Dynamic Recrystallization Mechanism Research Articles

A systematic study on thermo-mechanical behavior, processing maps and recrystallization mechanism of Incoloy825 superalloy during hot compression

This study conducted isothermal hot compression experiments on Incoloy825 superalloy, spanning temperatures from 1000 to 1150 °C, strain rates from 0.01 to 10 s−1, and a true strain of 0.69. Employing Electron Backscatter Diffraction and Transmission Electron Microscopy for characterization, the research systematically explored the alloy's thermal-mechanical behavior, hot processing maps, microstructural evolution, and dynamic recrystallization (DRX) mechanisms during hot deformation. True stress-strain curves were obtained for various deformation conditions, corrected, and used to establish a highly precise constitutive model. A hot processing map was constructed using the Dislocation Migration Model theory. Through comparative analysis with microstructures, it identified the optimal hot processing parameters for Incoloy825 superalloy within the range of 1110–1150 °C, 0.01–0.3 s−1, and 3.3–10 s−1. Microstructural analysis revealed a positive correlation between temperature and the extent of DRX in the alloy, with an acceleration in the transformation from Low-Angle Grain Boundaries (LAGB) to High-Angle Grain Boundaries (HAGB). The temperature of 1100 °C served as a critical point for the influence of strain rate on the microstructure. Below this temperature, DRX and HAGB proportions initially decreased and then increased with higher strain rates, while at higher temperatures, they directly correlated with strain rates. The study also investigated DRX mechanisms, determining Dynamic Discontinuous Recrystallization (DDRX) as the primary mechanism, more active at higher temperatures and strain rates. Continuous Dynamic Recrystallization (CDRX) served as a supplementary mechanism, especially in high-temperature and low-strain-rate deformation. Twins acted as favorable nucleation sites for DRX, facilitating both DDRX and Twin-DRX (TDRX) processes in Incoloy825 superalloy.

Investigation on deformation behaviors and dynamic recrystallization mechanism of spray formed Al–Zn–Mg–Cu alloy under hot compression

The thermal deformation behavior of spray formed Al–Zn–Mg–Cu alloy was investigated by the isothermal hot compression tests at the strain rates of 0.001–10 s−1 with the temperature range of 350–450 °C. An Arrhenius constitutive equation was established by the corrected strain-stress curves, and then the processing map was constructed based on the 3D instability map and 3D power dissipation map. The influence of strain rate and temperature on both flow stress and dynamic softening has been unveiled. The results show that dynamic recovery (DRV) is the primary softening mechanism and dynamic recrystallization (DRX) is substantively retarded due to the fine dispersed particles uniformly distributed in the spray formed alloy. Continuous dynamic recrystallization (CDRX) is the primary DRX mechanism at a low temperature or high strain rate. DRX grain was observed at the grain boundaries, especially at the triple junctions. The appropriate thermal deformation condition is recommended at the temperature range from 430 °C to 450 °C and strain rates from 0.003 s−1 to 0.1 s−1.

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.

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.

Study of rotational dynamic recrystallization during warm compression of an Mg-Zn-Nd-Zr alloy

The dynamic recrystallized grains obtained by rotational dynamic recrystallization (RDRX) mechanism are finer and have fewer defects, which can effectively improve the performance of magnesium alloys. However, the impact of temperature and strain on RDRX is currently unclear. In this study, an extruded Mg-Zn-Nd-Zr alloy with trace amounts of rare earth elements and fine grain size was used as the raw material, and a warm deformation temperature interval was selected, which suppressed the large-angle migration, reduced the activity of twinning, and successfully ensured RDRX as the main recrystallization mechanism. The effects of temperature and strain on RDRX of magnesium alloys were systematically investigated, and it was found that the compression temperature and strain jointly affected the formation of RDRX. The RDRXed grains emerged during the dynamic softening stage and abundantly developed during the dynamic equilibrium stage. The percentage of the RDRXed grains increased with the increase of temperature for temperatures below 290 °C and decreased with the increase of temperature for temperatures above 290 °C at low strain levels (0.4). The percentage of RDRX monotonically increased with the increase of compression temperature at high strain (0.7). The size of the recrystallized grains increased with the increase of compression temperature. The formation of the RDRXed grains could effectively release the local strain and form a strain free region without distortion, resulting in strain softening.

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.

Microstructure evolution and deformation mechanism with comparison of Ta-2.5 W and Cu under detonation load

The comparison of microstructure evolution of Cu and Ta-2.5 W liner during explosively formed projectile (EFP) formation was studied. The electron backscatter diffraction method (EBSD) was used to statistically characterize the microstructure of the liner before and after deformation. Both recycled EFPs show strong fiber texture and different degrees of recrystallization. The center of the recycled Cu EFP has strong <001> and <111> preferred orientations along the EFP axis, and the density of the texture changes with the deformation strain. Cu EFP has extensive dynamic recrystallization, up to 88%, which is considered to be a traditional dynamic recrystallization mechanism, the temperature is the main controlling factor in the refinement process. On the contrary, the recycled Ta-2.5 W EFP has a strong <101> fiber preferred orientation, and almost no dynamic recrystallization occurs, large strain deformation is the main factor for the microstructure fragment.

