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The high-pressure and high-temperature structural, mechanical, and dinamical stability of rhodium has been investigated via synchrotron X-ray diffraction using a resistively heated diamond anvil cell and density functional theory. The isothermal compression data have been fitted with a Rydberg-Vinet equation of state (EoS) with best-fitting parameters V 0 =55.046(16) Å 3 , K 0 = 251(3) GPa, and K 0 ′ = 5.7(2). The thermal equation of state has been determined based upon the data collected following four different isotherms and has been fitted to a Holland and Powell thermal equation-of-state model with α 0 = 3.36(7)x10 - 5 K - 1 . The measured equation of state and structural parameters have been compared to the results of ab initio simulations. The agreement between theory and experiments is generally quite good. The present results solve controversies between previous studies which reported values of the bulk modulus from 240 to 300 GPa. [ABSTRACT FROM AUTHOR]

Triple-layer stainless-steel clad plate having 317L stainless steel (SS317L) as cladding layer and ASTM SA516 GR60 (GR60) as backing layer was successfully fabricated through vacuum hot roll bonding (VHRB) at 1373 K (1100 °C) temperature and strain rate regime of 1–5 s−1, which were identified through process efficiency maps of the base materials (SS317L and GR60). The process efficiency maps were constructed by conducting isothermal compression tests within the temperature range of 1173 K (900 °C)–1473 K (1200 °C) and 0.1–50 s−1strain rate regime. Effect of post-rolling heat treatments on the mechanical properties of clad plate was studied after solutionization at 1173 K (900 °C) for 1 h followed by cooling at different rates, i.e., water quenching, air cooling, and furnace cooling. As compared to other post-rolling heat treatments, the ultimate tensile strength, uniform plastic elongation, and maximum shear strength showed a significant change from 524 MPa, 0.46 and 519 MPa to 652 MPa, 0.36 and 410 MPa, when the normalized clad plate was solutionized at 1173 K (900 °C) and water quenched. A drastic change in shear fracture mode from gradual failure in normalized condition to catastrophic failure was also noticed after water quenching. These changes are essentially manifestation of the microstructural change in GR60 layer which led to the change in mechanical properties. [ABSTRACT FROM AUTHOR]

Al–Ti–C/7075 aluminum matrix composites (referred to as 7075-ATC) containing uniformly distributed TiC particles and traces of TiAl3 particles were produced by introducing 2 wt. % Al–Ti–C master alloy through stir casting. Isothermal thermal compression behavior at 300 °C–450 °C and 0.001 s−1 to 1 s−1 strain rates was studied in a Gleeble-3800 thermal simulation tester. Peak stress is influenced by deformation temperature and strain rate, reaching its maximum at low temperatures and high strain rates. The activation energy of the final thermal deformation is 150.11 kJ/mol, attributed to particle reinforcement. A sinusoidal hyperbolic Eigen structure equation for composites considering strain compensation is developed to describe the rheological stresses in composites. Dynamic recrystallization at 450 °C and a strain rate of 0.001 s⁻1 enhances composite molding properties. After hot compression, composites exhibit higher activation energy (Q) than cast 7075 and in situ particle-reinforced 7075 due to the obstruction of dislocations by the particles, grain refinement, and pinning effect on the grains. Based on the experimental results, an intrinsic model considering strain compensation was developed to accurately predict the thermal deformation behavior. EBSD results indicated that dynamic softening primarily occurred through dynamic restitution and partial recrystallization. The efficiency of softening peaked at 39% under a strain of 0.6, deformation temperatures between 350 °C and 450 °C, and strain rates ranging from 0.0009 s⁻1 to 0.0111 s⁻1. [ABSTRACT FROM AUTHOR]

A novel Al-Cu-Ni composite, featuring Ni-Al3Ni2/Al3Ni core–shell intermetallics within its matrix produced via powder metallurgy, was subjected to isothermal compression tests at different conditions so as to garner an insight into its hot deformation behaviour. These experiments were conducted from 300 to 500 °C, with strain rates varying from 0.0001 s−1 to 0.1 s−1. It is found that the flow stress is influenced by both strain rate and temperature. As the deformation temperature reduced or the strain rates increased, the peak stress level increased. To characterize the flow stress of the composite, a sine-hyperbolic constitutive equation was developed and the calculated value of activation energy (234 kJ/mol) was substantially higher than that for the self-diffusion of pure Al. Subsequently, the strain-compensated Arrhenius model and the artificial neural network (ANN) model were developed to predict the composite flow behaviour. With a lower average absolute relative error of 2.266%, a smaller root means square error of 0.668 MPa, and a higher correlation coefficient of 0.999 than the Strain-compensated Arrhenius model, the ANN model is more predictable. The processing maps show that the ideal hot working conditions for the composite are between 400 and 500 °C, with strain rates between 0.0001 s−1 and 0.01 s−1 with an efficiency of 37%. The uneven distribution in the shape and size of Core–shell/Al3Ni intermetallic compounds influenced the flow stress curves, leading to dynamic recrystallization (DRX), followed by partial dynamic recovery (DRV), and ultimately strain hardening at 0.01 s−1 & 0.1 s−1. The occurrence of recrystallization and recovery up to a specific strain followed by strain hardening at all the deformation temperatures is a rare phenomenon and has been attributed to the structure and composition of core–shell intermetallics. The occurrence of work hardening at higher strains throughout the operational range of temperatures imparts greater reliability to structural components. [ABSTRACT FROM AUTHOR]

Titanium alloy, Ti–6Al–2.2Mo–1.4Cr–0.4Fe–0.3Si (BT3-1), is a two phase α + β alloy developed for applications in rocket engines, gas turbine engines, and aircraft frames for service up to a temperature of 450 °C. The hot workability of this alloy has been studied through isothermal hot compression testing in the temperature and strain rate (ε ˙) range of 800 °C to 1000 °C and 10−3 to 10 s−1, respectively, in a thermomechanical simulator. Processing maps using dynamic material model has been generated and different regions of the map were correlated with microstructural observations. The flow stress data were fitted in Arrhenius strain-compensated model and constitutive equations were developed. Optical microstructures revealed elongated grains, kinking of α phase, flow localisation, and adiabatic shear bands at lower temperatures. Super-plasticity was found to be operative at low temperature of 850 °C and ε ˙ 10−3 s−1, whereas dynamic recrystallization (DRX) was dominating at high temperatures of 950 °C to 1000 °C and ε ˙ of 10−3 s−1. Finite element analysis showed the flow localization in the unstable regions of processing map. Enhanced hot workability was achieved above 950°C in the ε ˙ of 10−2−10−3 s−1 due to initiation of DRX in view of an increase in the β phase fraction. [ABSTRACT FROM AUTHOR]

