DRX Grains Research Articles

Characterization of hot deformation and microstructure evolution of a new metastable β titanium alloy

The hot deformation characteristics of as-forged Ti−3.5Al−5Mo−6V−3Cr−2Sn−0.5Fe−0.1B−0.1C alloy within a temperature range from 750 to 910 °C and a strain rate range from 0.001 to 1 s−1 were investigated by hot compression tests. The stress−strain curves show that the flow stress decreases with the increase of temperature and the decrease of strain rate. The microstructure is sensitive to deformation parameters. The dynamic recrystallization (DRX) grains appear while the temperature reaches 790 °C at a constant strain rate of 0.001 s−1 and strain rate is not higher than 0.1 s−1 at a constant temperature of 910 °C. The work-hardening rate θ is calculated and it is found that DRX prefers to happen at high temperature and low strain rate. The constitutive equation and processing map were obtained. The average activation energy of the alloy is 242.78 kJ/mol and there are few unstable regions on the processing map, which indicates excellent hot workability. At the strain rate of 0.1 s−1, the stress−strain curves show an abnormal shape where there are two stress peaks simultaneously. This can be attributed to the alternation of hardening effect, which results from the continuous dynamic recrystallization (CDRX) and the rotation of DRX grains, and dynamic softening mechanism.

Microstructural Evolution and an Improved Dynamic Recrystallization Kinetic Model of a Ni-Cr-Mo Alloy in Hot Deformation.

Microstructural evolution and dynamic recrystallization (DRX) behaviors of a Ni-Cr-Mo alloy were researched utilizing hot compressive experiments. The changed features of dislocation, subgrain and grain structure correlating to forming parameters were examined by transmission electron microscope (TEM) and electron backscatter diffraction (EBSD). Results illustrate that the consumption of dislocation and the coarsening of substructure/DRX grain are prominently enhanced with an increased forming temperature. However, the annihilation/interaction of dislocation and the expansion of subgrain/DRX grain boundary can be limited at a larger strain rate. Meanwhile, considering the discrepancy in DRX variation rates concerning the strain rate’s ranges, an improved DRX kinetic model was developed. Compared to the classical DRX kinetic model, the good consistency between the forecasted and tested results demonstrates that the established improved DRX kinetic model can precisely characterize the DRX features of the Ni-Cr-Mo alloy over a wide strain rate range. Additionally, the EBSD’s quantitative statistical results proved that the variation of DRX grain size can be supremely defined as the power formulation of the forming temperature and strain rate.

Prediction of anisotropic deformation behavior of TA32 titanium alloy sheet during hot tension by crystal plasticity finite element model

An in-depth understanding of the anisotropic deformation behavior of titanium alloy sheet during hot deformation has important significance to fully exert the forming performance of the materials. In this work, a crystal plasticity finite element model (CPFEM) was established to accurately predict the anisotropic deformation behavior of TA32 titanium alloy rolled sheet during hot tension. An additional constitutive relationship was introduced into CPFEM to define the grain boundary sliding (GBS) mechanism. Meanwhile, the cellular automata (CA) model was embedded into CPFEM to simulate the dynamic recrystallization (DRX) behavior which has a significant effect on anisotropy during hot deformation. The results showed that the proposed model accurately predicts the stress-strain responses, r-values and DRX-acted microstructure evolution of TA32 alloy during hot tension along roll direction (RD) and transverse direction (TD). The transverse texture of the initial sheet results in the r-value of TA32 alloy for TD tension is higher than that for RD tension. Additionally, the higher dislocation density, especially geometrically necessary dislocation (GND) density, caused by more inhomogeneous plastic deformation during TD tension is the main reason for the larger flow stress of the material. Meanwhile, more dislocation density makes the volume fraction of DRX for TD tension higher than that for RD tension. The occurrence of DRX weakens the deformation anisotropy of TA32 alloy, which is mainly due to the fact that DRX enhances the effect of GBS and promotes the compatible deformation between grains, and the generation of substantial DRX grains with random orientation reduces the intensity of texture.

