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The hot compression of the as-cast Fe-21Mn-0.7C–0.1Si twinning induced plasticity (TWIP) steel was investigated at the deformation temperature range of 950–1100 °C and strain rates of 0.01–5 s−1, using a GleebleTM thermo-mechanical simulator, to determine the hot deformation behaviour and analyse the recrystallisation mechanism. The results showed that the flow curves were characterised by yield-point-elongation (YPE) and dynamic recrystallisation (DRX) as the principal restoration mechanisms. The activation energy (Q) was calculated to be 394.975 KJ mol−1, which implies that the recrystallisation is sluggish in the whole range of the deformation conditions. Furthermore, the processing maps were generated according to the dynamic material model (DMM). The processing map was subdivided into different domains for the microstructural observations. The ideal hot deformation parameters of as-cast high Mn TWIP steel were obtained in the deformation condition range of 1087–1098 °C/10−1.2-10−0.17 s−1. Moreover, the microstructure analysis revealed that the DRX grains were twinned and nucleated through the bulging mechanism at the serrated grain boundaries, accompanied by twin boundaries migration created in the DRX grains by growth accidents, which contributed significantly to the growth of the DRX. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) is a near-net-shape manufacturing method that can fabricate complex components in one step. Post-processing methods, such as hot forging, can be used in conjunction with AM to leverage the properties and efficiencies of both processes by minimizing solidification defects and anisotropic mechanical properties mechanical properties, such as fatigue resistance and strength. In this study, hot compression tests were conducted under different conditions to evaluate the hot deformation behavior of additively manufactured Inconel 718 samples using constitutive equations and processing maps. The results indicated that the flow stress was significantly affected by the deformation parameters, which increased with decrease in temperature and increase in strain rate. Constitutive equations and processing maps were obtained using experimental data to evaluate the hot deformation behavior under different conditions. According to the processing map, a maximum efficiency of 35% for Inconel 718 was obtained at a strain rate of 0.001 s−1 and a temperature of 1000 °C, where complete dynamic recrystallization occurred. Under these optimized conditions, an isotropic fine microstructure was developed with a mean grain size of 2.3 μm. [ABSTRACT FROM AUTHOR]

Characterization of hot deformation behavior of Ti-6Al-4V-0.5Ni-0.5Nb titanium alloy was investigated through isothermal compression at various temperatures from 750 to 1 050 °C and strain rate from 0.01 to 10 s−1. The isothermal compression experiment results showed that the peak stress of Ti-6Al-4V-0.5Ni-0.5Nb titanium alloy decreased with the temperature increasing and the strain rate decreasing. The softening mechanism was dynamic recovery below Tβ and changed to dynamic recrystallization above Tβ. The arrhenius-type relationship was used to calculate the constitutive equation of Ti-6Al-4V-0.5Ni-0.5Nb alloy in two-phase regions. It was found that the apparent activation energies were 427.095 kJ·mol−1 in the α+β phase region and 205.451 kJ·mol−1 in the β phase region, respectively. On the basis of dynamic materials model, the processing map is generated, which shows that the highest peak efficiency of power dissipation of 56% occurs at about 1 050 °C/0.01 s−1. It can be found in the processing maps that the strain had significant effect on the peak region of power dissipation efficiency of Ti-6Al-4V-0.5Ni-0.5Nb alloy. Furthermore, optimized hot working regions were investigated and validated through microstructure observation. The optimum thermo mechanical process condition for hot working of Ti-6Al-4V-0.5Ni-0.5Nb titanium alloy was suggested to be in the temperature range of 950–1 000 °C with a strain rate of 0.01–0.1 s−1. [ABSTRACT FROM AUTHOR]

The hot deformation behaviors of the 20wt% SiCp/Al-Cu-Mg-Ag composite were studied by establishing processing map and characterizing the microstructure evolution. The hot deformation behavior of the SiCp/Al-Cu-Mg-Ag composite was analyzed through stress-strain curves, and a constitutive equation for its hot deformation was established. Based on the dynamic material model, a processing map for the composite was constructed. The results indicate that the true stress decreases rapidly with increasing temperature and tends to stabilize or slightly decrease after reaching its peak. Furthermore, the peak stress increases with decreasing deformation temperature or increasing strain rate. The flow stress behavior of the SiCp/Al-Cu-Mg-Ag composites can be described by a hyperbolic Arrhenius equation, with a heat activation energy (Q) of 222.3 kJ/mol. The SiCp/Al-Cu-Mg-Ag composite can be deformed stably in the high-temperature, low-strain-rate region. The optimal deformation conditions are identified as 475-500°C and 0.01-0.1s-1, with a maximum dissipation efficiency of 34%.

Isothermal compression tests for ERNiCrMo-3 alloy specimens were conducted under temperatures of 990–1170 °C with strain rates of 0.01–10 s−1. Hot deformation behavior of ERNiCrMo-3 was analyzed based on the obtained flow stress curves. Three constitutive models were developed to anticipate the flow stress: the Arrhenius model compensated by strain, the Arrhenius model optimized by genetic algorithm (GA), and the artificial neuron network (ANN) model. The correlation coefficient (R) and average absolute relative error (AARE) were used to assess the predictive ability for these three models. The R values of the strain-compensated, GA optimized, and ANN models were 91.04, 93.54, and 99.01%, respectively, while the AARE values were 12.30, 8.19, and 2.92%, respectively. Furthermore, the absolute relative error of the ANN model was the most concentrated and mainly around 0. Therefore, the ANN model provides the maximum predictability and accuracy for flow stress. The ANN model was implemented via subroutine USRMTR in DEFORM 2D to simulate the hot compression process of the ERNiCrMo-3 alloy specimens. The numerical results were in good agreement with the experimental results, indicating a high potential for applicability to actual production processes. Finally, hot working characteristic of ERNiCrMo-3 alloy was analyzed by processing map and microstructural investigation. According to the result, the suitable thermal processing domain for ERNiCrMo-3 alloy should be at a temperature range of 1130–1170 °C and a strain rate range of 0.03–0.36 s−1. [ABSTRACT FROM AUTHOR]