Herein, the hot deformation behavior of a near-α Ti-5Al-1Sn-1 V-1Zr-0.8Mo (Ti-5111) titanium alloy was studied at 870-1050 °C during isothermal compression tests at a strain rate of 0.01-10.0 s−1. The microstructural evolution mechanism in the titanium alloy was systematically analyzed. Results show that the flow stress values rapidly increase to the peak value and gradually decrease as the strain variable increases. Further, the peak stress declines with the increasing deformation temperature. The apparent activation energy values of (α + β) and β regions are 438 and 206 kJ mol−1, respectively. The variation of flow stress against temperature and strain rate is established using the constitutive equation. The safe processing zones are 890-960 °C and 960-1010 °C at strain rates of 0.01-0.3 s−1 and 0.1-2 s−1, respectively, as determined using the hot processing diagram. The maximum energy dissipation efficiency is 0.59 at 0.01 s−1 and 930 °C, which is the optimum processing technique. The flow instability for the Ti-5111 alloy will occur at a high strain rate when shear bands and microscopic cracks appear in the deformed microstructures. Therefore, processing Ti-5111 alloy in unstable zones of the hot processing diagram should be avoided. [ABSTRACT FROM AUTHOR]

Achieving superior properties in hot working demands the integration of constitutive modeling, precise microstructure control, and the rigorous identification of safe and efficient conditions. To address this, a powder metallurgy Al–Zn–Mg alloy underwent isothermal compression tests under conditions of 300–500 °C and 0.1–0.0001 s−1. The experimental outcomes indicate that the flow stress of the Al–Zn–Mg alloy exhibits dynamic recrystallization as the predominant softening mechanism observed across all investigated hot working parameters. An Arrhenius-type model integrated with strain was constructed to describe its hot working behavior. Establishing processing maps, while considering the effect of strain, facilitated the assessment of the workability of the Al–Zn–Mg alloy. Constructed processing maps suggest that recommended processing conditions fall within the range of 475–500 °C and 0.001–0.0001 s−1, revealing the presence of uniform equiaxed grains and recrystallized structures. Samples compressed at 300 °C/0.1 s−1 exhibited adiabatic shear bands and partial recrystallization, while microcracks were found in samples deformed at 400 °C/0.1 s−1 and 500 °C/01 s−1. The microstructural changes were analyzed using EBSD, employing various maps, including IPF, KAM, GOS, and GAM, to assess dislocation density, grain misorientation, and their correlation with recrystallization in relation to both strain rate and temperature. [ABSTRACT FROM AUTHOR]

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]

Engine components, particularly exhaust valves, are manufactured by a specific forming process known as electric upsetting, which contributes to microstructures with finer grains which enhance the performance of these components. To this end, it is necessarily required to describe the grain evolution behaviors of heat-resistant alloys during the electrical-thermal-mechanical coupling forming process. The grain evolution behaviors of Ni80A superalloy including dynamic recrystallization (DRX) kinetics models and mesoscale cellular automaton (CA) model are solved from the acquired stress–strain curves in resistance heating isothermal compression tests. Following which, a multi-field and multi-scale coupling FEM model is established by embedding the multi-scale grain evolution models into the electrical-thermal-mechanical multi-field coupling compression model. Then the grain evolution behaviors in isothermal compressions with processing conditions are reproduced by simulations. The results reveal that during the isothermal compressions, recrystallized grains intend to bulge and generate around the original grain boundaries, representing as 'necklace' microstructures inhomogeneously distributed in the matrix, and then such grain morphology is gradually replaced by refined and equiaxed DRX grains. For a fixed strain, grain size decreases with decreasing temperature and increasing strain rate. Finally, the EBSD characterization results show that the developed FEM model can well describe the grain evolution behaviors of Ni80A superalloy in electrical-thermal-mechanical coupling compression process. [ABSTRACT FROM AUTHOR]

Amorphous ices are usually classified as belonging to low-density or high-density amorphous ice (LDA and HDA) with densities ρLDA ≈ 0.94 g/cm3 and ρHDA ≈ 1.15−1.17 g/cm3. However, a recent experiment crushing hexagonal ice (ball-milling) produced a medium-density amorphous ice (MDA, ρMDA ≈ 1.06 g/cm3) adding complexity to our understanding of amorphous ice and the phase diagram of supercooled water. Motivated by the discovery of MDA, we perform computer simulations where amorphous ices are produced by isobaric cooling and isothermal compression/decompression. Our results show that, depending on the pressure employed, isobaric cooling can generate a continuum of amorphous ices with densities that expand in between those of LDA and HDA (briefly, intermediate amorphous ices, IA). In particular, the IA generated at P ≈ 125 MPa has a remarkably similar density and average structure as MDA, implying that MDA is not unique. Using the potential energy landscape formalism, we provide an intuitive qualitative understanding of the nature of LDA, HDA, and the IA generated at different pressures. In this view, LDA and HDA occupy specific and well-separated regions of the PEL; the IA prepared at P = 125 MPa is located in the intermediate region of the PEL that separates LDA and HDA. Recently, a medium-density amorphous ice (MDA) was synthesized via ball-milling of hexagonal ice, adding complexity to our understanding of the phase diagram of supercooled water and amorphous ice. Here, the authors use molecular dynamics simulations to show that, depending on the employed pressure, isobaric cooling can generate a continuum of amorphous ices with densities that expand in between those of low- and high-density amorphous ices, with some of these amorphous ices being remarkably similar to MDA. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of 300M ultra-high strength steel is investigated through isothermal uniaxial compression tests under various thermo-mechanical processing conditions of 900-1250 °C and 0.01-50 s−1. Using the friction-corrected data of the experimental flow stress, the strain-compensated Arrhenius-type model, modified Johnson–Cook model and Khan–Huang–Liang model are developed. Based on the analysis of the reason of large deviation, the modified Johnson–Cook and Khan–Huang–Liang models are improved. The strain-compensated Arrhenius-type model exhibits the highest prediction accuracy. The determination coefficient and average absolute relative error of the strain-compensated Arrhenius-type model are 0.9971 and 3.57%, respectively. Meanwhile, the improved version of the modified Johnson–Cook model records the determination coefficient of 0.9964 and average absolute relative error of 3.59%, and the improved Khan–Huang–Liang model records 0.9949 and 5.08%. In view of the prediction accuracy and computation complexity, the improved versions of the modified Johnson–Cook and Khan–Huang–Liang models are preferred models. The improved phenomenological constitutive models enable us to predict the hot deformation behavior effectively for the optimization of the thermo-mechanical processing parameters of 300M ultra-high strength steel. [ABSTRACT FROM AUTHOR]

In this paper, the isothermal thermal compression simulation test of 2024 aluminum alloy was carried out. The deformation temperature is 573-723 K, the strain rate is 0.01-10 s−1, and the deformation amount is 50%. The experimental results show that the change of flow stress is inversely proportional to the deformation temperature, but directly proportional to the strain rate. OM and TEM were used to observe the microstructure after thermal deformation, the increase of temperature and the decrease of strain rate contribute to the formation of recrystallization and the decrease of dislocation density, which is the main reason for dynamic softening. The thermal deformation activation energy of 2024 aluminum alloy is 201.62 kJ/mol. The experimental peak stress constitutive model is in good agreement with the calculated value. Based on the Prasad instability model and the dynamic material model, the hot working diagram of 2024 aluminum alloy is established to construct the true strain of 50%. The ideal deformation conditions are the deformation temperature of 573-673 K and strain rate of 0.01-0.1 s−1. [ABSTRACT FROM AUTHOR]