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.

Deep learning-based modeling of the strain rate-dependent thermomechanical processing response for a novel HIPed P/M nickel-based superalloy

Understanding and modeling the thermomechanical processing (TMP) response of a novel HIPed powder metallurgy (P/M) superalloy is crucial for its industrial application. This research characterizes the TMP-responding behavior of a novel HIPed FGH4113A P/M superalloy at 1000–1150 ℃ with strain rates of 0.01–5 s−1. The results depict that the adiabatic temperature rise during high-strain-rate TMP will accelerate the stress softening. A two-stage deep learning (DL)-based constitutive model framework, coupled with the deformation-induced temperature rise and its influence on flow stress, was first proposed and compared with the traditional Arrhenius-type model. Two types of DL approaches including the backpropagation (BP) and long short-term memory (LSTM) neural networks were trained and compared separately. It is noted that the LSTM neural network, considering previous deformation history in its unique gate structure, depicts the best prediction accuracy and generalization ability under large strains than other models. Then the strain rate-dependent hot workability and flow softening mechanisms were modeled and discussed. High-strain-rate deformation (5 s−1) in certain temperatures (1110–1150 ℃) can avoid unstable defects and transform the generated deformation heat into the driving force for the activation of multiple dynamic recrystallization mechanisms. Therefore, the near fully recrystallized microstructure can be achieved similarly to that at 0.01 s−1, indicating the feasibility and superiority of the high-strain-rate TMP of P/M superalloys in a certain temperature range.

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.

Orientation-dependent dynamic shearing properties and underlying failure mechanisms of laser powder bed fusion of CoCrFeNi high-entropy alloy

In order to study the influence of building orientation on the dynamic shearing properties and failure mechanism of laser powder bed fusion (LPBF) of CoCrFeNi high-entropy alloy (HEA) under impacting load, a series of high speed impact tests were systematically conducted on a split Hopkinson pressure bar (SHPB) device at different strain rates. For this purpose, flat hat-shaped samples with a preset shear region were designed. The samples HS0 and HS90 respectively possessed a shear direction parallel and perpendicular to the building orientation. The respective columnar grain orientations of HS0 and HS90 influence the synergistic interaction between dislocation slip and deformation twinning, which is reflected in the differences in mechanical properties. It was observed that HS0 had higher shear yield strength whereas HS90 exhibited better plasticity. Moreover, the two samples show different adiabatic shear sensitivities as adiabatic shear bands (ASBs) were observed when the shear strain reached ∼9.5 and 11.2, respectively. Typical dynamic responses such as adiabatic temperature rise and grain refinement took place in the shear regions. Further, the formation of ultrafine equiaxed grains may be explained using the classical rotational dynamic recrystallization (RDRX) mechanism, which can furnish a sound theoretical basis to understand the deformation behaviors and mechanisms of LPBF CoCrFeNi HEA under impact loads.

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.

Effect of reinforcement particles and multipass of friction stir processing on microstructure and mechanical properties of aluminium alloy

The present study focuses on the successful fabrication of aluminium metal matrix composites (AMMCs) using friction stir processing (FSP) and micro-sized SiC as reinforcement particles (RPs). The microstructure of Al6061-T6/SiC AMMCs in the stir zone was examined using Electron Backscatter Diffraction (EBSD), Energy Dispersive Spectroscopy (EDS), and Scanning Electron Microscopy (SEM). The incorporation of SiC particles and the refinement of grain structure resulted in upgraded mechanical properties of the AMMCs achieved through three FSP passes. These enhancements were concerning from the reduction in grain size and more orderly dispersal of SiC particles. Moreover, the microhardness of the AMMCs enhanced by 41.79%, by augmenting the FSP passes, which can be characterized by the refinement in grain structure, facilitated by the dynamic recrystallization (DRx) mechanism.

Hot compressive deformation behavior and microstructural evolution of the spray-formed 1420 Al–Li alloy

The 1420 Al–Li alloy has been widely used in the aerospace field. To investigate the hot workability of the alloy, a series of hot compression tests were carried out on the spray-formed alloy in the temperature range of 300°C–450 °C with strain rates of 0.0001s−1-10s−1. First, an improved Johnson-Cook model was developed by considering the coupling effect of strain, strain rate, and temperature, and the prediction error of the model was reduced to 5.3 %. Subsequently, processing maps with various strains were established. In addition, the microstructural evolution under various deformation conditions was systematically studied using the electron backscatter diffraction (EBSD) technique. The alloy exhibited uniform deformation under the synergistic effect of the continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) mechanisms. Finally, the feasible hot working windows were identified as 425°C–450°C and 0.01s−1-0.1s−1 based on processing maps and microstructural evolution results. This work could offer comprehensive guidance for the hot working process of 1420 Al–Li alloy from both the macro and the micro aspects.

