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This study investigated the effect of extrusion ratio on the microstructural evolution and mechanical properties of the as-extruded short carbon fibers (SCFs) reinforced AZ31 alloy composite, and the microstructural development of the composite during extrusion was thoroughly investigated. The dominant dynamic recrystallization (DRX) mechanisms are particle simulated nucleation, continuous DRX, and discontinuous DRX. The addition of SCFs promotes the dynamic recrystallization during hot extrusion. As extrusion ratio increases, the interfacial bonding degree of the composite increases gradually, and the composite with an extrusion ratio of 25:1 exhibits the finest DRXed grains and the best mechanical performance with a yield strength of 171 MPa, an ultimate tensile strength of 258 MPa and an elongation of 6.0%. The enhanced strength is mainly attributed to grain refinement strengthening and dislocation strengthening, which are induced by the DRXed grains and the added SCFs. [ABSTRACT FROM AUTHOR]

Interfacial bonding behavior of 7050 aluminum alloy clad plates during hot-roll cladding under different vacuum degrees was investigated. The results demonstrated that the bonding effect of the interface was positively correlated with the vacuum degree. Due to severe surface oxidation at 105 Pa, the metal on both sides of the interface did not undergo metallurgical bonding and mainly maintained physical contact, with an ultimate tensile strength (UTS) of only 209 MPa across the interface. At 102 Pa, the large-scale migration of original interfacial grain boundary was still inhibited and continuous dynamic recrystallization occurred mainly at the interface with bulging only locally, which directly led to brittle fracture. At 10–1 Pa, significant discontinuous dynamic recrystallization (DDRX) occurred at the interface, resulting in the complete elimination of the original interface. And UTS across the interface was 338 MPa, reaching the level of the matrix. Therefore, interfacial metallurgical bonding could be achieved by reducing the oxidation of interface and further inducing DDRX during hot-roll cladding. [ABSTRACT FROM AUTHOR]

In this paper, a new fabrication technique for Mg-3Al-1Zn (AZ31) magnesium alloy tube, called tube extrusion expander shear (TEES), was proposed based on the existing extruded shear (ES) technique. The finite-element modeling (FEM) was used to simulate the forming process of TEES. The electron back-scattered diffraction (EBSD) was used to study the microstructures and textures evolution of AZ31 magnesium alloy during TEES process. The mechanical properties of the formed tube were tested. The results show that TEES process can effectively refine the grain size and weaken the basal texture. The hardness and plasticity of the tube processed by TEES process are significantly improved, the maximum elongation is 15%, and the hardness is 78 HV. Based on the analysis of intragranular misalignment axis (IGMA), the evolutions of twins in the TEES process were studied. It was found that twins and basal slip were the main deformation modes in the early deformation zone. With development of TEES process the twins disappear and multiple sliding systems were activated. The results show that the turning and shearing zones of TEES process are beneficial to the activation of multiple slip systems. [ABSTRACT FROM AUTHOR]

Refining the grains of magnesium alloys can improve their mechanical properties. However, in compression at elevated temperatures, grain refinement and the absence of defects in a material are always incompatible. Although increasing the strain and strain rate or lowering the hot deformation temperature is beneficial for obtaining a fine grain size, it also increases the risk of defects such as cracks in the material. Therefore, the hot deformation behavior and grain refinement mechanism of the Mg-9Al-1Zn alloy are systematically studied in this paper. The results show that the deformation mechanisms of magnesium alloys are different when the lnZ values are at different intervals and that prismatic slip is more conducive to dynamic recrystallization than basal slip, which enables the material to exhibit a fine grain size after compression at elevated temperatures. When the Mg-9Al-1Zn alloy is hot deformed at 350 °C ≤ T ≤ 400 °C, 0.5 s−1 ≤ ε ˙ ≤ 5 s−1, and ε = 0.8, its dominant grain refinement mechanism is prismatic slip, at which time the material has good hot processing properties and there is no risk of cracking during deformation. After compression at 400 °C/5 s−1, the grain size is only 3.8 μm, and the hardness is as high as 84.2 kgf/mm2. The results of this study have important theoretical significance for achieving grain refinement of magnesium alloys and further improving their properties. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The evolution of the microstructure and hardness changes in the Au-15Ag-12Cu-6Ni alloy during the processes of cold rolling and annealing were investigated and the heat treatment regimen for the alloy was optimized in this article. The hardness of the alloy continuously increases with the cold rolling reductions, leading to continuous deformation of the grains during the cold rolling process, ultimately resulting in smaller grain sizes. Subsequent annealing induces recovery and recrystallization, achieving complete recrystallization at 700 °C. An intriguing softening effect is observed after annealing at 700 °C, manifesting in a significant reduction in hardness to 238 (Hv0.5). The cold deformation texture of the alloy aligns with the recrystallization texture type, exhibiting only a certain degree of angular deviation. This is primarily characterized by <111>//RD texture and a texture deviating 60° from RD towards TD. The performance of the finished sheet improves with the precipitation of ordered phases AuCu after a 300 °C heat treatment for 0.5 h, resulting in a remarkable hardness of 380 (Hv0.5). [ABSTRACT FROM AUTHOR]

[Display omitted] Microparticle hydrodynamic penetration (HDP) may be associated with the erosion regime in cold spray processing and other high-velocity impact events. Here, in an experimental approach where we can individually launch particles and study the impact sites, we explore copper microparticles impacted on copper substrates at velocities above 900 m/s where HDP begins. We lift cross-sectional lamellae from the impact sites with a focused-ion beam for further microstructural characterization using electron backscatter diffraction and scanning transmission electron microscopy. Due to the gradients of strain, strain rate, and temperature associated with HDP, heterogeneous microstructures result. The structural evolution processes observed include deformation twinning and multiple dislocation-mediated grain recrystallization mechanisms—geometric dynamic recrystallization (gDRX), discontinuous DRX (dDRX), and meta DRX (mDRX). The higher strains at the interface lead to the most significant structural changes and complex mechanisms. In contrast, there is a gradient to more conventional dislocation plasticity away from the interface (on either the particle or substrate side). These microstructural observations are consistent with the deformation map for copper and extend the observations of impact-induced recrystallization across new regimes of behavior. [ABSTRACT FROM AUTHOR]

Large-scale metal additive manufacturing (AM) provides a unique solution to rapidly develop prototype components with net-shape or near-net shape geometries. Specifically, additive friction stir deposition (AFSD) is a solid-state method for large-scale metal AM that produces near-net shape depositions capable of high deposition rates. As AFSD is utilized for a broader range of applications, there is a need to understand deposition strategies for larger and more complex geometries. In particular, components with larger surface areas will require overlapping deposition passes within a single layer. In this study, the AFSD process was used to create depositions utilizing multiple passes with a varying deposition path overlap width. The effects of overlapping parallel pass depositions on the mechanical and microstructural properties of aluminum alloy 7075 were examined. The grain size and microstructural features of the deposited material were analyzed to evaluate material mixing and plastic flow in the observed overlap regions. Additionally, hardness and tensile experiments were conducted to observe the relationship between the overlap width and as-deposited material behavior. In this study, an ideal overlap width was found that produced acceptable as-deposited material properties. [ABSTRACT FROM AUTHOR]