With an aim to study the hot workability and establish the safe working zone for Ni-based superalloy XH43, cylindrical specimens were subjected to hot isothermal compression test at different temperatures (1173-1373 K) and strain rates (10−3-10 s−1) using Gleeble thermo-mechanical simulator. Strain rate sensitivity and Zener–Hollomon parameter have been calculated. Processing maps and constitutive equations have been developed and verified with the experimental results. It is observed that dynamic recrystallization (DRX) is the principal flow softening mechanism. Strain rate sensitivity obtained through constant strain rate test (CSRT) m and through cyclic strain rate jump test (CSRJT) m' is found to have close match initially up to 0.3 strain. Subsequently at higher strain m has marginal reduction, whereas m' decreases drastically to low value. This is attributed to dynamic softening at higher strain, which is predominant in case of CSRJT where cyclic test is assisting the softening process. Activation energy Q obtained through CSRT is found to be slightly higher than activation energy (Q') obtained through dynamic test like CSRJT and jump temperature test (JTT). This indicates less dragging force for deformation of alloy in dynamic tests, which is closer to industrial practice. It is also found that alloy has good workability in the temperature range of 1173-1373 K at strain rates of 0.01-0.001 s−1. In this range of parameters, the alloy follows the constitutive equation very closely. [ABSTRACT FROM AUTHOR]

Measurements of the electrical resistance of shock-compressed aluminum are used in the present study to estimate the concentration of point defects generated by the shock wave front. The parameters of the physical state of a thin metal sample are found by means of modeling the shock wave processes in the measurement cell. Experimental values of the specific electrical resistance of aluminum are compared with predictions of the equilibrium electrical resistance model. The proposed model ensures an adequate description of currently available reference data on equilibrium isothermal compression and isobaric heating of aluminum. At the same time, the shock wave experiment yields a higher specific electrical resistance than that predicted by the model of the electrical resistance of an equilibrium defectless crystal. The detected difference in the specific electrical resistances testifies to generation of defects of the crystal structure of the metal subjected to dynamic compression. Under the assumption of predominant formation of vacancies, the concentration of defects in aluminum is estimated as a function of the shock wave pressure. The number of defects in the metal increases with an increase in the shock wave pressure. The data obtained are qualitatively consistent with available results for copper and silver, which allows one to claim that generation of defects under shock compression has common specific features for these metals. The physical state of shock-compressed aluminum is thermodynamically nonequilibrium and includes numerous defects. [ABSTRACT FROM AUTHOR]

Phenomenological and physically based constitutive models to predict the hot deformation behavior in Ti–6Al–2Zr–2Sn–3Mo–1.5Cr–2Nb alloy are established and compared. The true stress–true strain data obtained from isothermal uniaxial compression tests under diverse thermo-mechanical processing conditions of 890–1010 °C and 0.001–10 s−1 are employed to establish constitutive models. The strain-compensated Arrhenius type model and modified Johnson–Cook model are chosen as a phenomenological constitutive model, while the modified Zerilli–Armstrong model as a physically based constitutive model. The selected constitutive models are improved to increase predictability. The modified Zerilli–Armstrong model proposed in the current work has higher prediction accuracy and simpler equation than the modified Johnson–Cook model and strain-compensated Arrhenius type model. The values of determination coefficient and average absolute relative error of the proposed Zerilli–Armstrong model are 0.9945% and 5.36%, respectively. In view of the prediction accuracy and computation complexity, the proposed modified Zerilli–Armstrong model is the preferred constitutive model for the Ti–6Al–2Zr–2Sn–3Mo–1.5Cr–2Nb alloy. It is because this proposed model takes account of the coupled effects of strain, temperature and strain rate as a simple equation. [ABSTRACT FROM AUTHOR]

The present study conducted the isothermal compression of 2024/6061 aluminum alloy bimetallic casting blank using a Gleeble-3500 thermal simulator in the temperature range of 300-450 °C and strain rate range of 0.01-5 s−1 to clarify the interface bonding mechanism. The effect of temperature and strain rate on the stress was studied, and the strain-compensated constitutive model was established. The effects of element diffusion on the interface bonding were clarified. It is found that the stresses decrease with increasing compression temperature and decreasing strain rate. The stress softening behavior is attributed to the combined effect of strain hardening and dynamic softening. The material constants in constitutive model considering compensation of strain are calculated, and the modified constitutive model reflects a relative low predictability of the interface bonding behavior. The sub-grains with low-angle grain boundaries are transformed into the recrystallized grains with high-angle grain boundaries due to the DRX in the bonding interface. The interface recrystallized grains and microstructural reconstitution are the main interface bonding behavior. The diffusion of interface elements is accelerated and the width of bonding layer increases with increasing compression temperature and decreasing strain rate. The continuous distribution of element diffusion in the bonding interface is enhanced. The interface bonding mechanism of the bimetallic blank is mainly characterized by a metallurgical bonding effect. [ABSTRACT FROM AUTHOR]

This paper describes the thermodynamic properties of zirconium in a high-pressure region. The available experimental data on isothermal and shock compression of this metal are summarized in the form of a simple model that specifies a pressure function of the specific volume and specific internal energy. The results of calculations of the thermodynamic characteristics of the body-centered cubic crystalline phase and zirconium melt are presented in comparison with the available experimental data in the studied range of thermodynamic parameters. The resulting equation of state can be used in the numerical modeling of adiabatic processes at high energy concentrations. [ABSTRACT FROM AUTHOR]

This study evaluated dry-in-place lubricants used for cold forging. A group of isothermal compression tests with a strain rate ( ε ˙ ) range of 0.001–1 s−1 and temperature (T) range of 30–400 °C were completed. The flow stress (σ) curves of annealed steel S45C were obtained, and a corresponding Hensel—Spittel model was developed to support finite element (FE) simulation. The sensitivity of the steady combined forward and backward extrusion (SCFBE) test proposed in another study was improved by approximately 20% after it was optimized using the results of the FE simulations. Key parameters were identified, and the calibration curves after optimization were obtained. On the basis of the optimized test, a friction testing setup with a heating system was developed, in which the die temperature could be adjusted from room temperature (RT) to 230 °C. Three dry-in-place lubricants and conventional phosphating lubricant were tested, and the friction factors (m), forming loads, and ejection loads were measured. The surface features of the specimens after testing were also investigated. According to the testing results, of the three tested dry-in-place lubricants, the mica type was the best. In addition, the optimized friction testing design was verified as effective. [ABSTRACT FROM AUTHOR]

