Dynamic Recrystallization Evolution Research Articles

The influence of heat treatment process on the dynamic recrystallization evolution mechanism of Inconel 718 during high-speed machining

This study aims to investigate the cutting mechanisms of Inconel 718 alloy under different heat treatment processes and the grain refinement patterns of the transformed layer. By establishing a constitutive model suitable for cutting and importing it into DEFORM-3D for heat treatment processing and single-factor cutting experiment simulation, the effects of heat treatment processes and cutting parameters on cutting force, cutting temperature, and surface grain refinement were studied. The results indicate that the increase in cutting force is maximum, approximately 12 %, after the aging temperature is raised from 668 °C to 718 °C. The cutting force generated after aging heat treatment shows a negative correlation with cutting speed, whereas the cutting force after solution heat treatment rises significantly between 1400 and 1600 mm/s. The maximum cutting temperature occurs in workpieces after solution heat treatment, about 112 % of that of workpieces treated at 718 °C aging heat treatment. At the onset of cutting, the size relationship of the original grain volume is as follows: untreated < solution heat treatment < aging heat treatment; the number of nucleation points for dynamic recrystallization at grain boundaries is as follows: aging heat treatment < solution heat treatment < untreated. The most significant increase in the number of dynamic recrystallizations is observed after aging heat treatment at 621 °C, with the relationship of the number of recrystallizations in different cutting deformation zones being: secondary deformation zone < primary deformation zone < tertiary deformation zone. With the increase in cutting depth, the grain size of the workpiece after solution heat treatment first increases then decreases during the cutting process; the grain size of the workpiece after aging heat treatment first decreases then increases. The grain size of the workpiece during the cutting process after heat treatment is negatively correlated with cutting speed. Specifically, when the cutting speed is 600 mm/s, the grain size after solution heat treatment is the largest, about 1.1 times that of the 718 °C aging heat-treated workpiece.

High temperature performance of additively manufactured Al 2024 alloy: Constitutive modelling, dynamic recrystallization evolution and kinetics

The current study investigates the high-temperature deformation behaviour, and microstructural evolution of the laser powder bed fused, Ti modified Al 2024 alloy. The high-temperature performance was evaluated using a hot compression test performed in the temperature range of 200–350 °C and strain rate range of 0.1–10 s−1. The flow behaviour at elevated temperatures at different strain rates can provide us insight into the high temperature application and can also be utilized for optimization of deformation-based post processing technique. The deformation-based post processing method utilizes work hardening to improve the mechanical properties and to reduce the inherent defect of additively manufactured parts, such as pores and lack of fusion. The optimal deformation conditions for these processes can be obtained from the processing map. The flow stress during different deformation conditions (strain, strain rate and temperature) was predicted using different phenomenological models such as Johnson-Cook (JC) model, strain compensated Arrhenius equation, and artificial neural network (ANN). The JC model was observed to be the least suited method in the current investigation, whereas the ANN method was observed to be best suited for predicting flow stress with an average absolute relative error of 0.5% and a correlation coefficient of 0.9998. Different deformation mechanisms such as dynamic recovery (DRV) and dynamic recrystallization (DRX) were investigated for different deformation conditions using empirical models, finite element analysis (FEA) and microstructural characterization using TEM, and EBSD. The primary DRX mechanism in the current study was observed to be continuous dynamic recrystallization or CDRX mechanism.

Microstructure and microtexture evolution of dynamic recrystallization of a Ni-based superalloy under high-throughput gradient thermal compression

The GH4169 alloy with high through-put gradient distribution of strain and microstructure was obtained by thermal compression of double-frustum specimens at 1050 °C, 0.4 s−1 deformation condition. The effect of strain on the evolution of the microtexture and recrystallization of the alloy was investigated using electron backscatter diffraction (EBSD). The strain gradually increases from the edge to the center of the compressed sample, accompanied by increased recrystallization. As the strain increases, new Σ3 boundaries are generated within the dynamic recrystallization (DRX) grains, affecting the deformation microstructure in the subsequent deformation process and gradually decreasing the overall maximum intensity of the microtexture. The deformed grains are oriented in the <101> direction parallel to the compression direction (ND, equivalent to normal direction), and the orientation of the recrystallized grains is in the <001> direction with low pole density. With increasing strain, Brass and Goss of α-fiber textures characterized by {110}<uvw> textures gradually weaken, and the volume fraction of the Rotated Cube increases under the effect of shear stress.

