔ В19′ and В2 ↔ R ↔ В19′ in cast and powder Ni55–Ti45 alloys is studied. A way of calculating temperature dependence n(T) of the relative amount of transformed phase from measurements of the martensitic peak of internal friction is proposed. Experimental dependences n(T) at various amplitudes of deformation and heating rates are obtained. Based on the thermodynamics of equilibrium processes, a theoretical model of thermoelastic transformation is developed and a formula for calculating dependence n(T) is obtained. Theoretical dependence n(T) agrees with the experimental data.

Microstructure Evolution and Mechanical Stability of Retained Austenite in Medium-Mn Steel Deformed at Different Temperatures.

The temperature-dependent microstructure evolution and corresponding mechanical stability of retained austenite in medium-Mn transformation induced plasticity (TRIP) 0.17C-3.1Mn-1.6Al type steel obtained by thermomechanical processing was investigated using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD) techniques. Specimens were deformed up to rupture in static tensile tests in the temperature range 20–200 °C. It was found that an increase in deformation temperature resulted in the reduced intensity of TRIP effect due to the higher stability of retained austenite. The kinetics of strain-induced martensitic transformation was affected by the carbon content of retained austenite (RA), its morphology, and localization in the microstructure.

Microstructure analysis of martensitic low alloy carbon steel samples subjected to deformation dilatometry

Low alloy martensitic steels are commonly used in structural and wear resistant applications due to their excellent mechanical properties and abrasion resistance. Martensite phase is generally achieved by rapid cooling, and prior deformation in the austenite region also affects the martensite transformation. It is important to understand the martensite transformation when there is deformation above Ae3. Deformation and quenching simulations have been performed using dilatometry on a low alloy carbon steel. The aim was to determine the influence of deformation above Ae3 (prior deformation) on, firstly, the austenite grain size and shape, and secondly, the martensitic microstructure and variant selection. In addition, the hardness of the martensitic structure due to prior deformation has been investigated. The experimental results obtained from electron backscatter diffraction and microhardness tests on the deformation dilatometry test samples were analysed. The orientation relationship Kurdjumov-Sachs has been used to analyse the martensitic variants. The results revealed a deeper understanding of prior austenite grain structure's effect on the martensitic transformation kinetics and its morphology. The martensite laths' misorientation interval 15–48° were used to visualise the prior austenite grain size. The martensitic lath structure is more refined due to increased prior deformation. Shorter martensite formation time promotes a single dominating packet within the prior austenite grain.

Every midwife matters

Low alloy martensitic steels are commonly used in structural and wear resistant applications due to their excellent mechanical properties and abrasion resistance. Martensite phase is generally achieved by rapid cooling, and prior deformation in the austenite region also affects the martensite transformation. It is important to understand the martensite transformation when there is deformation above Ae3. Deformation and quenching simulations have been performed using dilatometry on a low alloy carbon steel. The aim was to determine the influence of deformation above Ae3 (prior deformation) on, firstly, the austenite grain size and shape, and secondly, the martensitic microstructure and variant selection. In addition, the hardness of the martensitic structure due to prior deformation has been investigated. The experimental results obtained from electron backscatter diffraction and microhardness tests on the deformation dilatometry test samples were analysed. The orientation relationship Kurdjumov-Sachs has been used to analyse the martensitic variants. The results revealed a deeper understanding of prior austenite grain structure's effect on the martensitic transformation kinetics and its morphology. The martensite laths' misorientation interval 15–48° were used to visualise the prior austenite grain size. The martensitic lath structure is more refined due to increased prior deformation. Shorter martensite formation time promotes a single dominating packet within the prior austenite grain.