The effect of hot isothermal compression on the flow stress of low-carbon steel was studied using a Gleeble 3500 stimulator at temperatures from 900 to 1200°C and deformation rates from 0.01 to 10 sec– 1. The flow stress was analyzed at elevated temperatures using a hyperbolic sine function. The material constants were determined in the range of true deformation rates from 0.1 to 0.7. The dislocation structure of low-carbon steel was studied after the deformation at 1100°C and cooling at a rate of 5 K/sec. A governing equation for describing and simulating the low-carbon steel behavior under high-temperature deformation was derived and justified. It was shown that the obtained equation can be used to provide a reliable and valid description of the low-carbon steel behavior under hot forming with a mean relative error of 5.1219% and a correlation coefficient of 0.9886. The equation can be used to model and optimize the process parameters of hot deformation of steel and to predict the evolution of its microstructure. [ABSTRACT FROM AUTHOR]

A new scheme for isothermal gas compression process implementation using only a cooling liquid as a liquid piston and as cooling liquid injection was developed. Two options of isothermal gas compression process implementation within the framework of the proposed scheme were studied and the theoretical foundations for their calculations were developed. The conducted numerical experiments made it possible to determine the compression process time, the required liquid piston speed for the isothermal compression process implementation for a given amount of the injected liquid, and the required amount of the injected liquid for a given law of liquid piston speed. The numerical experiments confirmed the possibility of isothermal monatomic gas compression process implementation with a high adiabatic coefficient. [ABSTRACT FROM AUTHOR]

This work aims to develop an internal–state–variable based unified viscoplastic constitutive model for TC11 titanium alloy, and embed it in finite element (FE) software to simulate its microstructure evolution during the high-temperature deformation process. Firstly, the flow and softening mechanisms of TC11 alloy with strip primary alpha phase ( α p ) were investigated via isothermal compression tests at deformation temperatures (T ) of 850 °C to 950 °C, strain rates ( ε ˙ ) of 0.1 to 10.0 s−1, and true strains (ε ) of 0.223 to 0.916. Further, the effects of deformation parameters on the phase transformation and globularization of TC11 alloy were studied via the observation and quantitative analysis of microstructure. The strip α p globularization fraction increases with increasing T and ε but decreases with increasing ε ˙ . Additionally, the phase transformation from α p to beta phase promotes the globularization of the strip α p but reduces the dislocation density. Accordingly, a set of unified viscoplastic constitutive equations coupling multiple internal variables of TC11 alloy was established and modified. The results demonstrate that the calculated flow stress and globularization fraction are consistent with the experimental data. Finally, this constitutive model was embedded into the FE software Simufact to simulate the microstructure evolution of TC11 alloy during the uniaxial compression process. The simulated geometric dimensions and microstructure distribution characteristics are in good agreement with the experimental results. The beta phase volume fraction and the strip α p globularization fraction increase with increasing the ε , and their maximum values are concentrated in the central area of the compressed specimen. [ABSTRACT FROM AUTHOR]

The hot deformation behavior and dynamic recrystallization mechanism of a new High Strength Martensitic Stainless Steel (HSMSS) for aero bearing were systematically studied by the single-pass isothermal compression tests via theoretical calculations and multi-scale experimental characterizations. The true stress-strain curves and flow behaviors under different deformation temperatures of 900 °C to 1150 °C and strain rates of 0.01 to 10 s−1 were analyzed, and the critical deformation conditions for the occurrence of dynamic recrystallization were determined based on the Zener-Holloman model. Furthermore, it is found that the increasing deformation temperature and decreasing strain rate promote dynamic recrystallization. The correlation between the microscopic mechanism of dynamic recrystallization and deformation parameters is clarified. It is found that the high strain rate activates the post-dynamic recrystallization and improves the dynamic recrystallization fraction. And the relationship between strain-induced precipitations and deformation conditions is explored. Finally, based on the dynamic material model and Prasad instability criterion, the hot processing map is established, and the optimized processing parameters are determined. It indicates that softening mechanism modifies with the distinct power dissipation efficiency. The critical power dissipation efficiency in HSMSS is presented for the first time, and the high-resolution observation shows that the lower critical power dissipation efficiency is caused by the lower stacking fault energy. This study highlights a theoretical basis for the hot-working process and dynamic recrystallization mechanism in HSMSS. [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]

To clarify the hot deformation process characteristics of 5 vol.%TiBw/TA15 composites with three-dimensional (3D) meshed structures, isothermal compression experiments are performed at the temperature of 1173–1373 K with strain rates of 0.001–1 s−1. Two criteria (Prasad and Murty) are employed to study the hot workability of the TiBw/TA15 composites. It is found that typical deformation instability defects (flow localization) are observed in the instability domains in the processing maps. The effects of strain rates and deformation temperatures on the microstructure evolution of the composites are also investigated. The flow stress curve is a manifestation of the deformation behavior of the material, which could reflect a part of the deformation behavior. To better understand the relationship between flow stress and hot deformation parameters, the constitutive equations of composites in the different phase regions (α + β region and β region) are established by combining the deformation temperature, strain rates and true strain. The calculation results show that the hot deformation activation energy is 563.487 kJ mol - 1 and 255.084 kJ mol - 1 in the α + β phase region and β single-phase region, respectively. The experimental results could facilitate the understanding of the hot deformation behavior of 5 vol.%TiBw/TA15 composites. [ABSTRACT FROM AUTHOR]

The focus of designing next-generation gasoline engines is to regulate fuel pressure to reduce fuel consumption and improve performance. In the present study, a novel process for manufacturing high-pressure common rail that is based on forging technology was developed. First, 304 stainless steel raw material was tested for isothermal compression deformation by using different strain rates at different temperatures. Then, a corresponding model, which covers a wide temperature range of 800 to 1200 °C, was established to simulate the real forging process of common rail through a comparative analysis of the revised Arrhenius model and modified Hensel–Spittel model. Second, to improve the common rail's anti-intergranular corrosion capability, mechanical strength, and fatigue resistance during use, the microstructure after hot deformation was analyzed, and the volume fraction of δ-ferrite was quantified. Third, the design of the forging process was analyzed through finite element simulation and was then experimentally validated; the common rail forging parts were formed through two-step forging and flash cutting. Then, the heating treatment process after forming was analyzed, and the results revealed that the δ-ferrite content was reduced to 1%. Finally, a manufacturing process for high-pressure common rail was determined. The results indicate that the common rail forgings produced through the aforementioned process had no mixed crystals or coarse grains, and the intergranular corrosion rate was lower than 0.66 g/m2·h. The yield strength was higher than 220 MPa, the tensile strength was greater than 610 MPa, and the elongation was higher than 52%, which supports the rationality of the manufacturing process. [ABSTRACT FROM AUTHOR]

An approach is proposed making it possible to construct the shock adiabats of molecular crystals of nitro compounds based on the data on their isothermal compression. For this purpose, an equation of state for a crystal of pentaerythritol tetranitrate (PETN) was constructed. The employed comparative analysis of the experimental data on the shock-wave compression of a simple PETN crystal with calculations carried out using the proposed approach to converting the isothermal compression pressures to the shock adiabat and the constructed equation of state of the PETN showed that the experimental and calculated pressure values are within the experimental error. [ABSTRACT FROM AUTHOR]