Kinetics and microstructure evolution of dynamic recrystallization of medium-Mn steel during hot working

The dynamic recrystallization (DRX) behavior and microstructure evolution of medium-Mn (0.15C–10Mn) steel were investigated through isothermal hot compression tests. The flow stress–strain curves and microstructure analysis, in wide ranges of temperatures (900–1150 °C) and strain rates (10−3 - 1 s−1), were employed to establish constitutive equations and a grain size evolution model. Since the material constants were calculated based on polynomial function of strains, strain compensation was introduced into constitutive analysis. Comparison and verification showed that the constitutive equation had a high predictive ability. The correlation coefficient and average absolute relative error were 0.99 and 4.46%, respectively, which confirm the accuracy and guidance of the model. Metallographic observation was used to implement the grain size evolution analysis of the medium-Mn steel. Microstructure evolution was characterized with a gradual increase in average recrystallized grain size and an obvious expansion in the range of grain size distribution with both deformation temperature and strain rate, which were attributed to the competition between nucleation and grain boundary migration. Besides, a grain size evolution model was established to analyze the microstructure evolution.

Deformation behavior of a new Ni-Co base superalloy GH4251 during hot compression

The deformation behavior of a new Ni-Co base superalloy GH4251 under hot compression tests within the deformation strain window of 0.36 to 1.2 was investigated in the temperature range of 1050 ∼ 1170 °C and strain rate range of 0.001 ∼ 1 s−1. Based on the analysis of true stress-strain curves, constitutive equations were established to describe the rheological behavior during hot compression. Microstructure evolution was investigated by transmission electron microscope (TEM), scanning electron microscope (SEM) and optical metallography (OM). The results show that flow behavior of GH4251 alloy is combinedly determined by the effect of work hardening and dynamic recrystallization (DRX). The deformation activation energies at strain of 0.36 to 1.2 are calculated to be 311 ∼ 536 kJ mol−1 in the super-solvus temperature region, and 796 ∼ 1064 kJ mol−1 in the sub-solvus temperature region. The recrystallization nucleation mechanism of GH4251 alloy is strain induced grain boundary migration (SIBGM). The occurrence and expansion of recrystallization are strongly promoted by high deformation temperatures and high strain rates, while the DRX grain size increases with elevated deformation temperature. When the deformation temperature is below 1090°C, the recrystallized grain can be extremely small (<17μm), which is rather independent on strain and strain rate. However, above 1110 °C the grain size at strain rate of 0.001s−1 is significantly larger than that of higher strain rates. The difference can be ascribed to the presence of γ′ phase, with which the development of dynamic recrystallization is postponed, while the growth of recrystallized grains is inhibited as well.

Tensile creep behavior of a heat treated β-solidified γ-TiAl alloy: The development of dynamic recrystallization and the role of B2 phase

The tensile creep behavior of a heat treated β-solidified γ-TiAl alloy has been investigated at 800 °C under 250–300 MPa. Results indicate that the heat treatment procedure proposed in this study can improve creep resistance of the alloy. Combined with kinetic analysis (stress exponent n = 3.36) and TEM observation, it can be inferred that creep deformation is dominated by viscous dislocation glide, and assisted by mechanical twinning. It is found that both twin boundary and TiB can hinder dislocation movement and strengthen creep resistance. During creep, there are obvious dynamic recrystallization (DRX) and B2 phase precipitation. On the one hand, DRX volume fraction increases with the increase of creep stress or the extension of creep time. Meanwhile, TiB can act as nucleation sites of recrystallized γ grains. On the other hand, there are two kinds of B2 phase precipitation behaviors: (ⅰ) thin B2 laths are formed in α2 lamellae; (ⅱ) blocky B2 phases are formed at colony boundary. Creep deformation is mainly completed by γ phase, B2 phase can involve in the deformation only under specific creep conditions. Due to poor deformation ability of B2 phase, creep voids prefer to nucleate at the γ-B2 interface and B2-colony interface. When voids are connected, cracks are formed and begin to propagate, eventually leading to creep failure in brittle-ductile mixed fracture.

Investigation of the hot deformation behavior and microstructure evolution of TiB2 +TiAl3/2024Al composite