The Role of Strain and Dynamic Recrystallization During Hot Deformation of a Fe–Ni–Cr‐Based Alloy

The hot deformation behavior of a Fe–Ni–Cr‐based superalloy is investigated by electron backscattered diffraction (EBSD) and processing map. The results show that the strain has an obvious effect on hot deformation. The flow instability domain at low temperature decreases with increasing strain. However, it expands with the increasing strain at high temperature. The optimized hot working domain at high temperature moves from low strain rate to high strain rate with the increase in strain. The hot deformation behavior of the alloy is correlated with dynamic recrystallization (DRX). The low fraction of DRX and local flow are responsible for the flow instability at low temperature. The DRX fraction rises with the increase in strain, which results in the reduction of flow instability domain at low temperature. The DRX grains grow rapidly at high temperature and low strain rate with increasing strain. The poor deformation compatibility between the large grains at high strain hinders the multiround DRX, which expands the flow instability at low strain rate and high temperature. The optimized hot working domain transforms from low strain rate to 2.0–10 s−1 at 1050–1170 °C with the true strain of 1.2 due to the appropriate DRX process.

Hot Deformation Behavior and Microstructural Evolution Based on the Processing Map of Dual-Phase Mg-Li Based Alloy.

The deformation behavior of the as-extruded Mg-Li-Al-Zn-Si alloy was studied by conducting a hot compression test, with a temperature range of 180–330 °C and a strain rate range of 0.01–10 s−1. The constitutive relationship of flow stress, temperature, and strain rate was expressed by the Zener–Hollomon parameter and included the Arrhenius term. By considering the effect of strain on the material constants, the flow stress at 240–330 °C could be precisely predicted with the constitutive equation (incorporating the influence of strain). A processing map was established at the strain of 0.7. The unsafe domains that are characterized by uneven microstructures were detected at low temperatures (<230 °C) or high temperatures (>280 °C), with high strain rates (>1 s−1). The optimum hot deformation region was obtained at a medium temperature (270–300 °C), with a peak power dissipation efficiency of 0.44. The microstructural evolution in different domains is investigated. The unstable domains are characterized by a non-uniform flow behavior and uneven microstructure. The observation showed that the dynamic recrystallization (DRX) process could easily occur at the safe domain with high power dissipation efficiency. For the α-phase, some features of continuous dynamic recrystallization can be found. The triple points serve as prominent nucleation sites for the β-phase DRX grains and the growth in the grains was carried out by subgrain boundary migration. The microstructure exhibits characteristics of discontinuous dynamic recrystallization.

Subdivision of Dynamic Recrystallization Mechanism in the Transition Zone and Microstructure Evolution of Incoloy825 Alloy

The hot deformation behavior of Incoloy825 alloy is investigated by isothermal compression test at the temperature range of 950–1150 °C with strain rates of 0.001–10 s−1. The dynamic recrystallization (DRX) mechanism in the transition zone is subdivided and clearly revealed. The results show that the instability domain is mainly located in the low temperature with high strain rate region (950–1050 °C, 1–10 s−1). The feasible domain can be divided into two parts: the first is located in the temperature range of 1000–1150 °C with a strain rate of 0.001 s−1, the second is located in strain rate of 0.01–1 s−1 at 1150 °C, and the optimum processing parameters is the temperature of 1150 °C with a strain rate of 1 s−1. A transition zone of the DRX mechanism appears during hot deformation, in which three DRX mechanisms occur, discontinuous dynamic recrystallization (DDRX) mechanism, continuous dynamic recrystallization mechanism (CDRX), and twin dynamic recrystallization (TDRX) mechanism. The formation of a DRX grain is the comprehensive effect of multiple mechanisms, which can promote and transform each other. Each mechanism contributes a different role.