This study investigates the constitutive equation and microstructure evolution of an experimental Fe–26.6Mn–9.8Al–1.0C lightweight steel at deformation temperatures of 850–1050 °C and strain rates of 0.01–5 s−1 via thermal–mechanical simulation. The flow stress curves of the steel are modified by considering the effects of friction and temperature rise. A high-temperature constitutive equation of the lightweight alloy is expressed using Arrhenius-type equation involving the Zener–Hollomon parameter, the constitutive equation based on peak stress and strain compensation (material parameters vary with different strain) were constructed, respectively, which can better predict the flow stress changes of the experimental steel during hot compression, the average absolute relative error (AARE) and R were calculated to be 5.6% and 0.98. DRX kinetic model of the experimental steel was also established, and the results show that the high temperatures and low strain rates are conducive to DRX. DRX is sensitive to thermal deformation temperatures and strain rates, but the sensitivity to temperatures is higher than that to strain rates. Deformation twin and dislocation slipping are the main deformation mechanisms in the experimental steel at the low deformation temperature of 850 °C. At the higher temperature of 1050 °C, the deformation mechanisms are dislocation slipping and deformation banding. [ABSTRACT FROM AUTHOR]

The isothermal compression tests were conducted to study the hot compression behavior of Al-Zn-Mg-Sc alloy with high Zn concentration using a Gleeble-3500 thermal simulator in the temperature range of 300-450 °C and strain rate range of 0.01-5 s−1. The stress softening behavior was analyzed, and the constitutive model was established to describe the hot compression behavior of the high Zn alloy. The microstructure evolution mechanism was clarified by optical microscopy and electron backscatter diffraction. The results indicate that the true stress rapidly increases to the peak value with the increasing accumulative true strain, and finally reaches to a steady state. As the strain rate increases and temperature decreases, the peak stress increases, and the isothermal compression behavior is regarded as a competing process of work hardening and flow softening. The softening mechanism is highly affected by the compression temperature and strain rate. The Al-Zn-Mg-Sc alloy with high Zn is characterized by the dynamic recovery at the low temperature and high strain rate. And both the dynamic recovery and dynamic recrystallization dominate at the high temperature and low strain rate. The relatively stronger ⟨ 111 ⟩ orientation plays a key role in developing the recrystallization grains. As the compression temperature increases and strain rate decreases, many sub-grains with low-angle grain boundaries are transformed into recrystallized grains with high-angle grain boundaries. The main softening mechanism is also transformed from dynamic recovery to dynamic recrystallization. [ABSTRACT FROM AUTHOR]

The high-temperature deformation behavior of Ti-6.5Al-2Sn-4Zr-4Mo-1W-0.2Si alloy with lamellar starting structure was investigated by carrying a series of isothermal compression tests at temperatures of 850-1030 °C and strain rates of 0.001-10 s−1 on the Gleeble-3500 simulator. Strain-rate sensitivity exponent and deformation activation energy have been analyzed associated with the dynamic softening behaviors. Meanwhile, different identification approaches like power dissipation distribution and work-hardening derivative have been adopted to identify the softening behaviors corresponding to different deformation parameters. Then constitutive models based on the dislocation evolution have been employed to characterize the flow curves of Ti-6.5Al-2Sn-4Zr-4Mo-1W-0.2Si alloy. Finally, microstructure observation has been carried out to verify the dynamic softening behaviors occurred under different deformation conditions. [ABSTRACT FROM AUTHOR]

The possibility of constructing the equation of state of a crystalline substance based on a linear combination of the Planck–Einstein functions is shown using the example of corundum α-Al2O3. Two versions of the corundum equation of state are obtained on the basis of functions F(V,T) and G(P,T) as a result of the self-consistency of the heat capacity values, the enthalpy increment, PVT data, the coefficient of thermal expansion, and the adiabatic modulus of elasticity. Both equations provide an acceptable description of the above properties in a wide range of variables (up to a pressure of 165 GPa and a temperature of 2250 K). [ABSTRACT FROM AUTHOR]

To clarify the deformation behaviors and mechanism of various kinds of inclusions in type 430 stainless steel during hot rolling, isothermal compression experiments using Gleeble-3500 thermo-mechanical simulator were conducted with different deformation temperatures [1273 K to 1473 K (1000 °C to 1200 °C)], reduction ratios (25 to 75 pct), and strain rates (0.01 to 10 s−1). Experimental results showed that the typical inclusions in the as-cast of type 430 stainless steel were single-phase CaO–SiO2–Al2O3–MgO inclusions, single-phase MgO–Al2O3–TiOx–Cr2O3–MnO inclusions, and multi-phase CaO–SiO2–Al2O3–MgO + MgO–Al2O3–TiOx–Cr2O3–MnO inclusions. Only the CaO–SiO2–Al2O3–MgO phases in inclusions were deformable during isothermal compressive deformation as the temperature exceeded 1273 K (1000 °C) but the MgO–Al2O3–TiOx–Cr2O3–MnO phases did not. Higher deformation temperature, reduction ratio, and strain rate promoted the deformation of CaO–SiO2–Al2O3–MgO phases and resulted in larger average aspect ratio of them after the isothermal compression. The deformation behavior of multi-phase inclusions depended on the major phase, i.e., either CaO–SiO2–Al2O3–MgO or MgO–Al2O3–TiOx–Cr2O3–MnO. Young's modulus, solidus and liquidus temperatures, and liquefaction rate of inclusions were calculated and compared. Experimental and calculated results demonstrated that liquefaction rate higher than 40 pct could be a better index to quantitatively evaluating the deformability of inclusions during isothermal compression. [ABSTRACT FROM AUTHOR]

The dynamic recrystallization (DRX) behavior of the extruded AZ80A magnesium alloy during plastic deformation was studied by coupling the physical-based finite element (FE) method and the developed cellular automata (CA) model. Isothermal compression tests were conducted by Gleeble-3800 thermal simulator at different temperatures of 598 K, 623 K, 648 K, 673 K, 698 K, and 723 K, and different strain rates of 0.001 s−1, 0.01 s−1, 0.1 s−1, and 1 s−1 to obtain the corresponding flow stress–strain curves. The constitutive model was established based on the analysis of the flow stress–strain curves. Moreover, parameters of the CA model were found. Based on the CA model, the DRX model was built. The established constitutive model and the DRX model were embedded in DEFORM-3D software to simulate the grain evolution under various deformation conditions. This combined method was capable of predicting the evolution of flow stress, DRX volume fraction, and DRX grain size in various deformation conditions. The results show that the error between the recrystallization volume fraction predicted by the finite element simulation and the CA model and the experimental results is less than 12.0%, and the error between the peak stress predicted by the CA model and the measured value remains within 8.0%. The prediction results of the combined methodology of the CA model and the FE simulation are consistent with the experimental results, which verify the usefulness and the prediction prospect of the coupled method. This method was probably a feasible choice to predict the DRX grain refinement of the thermal deformation process of the extruded AZ80A magnesium alloy. The dynamic recrystallization (DRX) behavior of the extruded AZ80A magnesium alloy during plastic deformation was studied by coupling the physical-based finite element (FE) method and the developed cellular automata (CA) model. The results show that the error between the recrystallization volume fraction predicted by the finite element simulation and the CA model and the experimental results is less than 12.0%, and the error between the peak stress predicted by the CA model and the measured value remains within 8.0%. [ABSTRACT FROM AUTHOR]