Strain-induced heterogeneous bimodal microstructure behavior of Mg-Gd-Y-Zn-Zr alloy containing LPSO phase during hot compression

In this study, the isothermal compression experiments of Mg-Gd-Y-Zn-Zr alloy at 450 °C and 0.01 s−1 under different strains were carried out to investigate the microstructure evolution and the formation mechanism of the heterogeneous microstructure. The microstructure of the sample with a strain of 1.4 exhibited significant heterogeneous microstructure characteristics with bimodal grain and bimodal texture distribution. The particle-stimulated nucleation (PSN) mechanism activated by intergranular block-shaped LPSO phases and the continuous dynamic recrystallization (CDRX) mechanism developed layer by layer towards grain interior promoted grain refinement and the formation of the bimodal grain distribution characteristics. Moreover, the stress-induced dynamic precipitation of Mg5RE particles became more significant with increasing strain, and the interaction of Mg5RE particles with dynamic recrystallization (DRX) grains further refined the DRX grains and exacerbated the degree of bimodal grain distribution. The grains with the <0001> axis between CD and TD and grains with the <0001> axis perpendicular to CD slipped along basal and prismatic planes, respectively, leading to the gradual deflection of the <0001> axis toward CD and the formation of a strong basal texture with <0001> axis parallel to CD during thermal compression. At the same time, the coarse deformed grains with strong basal texture were preserved during compression deformation due to small strain energy storage. Inhomogeneous plastic deformation, randomly oriented refined DRX-ed grains and dynamically precipitated Mg5RE particles together lead to the formation of the heterogeneous microstructure. This study provides theoretical guidance for preparing of high-performance Mg-RE alloys with heterogeneous microstructure.

Dynamic recrystallization behavior of selective laser melted 316L stainless steel

The present work deals with the hot deformation behavior of selective laser melted 316L stainless steel with an emphasize on the involved recrystallization mechanisms. Toward this end, a series of hot compression test have been conducted in the temperature range of 700–1000 °C under the various strain rates of 0.001, 0.01 and 0.1s−1. The flow pattern analysis through Jonas-Poliak method verifies the occurrence of dynamic recrystallization in whole investigated temperature range. The intensified substructure development and continuous recrystallization is identified as the main softening mechanism in the course of thermomechanical processing. This causes appearance of a broad peak and low softening fraction in corresponding flow curves. The cellular substructure in the as-printed state facilitates low-angle into high-angle boundaries conversion, which provide a proper condition for the occurrence of continuous mechanisms and increases the rate of recrystallization. However, detailed investigation of the sub-boundary maps indicates the contribution of discontinuous and geometric dynamic recrystallization mechanisms. Dynamic recrystallization causes substantial refinement; and the percentage of the grain holding size lower than 10 μm increases from 2 % in printed microstructure to 16.8 % and 24 % in the microstructure deformed at 700 and 1000 °C.

Deformation behaviour, microstructure evolution and dynamic recrystallization mechanism of AZ31 magnesium alloy under co-extruded by Mg-Al composite billet

Conventional methods for hot extrusion of magnesium (Mg) alloy sheets have limitations for microstructure improvement and mechanical property enhancement. Co-extrusion of Mg alloy with an Al alloy core provides an opportunity for refining the grain size and improving basal texture. This study introduces a novel severe plastic deformation (SPD) method, Direct Extrusion-Continuous Shear (DE-CS), utilizing 6063 Al alloy as the core to fabricate innovative Mg/Al clad composite sheets. Monolithic Mg sheets (non-co-extruded condition) are extruded under identical conditions for comparison. By evaluating the microstructure and mechanical properties of AZ31 Mg alloy under co-extrusion and non-co-extrusion conditions, the positive effect of Mg-Al composite billet co-extrusion on AZ31 Mg alloy is established. The grain refinement effect in co-extruded samples is superior, enhancing plasticity without significant reduction in tensile strength. The microstructure evolution and dynamic recrystallization (DRX) behaviour of AZ31 Mg alloy during co-extrusion were analyzed comprehensively. The results indicate that, in the initial stages of deformation, various variants of {10−12} extension twins (ETs) play a crucial role in refining the original grains, forming initial [10−10]//ED fiber texture components alongside other non-basal components. Upon entering the shear deformation (SD) zone, deformed twins disappear, and small dynamically recrystallized (DRXed) grains emerge along boundaries of coarse deformation grains and within the grains. Strong shear deformations and compressive stress from transverse direction (TD) induce intensified prismatic <a> and pyramidal <c+a> slip, promoting continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX). CDRX predominantly affects elongated deformed grains, forming an [10−10]//ED fiber texture through high-energy grain boundary segmentation. Subsequently, compatible stress increases due to the activity of non-basal slip dislocation and the reduction in grain boundary (GB) size. DDRX emerges as the dominant mechanism, generating randomized [10−10]//ED fiber and non-fiber textures within parent grains and at boundaries.