Analysis of interface migration and isothermal martensite formation for quenching and partitioning process in a low-carbon steel by phase field modeling

A modified two-dimensional phase field microelasticity model coupling the Cahn–Hillard equation is applied to investigate the microstructural evolution of interface migration and isothermal martensitic transformation accompanying carbon diffusion and redistribution during quenching and partitioning (Q&P) process in a low-carbon steel. In the modeling, the Kim–Kim–Suzuki model is adopted to depict interface conditions for carbon diffusion, while the transformation behavior during partitioning is assumed as a displacive manner. Simulations were done for one-step Q&P processes with various partitioning temperatures. Simulated results reveal that carbon enrichment within untransformed austenite varies significantly with the local microstructural features formed during Q&P process. With the proposed phase field model, the isothermal martensite formation and migration of existing austenite–martensite interfaces during partitioning are realized by simulation. It is also revealed that the interface migration behavior during partitioning is strongly correlated with the spatial distribution of the local elastic strain energy inherited from quenching process. Furthermore, temperature dependence of isothermal martensitic transformation kinetics is also studied, with the competition between martensitic transformation and reverse transformation during partitioning, a favorable partitioning temperature is found to have the maximum amount of isothermal martensite formed during partitioning.

Mechanical properties of cold-rolled metastable Cr–Mn–Ni–N austenitic stainless steel at low ambient temperature

A Cr–Mn–Ni–N series high strength metastable austenitic stainless steel (14Cr10Mn) was used to investigate the effect of cold rolling reduction on mechanical properties at various low testing temperatures. Microstructures of tested samples were observed by transmission electron microscope (TEM) and electron back scatter diffraction (EBSD) at the gauge section. The experimental results show that the size of the rib-like α′- martensite formed during tensile testing is sensitive to temperature but insensitive to cold rolling reduction. The results also show that tensile strength is more sensitive to temperature than yield strength, while the effect of cold rolling is completely opposite. The cold rolling inhibits the martensite transformation kinetics of the tensile process after promoting it at a certain temperature condition, and the promotion effect reaches a maximum value approximately 4% when the cold rolling reduction is 10%. However, it also suppresses the α′- martensite content finally formed during tensile testing due to the high stress-strain state when the cold rolling reduction exceeds 10%, while a larger cold reduction promotes the production of α′- martensite. In addition, lowering temperature can effectively promote the formation of ε-martensite at the end of the Stage I of work hardening, and becomes a transitional phase of subsequent transformation to α′- martensite, which directly leads to the enhancement of strength in the stage II of work hardening.

Deformation-induced martensitic transformation kinetics and correlative micromechanical behavior of medium-Mn transformation-induced plasticity steel

An in situ high-energy X-ray diffraction (HE-XRD) technique was mainly used to investigate the micromechanical behavior of medium-Mn Fe-0.12C-10.16Mn-1.87Al (in wt%) transformation-induced plasticity (TRIP) steel subjected to intercritical annealing at 625 °C, 650 °C, 675 °C and 700 °C for 1 h. As the intercritical annealing temperature increased, the volume fraction of retained austenite (RA) and ultimate tensile stress (UTS) increased, while the Lüders strain and yield stress (YS) decreased. The incremental work-hardening exponent of experimental steel increased with increasing intercritical annealing temperature. The overall trend of the transformation kinetics of the RA with respect to the true strain followed the sigmoidal shape predicted by the Olson and Cohen (OC) model. Load partitioning occurred among the ferrite, austenite and martensite immediately after entering the yielding stage. Because the stability of the RA decreased with increasing intercritical annealing temperature, the load undertaken by the martensite increased. The moderate transformation kinetics of the RA and effective load partitioning among constituent phases were found to contribute to a favorable combination of strength and ductility for this medium-Mn TRIP steel.

Effect of stresses on martensite transformation kinetics and transformation plasticity of S34MnV steel

Expansions of martensite transformation in S34MnV steel are studied under tensile and compressive stresses using a Gleeble-3500 thermo-mechanical simulation system. Coupled analyses of the experimental data are conducted to simultaneously determine the transformation kinetic parameters in the Koistinen-Marburger equation and the transformation plasticity coefficient in the Greenwood-Johnson model of martensite transformation. Such components as elastic strain, thermal strain and transformation strain are extracted from the total strain so as to determine the transformation plasticity strain under various loads. Transformation plasticity data are fit into the Greenwood-Johnson model to obtain the transformation plasticity coefficient K. Transformation plasticity coefficient K in the Greenwood-Johnson model has a constant value under tensile stresses and another lower value under compressive stresses. Effects of applied stresses on kinetic parameters α and Ms in the Koistinen-Marburger model are evaluated but found insignificant.