The isothermal compression experiments of annealed rare earth microalloyed Ti64-xSi-ySc alloys were carried out on an MMS-100 thermal simulator in the temperature range of 800-950 °C and strain rate range of 0.01-10 s−1. The Arrhenius constitutive models of the alloys were established, and it was found the deformation activation energies of Ti64, Ti64-0.25Si, Ti64-0.3Sc, and Ti64-0.25Si-0.3Sc alloys were 497.65 KJ/mol, 485.6 KJ/mol, 549.13 KJ/mol, and 494.98 KJ/mol, respectively. Indicating the addition of scandium can increase the thermal deformation activation energy, which was unfavorable to the processing performance of the alloys, while silicon reduced the thermal deformation activation energy. The hot processing maps of materials demonstrated that the optimal processing area of Ti64 and Ti64-0.25Si alloys were in the range of temperature 850-950 °C and strain rate 0.01-0.1 s−1, while Ti64-0.3Sc and Ti64-0.25Si-0.3Sc alloys were more desirable for thermal deformation at the temperature range of 800-900 °C and the strain rate of 0.01-0.1 s−1. Based on electron backscatter diffraction (EBSD) characterization, scandium as an α phase stabilizing element that can refine the recrystallized grains and raise the strain storage energy, which improved the efficiency of power dissipation but expanded the instability region on the hot processing maps of the alloys, while silicon as a β phase stabilizing element reduced the instability region. [ABSTRACT FROM AUTHOR]

The impacts of loading conditions on the mechanical response and DRX of A356 during single and double thermal compression were investigated. The results indicate that the strain hardening rate obtained during the second isothermal compression is far larger than that obtained during the initial isothermal compression. The microstructure after both single and double compression is dominated by deformed columnar grains and equiaxed recrystallized grains. The recrystallization fraction of the samples after double compression is greatly affected by its initial dislocation density and microstructure state. The microstructure examination shows that the evolution of the subgrain boundaries around the original grain boundaries and within the deformed columnar grains is the main mechanism for recrystallized grain formation in the A356 alloy. [ABSTRACT FROM AUTHOR]

Inconel 625 nickel alloy with its attractive high-temperature strength, excellent corrosion and oxidation resistance is mainly used for critical applications in demanding environments, in both as-cast and wrought conditions. Hot processing of this alloy is crucial for achieving its tailored mechanical properties due to the significant variation in microstructural changes with varying process parameters like temperature, strain, and strain rate. In this study, isothermal hot compression tests were carried out at temperatures ranging from 900 to 1100 °C, and under strain rates ranging from 0.01 to 1 s−1. The flow curves revealed three stages of deformation, including a substantial work-hardening stage followed by dynamic recovery and flow softening. Microstructural observations showed the occurrence of discontinuous dynamic recrystallisation (DDRX) as the dominant recrystallisation mechanism during the flow softening. Microstructural analysis suggested that the DRX was more sensitive to the test temperature as compared to the strain rate. An innovative material's constitutive model was developed, by combining Johnson–Cook (JC) and Avrami approaches, to predict work-hardening, dynamic recovery, and flow softening stages of deformation. The predicted flow behavior was in a good agreement with the experimentally measured data. The developed material model was integrated into DEFORM® 3D finite element (FE) simulation software as a user subroutine for the prediction of deformation behaviour in a double truncated cone (DTC) sample. Comparison between the experimentally measured data and the results of FE simulation on the DTC sample showed a very good convergence, indicating the suitability of the proposed material's constitutive model for large scale simulations. [ABSTRACT FROM AUTHOR]

The thermal equation of state (TEOS) for solids is a mathematic model among pressure, temperature and density, and is essential for geophysical, geochemical, and other high pressure–temperature (high P–T) researches. However, in the last few decades, there has been a growing concern about the accuracy of the pressure scales of the calibrants, and efforts have been made to improve it by either introducing a reference standard or building new thermal pressure models. The existing thermal equation of state, P(V, T) = P(V, T0) + Pth(V, T), consists of an isothermal compression and an isochoric heating, while the thermal pressure is the pressure change in the isochoric heating. In this paper, we demonstrate that, for solids in a soft pressure medium in a diamond anvil cell, the thermal pressure can neither be determined from a single heating process, nor from the thermal pressure of its calibrant. To avoid the thermal pressure, we propose to replace the thermal pressure with a well-known thermal expansion model, and integrate it with the isothermal compression model to yields a Birch–Murnaghan-expansion TEOS model, called VPT TEOS. The predicted pressure of MgO and Au at ambient pressure from Birch–Murnaghan-expansion VPT TEOS model matches the experimental pressure of zero (0) GPa very well, while the pressure prediction from the approximated Anderson PVT TEOS exhibit a big deviation and a wrong trend. [ABSTRACT FROM AUTHOR]

The hot deformation behaviour of the GH4169 alloy in two different initial states (homogeneous and mixed-crystal states) was investigated by performing isothermal compression tests at different strain rates (0.01-1 s−1) and deformation temperatures (1050-1150 °C). Hot-working diagrams were established for both alloy types, and the microstructural evolution in both alloy types during hot deformation was analysed to determine the corresponding deformation mechanism. The experimental results showed that the peak stress of the homogeneous alloy was lower than that of the mixed-crystal alloy for the same temperature and strain rate. Based on the processing maps, the flow instability domain of the homogeneous alloy exceeded that of the mixed-crystal alloy. The optimal processing parameters of the homogeneous alloy were 0.01-0.1 s−1/1050-1100 °C, and 0.01-0.1 s−1/1050-1080 °C (at a lower strain state) or 1100-1150 °C (at a higher strain state) was optimal for the mixed-crystal alloy. Microstructural analysis revealed that the differences in the hot deformation behaviour of the homogeneous and mixed-crystal alloys were caused by the different initial grain sizes and dynamic recrystallization (DRX) mechanisms. The main DRX nucleation method of the homogeneous alloy was discontinuous DRX, whereas that of the mixed-crystal alloy was continuous DRX and discontinuous DRX. [ABSTRACT FROM AUTHOR]