The hot deformation behavior and the associated microstructural evolution (which were the keys to decide mechanical properties) were studied using different deformation conditions for the quaternary Al–Cu–Li–Zn alloy containing 1.0 wt% Zn. The constitutive equations and processing map were established. Dynamic recrystallization (DRX) was related to the orientation of the initial grains. The DRX rarely occurred in the grains with an orientation near Al and mainly occurred in the grains with an orientation near Al. Particle simulated nucleation (PSN) promoted by pre-existed coarse T1 phase particles was the main mechanism of the DRX when the deformation temperature was below 450 °C. In the temperature range of 450–500 °C with a strain rate of 0.01 s−1, the DRX occurred by grain boundary bulging or the increase in the cumulative misorientation, but only small fraction of the DRX grains appeared. This work provided an important guideline for the optimization of deformation techniques and microstructures.

The AZ61 magnesium alloys are widely used in the automobile industry for load-bearing component applications due to their high strength-to-weight ratio. In this study, the effects of the incorporation of silicon carbide (SiCp) particles on the microstructure and hot deformation behavior of an AZ61 alloy fabricated by the stir casting process were studied. Investigation of the fabricated composite was carried out using the hot compression process under different deformation conditions (temperatures (280, 320, 360, 400, and 440 °C) and strain rates (0.001, 0.01, 0.1, and 1 s−1)). A constitutive equation was developed using the flow stress at a strain rate of 1.2. The results indicate that the predominant mechanism affecting the AZ61 alloy was dynamic recrystallization (DRX) arising from the dislocation climb. The microstructure of the AZ61/SiCp composite could be controlled by the process of DRX through particle stimulated nucleation due to the dislocation climb. Processing maps were developed to determine the workability parameters of the fabricated materials by examining the power dissipation efficiency and instability parameters. The processing maps revealed the workability domain to occur at a temperature of 440 °C and a strain rate of 0.001 s−1 for both the alloy and the composite. However, the AZ61/SiCp composites showed the maximum power dissipation efficiency (39%) and no instability region compared with the AZ61 alloy (38%). Therefore, the AZ61/SiCp composite has much better workability than the AZ61 alloy. There is good agreement between the typical microstructure, as illustrated by the processing map, and the findings of the microstructure measurements. [ABSTRACT FROM AUTHOR]

During the thermal deformation of aluminum alloy materials, the deformation conditions such as deformation volume, temperature and strain rate are important factors that influence the deformation mechanisms such as work hardening, dynamic recovery and dynamic recrystallization. Under the interaction of different deformation mechanisms, the properties of aluminum alloy materials will change significantly. In this study, isothermal hot compression experiments were conducted on the Al-7.92 Zn-1.64 Mg-2.00 Cu alloy to analyze its hot flow behavior (T = 250~450 °C, ɛ̇ = 0.001~1 s−1). The obtained flow behavior data were used to construct an Arrhenius-type constitutive equation and processing maps, investigating organizational evolution under diverse hot deformation conditions. The results show that the energy dissipation rate can reach 0.37 when the deformation temperature T = 380~450 °C and the strain rate ɛ̇ < 0.1 s−1, suggesting that the material is most suitable for thermal deformation processing at high temperatures and low strain rates. At a strain rate of 0.1 s−1 and a temperature of 450 °C, the percentage of recrystallized grains and substructures increased by 7.20% and 3.14%, respectively, compared to 300 °C, which is due to the severe dynamic recovery and dynamic recrystallization. At 350 °C and 0.1 s−1, there was a higher percentage of recrystallized grains and substructures, 5.44% and 5.87% higher, respectively, than at a strain rate of 1 s−1, indicating that the release of dislocation accumulation due to deformation storage energy will be more favored at low strain rates, which promotes the enhancement of the dynamic recrystallization mechanism. [ABSTRACT FROM AUTHOR]

The discovery of High entropy alloys (HEAs) and the deepened understanding of their physical metallurgy have raised the bar on microstructure design and choice materials selection for highly specialized, sensitive technological and structural integrity applications. This is on account of their unique phase constitution, facilitated by their multi-principal elemental compositions, which imparts excellent properties combinations in HEAs, which are rarely observed in conventional alloys. However, due to their shrinkage porosity, chemical composition heterogeneity, rough dendritic structure, and quasi-stable eutectic at grain boundaries make direct deployment in the as-cast condition, is problematic. As a result, using hot deformation techniques to create homogenous and fine microstructures in as-cast HEAs has gained attention as an effective strategy to resolve these shortcomings. A systematic review of studies on the hot deformation behaviour of different classes of high entropy alloys (HEAs), is summarized in this review paper. The plastic flow behaviour, phase, and microstructural evolution, mechanisms of hot deformation as well as the optimal hot deformation processing regions, derived from analysis of processing maps, were evaluated in this review. Factors such as alloy constitution, HEA phase(s) type, deformation processing parameters, and recrystallization mechanisms, were noted to influence the nature of microstructural evolution, plastic deformability, and material properties of the HEAs. The role and effectiveness of processing maps in establishing conditions for optimal tuning of the microstructures in HEAs to achieve the best product finish were also discussed.

Hot compression tests in the temperature range of 493-653 K and strain rates of 0.01-10.00 s−1 were used to evaluate the hot deformation behavior of 60Mg-30Pb-9.2Al-0.8B alloy. In order to optimize the hot working parameters, the Arrhenius constitutive equation and processing map with strain compensation were established on the dynamic material model (DMM). The results show that the stress-strain curves have three different stages of rising, peaking, and steady state during the hot compression with typical characteristics of work hardening (WH), dynamic recovery (DRV), and dynamic recrystallization (DRX). In addition, the improved Arrhenius strain compensation constitutive model has a higher precision than the traditional constitutive model. By dividing the processing map into three typical regions for analysis, the maximum power efficiency is obtained at ε = 0.4. The optimum hot working parameters are temperature range of 573K∼653K, and strain rate range of 0.01 s−1∼0.1 s−1. Instability usually occurs in the region with high strain rate and low temperature, and the main form of instability is cracking.