The present paper is concerned with the dynamic recrystallization of the Ti-6Al-4V alloy. Electron Backscatter Diffraction (EBSD) observations are performed after high-temperatures tensile tests, with the temperature ranging from 700 to ~950 °C, and the strain rates varying between 10−4 and 10−2/s. Based on the analysis of flow behavior, the dominant mechanism is identified, and a mechanism map is proposed. In particular, the conditions of 890 °C and strain rates ranging from 10−3 to ~10−2/s serve as the delineating boundary of dynamic recovery (DRV) and dynamic recrystallization (DRX). For superplastic deformation, the dominant softening mechanism is DRV. Consequently, the occurrence of continuous dynamic recrystallization (CDRX) can naturally be ascribed to the process of grain refinement. Then, a multi-scales physical-based constitutive model of CDRX is developed, demonstrating a good agreement is obtained between the experimental and calculated grain sizes, so the above model could be used to describe the grain growth for superplastic deformation. In conclusion, DRV and DRX in the superplastic forming of Ti-6Al-4V are studied in this study, the condition boundaries of their occurrence are distinguished, and a constitutive equation-based CDRX recrystallization mechanism is given, which might be employed in the fracture mechanism research. [ABSTRACT FROM AUTHOR]

In this paper, the microstructure evolution of as-cast and homogenized Mg-9Gd-4Y-2Zn-0.5Zr alloys during hot compression was studied by electron backscattered diffraction analysis. Specimens were compressed at 420 °C with reductions of 20, 40, and 70%. The results indicated that more recrystallized grains were obtained in the as-cast alloy, which was attributed to many block-shaped phase grains. Under the same conditions, the as-cast alloy had a finer microstructure and weaker texture. In the initial stage, dynamic recrystallization in the form of discontinuous dynamic recrystallization participated in deformation. Further deformation contributed to fine grains in the interior of deformed grains in the form of continuous dynamic recrystallization. Basal slip played an active part in the deformed grains, and the recrystallized grains activated pyramidal slip. [ABSTRACT FROM AUTHOR]

The rapid development of cold spraying technology for additive manufacturing of engineering components has made it a viable option for developing thick deposits from high-entropy alloys (HEAs). The microstructure of cold-sprayed CoCrFeNiMn deposit was investigated in this study using electron backscattered diffraction, scanning electron microscopy, and finite element analysis (FEA). The limited studies on the impact deformation behavior of the HEA during cold spraying, limiting our understanding of impact phenomena, and interactions between the HEA particles under ultra-high strain rate deformation motivated this study. From the microstructural characterization, heterogeneous microstructure appears to be formed in the cold-sprayed HEA deposit, comprising of equiaxed ultrafine grains at the particle–particle interfacial regions and coarse grains at the particle interiors. The FEA reveals large strain (> 250%) and temperature (> 90% of the alloy solidus temperature), mainly at the splat's interfaces. Adiabatic shear instability and rotational dynamic recrystallization resulting from heat accumulation and high strain are believed to be responsible for these observations during the ultra-high strain rate deformation of the HEA. The large deformation and grain refinement experienced by the HEA resulted in greater deposit hardness when compared with the sprayed powder, with the nanohardness increasing from 1.16 GPa in the powder to 5.14 GPa in the deposit. This study explores and provides an understanding of the deformation behavior of the HEA and the resulting microstructure during cold spraying. [ABSTRACT FROM AUTHOR]

Full‐field numerical modeling is a useful method to gain understanding of rock salt deformation at multiple scales, but it is quite challenging due to the anisotropic and complex plastic behavior of halite, together with dynamic recrystallization processes. This contribution presents novel results of full‐field numerical simulations of coupled dislocation glide and dynamic recrystallization of halite polycrystalline aggregates during simple shear deformation, including both subgrain rotation and grain boundary migration (GBM) recrystallization. The results demonstrate that the numerical approach successfully replicates the evolution of pure halite microstructures from laboratory torsion deformation experiments at 100–300°C. Temperature determines the competition between (a) grain size reduction controlled by dislocation glide and subgrain rotation recrystallization (at low temperature) and (b) grain growth associated with GBM (at higher temperature), while the resulting crystallographic preferred orientations are similar for all cases. The relationship between subgrain misorientation and strain follows a power law relationship with a universal exponent of 2/3 at low strain. However, dynamic recrystallization causes a progressive deviation from this relationship when strain increases, as revealed by the skewness of the subgrain misorientation distribution. A systematic investigation of the subgrain misorientation evolution shows that strain or temperature prediction from microstructures requires careful calibration. Plain Language Summary: Rock salt, which is dominantly composed of halite, has unique physical properties and plays a key role controlling the evolution of sedimentary basins and mountain chains. Such rocks are also important in petroleum systems, and are used for the geological storage of Geo‐Energy products. However, understanding rock salt behavior is challenging because multiple deformation and recrystallization processes often operate simultaneously when halite is subjected to stress. This contribution presents microdynamic numerical simulations that replicate the main processes that take place during halite deformation at different temperatures. These include glide of dislocations, which are crystallographic defects, and temperature‐controlled recrystallization processes including rotation of subgrains, nucleation of new grains, and migration of existing grain boundaries. The simulations are compared with laboratory experiments, and successfully reproduce them. Subgrain rotation is active at low temperatures, leading to the splitting of grains into smaller ones. As temperature increases, grain boundaries become mobile and grains grow to reduce the energy produced by dislocation glide. Although these processes strongly influence the resulting microstructure, the crystallographic axes are oriented similarly in all cases. We discuss how the effects of multiple microdynamic processes can be evaluated together to accurately estimate strain and the deformation conditions of rock salt. Key Points: The temperature‐dependent transition from subgrain rotation to grain boundary migration (GBM) is simulated, reproducing torsion experimentsIsotropic GBM changes grain size and shape but only slightly affects crystallographic preferred orientationThe relationship between subgrain misorientation and strain is influenced by dynamic recrystallization and thus by temperature [ABSTRACT FROM AUTHOR]

• Bimodal structure formed with the small amount of Ca (0.1wt% and 0.5wt%) in Mg-1Mn-0.5Al alloys. • Nanoscale Mg2Ca dynamic precipitated in unDRXed region, leading to the retard of the DRXed behavior and the formation of bimodal structure. • Tensile yield strength increased from 224 MPa in Mg-1Mn-0.5Al to 335 MPa in Mg-1Mn-0.5Al-0.1Ca and 352 MPa in Mg-1Mn-0.5Al-0.5Ca alloys. The effects of small additions of calcium (0.1% and 0.5% 1 1 All compositions in weight percentage.) on the dynamic recrystallization behavior and mechanical properties of as-extruded Mg-1Mn-0.5Al alloys were investigated. Calcium microalloying led to the formation of Al 2 Ca in as-cast Mg-1Mn-0.5Al-0.1Ca alloy and both Mg 2 Ca and Al 2 Ca phases in Mg-1Mn-0.5Al-0.5Ca alloy. The formed Al 2 Ca particles were fractured during extrusion process and distributed at grain boundary along extrusion direction (ED). The Mg 2 Ca phase was dynamically precipitated during extrusion process, hindering dislocation movement and reducing dislocation accumulation in low angle grain boundaries (LAGBs) and hindering the transformation of high density of LAGBs into high angle grain boundaries (HAGBs). Therefore, a bimodal structure composed of fine dynamically recrystallized (DRXed) grains and coarse unDRXed regions was formed in Ca-microalloyed Mg-1Mn-0.5Al alloys. The bimodal structure resulted in effective hetero-deformation-induced (HDI) strengthening. Additionally, the fine grains in DRXed regions and the coarse grains in unDRXed regions and the dynamically precipitated Mg 2 Ca phase significantly enhanced the tensile yield strength from 224 MPa in Mg-1Mn-0.5Al to 335 MPa and 352 MPa in Mg-1Mn-0.5Al-0.1Ca and Mg-1Mn-0.5Al-0.5Ca, respectively. Finally, a yield point phenomenon was observed in as-extruded Mg-1Mn-0.5Al-xCa alloys, more profound with 0.5% Ca addition, which was due to the formation of (10 1 ¯ 2) extension twins in unDRXed regions. [ABSTRACT FROM AUTHOR]