Effect of hot deformation parameters on dynamic recrystallisation mechanisms of super austenitic stainless steel

Hot compression tests on super austenitic stainless steel (SASS) are performed in the temperature range of 900–1200 °C and strain rates of 0.01–10 s−1. The results reveal that, at lower deformation temperatures of 900 and 1000 °C or lower strain rates of 0.01 s−1, 0.1 s−1 and 1 s−1, the dominant DRX mechanism of SASS can be summarised as: a large number of high-angle grain boundaries (HAGBs) are gradually developed from low-angle grain boundaries (LAGBs) and DRX grains are partially formed on HAGBs. However, the formation of DRX grains due to sub-grain rotation is the main DRX mechanism at higher temperatures of 1100 °C and 1200 °C and at the higher strain rate of 10 s−1.

Microstructural evolution of Al-7.3Zn-2.2Mg-2Cu (Al7068) alloy in T6 condition during isothermal compression using 3-dimensional processing map

Elevated temperature isothermal compression of Al-7.3Zn-2.2Mg-2Cu (Al7068) alloy in T6 condition was studied till a true strain of 0.69 in the working temperature and deformation rate range of 250–450 °C and 0.001–1 s−1, respectively. The rheological behaviour of the specimens showed a decrease in the flow stress values at the higher temperature and lower strain rates. The mean deformation activation energy at peak stress was estimated as 266 kJ/mol. 3D processing map suggested two safe working zones (I and II) for the current alloy. Zone I, with a peak efficiency of 57% located in the domain of 288–312 °C at 0.001 s−1, and zone II with an efficiency ≥ 48% located in the range of 400–450 °C and 0.001–0.044 s−1. The EBSD IPF micrograph of the compression specimens showed a dominance of deformed grains with few fine DRX grains near the grain boundary regions. The analysis showed that the microstructural evolution during hot compression progressed through the CDRX mechanism. TEM analysis confirmed precipitate coarsening with increase in processing temperature and decrease in the deformation rate.

Effect of Nb-V microalloying on hot deformation characteristics and microstructures of Fe-Mn-Al-C austenitic steel

The flow behavior and microstructure of Fe-Mn-Al-C austenitic steel and Nb-V microalloyed Fe-Mn-Al-C austenitic steel during uniaxial hot compression deformation are systematically studied in the present paper. The flow curves of both steels are analyzed, as well as constitutive equations and processing maps are established. The results reveal that the flow softening phenomenon of Nb-V microalloyed Fe-Mn-Al-C austenitic steel is more significant at low temperatures and low strain rates. Moreover, the hot deformation activation energy of Fe-Mn-Al-C steel is marginally affected by the addition of Nb-V. The uniformly distributed nano-sized (Nb,V)C particles, which precipitate in Nb-V microalloyed Fe-Mn-Al-C steel, act as the nucleation sites for dynamic recrystallization (DRX). These particles promote the DRX and pin the grain boundaries to restrain the growth of DRX grains. Nb-V microalloying renders a positive influence on the hot deformation stability of Fe-Mn-Al-C steel and broadens the optimum hot processing window. Based on the processing map and microstructure, the optimum hot processing windows of Nb-V microalloyed Fe-Mn-Al-C steel at the strain of 0.7 are determined as 894–1025 °C/0.01–0.14 s −1 and 1050–1200 °C/0.03–0.95 s −1 . • Effect of Nb-V microalloying on hot deformation characteristics and microstructures in Fe-Mn-Al-C steel was studied. • Nb-V led to flow softening of Fe-Mn-Al-C steel at low temperatures and low strain rates. • Nb-V improved the hot deformation stability of Fe-Mn-Al-C steel. • Nb-V increased the nucleation sites for dynamic recrystallization of Fe-Mn-Al-C steel.