The hot compression in the deformation temperature range of 523-673 K and strain rates of 0.001-1 s-1 was aimed to study the hot deformation behavior, processing map, and dynamic recrystallization (DRX) to confirm an optimum hot working condition of Mg-Zn-Zr alloy. The strain-stress results by using the Gleeble-1500 simulator indicated that the flow stress decreases with increasing temperature or decreasing of strain rates, and the Medium Gaussian Kernel (correlation coefficient (R) = 0.9806, absolute relative error (AARE) = 3.28 %) has better predicting capacity. Based on the processing map and constitutive equation, the optimum hot-working condition for Mg alloys can be determined to be at hot compression temperature and strain rates in the range of 593-623 K and 0.01-0.001 s-1 with a peak value of power dissipation efficiency (PDE) which is reaching to 37 %. [ABSTRACT FROM AUTHOR]

Cu-bearing steels are widely used in the shipbuilding and medical industries because of their excellent strength, corrosion resistance, and antibacterial properties. In this study, the instability behavior of ship plate steels with the Cu contents of 0.98 and 1.62% during hot deformation was studied through a hot compression deformation experiment. The hot processing maps of the Cu-bearing ship plate steels were constructed based on the dynamic material model and Prasad instability criterion. Then, the preparation process of the test steel was analyzed and predicted. Results showed that the hot working instability zone of the ship plate steels with different Cu contents decreased with the increase in strain, and the addition of the alloying element Cu can significantly increase the hot working instability zone of the ship plate steels. The optimal parameters for the hot deformation of the tested steels were obtained as follows: temperatures T(0.98% Cu) of 1323-1423 K and T(1.62% Cu) of 1323-1423 K and strain rates ε ˙ (0.98Cu) of 3-7 s−1 and ε ˙ (0.98Cu) of 0.01-0.1 s−1. The existence of an instability zone in the test steels during thermal deformation could be ascribed to the preferential segregation of Cu at the grain boundary during processing. Then, grain boundary cracking, which reduced the machinability of the ship plate steels, correspondingly occurred. The hot working construction of test steels can enable optimal control of the preparation process. [ABSTRACT FROM AUTHOR]

The hot deformation behavior and microstructure evolution of the SAE8620RH gear steel were investigated through a single-pass hot compression test at deformation temperatures between 850 and 1100 °C and strain rates between 0.02 and 8.0 s−1 by 60% reduction. A novel strain compensation constitutive model was developed, and the 2D processing maps were established by Murty's criterion. Results showed that the relationship between material-related parameters and strain can be mathematically expressed by a highly reliable 8th-order polynomial. The constructed strain compensation constitutive model demonstrated remarkable predictive precision, as evidenced by the correlation coefficient (R) and the absolute values of average relative error (AARE) of 0.978 and 4%, respectively. The flow instability domains considerably expanded towards the high deformation temperature region as the strain increased. Microstructure analysis confirmed the accuracy of the processing map constructed by Murty's criterion. The most noticeable optimum processing windows for SAE8620RH gear steel at a strain of 0.7 occurred within the temperature range of 1000–1100 °C and the strain rate range of 0.3–1.0 s−1, due to high η values exceeding 0.3 and equiaxial dynamic recrystallization microstructure. [ABSTRACT FROM AUTHOR]

Ce addition in Mg improves its restricted ductility owing to inadequate number of deformation systems being hcp structure. Hot compression conducted on Mg-0.5wt% Ce alloy to identify the suitable deformation regime in processing maps. The flow stress (σ) response of such plastic deformation is governed by constitutive equations, established by a physical model on 0.1 to 0.5 true strain (ε) depends on hyperbolic-sinusoidal Arrhenius-type equations and also initiated with Zener–Hollomon parameter (Z) as specified by strain rate ( ε ˙ ) and deformation temperature. The average absolute relative error (AARE) and correlation coefficient (R) measure the correctness of the developed constitutive equation showing reasonable predictions of the modified flow stress. Processing map shows dynamic recovery (DRV) domain at 673–723 K and 0.001–0.1 s−1, corresponding to the suitable hot working regime, and also identifies unstable zones of flow stress behaviour. [ABSTRACT FROM AUTHOR]

The hot deformation characteristics of Cu–2Be alloy is studied within the temperature range of 650–950 °C and in strain rate of 0.001–1 s−1. The constitutive analysis and adaptive-network-based fuzzy inference system (ANFIS) were constructed for describing the hot deformation behavior. It is perceived that the developed ANFIS model can be used to accurately predict the hot deformation characteristic of the studied alloy. Corresponding equations for peak stress/strain are achieved and then, processing maps are developed based on the dynamic material model (DMM) theories. The results display that at lower strain, the deformation dissipation (η) increases with increasing temperature and decreasing strain rate; however at higher strain levels, η exhibits a noticeable decline at 900–950 °C and 0.01 s −1, in which momentous grain coarsening tends to happen. At high strain level, the optimal hot deformation domain of studied alloy should be at 850–950 °C and strain rate of 1–10 s−1, in which more uniform and fine grain structure is dominant due to the discontinuous dynamic recrystallization (DDRX). The correlation of recrystallized grains size with Z is determined in terms of power law. Moreover, the unstable flow regions are described in the processing maps using Prasad instability criterion.