Hot deformation behavior and microstructural evolution of a Ni-based alloy turbine disc were investigated with the ranges of 1025–1100 °C and 0.001–1 s−1. According to work hardening (WH) curve, the critical strain (stress) for dynamic recrystallization (DRX) was calculated; The DRX volume fraction models were constructed to simulate microstructure evolution behavior by Avrami equation. The microstructure analysis of the studied alloy was investigated by OM and TEM. At 1075 °C/0.1 s−1, the intragranular γ' phases can effectively prevent dislocations movement, forming a high density of dislocation substructures and subgrain boundaries in the grain. The critical stresses for DRX increase with the increase of strain rates and the decrease of temperatures, and the critical strains for DRX increase with decreasing temperature. DDRX are the main nucleation mechanisms, and the grain boundaries provide nucleation sites for dynamic recrystallized grains. The DRX behaviors were predicted by DRX volume fraction models, and the simulated results are close to the experimental results. [ABSTRACT FROM AUTHOR]

The current review work studies the adiabatic shear banding (ASB) mechanism in metals and alloys, focusing on its microstructural characteristics, dominant evolution mechanisms and final fracture. An ASB reflects a thermomechanical deformation instability developed under high strain and strain rates, finally leading to dynamic fracture. An ASB initially occurs under severe shear localization, followed by a significant rise in temperature due to high strain rate adiabatic conditions. That temperature increase activates thermal softening and mechanical degradation mechanisms, reacting to strain instability and facilitating micro-voiding, which, through its coalescence, results in cracking failure. This work aims to summarize and review the critical characteristics of an ASB's microstructure and morphology, evolution mechanisms, the propensity of materials against an ASB and fracture mechanisms in order to highlight their stage-by-stage evolution and attribute them a more consecutive behavior rather than an uncontrollable one. In that way, this study focuses on underlining some ASB aspects that remain fuzzy, allowing for further research, such as research on the interaction between thermal and damage softening regarding their contribution to ASB evolution, the conversion of strain energy to internal heat, which proved to be material-dependent instead of constant, and the strain rate sensitivity effect, which also concerns whether the temperature rise reflects a precursor or a result of ASB. Except for conventional metals and alloys like steels (low carbon, stainless, maraging, armox, ultra-high-strength steels, etc.), titanium alloys, aluminum alloys, magnesium alloys, nickel superalloys, uranium alloys, zirconium alloys and pure copper, the ASB propensity of nanocrystalline and ultrafine-grained materials, metallic-laminated composites, bulk metallic glasses and high-entropy alloys is also evaluated. Finally, the need to develop a micro-/macroscopic coupling during the thermomechanical approach to the ASB phenomenon is pointed out, highlighting the interaction between microstructural softening mechanisms and macroscopic mechanical behavior during ASB evolution and fracture. [ABSTRACT FROM AUTHOR]

A Mg-3Al-1Zn (AZ31) alloy with highly homogeneous fine grains was fabricated using a simple extrusion method named pre-die forging extrusion (PFE). The strain induced by the pre-forging process resulted in crystal defects and a higher driving force for dynamic recrystallization. The grain size of AZ31 alloy was significantly refined to 1.74 μm by using PFE for 60 s at 300 °C (300-60 s). The 300-60 s samples exhibited excellent mechanical properties of tensile yield strength of 305 MPa and elongation of 27%. The improvement in the mechanical properties of the PFE samples is mainly attributed to the grain refinement mechanism. An experimental basis for the appropriate temperature to refine the grains during extrusion is provided in this study. [ABSTRACT FROM AUTHOR]

The hot deformation behaviours of 316LN-Mn austenitic stainless steel were investigated by uniaxial isothermal compression tests at different temperatures and strain rates. The microstructural evolutions were also studied using electron backscatter diffraction. The flow stress decreases with the increasing temperature and decreasing strain rate. A constitutive equation was established to characterize the relationship among the deformation parameters, and the deformation activation energy was calculated to be 497.92 kJ/mol. Processing maps were constructed to describe the appropriate processing window, and the optimum processing parameters were determined at a temperature of 1107–1160°C and a strain rate of 0.005–0.026 s−1. Experimental results showed that the main nucleation mechanism is discontinuous dynamic recrystallization (DDRX), followed by continuous dynamic recrystallization (CDRX). In addition, the formation of twin boundaries facilitated the nucleation of dynamic recrystallization. [ABSTRACT FROM AUTHOR]

A novel material processing method, friction stir-surface mechanical attrition treatment (FS-SMAT) was conducted on pure magnesium plate and AZ31 magnesium alloy plate. Two types of stir tools, spherical stir tool and plane stir tool, are designed to process FS-SMAT to reduce the heat input compared with the traditional friction stir processing (FSP). Microstructure evolution during FS-SMAT and its effect on mechanical property are investigated. FS-SMAT has different effect on microstructure and mechanical property when using the spherical and plane stir tools. Different heat input and plastic deformation can be produced due to the specific shapes of stir tools. Using a spherical stir tool, the grain size of pure magnesium plate was refined to 1.74 μm. The micro-hardness was improved from 40 HV to 63 HV. In contrast, after FS-SMAT with a plane stir tool, the grain size and micro-hardness of AZ31 magnesium alloy are 0.91 μm and 125 HV, respectively. [ABSTRACT FROM AUTHOR]

This study examines the flow behavior and deformation mechanism of a FGH4113A superalloy with high γ′ content for different strain rates (0.01–1 s−1) at sub-solvus (1030, 1080 °C), near-solvus (1130 °C), and sup-solvus temperatures (1180 °C). The results indicated that the alloy exhibits four different flow behaviors: rapid softening after reaching peak stress (at 1030–1080 °C), slow softening after reaching peak stress (at 1130–1180 °C/0.1–1 s−1), steady state flow (at 1130 °C/0.01 s−1), and continuous hardening (at 1180 °C/0.01 s−1). The strain rate sensitivity exponent decreases as the flow behavior transforms from dynamic softening to continuous hardening. Moreover, the dynamic recrystallization (DRX) fraction decreases with increasing strain rate at sub-solvus temperatures, where an inverse trend was observed at near- or sup-solvus temperatures. These observations are influenced by the interplay of continuous original grain boundary migration (COBM), DRX, and grain growth. Meanwhile, the primary γ′ phase has different roles under distinct deformation conditions. At sub-solvus temperature, the primary γ′ phase facilitates DRX, grain refinement, and coordinated plastic deformation. At near-solve temperature, the primary γ′ phase predominantly contributes to coordinated plastic deformation. At the sup-solvus temperature, the γ′ phase entirely dissolves, with the grains coarsened by COBM continuously undergoing compressed, exhibiting continuous hardening.