Microstructural origin and control mechanism of the mixed grain structure in Ni-based superalloys

Mixed grain structure, as an incomplete recrystallization, should be homogenized and refined by subsequent processing to improve the mechanical properties of the aeroengine components. The microstructural origin and control mechanism is quite necessary for the microstructure homogenizing and grain refining through thermo-mechanical processing. In present research, microstructural origin and control mechanism of the mixed grain structure have been conducted deeply. With the consideration of temperature drop in practical industrial forging, the optimum processing parameters can be determined as 1110–1140 °C/1.0 s−1 to obtain homogeneous equiaxed grains. The microstructure evolution corresponding to the identified optimal parameters, viz., deformation temperature and strain rate, were systematically investigated. Higher dynamic recrystallization (DRX) fraction and coarser DRX grains can be observed at super-solvus temperature deformation (1140 °C). In addition, sub-solvus deformation (1110 °C) shows random orientated distribution while near< 001 > compression texture can be detected in super-solvus deformation. Particular attention was paid to the DRX mechanisms during hot deformation. Discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) occur simultaneously, and the synergistic effect of them contributes to microstructure control. Moreover, DDRX characterized by grain boundary bulging dominants the microstructure control. Progressive subgrain rotation labeled as CDRX can be regarded as an important assistant mechanism. The findings would provide theoretical support for microstructure control of Ni-based superalloys with mixed grain structure, which is of vital importance for components to obtain excellent performance.

Modeling of the Dynamic Recrystallization of Ti Microalloyed High‐Strength Steel

The dynamic recrystallization (DRX) and austenite microstructure evolution of Ti microalloyed high‐strength steel are investigated and modeled by thermal simulation experiments. The corresponding mathematical models are established based on DRX‐type flow stress curves and the austenite microstructure. A highly accurate austenite grain growth model under different heating conditions is established, which can predict the initial austenite grain sizes before deformation. Considering the effect of initial austenite grain sizes and deformation conditions, the key parameters (peak stress, steady stress, peak strain, and constants C and C1) of the DRX‐type flow stress model are determined, and the predicted DRX‐type flow stresses are in good agreement with the experimental values. The relationships between critical strain and peak strain(εc = 0.77εp), critical stress, and peak stress(σc = 0.82σp) are determined for experimental steel. The relationships between the initial austenite grain size and the key parameters (k, M, a, h) in the DRX kinetic model and the DRX grain size model are determined. The calculated and experimental DRX volume fractions and grain sizes are in good agreement. The results show that these mathematical models can accurately describe the DRX behavior of experimental steel.

Effect of welding speed on microstructure and mechanical properties of Al−Mg−Mn−Zr−Tialloy sheet during friction stir welding

Effects of welding speed on the microstructure evolution in the stir zone (SZ) and mechanical properties of the friction stir welding (FSW) joints were studied by OM, XRD, SEM, TEM, EBSD and tensile testing. Compared with the base metal (BM), an obviously fine dynamic recrystallization (DRX) microstructure occurs in the SZ and the DRX grain size decreases from 5.6 to 4.4 μm with the increasing of welding speed. Fine DRX microstructure is mainly achieved by continuous dynamic recrystallization (CDRX) mechanism, strain induced boundary migration (SIBM) mechanism and particle stimulated nucleation (PSN) mechanism. Meanwhile, the geometric coalescence and the Burke−Turnbull mechanism are the main DRX grain growth mechanisms. Among all the welding speeds, the joint welded at rotation speed of 1500 r/min and welding speed of 75 mm/min has the greatest tensile properties, i.e. ultimate tensile strength (UTS) of (509±2) MPa, yield strength (YS) of (282±4) MPa, elongation (El) of (23±1)%, and the joint efficiency of 73%.

A study of hot compression behavior of an as-cast FeCrCuNi2Mn2 high-entropy alloy

