Discontinuous Dynamic Recrystallization Research Articles

Recrystallization behavior and kinetic analysis of an Al-Cu-Li alloy during hot deformation and subsequent heat treatment

Al-Cu-Li alloys exhibit enhanced performance when possessing a high substructure proportion and a low recrystallization proportion. To achieve this, it necessitates a thorough understanding of recrystallization behavior during its hot working and heat treatment. To this end, isothermal compression tests were conducted on an Al-Cu-Li alloy in the temperature range of 350–500 °C and strain rate range of 0.01–10 s−1. The deformed specimens underwent solution treatment at 530 °C/2 h followed by water quenching, and aging treatment at 155 °C/27 h. The microstructures of the deformed and heat-treated specimens were characterized using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). During hot deformation, continuous dynamic recrystallization (CDRX) dominates when the natural logarithm of the Zener-Hollomon parameter (lnZ) >26 and discontinuous dynamic recrystallization (DDRX) predominates when lnZ ≤ 26. A low proportion kinetic model associated with lnZ was constructed to describe the DRX behavior, and the model parameters were optimized using genetic algorithm (GA) to improve accuracy. During heat treatment, substantial static recrystallization (SRX) occurs following deformation at lnZ > 30, while it is limited when lnZ < 27. The comparison of average geometrically necessary dislocations (GNDs) before and after heat treatment reveals that the consumption of dislocations increases with increasing lnZ. Statistical analysis indicates that the density of low/medium angle grain boundaries (L/MAGBs) can be increased and the recrystallization fraction can be decreased within the lnZ range of 24 to 27. Therefore, these specific hot deformation conditions are recommended as the optimal hot working window for the Al-Cu-Li alloy.

Deformation behavior of LPSO phases, grain refinement mechanism, and texture evolution of a Mg-Gd-Y-Zn-Zr alloy processed by forward extrusion combined with dual-directional angular deformation

In this study, a Mg-Gd-Y-Zn-Zr alloy was processed by forward extrusion combined with dual-directional angular extrusion (FE-DDAE), and the corresponding microstructure evolution, grain refinement mechanism, and texture were investigated systematically. The deformed materials were subjected to a combination of three-way compressive stress and shear stress, and five different areas were selected to study the typical deformation behaviors. The results show that microstructures are heterogeneous in different areas, and the grain size is refined from 138.70 μm to 37.18 μm through continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX). The block-shaped and lamellar long period stacking ordered (LPSO) phases can coordinate severe deformation through dissolution, tearing, breaking for the former, and bending, severe kinking, refining into small pieces for the latter. Moreover, the broken block-shaped LPSO can promote DRX process through particle-stimulated nucleation (PSN) mechanism, and the lamellar LPSO phases can hinder the dislocation motion to restrict DRX. A strong basal texture is observed during the initial stage of FE-DDAE process, and the basal texture intensity gradually weakens to 4.9 MRD due to the random orientations of high volume fraction of DRX grains. A mixed texture component is formed with basal planes inclined 50° from ED to TD, showing a trend of spreading.

Fabrication and performance evaluation of CICC jacket based on modified N50 austenitic steel for CFETR magnet

The hot deformation behavior of modified N50 austenitic stainless steel in the temperature range 950∼1250 °C and strain rate range of 0.01–50/s was studied by uniaxial compression experiment. The processing map and the constitutive equation for the finite element simulation were established, and the recrystallization mechanism was discussed. The results indicated that the dominant deformation mode DDRX (discontinuous dynamic recrystallization) increased with the rise of deformation temperature while the CDRX (continuous dynamic recrystallization) was on the contrary. There is a decrease in global recrystallization with increasing strain rate, up to a threshold 1/s beyond which the global recrystallization began significantly promotion owing to not only the adiabatic heat and higher stored energy, but also quick Post-DRX mechanism induced by delay quenching. The reasonable hot working interval was determined by a hot working map, then the most suitable hot extrusion parameters (1180°C-100 mm/s) were further obtained with the help of finite element simulation, and ultimately, the industrial hot extrusion trials of N50 pipes with Post-DRX features were further completed. The tensile performance of final jacket pipes was far beyond the current mainstream low-temperature austenitic structural steel and met the requirements of the new generation of superconducting coil jacket materials.