Flow behavior and microstructure evolution of as-forged austenitic stainless steel with high N were investigated by isothermal compression tests at 950-1200 °C with strain rate of 0.001-1 s−1 and strain of 30-50% using Gleeble-3800 thermal mechanical simulation machine. The hyperbolic sine constitutive equation was established during isothermal compression with different parameters. The activation energy and stress exponent were 550 KJ mol−1 and 4.715, which is lower than the value of as-casted austenitic stainless steel with high N and higher than other austenitic stainless steel such as 304 and 316. It indicates that the dynamic softening behavior is related to the original structure and material composition. The dynamic softening behavior and grain refining progress were studied employing microstructure analysis techniques. It was found by comparing with the as-casted microstructure, the dynamic recrystallization behavior for as-forged sample was more sensitive to strain rate and less affected by temperature, strain and original structure. This should mainly depend on the stacking fault energy related to the material composition. When strain rate is less than 0.1 s−1, the dynamic softening is characterized by serration, bulging and strain-induced separation of original grain boundary. While strain rate is 1 s−1, the nucleation and progress of dynamic recrystallization grain were related to formation and interaction of Σ3 twin boundaries. With the increase of strain, the recrystallization fraction increases linearly with the number of twin boundaries. The recrystallization fraction increased to 86.2% and the grain size was refined to 16.6μm depending on twinning mechanism by compressing to 50% at 1100 °C with strain rate of 1s-1. [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]

Dynamic recrystallization mechanism and microstructure evolution of a novel quasi-continuous network reinforced TiAl matrix composites, TiAl/B4C composites were studied in this paper. The isothermal compression experiments, the scanning electron microscopy, and the electron back-scattered diffraction were carried out. Besides the discontinuous dynamic recrystallization (DDRX), the continuous dynamic recrystallization occurred in γ-phase grains during the loading, characterized by crystal orientation accumulation. Additionally, a large number of 89 ± 3° grain boundaries associated with DDRX also appeared during the loading. With the temperature increasing or/and the strain rate decreasing, the volume fraction of recrystallized grains increased significantly, the < 010 > crystal direction of γ-phase grains within the matrix unit of present composites was gradually parallel to compression direction, and the texture changed from scatter to concentration. The variety of texture was mainly related to different dynamic recrystallization mechanisms in various conditions. [ABSTRACT FROM AUTHOR]

Aspects of regenerative heat exchange in a piston compressor are investigated. The most thermodynamically advantageous situation occurs when compression approaches an isothermal process. The heat balance equation, which compares the amount of heat released per piston compressor cycle and that removed through the outer surface of the working chamber, was used to develop a method for calculating heat absorbed by working chamber walls in a compressor depending on the duration of compressor operation. The developed procedure provided a basis for parametric analysis to determine the influence of the main operating parameters (pressure ratio in a stage, angular velocity of crankshaft rotation) on the final temperature and heating time of the walls. This procedure can be used for preliminarily estimating the operating time of a piston machine employing regenerative cooling in compressor mode. [ABSTRACT FROM AUTHOR]

Isothermal compression tests with different conditions were performed on an as-extruded WZ-A3 alloys with different level of boron and carbon. The results show that low angle grain boundaries (LAGBs) and γ′ phases with diameter greater than 300 nm increase rapidly and Σ3 twin boundaries (TBs) decrease after hot compression deformation at lower temperature for as-extruded alloys. In addition, compared to that of as-extruded state, the grains are refined after hot compression as the compression temperature decreases. The HB\C sample (alloy with higher B and C content) has more LAGBs and less TBs as well as lower complete recrystallization zone fraction compared with those for the LB\C sample (alloy with lower B and C content) for all the same compression conditions performed. Furthermore, under all identical compression conditions performed, the HB\C sample shows a higher peak stress (σp) than that of the LB\C sample. The HB\C sample has larger area fraction and smaller average size of γ′ phases (>300 nm) than that of the LB\C sample for all the same compression conditions performed. Hence, more γ′ particles (>300 nm) in HB\C have larger average inhibition force for boundaries migration compared with that in LB\C during hot compression deformation. The area fraction of γ′ phase (>300 nm) decreases with increasing of deformation temperatures and shows different variation characteristic with small amplitude decreasing of strain rate at different constant deformation temperatures. More γ′ phases exist in samples compressed at lower temperature, inhibiting dynamic recrystallization (DRX) behavior. In addition, the dissolution rate of fine γ′ phases is faster in the LB\C sample than that in the HB\C sample especially at 1100 °C compression temperature. Boron mainly stabilizes γ′ phases by inhibiting diffusion of solute atoms (Al, Ti) during hot compression and carbon mainly contributes to the precipitation of carbides. Continuous DRX (CDRX) and discontinuous DRX (DDRX) both happen during hot compression for the as-extruded WZ-A3 alloy. [ABSTRACT FROM AUTHOR]

The three-dimensional (3D) processing maps of cast Mg-9.0Gd-3.0Y-2.0Zn-0.5Zr alloy were established based on isothermal compression tests and dynamic material model (DMM). The stable and power-efficient forming domains were determined by considering both the instability and power dissipation efficiency maps. Multi-directional forging (MDF) was then simulated by employing finite element (FE) analysis in the Deform-3D software, using the 3D power dissipation efficiency maps as input. The optimal forging parameters were thus obtained for a large-scale ingot with 430 mm in diameter and 440 mm in height, i.e., a forging temperature of 450 °C and forging speed of 10 mm/s. Finally, a Mg-9.0Gd-3.0Y-2.0Zn-0.5Zr cake-shaped forged part with 900 mm in diameter and 100 mm in height was produced. After T6-heat treatment, the edge and center of the forged part exhibit homogeneous microstructure and relatively consistent properties, with the tensile strength, yield strength, and elongation being about 400 MPa, 320 MPa, and 14.0%, respectively. Using transmission electron microscopy, the main strengthening phases were revealed to be the dense nano-scale β′ phases that are uniformly distributed inside the material. [ABSTRACT FROM AUTHOR]

When manufacturing components for gas turbine engines from superalloys based on nickel and iron, the superplastic deformation of ultrafine-grained semi-finished products is used. The technology for obtaining such semi-finished products known as the getraising process is carried out in a nonoxidizing atmosphere. The deformation of such semi-finished products under conditions of superplasticity makes it possible to obtain high-quality details. This study substantiates the possibility of using a more economical process, i.e., an intense plastic deformation of superalloys by the method of torsion with uniaxial compression or tension in isothermal air conditions. It is shown that, in this case, the critical load on the tool is significantly reduced, and a one-pass process of deformation accumulation is provided, which is necessary for uniform grinding of grains in the material of large-sized superalloy products. [ABSTRACT FROM AUTHOR]