The tensile tests of the extruded ZK60 Mg containing a longitudinal weld seam were carried out at room and elevated temperatures, and the effects of induced microstructure inhomogeneity on tensile deformation behavior was clarified. The results show that the deformation mode, dynamic recrystallization (DRX), texture evolution and mechanical properties are strongly affected by the longitudinal weld seam, temperature, and loading direction. The room temperature (RT) deformation of welding zone is controlled by the dislocation slips with the association of some twins, while twinning plays significant roles in the accommodation of c-axis strain of the coarse grains on matrix zone. The deformation at RT stretched along extrusion direction (ED) and transverse direction (TD) are controlled by basal slip/twinning and basal slip/prismatic slip/twinning, respectively. During high temperature tension, the dislocation cross slip of pyramidal slip is activated, and grain boundary sliding occurred in welding zone, leading to the superplastic behavior. With the increase of tensile temperature, the predominant DRX mode is transformed from continuous DRX to discontinuous DRX. Moreover, the basal poles of the grains spread from TD towards ED with the decrease of maximum pole intensity when stretched along ED, while non-basal textures are transformed to 〈10–10〉 fiber texture when stretched along TD. The slip-dominated flow is seen during RT tension along ED, while twinning becomes predominant during RT tension along TD. The fine grain structure causes the superior RT tensile properties along ED of welding zone with ultimate tensile strength of 315 MPa and elongation to failure of 13.8%. With the increase of tensile temperature, the slipping-dominated deformation is transformed into twinning-dominated, causing the decrease of strength and increase of elongation.

Featured initial microstructures of Mg-11Gd-4Y-2Zn-0.5Zr alloy (wt%) were obtained by adjusting temperatures of solid solution and cooling methods, including island intergranular 18R and 14H LPSO phases with low-density stacking faults, differentially spaced lamellar intragranular 14H-LPSO phases, and network intergranular 18R-LPSO phases with high-density intragranular stacking faults. Effects of these featured LPSO phases and stacking faults on dynamic recrystallization (DRX) behavior were investigated via hot compression. Promoted DRX behavior via particle stimulated nucleation (PSN) is introduced by coexisting intergranular island 18R and 14H LPSO phases and intragranular wide spacing lamellar 14H-LPSO phases, contributing the highest DRX fraction of 42.6%. Conversely, it is found that DRX behavior with network intergranular 18R-LPSO phases and dense intragranular stacking fault is considerably inhibited with the lowest fraction of 22.8%. That is, the restricted DRX due to dislocations pinning by stacking faults overwhelms the enhanced DRX behavior via PSN of island intergranular 18R and 14H LPSO phases. Specially, compared with dense intragranular lamellar 14H-LPSO phases, high-density stacking faults exert a larger inhibition effect on DRX behavior.

Low absolute strength becomes one major obstacle for the wider applications of low/no rare-earth (RE) containing Mg alloys. This review firstly demonstrates the importance of grain refinement in improving strength of Mg alloys by comprehensively comparing with other strategy, e.g., precipitation strengthening. Dynamic recrystallization (DRX) plays a crucial role in refining grain size of Mg wrought alloys. Therefore, secondly, the DRX models, grain nucleation mechanisms and the related grain refinement abilities in Mg alloys are summarized, including phase boundary, twin boundary and general boundary induced recrystallization. Thirdly, the newly developed low-RE containing Mg alloy, e.g., Mg-Ce, Mg-Nd and Mg-Sm based alloys, and the RE-free Mg alloys, e.g., Mg-Al, Mg-Zn, Mg-Sn and Mg-Ca based alloy, are reviewed, with the focus on enhancing the mechanical properties mainly via the grain refinement strategy. At the last section, the perspectives and outstanding issues concerning high-performance Mg wrought alloys are also proposed. This review is meant to promote the deep understanding on the critical role of grain refinement in Mg alloys and provide reference for the development of other high strength and low-cost Mg alloys which are fabricated by the conventional extrusion/rolling processing.

A novel continuous expanding extrusion process for manufacturing Cu–Cr–Zr strips was proposed in the present study. The U-shaped strips with a cross-section of 420 mm × 19 mm were successfully prepared by taking the upward continuous casted Φ 28 mm rods as raw material. Electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) were employed to characterize the microstructure and precipitates, respectively, which revealed that the microstructure of the continuous extruded strip is very fine and uniform across the entire cross-section and the Cr precipitates are in a dispersed distribution in the matrix helping to improve the strength of the alloy. The average grain size is approximately 1 μm and much smaller than that of the as-cast state (in millimeters). The average micro-hardness, tensile strength, and electrical conductivity of the extruded strip are 120 HV, 328.8 MPa, and 82.6 % IACS, respectively, increasing approximately by 31.6 %, 29.3 %, and 125.5 % in comparison to these of the as-cast state. In addition, the fracture elongation can maintain a very high level (average value ∼28.9 %). The strengthening mechanisms were then quantitatively calculated, which showed that grain boundary strengthening, precipitation strengthening, and dislocation strengthening take comparable contributions. Thus, our investigations provide new insights into manufacturing high-performance Cu–Cr–Zr strips.

In this study, we investigated the hot deformation behavior of Ti–6Al–2Sn–4Zr–2Mo (Ti-6242) alloy and propose a method to derive optimal hot process parameters for grain refinement and avoidance of flow instability. Microstructural Risk Index (MRI) was introduced as a microstructural evaluation index consisting of grain size, standard deviation of grain size, and flow instability. The initial temperature of the material and the stroke speed of the die were selected as design variables. Finite element analysis (FEA) was used to calculate grain size and flow instability and determine MRI of the forgings. The grain size model coefficient and flow instability were calculated based on the flow stress curve and verified with optical microscope (OM) and electron backscatter diffraction (EBSD) analysis results. The Deep Neural Network (DNN) model was used to determine the optimal process parameters for the forging process. The MRI prediction accuracy of the trained DNN models showed excellent performance at 97.01 %. The MRI of the optimized process variables was improved by 7.95 % compared to the minimum MRI of the training data set. Optimized process parameters can improve the quality of forgings through grain refinement and avoidance of flow instability regions.

In this work, we systematically evaluated the effect of Si on the dynamic recrystallization (DRX) during hot deformation behavior of a novel high-strength rolled Medium Mn steel. To this end, the novel steel was subjected to compression test in the temperatures of range temperature of 950–1150 °C and the strain rate of range of 0.01–10 s−1. Numerical simulation, constitutive analysis, different models and processing maps were also developed to predict the volume fraction of DRX, which was further confirmed through electron backscatter diffraction (EBSD). The results show that some disparities are existed between the model predictions and the results. The EBSD micrographs of samples displayed prominent discontinuous DRX peak in the true stress-strain curves exhibit conventional equiaxed DRX particles. Most specifically, in initial stages the addition of Si increased the DRX and grain boundary migration, and the later stages of deformation the DRX was triggered after achieving the steady state. Therefore, the final microstructure appears as elongated austenite or localized DRX. Furthermore, the work hardening stage before the new round of DRX nucleation caused the stress to continue to increase after the steady state. These findings provide valuable insights into the complex behavior of materials under the influence of Si addition and enhancing our understanding of microstructural evolution during hot deformation.

The hot-working behavior of high-Mn austenitic steel for liquefied natural gas carriers at the deformation temperature in the range of 1073–1273 K and the strain rate in the range of 0.01–10 s−1 was studied on a Gleeble-3800 thermomechanical simulator using a compression test. Electron backscatter diffraction was used to study the microstructure after deformation. Under each deformation condition, a peak stress appears in the stress-strain curve, which conforms to traditional dynamic recrystallization hot-working flow stress curves. A hyperbolic sine-law-type constitutive equation was established to predict the peak stress. The thermal deformation activation energy was 414.19 kJ/mol, and the stress index n was 4.94. The texture of the deformed grains consisted of strong and weak fibers along the compression direction. The main recrystallization mechanism was discontinuous dynamic recrystallization. The grain size of the discontinuous dynamic recrystallization grains tended to increase with increasing deformation temperature or decreasing strain rate. Processing maps were drawn based on the dynamic material model. At high deformation temperatures, the power consumption factor of dynamic recovery was greater than that of dynamic recrystallization, whereas at low deformation temperatures, the power consumption factor of discontinuous dynamic recrystallization was greater than that of dynamic recovery. There are two flow instability regions in the processing maps, 1243–1273 K/1-10 s−1 and 1073–1203 K/0.05–10 s−1. The formation of a ‘necklace microstructure’ was the main cause of deformation instability. The optimized process parameters for industrial production were 1243–1273 K/1-10 s−1.