Discontinuous dynamic recrystallization behavior and texture evolution of large-size pure titanium flat ingot via electron beam cold hearth melting during short process direct hot rolling

Large-size pure titanium ingots melted by single electron beam cold hearth melting (EBCHM)) could be rolled into large-width and heavy-weight titanium strip coils using short process without forging. It is crucial to study the large-span refinement mechanism from highly coarse grains, whose sizes are in the order of ∼cm, to micronmeter. In this study, the recrystallization mechanism and texture evolution of pure titanium with a size of 1570 × 200 × > 8000 mm was investigated by multi-pass simulated rolling and experimental rolling. The results indicated the hot deformation can result in marked reduction in grain size of the as-cast grain, from 3 to 5 cm to 17–23 μm. The discontinuous dynamic recrystallization (DDRX) mechanism of a pure titanium ingot during direct multi-pass hot deformation causes the reconstruction of as-cast microstructure and refinement of hot rolling microstructure. Furthermore, DDRX occurred, during hot deformation, and was accompanied with weakening of deformation texture. Raising the initial hot deformation temperature results in a modification of the texture type of the {0001} crystal plane. The strength of the texture experiences a decrease initially and then eventually an increase. This alteration in strength is inversely related to the degree of dynamic recrystallization. Based on the simulated rolling experiment, the results of experimental rolling also found the coarse as-cast grains was broken and reconstructed. It has strength (average yield strength: 334 MPa, ultimate tensile strength: 371 MPa), ductility (total elongation: 30 %). Such a combination of mechanical properties makes the hot rolling plate a potential choice for sheet practical application.

High strain rate mechanical behavior of Ti-6Al-4V with micro–macro correlation under compressive loading

The application of Ti6Al4V in lightweight structures subjected to impact loads necessitates a comprehensive understanding of its dynamic response under high strain rates to ensure the safety and reliability of these components. In this paper, the macroscopic compressive mechanical behavior of Ti6Al4V under high strain rates was investigated through the split-Hopkinson pressure bar (SHPB) technique at both room temperature and 200 °C, followed by microstructure analysis of the compressed specimens, carried out employing a combination of optical microscopy (OM) and electron backscatter diffraction (EBSD), and elastic modulus and hardness measurements, performed by a nanoindentation instrument. At room temperature, both the modulus and strain hardening exponent of Ti6Al4V exhibited an initial increase before the strain rate reached 1000s-1, after which they decreased at 3400s-1. Meanwhile, the flow stress continued to rise with increasing strain rate. Microscopic observations revealed that twinning played a substantial role in the strain hardening effects. Notably, the basal slip system of the hcp (hexagonal close packed) α phase did not display a more favorable trend, while the c+a type slip systems became more active. Under a strain rate of 5000s-1, discontinuous dynamic recrystallization emerged as the dominant mechanism, resulting in an increased frequency of low-angle grain boundaries, as well as a reduction in grain size and dislocation density. These results provide a basis for explaining the mechanical behavior of Ti6Al4V under high strain rates and offer insights for the establishment of material models that take into account microstructure deformation mechanisms.

Insight on ultrasonic effect of Al[sbnd]Cu aluminum alloy joints fabricated by ultrasonic assisted non-thinning and penetrating friction stir welding

AlCu alloy joints of ultrasonic assisted non-thinning and penetrating friction stir welding (U-NTPFSW) and NTPFSW were prepared. The microstructure and mechanical properties of the joints were studied comparatively to elucidate the effect of ultrasonic. This study provided an in-depth understanding of the microstructure formation mechanism and strengthening mechanism of joints under the ultrasonic effect. Ultrasonics broadened the width of the stir zone (SZ) and stationary shoulder affected zone (SSAZ) by promoting the material plastic flow ability and changing the material flow at the weld root. The ultrasonic addition enhanced plastic heat production and promoted grain growth in SZ. Compared with NTPFSW, the SZ of both joints was dominated by continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) mechanisms, and geometric dynamic recrystallization (GDRX) grains were also present in U-NTPFSW. The mechanical properties of the joint were improved from 339 MPa to 348 MPa. Ultrasonics introduced numerous vacancies into the weld, which promoted the precipitation of the Al2Cu phase and increased the precipitated phase density of the thermal-mechanical affected zone (TMAZ). The interaction mechanism between the precipitated phase and dislocations was analyzed. The geometrically necessary dislocation (GND) density and residual stress of TMAZ were reduced due to ultrasonic vibration.