The hot deformation behavior of a new FeCrMo precision alloy is studied by a hot compression test in the temperature range of 950-1150 °C at a strain rate of 0.01-10 s−1. The results show that the flow stress increases with increasing strain rate and decreases with increasing temperature. To analyze the safe regions for temperature and strain rate for the new FeCrMo precision alloy for hot workability, processing maps are drawn by superimposing power dissipation and instability maps developed using the dynamic material model (DMM). The results show that there are two high-η stable regions when the true strain is 0.1-0.7, and that the area and shape of the instability zone are similar when the strain is in the range of 0.3-0.7. Meanwhile, microstructural observations demonstrate that both the strain rate and deformation temperature have a remarkable effect on the microstructure. The optimal deformation temperature of the alloy is 1100-1130 °C, and the deformation rate is 0.01 s−1. Therefore, high-temperature deformation processing of the alloy can be simulated by Deform-3D, and the simulation results obtained for the FeCrMo alloy are in agreement with the processes. The thermal deformation behavior of a new FeCrMo precision alloy was investigated in the temperature range of 950-1150 °C and the strain rate range of 0.01-10 s−1. The temperature and strain rate safety zones for the thermal machinability of the new FeCrMo precision alloy were analyzed by drawing the processing maps (DMM). Furthermore, high-temperature deformation of the alloy could be simulated by Deform-3D, and the FeCrMo precision alloy piston ring is successfully prepared to meet quality requirements. [ABSTRACT FROM AUTHOR]

The deformation behavior of Ti-48Al-2Cr-2Nb alloy with bimodal grain structure was studied using isothermal compression tests in the temperature range of 950-1100 °C and strain rate range of 0.001-0.1 s−1. The results show that the flow stress is greatly affected by the deformation temperature and strain rate, and decreases with decreasing strain rate and increasing temperature. All flow stress curves exhibit single peak characteristics, indicating that DRX is the main softening mechanism. The Arrhenius constitutive equation is established according to the relationship among flow stress data, strain rate and temperature. The activation energy for hot deformation and stress index are determined as 390.543 kJ·mol−1 and 2.573, respectively. According to the theory of dynamic material model, the hot processing maps are constructed and the stability and instability regions are identified. The peak power dissipation occurs in the regions of 960-1025 °C/0.001-0.005 s−1 and 1085-1100 °C/0.001-0.006 s−1, which suggests that these two regions can be regarded as the optimum processing window for the alloy. [ABSTRACT FROM AUTHOR]

The microstructure evolution and hot-compressive behaviour of high Cr–Co–Mo bearing steel under different deformation conditions were investigated by dynamic recrystallisation (DRX) kinetics analysis and simulation. The results showed that the thermal deformation parameters and carbide dissolution have a great influence on the rheological properties and microstructure. The flow stress decreases with the increase of temperature and the decrease of strain rate. The grain boundary pinning effect is weakened by the dissolution of carbides into the matrix, resulting in the rapid growth of DRX grains. The processing map of high Cr–Co–Mo bearing steel was divided into five regions, and the most suitable processing parameters can be defined as the temperature range of 1000–1070°C and strain rate range of 0.01–0.003 s−1. [ABSTRACT FROM AUTHOR]

Titanium and its alloys, owing to their properties like high strength, toughness, corrosion resistance and thermal stability, are employable in various engineering and medical applications. The properties of titanium alloys depend upon the processing routes and their final microstructure. Therefore, the present review paper compiles the deformation behaviour of various alloys during hot deformation using a physical simulation. Subsequently, the flow stresses are analysed and utilized to develop the processing maps and the constitutive equations that are advantageous for predicting deformation mechanisms during the hot deformation. Specific features reported in the flow stress curves include work hardening, flow softening and steady-state behaviour. In certain cases, the yield point drop and oscillatory behaviour or serrations are also observed. Softening and oscillatory behaviour is an indicator of either dynamic recrystallization or flow-instability, whereas yield discontinuity signifies locking and unlocking of dislocations. In the processing maps, high power dissipation efficiency, η, reveals safe processing conditions, and the η value higher than 40% demonstrates dynamic recrystallization or globularization in the deformed microstructure, whereas the instability domain expresses shear band, flow localization, void formation and wedge cracks in the deformed microstructure. Amongst all the constitutive equations, the Arrhenius-type hyperbolic sine equation is the most suitable for Ti alloys for calculating flow stress and predicting dominant deformation mechanism using activation energy Q and stress exponent n. [ABSTRACT FROM AUTHOR]

Hot compression tests were performed to investigate the hot deformation behavior of Fe-27.34Mn-8.63Al-1.03C lightweight steel and optimize the hot workability parameters. The temperature range was 900–1150°C and the strain rate range was 0.01–5 s−1 on a Gleeble-3800 thermal simulator machine. The results showed that the flow stress increased with decreasing deformation temperature and increasing strain rate. According to the constitutive equation, the activation energy of hot deformation was 422.88 kJ·mol−1. The relationship between the critical stress and peak stress of the tested steel was established, and a dynamic recrystallization kinetic model was thus obtained. Based on this model, the effects of strain rate and deformation temperature on the volume fraction of dynamically recrystallized grains were explored. The microstructural examination and processing map results revealed that the tested steel exhibited a good hot workability at deformation temperatures of 1010–1100°C and strain rate of 0.01 s−1. [ABSTRACT FROM AUTHOR]

The deformation and fracture characterization of an Mg−2Sn−1Ca alloy were studied through uniaxial isothermal compression tests. The flow stress curves, the efficiency of power dissipation, the instability parameter and the fracture behavior of an Mg−2Sn−1Ca alloy under the condition of various hot working parameters were investigated according to the experimental data. Processing maps were established by superimposing the instability map over the power dissipation map. It was found that flow stress reduces with increases in the deformation temperature and decreases in the strain rate. The processing of Mg−2Sn−1Ca alloys should avoid the instability region in which the conditions are high strain under high temperature and low strain under low temperature. At 473 K or a high strain rate, unidirectional cracks and fish scale cracks can be produced, and cracks can be avoided under the optimum processing area of 623–723 K/0.001–0.1 s−1. [ABSTRACT FROM AUTHOR]