A series of hot plane strain compression (PSC) experiments of the extruded Mg-6.03Zn-0.55Zr alloy were conducted on the Gleeble-3500 machine with strain rates of 0.01 s−1 to 10 s−1 and temperatures ranging from 300 °C to 500 °C to reveal the microstructure evolution during the secondary process. The effects of grain refinement and texture modification which were easily affected by the deformation mechanism and dynamic recrystallization (DRX) were systematically studied. Experimental results showed that the main deformation mechanism during PSC was basal slip (74.3 %–94.9 %) and assisted by prismatic slip (4.8 %–21.1 %) and pyramidal slip (0.3 %–4.6 %). Since the pyramidal slip and prismatic slip were more preferred to activate owing to the significant decrease of critical resolved shear stress (CRSS) at a higher temperature, the activation of non-basal slip promoted the c-axes of the grains deviated from compression direction which weakened the basal fiber texture. Moreover, the activation of non-basal slip could promote DRX behavior to some extent. Further analysis of the DRX mechanism showed that the continuous DRX (CDRX) by continuous rotation of low angle grain boundaries was dominant at lower temperatures and higher strain rates, while discontinuous DRX (DDRX) which nucleated at the grain boundaries played a more and more important role as the temperature increased and strain rate decreased. After characterizing the orientations of the DRXed grains, the CDRXed grains owned a similar grain orientation with the deformed grain while the DDRXed grains exhibited a fairly dispersed distribution, indicating that the weakening effect of the basal texture was greater with a higher DDRX fraction.

The hot compression tests of Fe–28Mn–11Al–1.5C–5Cr (wt.%) lightweight steel were carried out by Gleeble-3500 at temperature of 900, 1050 and 1150 °C with strain rates of 0.01 and 1 s−1. The effect of various precipitates on the hot deformation mechanism and dynamic recrystallization (DRX) mechanism was studied by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). When deformed at 900 °C, the dislocations tend to cut through intragranular κ carbides to form unidirectional microbands and deformation twins. The intergranular precipitates (intergranular κ carbides, B2 (FeAl type) precipitates and (Cr,Mn)23C6 precipitates) hinder the migration of the original grain boundaries, so that the discontinuous DRX (DDRX) is suppressed at the initial stage, but with the increase of strain, the dislocations accumulate at the grain boundaries to promote the nucleation of DRX grains. Meanwhile, the nucleation of DRX grains by continuous DRX (CDRX) mechanism within grains is also activated. Therefore, bimodal distribution of DRX grains is formed at low strain rate of 0.01 s−1, while the degree of DRX is low at high strain rate of 1 s−1. When the deformation temperature is 1050 °C, the content of microbands and deformation twins decreases. There are only a few B2 precipitates at the grain boundaries, so the original grain boundaries tend to bulge to promote DDRX nucleation. When deformed at 1150 °C, large-sized κ carbides are easily formed near the dislocations due to the fast diffusion rate of atoms, which inhibits the formation of microbands and deformation twins, and only slip bands are observed. There is no precipitate on the grain boundary, and the DDRX is the dominant mechanism of DRX. Moreover, the special yield-point-like elongation phenomenon has been proved to be caused by intragranular κ carbides.

A new titanium alloy with chemical composition of Ti–6Al–1Mo–1V–2Zr–2Cr–1Fe (wt.%) is designed and produced. The hot deformation behavior, microstructural evolution and texture evolution of the alloy after solution treatment are investigated in this paper. Firstly, the constitutive equation of solution-treated Ti–6Al–1Mo–1V–2Zr–2Cr–1Fe alloy with the consideration of strain compensation is obtained based on compressive test at the temperatures of 950–1100 °C and the strain rates of 0.01–10 s−1, which can be used to describe the flow behaviour at elevated temperatures. According to the corresponding constitutive equation, the flow stress of solution-treated alloy is accurately predicted, which is further verified by the experimental data. Furthermore, discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) are observed in the microstructures of the deformed alloys, where deformation temperature and strain rate have a significant effect on DDRX and CDRX processes of solution-treated Ti–6Al–1Mo–1V–2Zr–2Cr–1Fe alloy. Moreover, plastic deformation and dynamic recrystallization have a comprehensive influence on the texture evolution of solution-treated Ti–6Al–1Mo–1V–2Zr–2Cr–1Fe alloy. ηbcc-fiber textures of {100} and {110}, εbcc-fiber texture of {112} and ξbcc-fiber texture of {110} are the main texture compositions of the deformed samples, where all of the deformed samples exhibit a strong {100} texture.

With the improvement of thermal efficiency and the lightweight tendency of engine blades, Ni-based superalloy is widely used owing to its excellent performance in high-temperature atmospheres. This work studied the effects of surface oxidation, internal environmental attack, and matrix damage on the failure mechanism in a thin-walled casting Ni-based superalloy at 980 °C/160 Mpa. At the edge of the fracture, the sample suffered a severe environmental attack, resulting in the oxidation-affected zone forms. However, the loss of effective bear area induced by surface damage could not be the main reason for the sample's failure. At the interior of the matrix, voids were preferably initiated at the interface of MC carbides. As the increase of creep deformation, dynamic recrystallization (DRX) occurred at the tip of the voids, which increased the transverse grain boundaries and promoted crack propagation. Moreover, the DRX provided a short penetration path for the nitrogen, causing internal nitridation with AlN and Ti(Ta)N to precipitate. EBSD analysis confirmed that nitrides induced significant dislocations to accumulate at the boundaries of nitrides/γ, accelerating the failure of the sample.

In friction stir welding (FSW) of dissimilar Al/Mg alloys, the materials on both sides in weld nugget zone (WNZ) undergo extremely uneven high temperature and plastic deformation, resulting in a great difference in dynamic recrystallization (DRX) which determines the weld microstructure evolution. In this study, the multi-phase field model coupled with the dislocation density model is developed to conduct numerical simulation of DRX behavior in WNZ of Al/Mg alloys FSW with Mg placed on advancing side. It is found that during welding process, the grain size at the checking points in WNZ always decreases rapidly at first and then increases slowly to a stable value, while the dislocation density always increases first and then decreases to a stable level. After welding, the final grain size on Al's side is lower than that on Mg's side. As the welding speed decreases, the DRX becomes more intense, and the dislocation density curve fluctuates more frequently. The calculated final values of average grain size at both Al's and Mg's sides are in good agreement with the experimentally measured ones.

The high temperature deformation behavior and mechanisms of the cold-deformed CoCrCu1.2FeNi high-entropy alloy (HEA) were investigated by optical microscope (OM), scanning electron microscope (SEM) and electron backscattered diffraction (EBSD) at temperatures and strain rates of 950–1100 °C and 0.001–1 s−1, respectively. The results show that the flow stress increases as the deformation temperature decreases and the strain rate increases, and there is significant dynamic recrystallization (DRX) during the deformation process. 1050–1090 °C/0.02–1 s−1 and 975–1050 °C/0.002–0.2 s−1 are the optional hot temperature deformation regions. Discontinuous dynamic recrystallization (DDRX) occurs at different temperatures when the strain rate is 0.001 s−1 with a maximum recrystallization percentage of 90.28 %. The DRX degree gradually increases as the temperature rises from 950 °C to 1000 °C and from 1050 °C to 1100 °C. The maximum polar density of texture sharply increases to 11.78 at 1050 °C. The deformed microstructure leads to an increase in dislocation density, which could be effectively reduced by DRX.