Evolution of grain characteristics and dynamic recrystallization behavior of Cu–15Ni–8Sn alloy under different extrusion ratios

For atmospheric melting cast Cu–15Ni–8Sn alloy, hot extrusion tests were conducted on ingots of Cu–15Ni–8Sn alloy with varying extrusion ratios (5, 12 and 16) following homogenization and annealing. The investigation employed mechanical property tests, scanning electron microscopy and transmission electron microscopy to analyze the mechanical characteristics, dynamic recrystallization and twinning behaviors of the alloys subjected to different extrusion ratios. The findings revealed a reduction in the average grain size of the alloy as the extrusion ratio increased. The alloy undergoes dynamic recrystallization during hot extrusion, and the degree of recrystallization of the alloy escalated with higher extrusion ratios. The alloy underwent completely recrystallized at an extrusion ratio of 16, primarily driven by discontinuous dynamic recrystallization (DDRX). In addition, the alloy generated twins during the DRX process, and the twin boundaries provided favorable sites for the nucleation of DRX grains, which promoted the DRX of the alloy. Notably, at an extrusion ratio of 16, the alloy demonstrated impressive mechanical properties, with an ultimate tensile strength of 836 MPa and an elongation of 13.5 %. These results presented a substantial enhancement, showcasing a 54 % increase in the extruded ultimate tensile strength and a 350 % increase in the elongation compared to that of the alloy in the homogenized annealed state.

Heterogeneous dynamic recrystallization in the isothermal compression of Ti55-TiBw composite in α + β region

Dynamic recrystallization (DRX) mechanism of the primary α phase (αp) and β phases in the isothermal compression of TiBw reinforced Ti55 composite in the α + β region was investigated by characterizing the grain boundaries misorientation, local strain, subgrain/grain and dislocation morphologies. The results showed the significant heterogenous DRX in both αp and β phases due to the existence of TiBw. The αp recrystallized grains derived from the deformed αp grains either near or away from TiBw were attributed to the continuous dynamic recrystallization (CDRX) mechanism, in which the TiBw accelerated the recrystallization process of the neighboring αp grains. The evolution of β phase away from TiBw displayed the typical discontinuous dynamic recrystallization (DDRX) features. While the β phase near TiBw underwent the CDRX, where the TiBw reinforcements accelerated the accumulation of dislocations and the occurrence of rapid dynamic recovery (DRV). In particular, the effect of TiBw on the DRX was discussed in detail by considering the special crystal structure of TiBw. It was shown that the DRX grains tended to appear next to the incoherent interfaces (101)TiB, (101¯)TiB or the sharp curvature edges, such as tips and growth steps of the whiskers due to the stronger hindering effect for dislocation movement in these regions.

Investigation on microstructural and microhardness evolution of GH4698 superalloy under transiently varying strain rates

The high-temperature deformation behavior of GH4698 superalloy was explored via isothermal compressive tests under transiently varying strain rates. The impacts of loading types and deformation temperature on flow stress, microstructural evolution, and microhardness were explored, and the underlying nucleation mechanisms for dynamic recrystallization (DRX) were elucidated. Experimental results indicated that the flow stress decreased when the strain rate decreased transiently. Specifically, under loading type I (interrupted strain = 0.11), the flow stress was higher than that under loading type II (interrupted strain = 0.36). Moreover, the flow stress decreased with increase in deformation temperature. When the initial interrupted strain was high, a high degree of DRX was observed in the deformed microstructure. The DRX fraction of types I and II are 48 % and 61 %, respectively. Higher deformation temperatures accelerated the growth of DRX grains, and at a deformation temperature of 1100 °C, DRX fraction reaches 87 %. The microhardness of the DRX grains was higher than that of the deformed grains. At higher deformation temperatures, the γ′ phase dissolved, and the DRX grains grew, resulting in smaller microhardness of the DRX grains than that at lower deformation temperatures. However, microhardness was not sensitive to the loading type (i.e., the value of interrupted strain). Furthermore, discontinuous dynamic recrystallization (DDRX), activated by the initial bulging of grain boundaries, served as the fundamental mechanism for DRX nucleation. Similarly, continuous dynamic recrystallization (CDRX), characterized by the formation of subgrains through dislocation cell structures within individual grains, as well as the γ′ phase and twin boundaries, also played crucial roles in the nucleation of DRX during transiently variation states conditions.