A new biomaterial Ti–14Cr alloy was designed for biomedical applications. The manufacturing process of Ti alloys through hot deformation is crucial for controlling the grain structure and the mechanical performance of the alloy. In the present study, several compression tests at elevated temperatures (1123–1273 K) and strain rate ranges of 0.01–10 s−1 were conducted using a Gleeble-3800 thermomechanical simulator. A processing map of the studied alloy was constructed using the principles of the dynamic material model to evaluate the hot workability and deformation mechanisms at different ranges of temperature and strain rate. The resulting grain structure was correlated with the processing map.The processing map showed that adiabatic shear bands are expected to form at low temperatures (1123–1223 K) and moderate to high strain rates (1–10 s−1), whereas the nucleation of wedge cracks is likely to develop at the grain boundary at high temperatures and low strain rates (1248–1273/0.01 s−1). Consequently, a deterministic domain in the temperature and strain rate ranges of 1148–1273 K and 0.01–0.1 s−1, respectively, was identified as the domain of dynamic recrystallization with a peak efficiency of the order of ∼70% at 1173 K/0.01 s−1, and these were considered to be the optimum parameters for hot deformation. The constitutive flow behavior was modeled based on the hyperbolic–sinusoidal Arrhenius-type equations, and a mathematical relation was used to elucidate the influence of true strain on material constants.

During the thermal deformation of aluminum alloy materials, the deformation conditions such as deformation volume, temperature and strain rate are important factors that influence the deformation mechanisms such as work hardening, dynamic recovery and dynamic recrystallization. Under the interaction of different deformation mechanisms, the properties of aluminum alloy materials will change significantly. In this study, isothermal hot compression experiments were conducted on the Al-7.92 Zn-1.64 Mg-2.00 Cu alloy to analyze its hot flow behavior (T = 250~450 °C, ɛ̇ = 0.001~1 s−1). The obtained flow behavior data were used to construct an Arrhenius-type constitutive equation and processing maps, investigating organizational evolution under diverse hot deformation conditions. The results show that the energy dissipation rate can reach 0.37 when the deformation temperature T = 380~450 °C and the strain rate ɛ̇ < 0.1 s−1, suggesting that the material is most suitable for thermal deformation processing at high temperatures and low strain rates. At a strain rate of 0.1 s−1 and a temperature of 450 °C, the percentage of recrystallized grains and substructures increased by 7.20% and 3.14%, respectively, compared to 300 °C, which is due to the severe dynamic recovery and dynamic recrystallization. At 350 °C and 0.1 s−1, there was a higher percentage of recrystallized grains and substructures, 5.44% and 5.87% higher, respectively, than at a strain rate of 1 s−1, indicating that the release of dislocation accumulation due to deformation storage energy will be more favored at low strain rates, which promotes the enhancement of the dynamic recrystallization mechanism.

In this paper, a hot processing map that takes into the strengthening effect into account is optimized for the Al–10.0Zn–3.0Mg–2.8Cu alloy, mainly considering the crushing and dissolving behavior of the insoluble phase. The hot deformation experiments were performed by compression testing with strain rates ranging from 0.001 to 1 s−1 and the temperature ranging from 380 to 460 °C. The hot processing map was established at the strain of 0.9. It exhibits that the appropriate hot processing region is located at the temperature from 431 to 456 °C and its strain rate is within 0.004–0.108 s−1. The recrystallization mechanisms and insoluble phase evolution were demonstrated using the real-time EBSD-EDS detection technology for this alloy. It is verified that the work hardening can also be consumed by the coarse insoluble phase refinement with the strain rate increasing from 0.001 to 0.1 s−1, besides the traditional recovery and recrystallization, but the effect of the insoluble phase crushing was weakened when strain rate increased over 0.1 s−1. Better refinement of the insoluble phase was around strain rate in 0.1 s−1, which exhibits adequate dissolving during the solid solution treatment, leading to excellent aging strengthen effects. Finally, the hot processing region was further optimized, so that the strain rate approaches 0.1 s−1 instead of 0.004–0.108 s−1. This will provide a theoretical support for the subsequent deformation of the Al–10.0Zn–3.0Mg–2.8Cu alloy and its' engineering application in aerospace, defense and military fields. [ABSTRACT FROM AUTHOR]

The hot deformation process significantly affects the performance of the manufactured Zr alloy components in nuclear reactors. The hot deformation behavior of the Zr-1wt.% Nb alloy with an initial β-quenched microstructure was evaluated using hot compression test at the temperature range of 600-950 °C and the strain rate range of 0.001-0.8 s−1. The constitutive equation was determined using kinetic analysis. The strong effect of Nb on decreasing self-diffusion in Zr was the reason for the obtained large activation energy of 390 kJ/mol in the Zr-1Nb alloy. Based on the dynamic material model, the processing map was constructed at the strain of 0.8 to show the stable and unstable hot deformation regions. The microstructural features of the hot deformed samples were observed using optical and scanning electron microscopes. The results indicated that the hot deformed microstructures were fully recrystallized so that the grain size of the as-received microstructure of the Zr-1Nb alloy was reduced from 1 mm to less than 4 μm after hot deformation at 800 °C. The optimum region in the hot deformation of the Zr-1Nb alloy with dynamic recrystallized microstructure and the peak efficiency of 40% was located at the temperature range of 675-775 °C and the strain rate range of 0.001-0.01 s−1. On the other hand, flow localization and macro-surface cracking occurred within the strain rate range of 0.1-0.8 s−1. [ABSTRACT FROM AUTHOR]