Microstructure of the Advanced Titanium Alloy VT8M-1 Subjected to Rotary Swaging.

In this study, the microstructural behavior of the advanced Ti-5.7Al-3.8Mo-1.2Zr-1.3Sn-0.15Si (VT8M-1) alloy during rotary swaging (RS) was investigated. VT8M-1 has increased heat resistance and is considered a replacement for the Ti-6Al-4V alloy. It was shown that, during RS, the evolution of the primary a phase is characterized by the formation of predominantly low-angle boundaries according to the mechanism of continuous dynamic recrystallization. The density of low-angle boundaries increases three times: from 0.38 µm-1 to 1.21 µm-1 after RS. The process of spheroidization of the lamellar (a + b) component is incomplete. The average size of globular a and b particles was 0.3 μm (TEM). It is shown that the microstructures after RS (ε = 1.56) and equal-channel angular pressing (ECAP) (ε = 1.4) are significantly different. The temperature-velocity regime and the predominance of shear deformations during ECAP contributed to a noticeable refinement of the primary a-phase and a more complete development of globularization of the lamellar (a+b) component. EBSD studies have shown that RS leads to the formation of a structure with a higher density of low- and high-angle boundaries compared to the structure after ECAP. The results are useful for predicting alloy microstructure in the production of long rods that are further used in forging operations.

Systematic investigation of the microstructure evolution and dynamic recrystallization mechanisms of as-cast Fe–TiB2 composites under different hot deformation parameters

Fe–TiB2 composite shows great potential in lightweight materials for automotive parts due to its lightweight, high strength and high specific modulus etc. However, challenges remain with regard to establishing a fine hot working process of Fe–TiB2 composites. Here, a series of isothermal hot compression tests was conducted to systematically investigate the microstructure evolution and the dynamic recrystallization (DRX) mechanisms of as-cast Fe–TiB2 composites at different sets of hot deformation parameters. The results indicate the true stress drops more significantly after reaching its peak at low temperatures compared to high temperatures, since low temperatures favors the DRX through particle stimulated nucleation (PSN) in Fe–TiB2 composites, as featured by layers of DRXed grains surrounding TiB2 particles. Continuous dynamic recrystallization (CDRX) process gradually dominates as strain rate increase from 0.01 s−1 to 1 s−1 in Fe–TiB2 composites hot compressed to the true strain of 0.69 at 900 °C, as evidenced by the presence of DRXed grains with larger size and uniform distribution in matrix. DRX through PSN is the primary DRX mechanism at low temperature and low strain rate, while CDRX dominates the DRX mechanism at high temperature and high strain rate. Both DRX behaviors deepen with the increase of the strain. Different hot deformation parameters favor different DRX mechanisms. The increase in temperature and strain rate leads to a transition of the dominant recrystallization mechanism from the DRX through PSN to CDRX which is attributed to the competition for stored energy between the DRX through PSN and CDRX process.

Revealing microstructures evolution and dynamic recrystallization mechanisms of Mg–Sn–Mn alloy during compressive deformation at elevated temperature

The flow behavior of as-extruded Mg–3Sn-1.5Mn (wt.%) alloy was systematically researched via isothermal compression tests. The compressive temperatures (T) were from 250 °C to 400 °C, the strain rates were from 0.001 s−1 to 1s−1 and the true strain reached 0.69. Based on compression curves, flow stress apparently rose with increasing strain rate and/or decreasing temperature. Combined with the analysis of microstructure and processing map, the optimum working parameter was determined in the range of 350–400 °C, 0.01–1 s−1. According to electron backscatter diffraction (EBSD) analysis results, texture intensity significantly decreased and the basal (0001)//ED texture had transformed to basal <0001>//CD texture after compressive deformation obviously. Furthermore, the typical discontinue dynamic recrystallization (DDRX) and continue dynamic recrystallization (CDRX) were largely believed to be the major DRX mechanisms in Mg–3Sn-1.5Mn alloy. Both increasing temperature and decreasing strain rate had obvious influence on the degree of DRX. The activated slip systems in deformed grains were determined by the analysis of the in-grain misorientation axis (IGMA). As deformation temperature elevated, pyramidal <c+a> slip greatly activated and dominated compressive deformation.