In this investigation, cold-rolled Al1050 sheets underwent various passes of Friction Stir Processing (FSP), namely one, three, and five. Then, microstructural evolution was assessed by focusing on underlying restoration phenomena, including severe dynamic recovery (DRV) and continuous dynamic recrystallization (CDRX), and their corresponding effects on mechanical and surface properties were evaluated. Findings illustrated that initial cold-rolling on Al1050 and its high stacking fault energy are the primary driving forces for accelerating DRV, contributing to the supremacy of the DRV-induced softening over sub-grain strengthening caused by CDRX. Increasing the FSP pass number resulted in a drop in yield stress (YS), ultimate tensile strength (UTS), and microhardness values of the FSP-treated samples such that the UTS of one, three, and five passes FSPed samples decreased by ∼18 %, 32 %, and 35 %, respectively, compared to the cold-rolled Al1050. Conversely, the %elongation of the FSP-treated samples dramatically increased with increasing FSP pass number, which is evident from stress-strain curves and the fracture surfaces. Furthermore, increasing the FSP pass number increased the mean coefficient of friction (MCOF) and weight loss during the pin-on-disk test. Also, conducting various passes of FSP improved corrosion resistance compared to the base metal. However, increasing the FSP pass number reduced the corrosion resistance due to grain growth such that the one-pass FSPed sample illustrated better corrosion resistance than the five passes FSPed sample. Repeating the FSP led to excessive frictional heat input to the matrix, contributing to grain growth after increasing FSP passes, thereby decreasing mechanical properties and corrosion resistance.

Precipitation behavior and dynamic recrystallization (DRX) behavior of Mg–Zn–Y alloys with different Zn/Y atomic ratios under different extrsuion temperatures were systematically investigated in this work. The results shows that the types of precipitated phases in the casted alloys are changed with the increase of Zn/Y atomic ratio. After extrsuion, the brittle W-phases in Mg98.7Zn1Y0.3 and Mg98Zn1Y1 alloys are broken into finer particles along the extrusion direction, but the resistance of W-phases to grain growth is weak at higher extrusion temperature. However, Mg97.5Zn1Y1.5 alloy exhibits relatively stable grain size at different extrusion temperatures, due to the significant inhibitory effect of LPSO phases on grain growth at high temperatures. The banded LPSO phases with wide phase spacing can promote DRX behavior via particle stimulated nucleation (PSN) resulting in highest DRX fraction. Nevertheless, the lamellar LPSO phases could effectively hinder the grain boundary migration and dislocation motion, which is against the nucleation and growth of DRX grains. It is precisely due to the influence of LSPO phases on the DRX behavior and its own kinking effect that Mg97.5Zn1Y1.5 alloy has better heat resistance. Mg97.5Zn1Y1.5 alloy exhibits excellent tensile strength and ductility, with ultimate tensile strength (UTS) of 413 MPa, yield strength (YS) of 330 MPa and elongation (EL) of 12.1% after extrusion at 573 K. The good ductility is mainly due to the coordinated deformation ability of the LPSO phase and the activated non-basal slip effect. The synergistic effect of lamellar LPSO phase and kinking deformation effectively refines the microstructure of the alloy and improves the strength.

Abstract Bridge steel has been widely used in recent years for its excellent performance. Understanding the high-temperature Dynamic Recrystallization (DRX) behavior of high-performance bridge steel plays an important role in guiding the thermomechanical processing process. In the present study, the hot deformation behavior of Q370qE bridge steel was investigated by hot compression tests conducted on a Gleeble 3800-GTC thermal-mechanical physical simulation system at temperatures ranging from 900 ℃ to 1100 ℃ and strain rates ranging from 0.01 s−1 to 10 s−1. The obtained results were used to plot the true stress-strain and work-hardening rate curves of the experimental steel, with the latter curves used to determine the critical strains for the initiation of DRX. The Zener-Hollomon equation was subsequently applied to establish the correspondence between temperature and strain rate during the high-temperature plastic deformation of bridge steel. In terms of the DRX volume fraction solution, a new method for establishing DRX volume fraction was proposed based on two theoretical models. The good weathering and corrosion resistance of bridge steel lead to difficulties in microstructure etching. To solve this, the MTEX technology was used to further develop EBSD data to characterize the original microstructure of Q370qE bridge steel. This paper lays the theoretical foundation for studying the DRX behavior of Q370qE bridge steel.

In this paper, the differences in mechanical properties and high temperature (HT) deformation behavior between TiBw/Ti65 and TiBw/TA15 composites with network structure were studied. The alloy element distribution and microstructure of TiBw/Ti65 and TiBw/TA15 composites were characterized by the electron probe micro analyzer and transmission electron microscopy. The microstructure evolution during HT deformation was analyzed by electron back scatter diffraction. The mechanical properties of two composites were tested at room temperature and 600–750 °C. Arrhenius and artificial neural network models were developed to predict the peak stress and flow stress, respectively. The results show that the multiple alloying elements and silicide in TiBw/Ti65 refined the grains. TiBw/Ti65 composites had higher deformation activation energy and higher strength under the same deformation conditions. Based on the analysis of differences in microstructure, the strengthening mechanisms of TiBw/Ti65 compared to TiBw/TA15 was mainly from fine grain strengthening, dislocation density strengthening, and Orowan strengthening of silicide. The initial recrystallization temperatures for TiBw/TA15 and TiBw/Ti65 were 700 °C and 750 °C with strain rate of 0.001 s−1, respectively. The above results show that TiBw/Ti65 had better HT deformation resistance.

The deformation characteristics of as-extruded pure zinc were studied over a wide deformation temperature range from −40 °C to 300 °C. Two-cycle dynamic recrystallization was recognized for the first time to occur at different temperatures, leading to an oscillatory flow curve. The second stress peak was mitigated as the deformation temperature increased, while it disappeared at 300 °C. Different mechanisms, including twin dynamic recrystallization, twin-assisted grain boundary nucleation, and continuous mechanism were operative during the first dynamic recrystallization cycle, while the discontinuous mechanism was dominant during the second cycle. The accelerated dynamic recovery at high temperatures (200 °C) exhausted the driving force for the occurrence of the second dynamic recrystallization cycle. A distinct difference was observed between the microstructure developed at high and low temperatures. A bimodal recrystallized grains microstructure was formed at 25 °C, while a deformed microstructure including elongated grains was developed at 200 °C. Increasing the deformation temperature from 25 °C to 200 °C remarkably increased the grain orientation spread values and strengthened the final texture intensity, where the maximum texture intensity was remarkably increased from 9.95 to 30.64 multiple of a random distribution.