In this study, the hybrid aluminum matrix composite reinforced with TiB2 and TiAl3 particles was fabricated by in situ synthesis. Hot compression tests were performed at a deformation temperature range of 300 − 450 ℃ and strain rates of 0.001 − 1 s−1 on a Gleeble-3500 system to investigate the hot deformation behavior of the fabricated composite. The experimental results show that the flow stress was sensitively dependent on the strain rate and temperature, and the peak stress level increased with the decrease of deformation temperature or the increase of strain rates. A sine-hyperbolic constitutive equation with the hot deformation activation energy of 244.844 kJ/mol was established to describe the flow stress of the composite. Further, the effects of TiB2 and TiAl3 particles on the flow stress levels of the composite under different hot deformation conditions were described by the developed strengthening model. It found that the predicting values of yield strength calculated by the established model agreed well with the experimental data, and the nano-sized TiB2 had a greater contribution to the stress level of the composite compared to the micro-sized TiAl3. Based on the microstructure characterization, dynamic recovery (DRV) was found to be the main flow softening mechanism during hot deformation and the evolution of dynamic recrystallization (DRX) was insufficient. Micro-sized TiAl3 particles and TiB2 particle clusters can promote DRX nucleation and growth of newly formed grains, meanwhile, separated nano-sized TiB2 particles had a pinning effect on the dislocation migration leading to substructure formation, which was in favor of the development of DRV.

Modeling of Dynamic Recrystallization Evolution for Cr8 Alloy Steel and Its Application in FEM.

In the process of Cr8 roller production, the phenomenon of coarse grain size and uneven grain size often appears, which makes the mechanical properties of the material decrease sharply. Accurate dynamic recrystallization model is the basis for predicting the change of grain size during thermal processing, and is an important basis for refining grain and improving material properties. In this study, the isothermal compression experiment was carried out on Cr8 alloy steel at 900–1200 °C and 0.005–0.1 s−1 by Gleeble –1500D thermal simulation compressor, and the stress dates of Cr8 alloy steel were obtained. According to experimental data, the Kopp dynamic recrystallization model of Cr8 alloy steel was established. The dynamic recrystallization volume fraction obtained by Kopp model was compared with that obtained by experiment at the same temperature and strain rate. The correlation value was 0.988, and the root mean square error (RMSE) was 0.053, which proved that the DRX model established was reliable. Through the secondary development of the program, the DRX model of Cr8 alloy steel was written into the software Forge® to verify the microstructure evolution model. The compression process of a cylindrical specimen of Cr8 alloy steel at 0.1 s−1 and 1050 °C was simulated, and the DRX microstructure evolution of the alloy was calculated. The comparison between the final grain size calculation results and the test metallographic photos of samples in different deformation zones shows the relative error of the grain size was less than 10.6%, indicating that the DRX model of Cr8 alloy steel can better predict the dynamic recrystallization of Cr8 alloy steel.

Effect of activated slip systems on dynamic recrystallization during rotary swaging of electro-conductive Al-Cu composites

The study focuses on structure investigations of newly designed electro-conductive Al-Cu composites produced via room temperature rotary swaging with constant and altering swaging directions. The swaging route affected the activated slip systems and the development of dynamic recrystallization. Altering the swaging direction supported the activation of {100} <10-1> slip system at the expense of the {111} 〈110〉 one. All the swaged composites featured the tendency to form four dominant ideal texture orientations – deformation textures Cu (90°,35°,45°), B (120°,55°,45°), and Bb (60°,55°,45°), and recrystallization texture Cube (0°,0°,0-90°). However, their volume fractions differed. Samples swaged with altering direction exhibited high fractions of Cube orientation. Dynamic recrystallization dominated over deformation strengthening for the final 10 mm diameter composite swaged with altering directions. This composite also featured the highest presence of recrystallized grains and the smallest average grain size (6.0 µm).

Dynamic Recrystallization Evolution Mechanism and Cellular Automaton Simulation for Ea4t High-Speed Railway Axle Steel During Hot Deformation

Dynamic Recrystallization Evolution Mechanism and Cellular Automaton Simulation for Ea4t High-Speed Railway Axle Steel During Hot Deformation

The evolution of dynamic recrystallization and recrystallization texture during isothermal compression of NiTi shape memory alloy

Isothermal compression tests, electron backscatter diffraction (EBSD) observations and quantitative analysis are performed to investigate the effect of process parameters on the microstructure variables (i.e. recrystallized fraction, size of austenite grain and grain boundary misorientation) during isothermal compression of NiTi shape memory alloy. And the evolution of dynamic recrystallization and recrystallization texture for this alloy is thoroughly discussed in the present study. The results show that the dynamic recovery is a dominated softening mechanism at less than 0.5 strain. As the strain increases, the discontinuous dynamic recrystallization (original grain boundary bulging and strain-induced grain boundary migration) and the subsequent continuous dynamic recrystallization (subgrain rotation) also participate in the softening of NiTi shape memory alloy, leading to a steady state of flow behavior. In the deformation end stage, the grain refinement of the austenite phase due to the effect of dynamic recrystallization improves the flow stress of NiTi shape memory alloy. The texture intensity increases significantly with increasing strain during isothermal compression of NiTi shape memory alloy, and the occurrence of dynamic recrystallization during deformation promotes the formation of a strong γ-fiber texture {111}<uvw>//CA.