Cu–9Ni–6Sn alloys have received widespread attention due to their good mechanical properties and resistance to stress relaxation in the electronic and electrical industries. The hot compression deformation behaviors of the Cu–9Ni–6Sn–0.3Mn–0.2Zn alloy were investigated using the Gleeble-3500 thermal simulator at a temperature range of 700–900 °C and a strain rate range of 0.001–1 s−1. The microstructural evolution of the Cu–9Ni–6Sn alloy during hot compression was studied by means of an optical microscope and a scanning electron microscope. The constitutive equation of hot compression of the alloy was constructed by peak flow stress, and the corresponding 3D hot processing maps were plotted. The results showed that the peak flow stress decreased with the increase in the compression temperature and the decrease in the strain rate. The hot deformation activation energy was calculated as 243.67 kJ/mol by the Arrhenius equation, and the optimum deformation parameters for the alloy were 740–760 °C and 840–900 °C with a strain rate of 0.001~0.01 s−1. According to Deform-3D finite element simulation results, the distribution of the equivalent strain field in the hot deformation samples was inhomogeneous. The alloy was more sensitive to the deformation rate than to the temperature. The simulation results can provide a guideline for the optimization of the microstructure and hot deformation parameters of the Cu–9Ni–6Sn–0.3Mn–0.2Zn alloy. [ABSTRACT FROM AUTHOR]

The deformation characteristics of GH3128 were explored via tension experiments in the temperature region of 1023-1173 K and strain rate range of 0.001-1 s−1. The stress decreased as the temperature increased and the strain rate decreased. The obtained strain–stress curves were classified into two types: hardening and hardening–softening curves. To realise the unified prediction of the two types of stress–strain curves, a modified Johnson-Cook (JC)-Zerilli-Armstrong (ZA) constitutive model was established based on the deformation characteristics, in which the modified JC and ZA models were used to express the work-hardening and softening sections, respectively. At the same time, the peak strain was described as a function of lnZ to separate the work-hardening and softening sections. The comparison results suggest that the JC-ZA constitutive model can precisely express flow behaviour. In addition, a hot processing map for the GH3128 alloy was developed. The results showed that the high-energy dissipation region was mainly concentrated in the domain with a lower strain rate and higher temperature, where the instability domains were not included. The optimised working region was determined to be 1098-1173 K and 0.001-0.3 s−1. Microstructural observations showed that the main deformation mechanism of the stable regions was dynamic recovery (DRV), with a small amount of dynamic recrystallisation (DRX). These studies provided a theoretical basis for the processing design of GH3128 alloy components. [ABSTRACT FROM AUTHOR]

In the present research, the hot working behavior of a steel used in the shell roller manufacturing of twin-roll-casting was studied by means of Bahr Dil 805 dilatometer instrument at temperatures ranging from 950 to 1150 °C and at strain rates ranging from 0.001 to 1 s−1 to a strain of 0.6. OM and SEM microscopy was conducted to evaluate the microstructural changes during hot deformation. For anticipating the safe and unsafe conditions, a processing map was developed on the basis of dynamic material modelling. The results showed dynamic recrystallization as a main deformation mechanism (safe region) was occurred at temperatures ranging from 1000 to 1125 °C and strain rates ranging from 0.001 to 0.01 s−1 with power dissipation of 45-61%. In addition, low temperatures deformation (less than 1000 °C) could lead to the cracking or formation of a necklace microstructure. [ABSTRACT FROM AUTHOR]

The hot deformation behavior and microstructure evolution of the SAE8620RH gear steel were investigated through a single-pass hot compression test at deformation temperatures between 850 and 1100 °C and strain rates between 0.02 and 8.0 s−1 by 60% reduction. A novel strain compensation constitutive model was developed, and the 2D processing maps were established by Murty’s criterion. Results showed that the relationship between material-related parameters and strain can be mathematically expressed by a highly reliable 8th-order polynomial. The constructed strain compensation constitutive model demonstrated remarkable predictive precision, as evidenced by the correlation coefficient (R) and the absolute values of average relative error (AARE) of 0.978 and 4%, respectively. The flow instability domains considerably expanded towards the high deformation temperature region as the strain increased. Microstructure analysis confirmed the accuracy of the processing map constructed by Murty’s criterion. The most noticeable optimum processing windows for SAE8620RH gear steel at a strain of 0.7 occurred within the temperature range of 1000–1100 °C and the strain rate range of 0.3–1.0 s−1, due to high η values exceeding 0.3 and equiaxial dynamic recrystallization microstructure.

The dynamic recrystallization behavior of MP159 superalloy was investigated by performing hot compression tests in the deformation temperature range of 920–1070 °C and strain rates of 0.01–10 s−1. Processing maps were established based on flow curves, and the optimal hot processing region for MP159 alloy was identified at the deformation temperatures of 940–980 °C and a strain rate of 0.01 s−1. The influence of the processing parameters (true strain, temperature and strain rate) on the microstructure evolution was studied. The volume fraction and grain size of recrystallized grains increased with increasing strain rate and deformation temperature. Deformation twins that formed during hot deformation provided nucleation sites for dynamic recrystallization (DRX) and accelerated the DRX process. Discontinuous dynamic recrystallization (DDRX) was the dominant mechanism for the MP159 alloy at different deformation strains. [ABSTRACT FROM AUTHOR]

Flow behavior of three near eutectic Al–Si alloys with the same chemical composition but different average eutectic Si sizes (A1, 1.7 μm; A2, 4.4 μm; A3, 8.2 μm) was investigated by isothermal compression tests conducted on a Gleeble-3500 thermal simulator under four different temperatures (350 °C, 400 °C, 450 °C, and 500 °C) and four different strain rates (0.01 s−1, 0.1 s−1, 1 s−1, and 5 s−1), with a focus on the effect of eutectic Si size. Not only the flow behavior but also the processing map of near eutectic Al–Si alloys are affected by eutectic Si size. The overall trends of the flow stress–strain curves of the three alloys are similar, but their steady flow stresses σs are different: A1 alloy has the largest σs, followed by that of A3. Strain-compensated constitutive equations in the hyperbolic sine form were constructed to describe the flow stress behavior of the three alloys. Materials constants of the constitutive equations depend on eutectic Si size. The processing maps of the three alloys exhibit different characteristics. The instability domain of A2 alloy is restricted to strain rates larger than about 0.4 s−1, in contrast to the case of A1 and A3 alloys in which the instability domain occurs at both low and high strain rates. The results presented in this study indicate that eutectic Si size is an indispensable factor to be considered when dealing with the hot working of Al–Si alloys.