All available volume and elasticity data for the garnet end-members grossular, pyrope, almandine and spessartine have been re-evaluated for both internal consistency and for consistency with experimentally measured heat capacities. The consistent data were then used to determine the parameters of third-order Birch–Murnaghan EoS to describe the isothermal compression at 298 K and a Mie–Grüneisen–Debye thermal-pressure EoS to describe the PVT behaviour. In a full Mie–Grüneisen–Debye EoS, the variation of the thermal Grüneisen parameter with volume is defined as γ = γ 0 V V 0 q . For grossular and pyrope garnets, there is sufficient data to refine q which has a value of q = 0.8(2) for both garnets. For other garnets, the data do not constrain the value of q and we therefore refined a q-compromise version of the Mie–Grüneisen–Debye EoS in which both γ/V and the Debye temperature θ D are held constant at all P and T, leading to ∂ C V ∂ P T = 0 , parallel isochors and constant isothermal bulk modulus along an isochor. Final refined parameters for the q-compromise Mie–Grüneisen–Debye EoS are: Pyrope Almandine Spessartine Grossular V0 (cm3/mol)a 113.13 115.25 117.92 125.35 K0T (GPa) 169.3 (3) 174.6 (4) 177.57 (6) 167.0 (2) K 0 T ′ 4.55 (5) 5.41 (13) 4.6 (3) 5.07 (8) θ D0 771 (28) 862 (22) 860 (35) 750 (13) γ0 1.185 (12) 1.16 (fixed) 1.18 (3) 1.156 (6) for pyrope and grossular, the two versions of the Mie–Grüneisen–Debye EoS predict indistinguishable properties over the metamorphic pressure and temperature range, and the same properties as the EoS based on experimental heat capacities. The biggest change from previously published EoS is for almandine for which the new EoS predicts geologically reasonable entrapment conditions for zircon inclusions in almandine-rich garnets. [ABSTRACT FROM AUTHOR]

For the higher-dimensional dS spacetime embedded with black holes with non-linear charges, there are two horizons with different radiation temperatures. By introducing the interplay between two horizons this system can be regarded as an ordinary thermodynamic system in the thermodynamic equilibrium described by the thermodynamic quantities ( T eff , P eff , V , S , Φ eff ). In this work, our focus is on the thermodynamic properties of phase transition for the four-dimensional dS spacetime with different values of the charge correction ϕ ¯ . We find that with the increasing of the non-linear charge correction the two horizons get closer and closer, and the correction entropy is negative which indicates the interaction between the two horizons stronger and stronger. Furthermore, the heat capacity at constant pressure, isobaric expansion coefficient, and the isothermal compression coefficient have the Schottky peak at the critical point. However, the heat capacity as constant volume for the dS spacetime is nonzero. Finally, the dynamical properties of phase transition for this system have investigated based on Gibbs free energy, where exists the different behavior with that for AdS black holes. [ABSTRACT FROM AUTHOR]

Liquid−liquid transition (LLT) between two disordered phases of single-component material remains one of the most intriguing physical phenomena. Here, we report a first-order LLT in a series of ionic liquids containing trihexyl(tetradecyl)phosphonium cation [P666,14]+ and anions of different sizes and shapes, providing an insight into the structure-property relationships governing LLT. In addition to calorimetric proof of LLT, we report that ion dynamics exhibit anomalous behavior during the LLT, i.e., the conductivity relaxation times (τσ) are dramatically elongated, and their distribution becomes broader. This peculiar behavior is induced by isobaric cooling and isothermal compression, with the τσ(TLL,PLL) constant for a given system. The latter observation proves that LLT, in analogy to liquid-glass transition, has an isochronal character. Finally, the magnitude of discontinuity in a specific volume at LLT was estimated using the Clausius-Clapeyron equation. Liquid−liquid transitions (LLTs) have been reported for some molecular systems but are difficult to observe under high pressure conditions. Here the authors report and characterize a first-order LLT in a series of ionic liquids containing the trihexyl(tetradecyl)phosphonium cation and anions of different sizes and shapes, using calorimetric and dielectric measurements. [ABSTRACT FROM AUTHOR]

Nowadays, selective laser melting (SLM) represents an option for manufacturing parts from titanium alloys, especially from Ti-6Al-4V alloy. However, mechanical properties of parts made of SLM-produced Ti-6Al-4V, such as ductility and fatigue resistance, are significantly lower than that of wrought ones. The promising way to improve mechanical properties of SLM parts without expensive hot isostatic pressing can be combination SLM and deformation post-processing. Therefore, the goal of the present study is to investigate the flow stress behavior and microstructure evolution of Ti-6Al-4V fabricated by SLM in a wide temperature range in comparison with conventional manufactured material. In contrast to wrought material, SLM-produced Ti-6Al-4V shows high plastic flow instability at test temperatures of 20–900 °С, which was demonstrated via temperature sensitivity and softening rate. FEM-simulation of hot isothermal compression of samples was conducted in order to compare the deformation inhomogeneity between SLM-produced and wrought materials, namely, local strains e in the severe plastic deformation and dead metal zones. The microstructure in these characteristic zones of both materials deformed in (α + β)-field was examined by means of optical microscopy. The type of microstructure and grain size of the SLM-produced and wrought material were studied. It turned out that the deformation of SLM-produced Ti-6Al-4V at a lower temperature (800 °C) and a higher strain rate (1 s−1) makes it possible to obtain ultrafine-grained microstructure. This, in turn, opens the door to the production of Ti-6Al-4V parts with high mechanical properties via processing route SLM + metal forming. [ABSTRACT FROM AUTHOR]

An isothermal compression test of extreme-cooled 7055 aluminum alloy was performed on a thermomechanical simulator under the temperature of 250–450 °C and the strain rate of 0.001−1 s−1. The constitutive model and microstructure evolution of 7055 aluminum alloy during hot compression deformation were studied. We modify the Arrhenius (AR) model considering strain compensation, which can predict the flow stress accurately. The microstructure and dynamic softening mechanism under different deformation conditions were studied using electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The softening mechanism has gradually changed from dynamic recovery (DRV) to dynamic recrystallization (DRX) with increasing the temperature. With the increase of the strain rate, the softening mechanism has also changed from DRX to DRV. The main dynamic softening mechanism of extreme-cooled 7055 aluminum alloy is DRV and DRX. Finally, it is described that the DRX behavior is dominated by continuous dynamic recrystallization (CDRX). Simultaneously, partial discontinuous dynamic recrystallization (DDRX) exists at lower temperature. [ABSTRACT FROM AUTHOR]

Isothermal compression experiments of as-homogenized Mg-8.5Gd-4.5Y-0.8Zn-0.4Zr alloy are conducted at temperature range of 673-773 K (400-500 °C) and strain rate range of 0.001-1 s−1 in order to identify the optimized processing parameters. Results show that flow stress decreases with the decreasing strain rate at a given temperature and increases with the decreasing temperature at a specific strain rate. Based on the obtained true stress-strain curves, processing maps based on the Prasad criterion and the Murty criterion are separately constructed. Obviously, distributions of power dissipation and the instability regime in the case of the Prasad criterion are different from the corresponding ones in the case of the Murty criterion during hot deformation. Microstructure observations on deformed samples confirm that kink band and dynamic recrystallization, rather than microcrack and flow localization, occur at 698 K and 0.01 s−1. This issue verifies the accuracy of instability regions determined on the base of the Murty criterion. Consequently, the processing window determined on the base of the Murty criterion is more reliable than that identified on the base of the Prasad criterion. The optimized processing parameters are finally ascertained to be 698-748 K, 0.001-0.01 s−1, and 748-773 K, 0.01-0.1 s−1. [ABSTRACT FROM AUTHOR]