In this study, hot deformation behavior of an as-cast FeCrCuNi2Mn2 high-entropy alloy (HEA) was evaluated. For this purpose, hot compression tests were carried out in the temperature range of 600–1000 oC and initial strain rate range of 0.001–0.1 s-1. Flow stresses under different deformation conditions were then friction-corrected. Work hardening rate analysis was used to evaluate the occurrence of dynamic recrystallization. Microstructures of the hot compressed specimens were characterized using optical microscopy. Strain-dependent constitutive equations were developed using the data obtained from the Sellars–Tegart–Garofalo equation. The critical and peak strain and the critical and peak stress, as dynamic recrystallization parameters, were extracted from the work hardening rate versus stress curves. The results indicated that the modeled flow stresses were generally lower than the measured ones, which could be attributed to the impact of friction on the flow stress. Microstructural observations after hot compression tests as well as evaluation of work hardening rate versus stress curves showed typical dynamic recrystallization characteristics under different deformation conditions. In addition, with increase in deformation temperature and decrease in strain rate, more DRX grains were formed along grain boundaries and shear bands, resulting in a decrease in the flow stress. The size of the DRX grains was strongly affected by deformation temperature and increased with increase in temperature. The normalized critical stress and strain for the initiation of DRX were calculated as εc/εp = 0.60 and σc/σp = 0.86, respectively. The activation energy of hot deformation was determined to be 708 kJ/mol. It was noticed that the developed constitutive equations could accurately predict the flow stress behavior of the studied alloy over a wide range of experimental conditions.

Effect of heat treatment on the microstructure and mechanical properties of a multidirectionally forged Mg-Gd-Y-Zn-Zr-Ag alloy

Multidirectional forging (MDF) was successfully applied to fabricate large-size Mg-Gd-Y-Zn-Zr-Ag alloy in this work and effects of T4, T5 and T6 treatments on the microstructure and mechanical properties of the as-forged alloy were analyzed. Results show that dynamic recrystallization (DRX) occurs and second phase particles precipitate along the grain boundary during the MDF process. After annealing treatment (T4), the volume fraction and size of dynamic precipitates slightly increase at a lower temperature (430 °C) compared with those of MDFed sample, while they are dissolved into the α-Mg matrix at a higher temperature (450 °C). At the meantime, short plate-shaped long-period stacking ordered (LPSO) phases are observed in the DRX grains of the MDFed sample and then dissolved into the α-Mg matrix during annealing at both temperatures. Typical basal texture is identified in the MDFed sample, but the basal pole tilts away from final forging direction and rare-earth texture component with <112¯1> orientation parallel to penultimate forging direction becomes visible after annealing. The T6 sample annealing at 430 °C for 4 h and ageing at 200 °C for 34 h exhibits the superior strength and ductility in this study. The ultimate tensile strength, tensile yield strength and elongation to failure, which is 455 MPa, 308 MPa and 7.7%, respectively, are overall improved compared with the directly-aged (T5) sample. This paper provides a superior heat treatment schedule to manufacture high-performance large-scale Mg-Gd-Y-Zn-Zr-Ag components for industrial production.

Characteristics of dynamic softening during high temperature deformation of CoCrFeMnNi high-entropy alloy and its correlation with the evolving microstructure and micro-texture

The characteristics of dynamic recrystallization (DRX) of a CoCrFeMnNi high–entropy alloy (HEA) was investigated via hot compression testing in the temperature range 950–1100 °C and at true strain rates of 10−2 and 10−1 s−1. The discontinuous DRX was found to be the dominant mechanism corroborating the microstructural evolution. The progress of the initiation of DRX was investigated in terms of critical strain/stress required using the Poliak–Jonas analytical criterion. Consequently, a new kinetic model based on Avrami–type function was established for the HEA to predict the DRX fractional recrystallization. It was revealed that the volume fraction of DRX grains increased with increasing strain. In the case of 10−2 s−1, steady–state flow was achieved after the completion of one DRX process cycle resulting in further straining, leading to the occurrence of dynamic restoration processes involving formation of substructures and generation and annihilation of dislocations inside the DRX grains which effectively increased the fraction of partially deformed DRX (substructured) grains. A good agreement between the proposed DRX kinetics model and microstructure observation results validated the accuracy of DRX kinetics model for CoCrFeMnNi HEA. The preferred orientation of the non–recrystallized grains was towards the formation of <101> fiber texture, whereas a random micro–texture is revealed in the recrystallized grains.