The synergistic and interactive effects of slip systems and dynamic recrystallization on the weakening basal texture of Mg-Y-Nd-Zr-Gd magnesium alloy

Magnesium (Mg) alloys are known to exhibit strong basal texture following large plastic deformation. However, recent experimental studies have revealed that the Mg-Y-Nd-Zr-Gd series alloy displays a weak texture after undergoing 60% compression at 500 °C. The overall deformation texture is similar to that of dynamic recrystallization (DRX) subsets, and the (0001) pole figure of the deformed grain subsets does not concentrate entirely in the compression direction due to the activation of non-basal slip systems. It should be noted that DRX and non-basal slip systems cannot independently account for the final deformation texture. In this case, continuous dynamic recrystallization (CDRX) occurs, where the segregation of rare earth (RE) elements at grain boundaries (GB) impedes the movement of existing GBs and prevents the occurrence of discontinuous dynamic recrystallization (DDRX). Low-angle grain boundaries (LAGB), which are subject to local strain-regulated distribution, continue to absorb dislocations and produce new CDRXed grains. Notably, non-basal slip systems play a role in the generation and subsequent orientation behavior of DRXed grains. As DRX progresses, complex crystal rotations occur on both sides of the newly formed DRX interfaces, causing the orientation of the DRXed grains to gradually deviate from that of the deformed parent grains.

Hot Deformation Behavior and Microstructural Evolution of the As-rolled 7050Al Alloy

The hot deformation behavior of the as-rolled 7050 aluminum alloy was investigated using isothermal hot compression experiments with temperatures ranging from 300 to 460 °C and strain rates ranging from 0.001 to 1 s−1, up to a total strain of 1.1. A strain-compensated Arrhenius (SCA) model was established based on the experimental flow stress data. The predictive accuracy of the model was numerically evaluated using the Correlation Coefficients (R) and the Average Absolute Relative Error (AARE). Electron backscatter diffraction (EBSD) was used to characterize the effects of strain rate and compressive temperature on the microstructure evolution and recrystallization behavior. The results indicated that the geometric dynamic recrystallization (GDRX) occurred at high strain rates or low temperatures, while continuous dynamic recrystallization (CDRX) became the dominant recrystallization mechanism with increasing deformation temperature and decreasing strain rate. The work hardening effect was enhanced during the later stage of deformation, and discontinuous dynamic recrystallization (DDRX) became the main recrystallization mechanism.

Hot deformation behavior, superplasticity and microstructure evolution of a new hot isostatic pressed nickel-based superalloy

The new hot isostatically pressed (HIP) superalloy has demonstrated remarkable superplastic characteristics, as evidenced by studying the compression and tensile deformation behavior. To identify the superplastic deformation zone, the instability regions at various strain variables were overlaid onto the strain rate sensitivity index (m) distribution map at a strain of 0.6, resulting in the acquisition of a new hot working map. The tensile test results showed that under the conditions of 1080 °C-10−2.5 s−1 (0.35 < m < 0.43) and 1030 °C-10−3 s−1 (0.66 < m < 0.74) which located in the superplastic deformation zone in the new hot working map, the new HIPed superalloy exhibited superplasticity, and the elongation was 395 % and 410 %, respectively. Considering the hot working map and the microstructure evolution, the suitable hot working window was further optimized to be 1030–1080 °C and 0.001–0.005 s−1. At high strain rate and low temperature conditions, continuous dynamic recrystallization (CDRX) was the primary mechanism for dynamic recrystallization (DRX), while with the gradual decrease of strain rate, discontinuous dynamic recrystallization (DDRX) tended to occur and dominate the process. DDRX dominated under high temperature deformation condition.

Deformation behavior and microstructure evolution of AZ31 Mg alloy during gradient thermal compression

To achieve a broad range of gradient strain from the rim to the center of a single specimen, the size of the high-throughput double-cone (DC) specimen was optimized using finite-element-model (FEM) simulation. As the deformation increased, the flow stress of the DC specimen quickly reached the maximum value, then gradually declined, and finally tended to be stable. The gradient microstructures corresponding to the gradient strains from the rim to the center of the DC specimen compressed at a certain temperature and strain rate were obtained by only one compression testing. As the equivalent strain increased, the degree of dynamic recrystallization (DRX) gradually rose from the rim to the center of the compressed DC specimen. However, when the equivalent strain and strain rate remained constant, the degree of DRX increased steadily with rising deformation temperature in the compressed DC specimens. Furthermore, during compression of the DC specimens at temperatures of 250 °C and 300 °C, the primary DRX mechanism was continuous dynamic recrystallization (CDRX). At temperatures of 350 °C and 400 °C, the DRX mechanism shifted, as both CDRX and discontinuous dynamic recrystallization (DDRX) were observed. This suggested that the DRX mechanism underwent a change as the deformation temperature increased.