Dynamic recrystallization behavior during hot deformation of as-cast 4Cr5MoSiV1 steel

The dynamic recrystallization behavior of as-cast 4Cr5MoSiV1 steel was studied by hot compression tests conducted at various temperatures (900–1150 °C) and strain rates (0.01–10 s−1). Flow stress curves and microstructural observation were employed to experimentally identify the various flow mechanisms during deformation. A revised Sellars’ constitutive equation was adopted to construct the thermal activation energy map, which considered the effects of deformation temperature and strain rate on the material variables. The Johnson–Mehl–Avrami-Kolmogorov (JMAK) type equation $$X_{D} = 1 - \exp [ - k(\frac{{\varepsilon - \varepsilon_{c} }}{{\varepsilon_{p} }})^{m} ],(\varepsilon \ge \varepsilon_{c} )$$ was applied to characterize the evolution of dynamic recrystallization (DRX) volume fraction. The nucleation of DRX was performed by the bulging, sub-grain swallowing. The presence of dendrite segregation would affect the DRX to a large extent that the segregated alloying elements and carbide precipitates inhibited the migration of boundaries. The thermal activation energy varied from 4310 to 470 kJ/mol and the thermal activation energy increased sharply at temperature below 1000 °C due to the dendrite segregation. By further analysis of the true stress–strain curves, the material constant $$m$$ in JMAK type equation was determined to be 1.29366, indicating the DRX was difficult.

Effect of second phase particles on the dynamic recrystallization in Ni-W alloys during thermal compression

The existence of second phase particles may raise the deformation heterogeneity in the alloys, providing favorable sites of recrystallization nucleation in thermal deformation. The influence of large W second phase p articles (>1 µm) on the dynamic recrystallization in Ni-42W alloys (with 42 wt% W) is studied in this paper by electron backscattered diffraction (EBSD). The Ni-42W alloys are composed by NiW matrix and W particles. The W particles are of two kinds of shapes including ellipsoidal shape with a diameter of 3–10 µm and rod-like shape with 3 µm in width and 5–15 µm in length. The phenomenon of particles stimulated nucleation is observed in the Ni-42W alloys during thermal deformation. The recrystallized grains are located not only at the areas with high-angle grain boundaries but also at the deformation heterogeneities around W particles. A divergent distribution of deformation heterogeneities is formed around the ellipsoidal W particles and the distortion degree near the adjacent ellipsoidal particles can be accumulated. Large distortion exists at the tips of the rod-like particles. The deformation is weak at the middle region between rod-like particles with parallel alignment, which is not conducive to recrystallization nucleation. Based on the EBSD results, the dynamic recrystallization evolution diagram is established for Ni-42W alloys with large second phase particles.

Influence of Thermomechanical Treatment on the Properties of Alloys of the Mg–Al–Zn–Mn System

Magnesium alloys are subjected, after low-pressure casting, to hot-rolling and extrusion. It is shown that their structural states, for different rates of these processes, are determined by the joint development of dynamic recrystallization, formation of twins, and changes in the phase composition. It is demonstrated that the dissolution of metastable phase components and the corresponding decrease in the resistance of particles of the second phase to the displacements of grain boundaries with large disorientation angles in the process of recrystallization represent one of the causes of increase in the sizes of grains in the matrices of alloys. The mechanical properties of alloys are determined not only by the grain sizes and phase composition but also by the structural anisotropy formed as a result of thermomechanical treatment.

Study of the critical deformation dependence for dynamic recrystallization in low-carbon steels on the chemical composition

The article considers dependence of the critical deformation for dynamic recrystallization in low-alloy steels on the chemical composition. The article shows an improved model for forecasting the critical deformation for dynamic recrystallization, which allows considering the content of chemical elements in steel. The article analyzes the influence of the chemical composition of low-alloy steels on the value of critical deformation during hot deformation. The article shows that the developed mathematical model can be used in the system of automated control of the structure and properties of steels during hot rolling to forecast conditions for the development of dynamic recrystallization and to select the optimal chemical composition of steels.