The Gleeble-3500 thermal simulation tester was used to perform hot deformation behavior on the extruded AZ40 Mg alloy to analyze the trend of the true stress-strain curve after compression and to obtain the influence of the flow stress on the deformation temperature and strain rate. Subsequently, the constitutive equation was constructed for extruded AZ40 alloy based on the hyperbolic-sine relationship, and the thermal processing map of extruded AZ40 alloy was established based on the dynamic material model (DMM), thereby estimating the processing range of extruded AZ40 alloy. The results show that the rheological curve of extruded AZ40 alloy is characterized by obvious dynamic recrystallization. Furthermore, during the compression process, the peak stress of extruded AZ40 alloy decreases with the increase of deformation temperature, while increases with the increase of strain rate. Moreover, the proportion of dynamic recrystallized grains (DRGs) decreases with the increase of the strain rate under the same deformation temperature condition; while the DRGs size increases with the increase of the deformation temperature under the same strain rate condition. The coarse uncrystallized grains show obvious crystallographic orientations of 〈1010〉‖ND and 〈2110〉‖ND, while crystallographic orientation of DRGs is random distributed. Finally, through thermal processing map and tissue analysis, the optimal processing window was identified as T=573 K, $\dot \varepsilon $=0.1 s-1.

In this paper, the hot deformation behavior of Zn–22Al alloy was investigated by performing hot compression tests under different deformation conditions. The Arrhenius-type constitutive model was developed and the constants were determined for this alloy. In addition, the processing map was constructed using the principle of the dynamic materials model (DMM). The results show that the Arrhenius-type model, with an activation energy of 63.722 kJ/mol, can provide an accurate prediction of the flow behavior of the alloy at various conditions. The higher energy dissipation efficiency was observed in the high-temperature ranges and low strain rates. The results showed that the unstable processing zone of Zn–22Al alloy has mainly occurred at high strain rates and low-temperature region. Besides, it is found that the strain has less significant effects on instability parameter and power dissipation efficiency.

Investigation on the hot deformability and workability of stir cast 6 wt.% steel particles reinforced aluminium 6063 matrix composites was undertaken in this study. Flow stress – strain curves generated from hot compression tests performed at strain rates of 0.01, 0.1, 1, and 10 s−1, and temperatures between 200–400°C, were used to study the flow behavior of the composite, while processing map developed from analyses of the deformation data, was used to establish the deformation mechanisms and processing safe zones for effective workability. Flow stress oscillations were observed to be prevalent at lower deformation temperatures and strain rates; largely due to the settling of reinforcement particles at grain boundary vicinities, rather than a homogeneous distribution. Also, the flow behaviour was largely strain rate insensitive. The dominant flow mechanism based on the flow stress patterns, processing map and microstructural validation was established to be dynamic recovery. Safe regions for processing based on Murty's and Gegel's criteria established the safe processing zones to be ~270–400°C at 0.01–1.0 s−1 and 380–400°C at 10 s−1. Deformation processing was unsafe at 200–260°C at 0.01–1.0 s−1 and between 200–380°C at 1.0–10 s−1.

The present work reports the hot deformation behaviour of a recently developed low-cost α+β Ti alloy Ti-4Al-2.5V-1.5Fe-0.25O (in β-worked condition) during sub-transus processing. The strain rate sensitivity (m) map, kinetic analysis and microstructural characterization were used to understand the hot deformation behaviour. The samples deformed at high temperatures and low strain rate conditions showed high m values (>0.3). In contrast, low m values (<0.15) are observed for samples deformed at low temperatures and high strain rate conditions. Kinetic analysis indicates that dislocation glide and climb is the primary rate-controlling deformation mechanism in the α+β field. At high temperatures and low strain rates (850°C–950 °C; 3 × 10−4 s−1-10−2 s−1), dynamic globurization of α is the dominant microstructural mechanism, whereas kinking of α-lamellae is ascertained as the dominant mechanism at low temperatures and high-strain rate conditions (750°C–850 °C; 10−2 s−1-1 s−1). In β-phase, dynamic recovery and continuous dynamic recrystallization control the microstructural evolution at low strain rates (3 × 10−4 s−1 – 10−2 s−1), whereas bending and thinning dominate at high strain rates (10−2 s−1 – 1 s−1). The strain rate sensitivity map and microstructural characterization indicate that the optimum regime for converting lamellar-α into globurized-α is between 850 °C and 900 °C in the strain rate range of 3 × 10−4 s−1 to 10−2 s−1. However, orientation data from the mid-region of the selected compression-tested samples (corresponding to high and low 'm' values) indicates the formation of strong-α texture where {0001}//RD (radial direction) and {10-10} and {11–20}//CD (compression direction) along with the presence of macrozones. The present work emphasizes the need to understand both the macro and microtexture evolution (along with microstructural evolution) during subtransus processing to arrive at optimum processing conditions for secondary processing. • Sub-transus processing behavior of β worked Ti-4Al-2.5V-1.5Fe-0.25O alloy studied. • DRV and CDRX control the evolution of α and β phases at low strain rates. • At high temperatures and low strain rates, dynamic globurization of α dominates. • Optimum processing conditions do not ensure macrozone-free product. • Need to include texture control (macro and micro) in the processing map approach. [ABSTRACT FROM AUTHOR]