The welding kinetics of interface evolution and mechanism in IN718 alloy solid-state welding

The welding kinetics of interface evolution and mechanism inIN718 alloy solid-state welding are investigated systematically by comparing the hot compression behavior of the separated samples and conventional samples in the temperature range of 1000 °C–1160 °C and strain rate range of 0.1/s to 5/s. The separated samples obtain higher peak stress than conventional samples, and the kinetics analysis results show that separated samples provide higher structural factors and deformation activation energy. The activation energy of the interfacial microstructure evolution of the IN718 alloy was calculated to be 29.7948 kJ/mol. The evolution mechanism of the interface microstructure is characterized by the elimination of the interface second phase and the migration of straight interfacial grain boundaries (IGBs), which is inseparable from the occurrence of interfacial dynamic recrystallization. Interfacial dynamical recrystallization helps to regulate the chemical potential around the second phase for a continuous dissociation. The migration mechanism of the IGBs is influenced by the strain rates, which is continuous dynamic recrystallization (CDRX) for high strain rates and discontinuous dynamic recrystallization (DDRX) for low strain rates.

Why Do Grains Remain Roughly Equiaxed during Steady State Discontinuous Dynamic Recrystallization?

The combination of advection and migration of grain boundaries is analyzed on the basis of a simple mesoscale model, where parallelepipedic grains are considered under uniaxial compression straining. Strain hardening and dynamic recovery are described by the classical Yoshie-Laasraoui-Jonas equation. Grain-boundary migration is driven by the difference in dislocation densities between one representative grain and the average over the material. Finally, nucleation is assumed to occur at grain boundaries. Special attention is paid to the aspect ratio, which starts from unity (infinitely small cubic nucleus) and tends to zero when the grain disappears. In spite of the role of migration, the average shape of the grains is determined as a first approximation by their lifetimes.

Investigation on microstructure characteristics and mechanical properties of twin wire-directed energy deposition-arc fabricated TiAl alloy regulated by the line energy

The microstructure of TiAl alloy is extremely sensitive to the thermal history. During additive manufacturing, multiple thermal cycles and partial remelting of the TiAl deposition layers take place. Therefore, the heat input would exert significant influences on microstructural and mechanical characteristics of additively manufactured TiAl alloys. In this study, TiAl alloys were prepared successfully by twin-wire directed energy deposition-arc (TW-DED-arc). Systematic studies were conducted to regulate the microstructure characteristic and the mechanical property of the as-deposited TiAl alloys via the line energy. The results indicate strong effects of the line energy on the microstructure and performance of the TiAl alloys, which show alternative distribution of layer-band like microstructure with the dendritic grains and the fully lamellar colonies along the deposition direction. With the enhancement in the line energy, the layer-band like feature gradually weakens, and the fully lamellar colonies increase. In addition, the discontinuous coarsen phenomenon and the discontinuous dynamic recrystallization occurred, and the anneal twin was also formed. On the other hand, tensile fractures were observed in the dendritic grains region, and the maximum tensile strength was achieved with the medium line energy. However, the elongation and microhardness are proportional to the line energy. With the elevation in the line energy, the elongation and microhardness gradually increases and decreases, respectively. The microstructure formation mechanism of as-fabricated TiAl alloy is analyzed systematically, and the fracture mechanics was also discussed in detail. The findings of this research contribute not only to the methodology for fabrication of TiAl alloys with the novel TW-DED-arc process, but also to the deep understanding on the regulation of the microstructural and mechanical characteristics of the additively manufactured TiAl alloys.

A comparative analysis of a unique DRX process in achieving a homogeneous distribution of β grains in the single phase region of as-cast Ti644321 alloy

This study aims to investigate the distinctive characteristics of a specialized dynamic recrystallization (DRX) process, which results in a fine and uniform distribution of β grains within the single phase region of as-cast Ti644321 alloy. The formation of deformation bands (DB) and flow localization (FL) is a result of the instability region. On the other hand, the stability region exhibits significant dynamic recrystallization (DRX). The phenomenon of DRX encompasses continuous dynamic recrystallization (CDRX), discontinuous dynamic recrystallization (DDRX), and the coupling mechanism of DDRX and CDRX, which was discovered in this study. The occurrence of DDRX is attributed to grain boundary bulging, while CDRX is a result of the progressive rotation of subgrains. A strain rate of 0.1 s−1 was found to form a fine and uniform distribution of β grains. The formation of this microstructure is facilitated by a coupling mechanism that combines CDRX and DDRX, which involves the grain boundary strain concentration effect that triggers DDRX and the subgrain rotational nucleation process of CDRX. The deformation mechanism of the alloy during hot deformation varies depending on the η value. In the high η region, the primary deformation mechanism is mainly DDRX+CDRX, while in the medium η region, it transitions to CDRX+DRV. Ultimately, in the low η region, the primary deformation mechanism is DB + FL. The presence of a high proportion of DBs hinders DRX. This study provides novel insights into the mechanisms of DRX in β titanium alloys and emphasizes the significance of considering different forms of DRX.