Improving the high temperature strength of Mo alloys is a key problem to expand the application range of Mo alloys. In this study, the Mo-1.5 wt%Ti3AlC2 alloy was designed by introducing new two-dimensional (2D)-layered ceramic particles Ti3AlC2 into Mo. The peak flow stress of the Mo-1.5 wt%Ti3AlC2 alloy reaches 308 MPa at 1200 °C. The diffusion activation energy Q of the Mo-1.5 wt%Ti3AlC2 alloy is as high as 533.38 kJ/mol, which is higher than that of pure Mo (480 kJ/mol). Sintering in the reducing atmosphere of hydrogen at high temperature, the Ti3AlC2 consumes a large amount of energy to form AlTi3 and Ti5O9, which leads to an increase in the diffusion activation energy. We have established the constitutive equation of the Mo-1.5 wt%Ti3AlC2 alloy, and studied the microstructure evolution and deformation mechanism under hot compression. The results show that the stress index of n1 > 3 indicates that the plastic deformation mechanism was a dislocation mechanism. With the addition of Ti3AlC2, a large number of dislocations were produced in the alloy at the early stage of hot deformation. With increasing temperature, the dislocation entanglement gradually cancels out, resulting in the decrease of dislocation density. With the increase of temperature and deformation rate, the dynamic recrystallization (DRX) mechanism of the Mo-1.5 wt%Ti3AlC2 alloy was mainly continuous dynamic recrystallization (CDRX) at 1200 °C/0.01 s−1 and discontinuous dynamic recrystallization (DDRX) at 1600 °C/10 s−1. This work provides a new research direction for designing high performance Mo alloys.

This review article provides an in-depth discussion on the hot deformability, processing map analysis, and microstructural development in superalloys, as well as the associated constitutive equations employed in flow stress prediction. It describes how hot working can improve the grain structure of superalloys by dynamic recrystallization (DRX), reduce defects, and enhance their mechanical characteristics. The formation of necklace structures, work-hardening analysis to identify the existence and commencement of dynamically recrystallized grains and the influence of processing conditions on DRX grain size are all addressed in this article. The influence of deformation variables, described by the Zener-Hollomon parameter - the occurrence of phases, dynamic precipitation, and alloying elements on the thermomechanical response, and the restoration processes of DRV and DRX are discussed in detail. The utilization of processing maps as a means to determine the most favourable processing conditions and identify the instability regime, encompassing flow instability, defects and cracking, that may arise during the hot-working of superalloys are discussed. Specifically concerning the constitutive modelling of flow stress for characterizing material flow (at various deformation strain rates, temperatures, and strain), the application of threshold stress (as a result of phase transformation during hot deformation), temperature-dependent Young's modulus, and comparing the experimentally observed activation energy and deformation stress exponent to the values predicted by creep theories, are discussed. Also, an analysis of the various modelling techniques and equations for predicting flow curves during hot-working processing is evaluated. Finally, some recommendations are made regarding the potential future research directions.

In the field of specialty electronics and communications, there is a critical demand for magnesium (Mg) alloy sheets that possess exceptional mechanical properties and electromagnetic interference shielding effectiveness (EMI SE). This paper aims to develop a cost-effective and straightforward process for preparing a research proposal that combines excellent mechanical properties and EMI SE. After undergoing extrusion treatment, the Mg–6Zn–1La-0.5Zr alloy demonstrates an apparent bimodal microstructure, with an average grain size of approximately 2.55 μm. Subsequently, following a 37% rolling treatment, the grain size increases to about 5.29 μm. This increase in grain size is attributed to grain growth resulting from holding prior to the multi-pass rolling treatment. Notably, the Mg–6Zn–1La-0.5Zr alloy, subjected to extrusion and 75% rolling treatment, exhibits remarkable mechanical properties and EMI SE, with ultimate tensile strength (UTS), yield strength (YS), and elongation (EL) values of 337.5 MPa, 227.3 MPa, and 12.5%, respectively. Furthermore, the EMI SE ranges from 79 dB to 110 dB within the frequency range of 30–1500 MHz. The exceptional mechanical properties are attributed to the synergistic effects of various strengthening mechanisms, including grain boundary strengthening, second phase strengthening, dislocation strengthening, heterogeneous deformation-induced strengthening, and texture. Similarly, the superior EMI SE is attributed to the alloy's higher electrical conductivity, strong basal texture, and uniformly diffused second phase.

In this paper, the dynamic precipitation and dynamic recrystallization (DRX) behaviors of Mg-7Gd-2Nd-0.5Zr (wt.%) alloy during thermal compression were investigated by optical microscopy (OM), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The hot compression tests were performed at 350–500 °C with strain rates of 0.003–1 s−1 and a strain of 0.7. The results indicate that dynamic precipitation and DRX occur in the deformed region under appropriate conditions, and that dynamic precipitation precedes DRX. Elevated deformation temperature and strain rate facilitate DRX but weaken dynamic precipitation. The dynamic precipitates were β (Mg5Gd) phases and were mainly located at the grain boundaries in the deformed regions. DRX can be promoted when the size of the granular precipitates is larger than 200 nm. The second phase particles located at the grain boundaries of the recrystallized grains can pin the grain boundaries to refine the recrystallized grains. There are three mechanisms of recrystallization nucleation: grain boundary bowing nucleation, dislocation pile-up induced nucleation, and particle-stimulated nucleation (PSN). Moreover, a critical strain model and a kinetic model for the DRX of the alloy were developed.

Due to the high deformation resistance and poor thermal ductility of the new cast GH4151 alloy ingots, cracks are easy to occur during cogging process. For clarifying the effects of deformation parameters on microstructural evolution and dynamic recrystallization (DRX) nucleation mechanisms. In this work, the causes of crack formation and extension were first investigated using SEM and EBSD. The study revealed that the reasons for crack formation and propagation are the MC carbides at the original grain boundaries, large-size γ′ phase, residual eutectic phases, and tiny pores near the grain boundaries. Subsequently, a series of hot compression tests were performed using a Thermecamastor-Z thermo-mechanical simulator at temperatures ranging from 1080 °C to 1160 °C and a strain rate range of 0.01–10 s−1. The constitutive equation of the Arrhenius model and the hot working map was established, determining activation energy(Q) of 1086.58 kJ·mol−1. Large-size γ′ is coherent with the matrix. For the γ+γ′ dual-phase region, heterogeneous strain-induced dynamic recrystallization (HDRX) occurs, and discontinuous dynamic recrystallization (DDRX) is the main nucleation mechanism for DRX. However, for γ single-phase region, DDRX plays a more significant role. Furthermore, the MC phase (>1 μm) has different crystal orientations with the γ matrix and acts as sites for recrystallization through particle-stimulated nucleation (PSN). Finally, a fine and uniform grain structure can be obtained in the temperature range of 1120–1135 °C and the strain rate range of 0.1 s−1 to 1 s−1.

The hot deformation behavior of Cu–Sn–Ti–(Cr) alloys was studied using Gleeble-1500D thermo-mechanical simulator ranging from 550 to 950 °C, and the strain rate was 0.001–10 s−1. The microstructure evolution of the alloy was analyzed using characterization methods such as electron backscatter diffraction (EBSD), scanning electron microscope (SEM) and transmission electron microscope (TEM). Cu–Sn–Ti–(Cr) alloys were calculated by establishing the constitutive equation of the alloy. The activation energies of Cu–Sn–Ti and Cu–Sn–Ti–Cr alloys are 275.884 and 283.550 kJ/mol, respectively. The results indicate that the addition of Cr element has an inhibitory effect on the nucleation and improve refinement of dynamic recrystallization (DRX) in Cu–Sn–Ti alloy. The texture of Cu–Sn–Ti alloy is Cu texture at 750 °C and the texture contained in Cu–Sn–Ti alloy is Goss texture, Cubic texture and Cu texture when the temperature is raised to 950 °C. The texture of Cu–Sn–Ti–Cr alloy at 750 °C is Goss texture. The Goss texture transforms into Cubic texture and Cu texture when the temperature is raised to 950 °C. The precipitates present in Cu–Sn–Ti alloy include CuSn3Ti5 phase and Cu4Ti phase. The addition of Cr element adds a new phase of Cr to the alloy and also makes the distribution of precipitates more uniform and increases in quantity.