Alter martensitic phase transformation kinetics by forming Ni-rich nanolayer in metastable austenitic steels

A 5 nm Ni-rich nanolayer has been introduced along nanoscale martensite/austenite phase boundaries (PBs) by one-step low-temperature annealing treatment of cold-rolled meta-stable austenitic steels. Control experiments reveal that the martensitic phase transformation kinetics can be significantly altered by presence of the nanolayers. The growth of pre-existed martensites is substantially suppressed while the martensite nucleation in austenites is less affected, as revealed by a statistical investigation on the martensite size distribution under different tensile strains. Enhanced strength and excellent ductility have been achieved simultaneously in the annealed samples, demonstrating that PBs can be effectively engineered to achieve optimized mechanical properties.

To correlate the phase transformation and mechanical behavior of QP steel sheets

The Quenching and Partitioning steels (QP steel) have received attention due to their deformation-induced martensitic transformation (DIMT) behavior. However, this DIMT behavior makes the stress-strain response of QP steel more complex to predict. In this paper, a comprehensive study of the DIMT behavior of QP980 steels was carried out in which an extended martensitic transformation kinetics model was further developed to incorporate the stress state, temperature and strain rate. To further correlate the microstructure evolution and macromechanical behavior, a modified plastic hardening equation considering martensitic transformation strengthening, thermal softening and strain rate strengthening effects was proposed. The impact of temperature and strain rate on the stress-strain response (first-order effect) of QP steels has been decoupled into two parts: (i) the thermal and strain-rate effect on traditional strain hardening and (ii) the temperature- and strain rate- dependent DIMT behavior on martensitic transformation-induced hardening. The correlation between the microstructure volume fraction and yield surface evolution (second-order effect) in stress space was investigated. The kinematic hardening behavior was also studied to explore the Bauschinger effect with different phase transformation rates. This extended model, therefore, provides a good description of the complex stress state-, strain rate- and temperature-dependent mechanical behavior of QP steels.

Development of 3rd generation Medium Mn duplex steels for automotive applications

ABSTRACTThe mechanical behaviour and fracture were studied in a Fe–5Mn–2.5Al–0.2C (in wt-%) Medium Mn steel. Metallographic and magnetic measurements confirm the significant influence of the transformation kinetics of the strain-induced martensite on the mechanical properties and strain heterogeneities (Lüders and Portevin-Le Chatelier-like phenomena). An accurate study of isothermal evolutions of the microstructure, associated with atomistic calculations, complements current thermodynamic databases to quantify the nature and volume fraction of phases at different temperatures. A kinetic approach then predicts the influence of annealing conditions on the composition of retained austenite, key parameter for the martensitic transformation kinetics. This supports quantitative modelling of the influence of the intercritical annealing temperature on the ultimate tensile strength for industrial developments of these new grades.

Stress state-dependent mechanics of additively manufactured 304L stainless steel: Part 1 – characterization and modeling of the effect of stress state and texture on microstructural evolution

The effect of stress state and crystallographic texture on strain-induced martensitic transformation kinetics in 304L stainless steel (SS304L) components made by additive manufacturing were investigated. Mechanical tests under uniaxial tension, uniaxial compression, and pure shear were performed. Experimental results showed that the rate of strain-induced martensitic phase transformation, with respect to plastic strain, was highest under uniaxial compression, followed by uniaxial tension, and lowest under pure shear. The higher rate of phase transformation under uniaxial compression than tension in the additively manufactured SS304L contradicts the trends often, but not always, observed in texture-free conventionally processed austenitic stainless steels. The combined effects of stress state, crystallographic texture, and chemistry were studied, for the first time, to develop a new strain-induced martensitic phase transformation kinetics equation for additively manufactured SS304L that captures the microstructural evolution as a function of plastic strain and these factors.