Study on Hot Deformation Behavior and Dynamic Recrystallization Mechanism of Cu‐Ti‐Fe Alloy

Hot compression experiments with the deformation temperatures of 750–950 °C and the strain rates of 0.01–10 s−1 are carried out on a Gleeble‐3500 thermal‐mechanical simulator. The flow behavior and dynamic recrystallization (DRX) mechanism of the Cu‐Ti‐Fe alloy are systematically studied under different hot deformation conditions. According to the curves of flow stress and work hardening rate, the DRX critical condition of the alloy is obtained, and the critical stress value of DRX is small under high‐temperature and low‐strain rate. After fitting, the logarithmic values of the critical stress and critical strain have a linear relationship with lnZ, which indicates that the alloy is more prone to DRX at high temperatures and low‐strain rates. The Arrhenius constitutive model of the alloy is established, the linear correlation coefficient (R2) is 0.984. Combined with the microstructure of Cu‐Ti‐Fe alloy, the microstructure evolution characteristics and DRX mechanism are elucidated. The dominant mechanism of the alloy under the deformation temperature of 750–950 °C is the DRX mechanism. The low‐angle grain boundaries (LAGBs) transform into high‐angle grain boundaries (HAGBs) and continuous dynamic recrystallization (CDRX) grains form. Abundant dislocations gather near the HAGBs, causing grain boundaries to protrude. High‐temperature conditions make the dislocations disappear, forming discontinuous dynamic recrystallization (DDRX) grains.

Investigation of deformation behavior of Mg-2Ho alloy based on hyperbolic sine constitutive equation and PSO-BP neural network

In this study, uniaxial hot compression experiments were conducted on as-cast Mg-2Ho binary alloy that had undergone heat treatment. The hot deformation behavior of the alloy and the influence of strain rate (0.001–1 s−1) and deformation temperature (300–450 °C) on the mechanical properties were systematically studied. The microstructure and dynamic recrystallization (DRX) mechanisms of the alloy were analyzed in detail using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) techniques. A strain-compensated Arrhenius constitutive equation based on Zener-Hollomon parameter and a particle swarm optimization-backpropagation artificial neural network (PSO-BP ANN) based on machine learning (ML) were established to study the flow behavior of the alloy. The experimental results demonstrate that the flow stress decreases with increasing temperature and/or decreasing strain rate. The elevated temperature promotes the occurrence of DRX, resulting in a softening behavior observed in the stress-strain curve. The DRX mechanisms for alloys primarily involve continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX). Further evaluation was conducted by using the correlation coefficient (R2) and mean squared error (MSE) to assess the constitutive equation and PSO-BP ANN. The prediction accuracy of the constitutive equation is poor (R2 =0.924), whereas the measured flow stress and predicted flow stress by PSO-BP ANN exhibit good consistency (R2 =0.99948), making it widely applicable for analyzing and predicting the hot deformation behavior of Mg-2Ho alloy under different experimental conditions.

Thermal deformation behavior and microstructure evolution of GH141 superalloy during double-cone gradient compression

Thermal deformation behavior and microstructure evolution of GH141 alloy were researched efficiently by a high-throughput double-cone (DC) gradient compression to provide support for the formulation of forging process and gaining ideal microstructure. A wide gradient equivalent strain distribution was obtained for the DC specimens under different compression temperatures. The flow stress during DC gradient compression increased rapidly at the beginning of deformation, then decreased rapidly after reaching a certain peak, and finally tended to steady with the increase of deformation. The obvious gradient microstructure was obtained when compressing at 1050 °C, 1075 °C and 1100 °C. But when compressing at 1125 °C and 1150 °C, the grains were uniformly equiaxed inside the DC specimens with gradient strains. Continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) existed simultaneously in the DC specimen compressed at 1050 °C. The dynamic recrystallization (DRX) mechanism shifted towards the DDRX with the rising of compression temperature. In short, increasing the deformation temperature can obtain uniform equiaxed grain microstructure inside a GH141 superalloy with different strains, which has an important guiding role the fabrication of GH141 ring rolled parts.