In this work, the hot deformation behavior of Fe-8Mn-7Al-5Ni-xV(x = 0, 0.4, 0.8)-0.3C low-density steel has been investigated at 950, 1000, and 1050 °C, along with strain rates of 0.01, 0.05 and 0.1 s−1. The constitutive equation and processing maps are established, and the microstructure of unstable regions and the influence of V element on DRX are analyzed. The optimum hot working conditions of 0 V steel, 0.4 V steel, and 0.8 V experimental steel fall within a strain rate of 0.01∼0.02 s−1. The optimum deformation temperatures are about 950 °C, 1050 °C, and 950∼970 °C or 1020∼1050 °C, respectively. Adding V element leads to the formation of the VC precipitation phase in ferrite, consuming many carbon atoms and weakening austenite stability in the steel. [ABSTRACT FROM AUTHOR]

In this work, the vacuum arc-melting was used to prepare the Ti-10V-5Al-2.5Fe-0.1B alloy. Single-pass isothermal compression experiments were carried out on the alloy in the temperature range of 770–920 °C at strain rates of 0.0005–0.5 s−1. The BP model optimized by the bald eagle search algorithm (BES-BP), the BP model optimized by the sparrow search algorithm (SSA-BP), and the BP model optimized by the gray wolf optimization algorithm (GWO-BP) were developed for high-precision prediction of flow stress. The above models were compared by using the mean square correlation coefficient, root mean square error, and average absolute relative error between the predicted and experimental flow stress. The three prediction accuracy parameters have indicated that the BES-BP model has a higher accuracy for flow stress prediction at the known and the new process parameters. A hot processing map based on the dynamic materials model was developed by using the flow stress predicted in the framework of the BES-BP model, and EBSD analysis was performed as well. The results show that the degree of dynamic recrystallization increases with an increase in the power dissipation factor, and the formation of deformation bands is the main cause of instability. The minimum critical stress for inducing dynamic recrystallization of the alloy was found to be 13.13 MPa at 890 °C/0.0005 s−1. Moreover, the power dissipation factor increases with a decrease in critical stress. In addition, microstructure validation data reveal that the dynamic recrystallization model has a high accuracy for critical stress prediction, confirming that the critical stress increases with a decrease in the dynamic recrystallization fraction. • A new two-phase titanium alloy Ti-10V-5Al-2.5Fe-0.1B as an experimental material. • The bald eagle search algorithm, he sparrow search algorithm , and the gray wolf optimization algorithm were used to optimize the BP neural network. • The prediction accuracy of the BES-BP model is higher than that of the SSA-BP model and the GWO-BP model. • Different regions of microstructure evolution were verfied for the accuracy of the hot processing map. • Microstructural validation was carried out to verify the accuracy of the dynamic recrystallization critical model. [ABSTRACT FROM AUTHOR]

In this study, tensile tests for magnesium–manganese rare earth alloy (MnE21) were conducted with a WDW-300 high-temperature universal testing machine at different temperatures (300 °C~500 °C) and strain rates (1 × 10−4s−1~1 × 10−1s−1). The high temperature thermal deformation behavior, dynamic recrystallization, and texture of MnE21 magnesium alloy were analyzed by combining the constitutive equation, hot processing map, and electron backscatter diffraction (EBSD). The results show that the strain compensation equation can accurately predict the thermal deformation behavior. According to the hot processing map, the optimal processing regions were determined to be 350 °C, ε ˙ = 1 × 10−2s−1~ ε ˙ = 1 × 10−4s−1, and 450–500 °C, ε   ˙ = 1 × 10−1s−1~ ε ˙ = 1 × 10−4s−1. Based on the EBSD analysis, it was found that dynamic recrystallization of the alloy occurs above 350 °C, it was concluded that dynamic recrystallization was more adequate at 450 °C by analyzing the grain orientation and grain boundary difference orientation distribution. In addition, the texture index at different temperatures was also analyzed and it was found that the material showed a typical extrusion texture internally. During dynamic recrystallization, (01-11) [2-1-11], texture was produced. [ABSTRACT FROM AUTHOR]

This article reports the flow stress behaviour of ASTM A335 P92 steel. Uniaxial isothermal compression experiments were conducted to examine the hot deformation behaviour of P92 steel in a Gleeble® 3500 thermal–mechanical simulator. The test conditions were 0.01–10 s−1 strain rate and 850–1000 ℃ deformation temperature. Constitutive equations and processing maps developed were used to describe the hot deformation process. The results showed that the flow stress–strain curves exhibited a dynamic recovery (DRV) behaviour as the dominant softening mechanism. The flow stress decreased with an increase in the deformation temperature or a decrease in strain rate. Using the Arrhenius equation, the stress exponent and the activation energy values were 8.0 kJ.mol−1 and 487.56 kJ.mol−1, respectively. The correlation between the constructed processing maps and microstructure showed that the optimal process parameters occurred at a lower strain rate in the region of 0.1 s−1 and deformation temperatures of 900–950 ℃ and 1000 ℃ for the steel investigated. [ABSTRACT FROM AUTHOR]

The isothermal hot compression tests of Ti–15Al–12Nb alloy under wide range of strain rates (0.01–10.00 s−1) and deformation temperatures (950, 1000, 1050, and 1100 °C) were carried out using Gleeble-3500 thermo-simulation machine. A constitutive equation represented as a function of temperature, strain rate and true strain was developed, and the hot deformation apparent activation energy is calculated to be about 453 kJ·mol−1. By employing dynamic material model (DMM), the processing maps of Ti–15Al–12Nb alloy at various strains were established. Maximum efficiency of about 57 % for power dissipation is obtained at high temperature and low strain rate. Owing to the high power dissipation efficiency and excellent processing ability in dynamic recrystallization (DRX) zone for metal material, the optimum processing conditions are selected as the temperature range of 1050–1100 °C and the strain rate range of 0.01–0.10 s−1. Using transmission electron microscopy (TEM) studies, it is found that the dislocation density is directly associated with the value of processing efficiency. It is observed that when the processing efficiency is about 22 %, the dislocation density is reasonably large. The flow instability region occurs at strain rate of 10.00 s−1 with cracks, which should be avoided during hot processing to obtain the required mechanical properties. [ABSTRACT FROM AUTHOR]