In this paper, Fe−8.5Mn−1.5Al light−weight medium Mn steel is used as the research object, and the hot compression test is conducted by Gleeble−3500 thermal simulation tester. The dynamic reversion and dynamic recrystallization (DRX) processes are analyzed according to the true stress−strain curve; the θ−σ work−hardening rate curve is plotted by P−J double differential method to analyze the influence law between work−hardening and dynamic reversion and recrystallization softening effect of the material; the DRX critical strain model is established to analyze the influence law of deformation parameters on DRX; Based on the dynamic material model theory, the hot working diagram and three−dimensional power dissipation diagram are constructed, and the best hot working area is determined by combining the microstructure of the material. Finally, based on the above research content, a systematic overview of the dynamic softening effects of DRX and dynamic recovery (DRV) will be provided.

The Ni61Fe10Cr10Al17Mo2 high-entropy alloys (HEAs) with low density have been developed with great potentials for applications. The forging process is one of the important methods for fabricating components. Accordingly, the study of the deformation behavior of HEAs is the essence in the processing and molding of this material for using in industry. Moreover, there are multiple phases with hierarchical structures in the as-cast Ni61Fe10Cr10Al17Mo2 alloys, with the face-centered cubic (FCC) phase as the matrix phase accompanied with hard body-centered cubic (BCC) B2 phase. Here, the hot deformation behaviors of the homogenized Ni61Fe10Cr10Al17Mo2 alloy were investigated at strain rates ranging from 0.001 to 1.0 s−1 and temperatures ranging from 1000 to 1200 °C via isothermal compression tests. The true stress-strain curves were used to reveal the relationship between the flow stress and the deformation temperature and strain rate. The constitutive equations describing the correlations between the flow stress and hot compression parameters were constructed. At the same time, the dynamic material model and instability criterion were used to plot the hot processing map. Furthermore, the deformed microstructures and the dynamic recrystallization of alloy were investigated. Combined with the processing map, the optimal processing route is obtained.

In this paper, the effect of extrusion temperatures (250 °C, 300 °C and 350 °C) on the microstructure, second phases particle, texture, and mechanical properties of the Mg–5Sn–1Si–0.6Ca alloy were discussed. The results show that after extrusion the second phases in the alloy were broken and distributed along the grain boundary. Decreasing the extrusion temperature is beneficial to dynamic precipitation and grain refinement. During the extrusion process, a large number of Mg2Sn nanoprecipitates are dynamically precipitated from the Mg matrix and their number increased and their size decreased with the decrease of extrusion temperature. The grain size was refined from 5.8 μm to 3.328 μm with the extrusion temperature decreasing from 350 °C to 250 °C. Besides, the texture intensity was also reduced with the decrease in extrusion temperature. The strength and plasticity of the Mg–Sn–Si–Ca alloys are simultaneously improved by the method of “solid solution + low-temperature extrusion”. When the extrusion temperature is 250 °C, the alloy obtains superior engineering mechanical properties with the yield strength of 287 MPa, ultimate tensile strength of 343 MPa and elongation to failure of 23.3%. The high strength is mainly attributed to the combined effect of grain size, weak texture, and high density of precipitation. The good ductility is mainly attributed to the grain refinement and high Schmid factors of basal slip.

In this study, hot rolling treatment followed by water quenching was conducted on a TC18 titanium alloy in β single-phase region with varying reductions. Experimental evidences from X-ray diffraction and transmission electron microscopy indicate the formation of α phase, induced by sufficient stress and assisted by ω phase. In addition, the existence of α'' phase and diffuse streaks were also observed during the hot working processing. Furthermore, dynamic recrystallization (DRX) including continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) was proved to exist in the hot rolling process. During the whole DRX process, with increasing the deformation degree, recrystallized grains nucleated preferentially at high-energy areas such as grain boundaries and shear bands, then accumulated and grew until achieving a complete recrystallization state. It should be noted that DDRX mainly occurred at the grain boundaries, while CDRX grains nucleated within the shear bands. The elongation gradually decreased and tensile strength gradually increased with the increment of the deformation degree.

GH4738 superalloy is a key material for gas turbine engines, yet its relatively poor thermoplasticity and narrow temperature range for hot working deteriorate grain structure uniformity and thereafter service performance. Employing hot compression experiments and finite element analysis (FEA), the present study examined the thermoplasticity of the GH4738 alloy and proposed a fast approach to establishing its dynamic recrystallization (DRX) model. The hot working conditions were considered in the 1000–1160 °C temperature range under strain rates of 2–26 s−1 up to a true compressive strain of 0.69. Friction- and temperature-corrected stress-strain curves were obtained, based on which the efficiency of power dissipation and constitutive equations were constructed. It reveals that DRX is the dominant softening mechanism in the GH4738 alloy, where the sensitivity of flow softening positively correlates with lower temperatures and higher strain rates. The appropriate hot working condition for the alloy is temperatures around 1040–1080 °C and a strain rate larger than 8 s−1. The final grain sizes (d) and fractions of DRX (Xdyn) were minimized using the stochastic gradient descent algorithm based on 120 sets of data within the framework of the Avrami equation. It is shown that the formulated model and its integration into the FEA not only yield satisfactory agreement with the experiment but effectively avoid the complexity involved in the traditional method. The study provides key inputs for predicting the flow behavior and grain structure of the GH4738 superalloy, which shall be critical for process development and optimization of industrial manufacturing processes.

High-temperature flow features of the Al−Zn−Mg−Cu−Zr aluminum alloy was revealed by hot compression tests. The evolution mechanisms of dislocation clusters, subgrain, and dynamic recrystallization (DRX) grains, are thoroughly explored by EBSD and TEM analysis. Experimental results suggest that the high strain rate can exacerbate dislocation clusters formation, as well as subgrain nucleation/accumulation, inducing the increasing of flow stress. Nevertheless, the noticeable annihilation of substructures, as well as the growth of DRX grains, emerge at the higher temperature, causing the descending of flow stress. Three types of DRX nucleating mechanisms, i.e., discontinuous DRX (DDRX), geometric DRX (GDRX) and continuous DRX (CDRX) are activated in the Al−Zn−Mg−Cu−Zr aluminum alloy during hot compression. Simultaneously, the GDRX often appears at a high compressed temperature or a low strain rate. A physically-based (PB) model is proposed to collaboratively reconstruct true stresses and microstructure evolution features. The estimated values of true stress, DRX fractions and average grain size preferably fit the experimental data, indicating the proposed PB model can precisely catch the thermal compression behaviors and microstructure evolution characteristics of the Al−Zn−Mg−Cu−Zr aluminum alloy.

In this paper, the flow behavior and evolution of microstructure during the hot forging process are predicted using numerical simulation, providing a reference for optimizing the process. The flow stress-strain curve of 30Cr2Ni3MoV steel was obtained by conducting hot compression experiments using Gleeble-3500 thermal simulator. The constitutive and dynamic recrystallization (DRX) cellular automaton (CA) models were established by analyzing the thermal deformation behavior, considering work hardening and DRX softening. This model was optimized by combining the dislocation density difference drive mechanism, increasing the total number of grain orientations, and then implementing Hash mapping to obtain the actual grain orientation. The simulation results of strain and strain rate in the process of thermal deformation were obtained through the constitutive model. Compared with the results of the hot compression experiment and the metallographic experiment, the accuracy of the simulation results of the DRX CA model was verified. Finally, the real-time updating module of deformation parameters is established, and the real-time process parameters of deformation calculation are updated to the CA model. The simulation results are consistent with the experimental results through metallographic experiments.