Mechanisms of Grain Structure Evolution in a Quenched Medium Carbon Steel during Warm Deformation

The as-quenched medium-carbon low-alloy Fe-0.36wt.%C-1wt.%Cr steel was subjected to warm deformation via uniaxial compression at temperatures of 400–700 °C and strain rates of 10−4–10−2 s−1. At low temperatures (400–550 °C), the microstructure evolution was mainly associated with dynamic recovery with the value of activation energy of 140 ± 35 kJ/mol. At higher temperatures (600–700 °C), dynamic recrystallization was developed, and activation energy in this case was 243 ± 15 kJ/mol. The presence of nanoscale carbide particles in the structure at temperatures of 400–600 °C resulted in the appearance of threshold stresses. A two-component &lt;001&gt;//compression direction (CD) and &lt;111&gt;//CD deformation texture was formed during deformation. Deformation at the low temperatures resulted in the formation of elongated ferritic grains separated mainly by high-angle boundaries (HAB) with a strong &lt;001&gt;//CD texture. The grains with the &lt;111&gt;//CD orientation were wider in comparison with those with the &lt;001&gt;//CD orientation. The development of substructure in the form of low-angle boundaries (LAB) networks was also observed in the &lt;111&gt;//CD grains. The development of dynamic recrystallization restricted the texture formation. The processing map for warm deformation of the 0.36C-1Cr steel was constructed.

Physical Modeling of the Evolution of the Microstructure of an Ni–Cr–Co–Nb–Ta–Mo High-Temperature Alloy during Hot Plastic Deformation

The hot torsional deformation of an austenitic Ni–Cr–Co–Nb–Ta–Mo superalloy is subjected to physical modeling. The influence of temperature–deformation parameters on the evolution of the alloy microstructure is studied, and the development of dynamic recrystallization as a function of these parameters is estimated. The results obtained can be used for developing and optimizing the conditions of hot plastic deformation of similar alloys.

Evolution of Dynamic Recrystallization in 5CrNiMoV Steel during Hot Forming

The dynamic recrystallization (DRX) behavior of 5CrNiMoV steel was investigated through hot compression at temperatures of 830–1230°C and strain rates of 0.001–10 s−1. From the experimental results, most true stress-strain curves showed the typical nature of DRX that a single peak was reached at low strains followed by a decrease of stress and a steady state finally at relatively high strains. The constitutive behavior of 5CrNiMoV steel was analyzed to deduce the operative deformation mechanisms, and the correlation between flow stress, temperature, and strain rate was expressed as a sine hyperbolic type constitutive equation. Based on the study of characteristic stresses and strains on the true stress-strain curves, a DRX kinetics model was constructed to characterize the influence of true strain, temperature, and strain rate on DRX evolution, which revealed that higher temperatures and lower strain rates had a favorable influence on improving the DRX volume fraction at the same true strain. Microstructure observations indicated that DRX was the main mechanism and austenite grains could be greatly refined by reducing the temperature of hot deformation or increasing the strain rate when complete recrystallization occurred. Furthermore, a DRX grain size model of 5CrNiMoV was obtained to predict the average DRX grain size during hot forming.

Verification of Dislocation Density and Dynamic Recrystallization in Deformed Pure Copper

The mechanisms of dynamic recovery and dynamic recrystallization significantly affect the mechanical behavior and microstructure of the materials deformed at high temperatures. The modified Kocks and Mecking (K–M) model was used to assess the evolution of dislocation density of pure copper under high-temperature compression. The relationship between the deformation conditions and model parameters was derived and verified. The model offers quantitative prediction of flow stress curves, a recrystallized fraction, and recrystallized grain size under different conditions. The model can well integrate the recrystallization mechanism during deformation. The dislocation density and dynamic recrystallization evolution of pure copper provide a basis for optimizing thermomechanical processing in different fields of industry.

Microstructure and microtexture evolution of dynamic recrystallization during hot deformation of a nickel-based superalloy

Effect of strain rate route on the microstructure and microtexture evolution during the dynamic recrystallization (DRX) of a nickel-based superalloy subjected to the isothermal compression tests was investigated using electron back-scatter diffraction. The evolutions of microtexture components and fiber textures and the role of Σ3 boundaries in microstructure on the pole density in the partially and fully DRX processes were explored. The α-fiber in Euler space is regarded as the compression microtexture. The locally organized substructures in the matrix grains are formed on certain {111} slip planes with the high Schmid factor. Although the dislocation-free DRX grains show the random orientated distribution, the weak recrystallization 〈001〉 fiber parallel to the compression axis (ND) is developed at the high strain in the fully DRX processes. Whereas the compression 〈101〉 fiber parallel to ND in the partially DRX processes is sharpened. Moreover, the instantaneous decrease of strain rate leads to the highest fraction of Σ3 grain boundaries, indicating the lowest pole density. Cube-Twin component adjacent to Cube component contributes partly to the formation of Σ3 grain boundaries. The findings provide insights into the microtexture characteristics and enhance the understanding of the orientation dependence of the mechanical behavior of nickel-based superalloys.