Orientation-dependent dynamic recrystallization of super austenitic stainless steels

Herein, the hot compression of a super austenitic stainless steel (SASS) containing 7Mo–0.46N–0.02Ce is conducted at different temperatures (900–1200 °C) under a strain rate of 10 s−1. The effect of angle between solidification direction of columnar crystals and loading direction (0°, 30°, 60° and 90°) on microstructural evolution of SASS is studied using OM and EBSD. The results reveal that, at low temperatures of 900 °C and 1000 °C, the dynamic recrystallization (DRX) degree of the 30° and 60° samples is higher than that of the 0° and 90° samples, however, the complete DRX has not occurred. At high temperatures of 1100 °C and 1200 °C, the DRX degree of SASS increases with the decrease of angle between solidification direction of columnar crystals and loading direction. Three kinds of DRX mechanisms for samples with different columnar crystal characteristics are observed, i.e., discontinuous dynamic recrystallization (DDRX), continuous dynamic recrystallization (CDRX) and a combination of DDRX + CDRX mechanism. However, under the same deformation conditions, preferentially triggered and dominant DRX mechanisms of samples with different columnar crystal characteristics are different. In the 0° and 90° samples, a large number of high angle grain boundaries (15° ≤ HAGB ≤65°) are developed, and new DRX grains are formed on them. While in the 30° and 60° samples, preferential expansion nucleation and growth of DRX grains take place on original GBs. At 1200 °C, the DRX degree of SASS reaches a maximum of ∼0.97 when the angle between solidification direction of columnar crystals and loading direction is 0°.

Dynamic precipitation and recrystallization mechanism during hot compression of Mg-Gd-Y-Zr alloy

Hot compression tests of Mg-Gd-Y-Zr alloy at different deformation temperatures and strains were carried out with Gleeble-1500 simulator at strain rate of 0.002 s −1 . The microstructure evolution of 400 °C/0.002 s −1 sample under different strain was analyzed emphatically by transmission electron microscopy and electron backscatter diffraction technology. Dynamic precipitation characteristics and nucleation-expansion mechanism of dynamic recrystallization (DRX) were discussed in detail. The results indicated that the dynamic precipitation takes place prior to DRX, and the morphology, size and distribution of precipitates change with increasing strain. At the later stage of deformation, the large-size hard phase β-Mg 5 (Gd,Y) can induce the particle-stimulated nucleation (PSN) mechanism under large strain and act as an effective nucleation site for DRX. In addition, we constructed a schematic diagram of the DRX nucleation-expansion mechanism of Mg-Gd-Y-Zr alloy under high temperature deformation. The first layer of DRX grains is formed by discontinuous dynamic recrystallization (DDRX) mechanism characterized by grain boundary bulge out, and the precipitates distributed at the original grain boundary promote DDRX nucleation; The expansion of necklace structure depends on continuous dynamic recrystallization (CDRX) mechanism; Subgrain division can further refine DRX grains.

Dynamic recrystallization behavior and microstructure evolution of a new Mg-6Zn-1Gd-1Er alloy with and without pre-aging treatment

To compare the dynamic recrystallization (DRX) behavior, microstructure evolution, and texture change of a new Mg-6Zn-1Gd-1Er alloy with and without pre-aging treatment, the uniaxial hot compression tests were carried out in the range of 10 −3 s −1 -1 s −1 and 280 °C–380 °C. The results show that both the fraction and size of DRX grain increase with the increase of temperature, while the increase of strain rate shows the opposite trend. The microstructure mostly exists as a necklace structure, while there are a lot of twins in the microstructure at the condition of 280 °C/1 s −1 . DRX grains mainly nucleate and grow through the mechanisms of continuous dynamic recrystallization (CDRX), particle stimulated nucleation (PSN), and twin-induced dynamic recrystallization (TDRX). The pre-aging treatment sample is more conducive to DRX than the solution heat-treated sample at the same deformation conditions. This is mainly because the deformation activation energy of the alloy with pre-aging treatment is lower, and the interaction of the pre-existed precipitates with dislocations promotes the DRX behavior. At the condition of 380 °C/10 −3 s −1 , compared with the solution heat-treated sample, the pyramidal <c + a> slip was active in the deformed grains of PT of pre-aging treatment alloy, which corresponded to the PT split from CD to TD and tilt about 15°. Similarly, at the condition of 380 °C/1 s −1 , the main deformed grains of PT1 and PT2 in the pre-aging treatment sample tilted the basal texture from CD to TD under the action of pyramidal <c + a> slip to form a bimodal texture. • The DRX behavior of a new Mg-6Zn-1Gd-1Er alloy with and without pre-aging treatment was studied. • The microstructure evolution and texture change of Mg-6Zn-1Gd-1Er alloy with and without pre-aging treatment was studied. • The pre-aging treatment sample is more conducive to DRX than the solution sample at the same deformation conditions. • The basal texture of the pre-aging sample occurs to tilt from CD to TD under the action of pyramidal <c + a> slip.

Kinetic model for describing continuous and discontinuous dynamic recrystallization behaviors of 2195 aluminum alloy during hot deformation

2195 aluminum alloy is widely used to manufacture the external tanks of space shuttles and aircraft skins, and its mechanical properties are substantially affected by dynamic recrystallization occurring in its microstructure. In this study, hot compression experiments were performed on 2195 aluminum alloy to investigate its dynamic recrystallization (DRX) behavior. The results indicated that discontinuous (DDRX) and continuous dynamic recrystallization (CDRX) both occurred in the alloy from 300 °C to 520 °C at strain rates of 0.01–10 s −1 . The microstructure analysis revealed that DDRX grains formed at grain boundaries, while CDRX grains appeared in the triangular grain boundary region with transition grain boundaries or within grains. The dominant DRX mechanism changed from DDRX to CDRX when the strain was greater than 1.2. Moreover, at higher temperatures or lower strain rates, the number of CDRX grains increased, while the number of DDRX grains decreased. Finally, to quantitatively describe the DDRX and CDRX kinetics of 2195 aluminum alloy, the critical conditions were used to establish a composite kinetics model that was consistent with the experimental results, and which suitably predicted the volume fraction of DRX grains formed via the two different DRX mechanisms. • A strain of 1.2 was the transition point between the two recrystallization mechanisms for 2195 aluminum alloy under thermal compression. • Upon increasing the temperature or decreasing the strain rate, CDRX grains increased, while DDRX grains decreased. • Critical conditions of dynamic recrystallization were found and the critical stress, critical strain and other stress of model were established. • A composite kinetics model was proposed by considering the characteristics of DDRX and CDRX.

Effect of Y addition on microstructure evolution and precipitation of Cu-Co-Si alloy during hot deformation

The effects of Y for the microstructure evolutions of Cu-Co-Si alloys during hot deformation were investigated. The hot deformation behaviors for Cu-2.6Co-0.65Si and Cu-2.6Co-0.65Si-0.2Y alloys were carried out on the Gleeble-1500 simulator with the strain rates from 0.001 to 10 s −1 and temperatures from 500 °C to 900 °C. The hot deformation activation energies for two copper alloys were calculated and the constitutive equations were also established. According to the true stress-strain curves and EBSD image analysis, it showed that the nucleation of dynamic recrystallization (DRX) grain and the growth of DRX grain were promoted with the addition of 0.2 wt% Y. Electron backscatter diffraction (EBSD) was used to characterize the microstructure of the hot deformed Cu-Co-Si alloy. The electrode diagram and ODF diagram were established to analyze the textures. The texture strength and the number of small angle grain boundaries were reduced by the addition of 0.2 wt% Y. The microstructure of two alloys was analyzed by transmission electron microscopy, it was found that a large number of Co 2 Si nanoparticles were distributed on the copper matrix. Y could promote the precipitation process of δ-Co 2 Si, and these nanoparticles interacted with dislocations during the hot deformation process to improve the deformation resistance. • Hot deformation behavior of the Cu-Co-Si alloy was investigated. • The addition of Y promoted the nucleation of DRX and refined the recrystallized grains. • The addition of Y can obtain more precipitates.