High-temperature Deformation Process Research Articles

МАТЕМАТИЧНА МОДЕЛЬ ВПЛИВУ ПОВОРОТУ ВИДОВЖЕНИХ ЗЕРЕН НА ПРОЦЕС ВИСОКОТЕМПЕРАТУРНОГО ДЕФОРМУВАННЯ КЕРАМІКИ НА ОСНОВІ НІТРИДУ КРЕМНІЮ

The speed of direct high-temperature extrusion of ceramics based on silicon nitride was analyzed. The influence of rotation of elongated grains on mass transfer processes and deformation rate is established. The influence of the parameters of the high-temperature deformation process on the deformation rate is shown. An equation is proposed that describes the effect of rotation of elongated grains on the strain rate. The described equation of strain rate can be used to create technological processes of plastic deformation of ceramic materials.

МАТЕМАТИЧНА МОДЕЛЬ ВПЛИВУ ЗЕРНОГРАНИЧНОГО КОВЗАННЯ НА ПРОЦЕС ВИСОКОТЕМПЕРАТУРНОГО ДЕФОРМУВАННЯ КЕРАМІКИ НА ОСНОВІ НІТРИДУ КРЕМНІЮ

The speed of direct high-temperature extrusion of ceramics based on silicon nitride was analyzed. The influence of grain boundary slip and viscous flow of the intergrain phase on mass transfer processes and deformation rate is established. The influence of the parameters of the high-temperature deformation process on the deformation rate is shown. An equation is proposed that describes the effect of grain boundary slip and viscous flow of the intergranular phase on the strain rate. The described equation of strain rate can be used to create technological processes of plastic deformation of ceramic materials.

Initiation mechanism of micro-defects in polycrystalline iron under high-temperature stress coupling effect

To investigate the failure mechanism of high-temperature fracture in polycrystalline iron, this study conducted in-situ observation experiments to study the dynamic damage evolution process of iron under tensile loading at high temperatures. Meanwhile, through molecular dynamics simulation, the micro-defect initiation mechanism of polycrystalline iron under the coupling effect of high temperature and stress was revealed at the microscopic scale. The results indicate that during the high-temperature deformation process of polycrystalline iron at 1400 K, grain boundary slip is the main deformation mechanism. When the grain boundary slip is obstructed, stress concentration can easily occur at the grain boundaries (especially the triple junctions), leading to crack initiation. Furthermore, molecular dynamics simulations have shown that in the initial stage of deformation, with increasing strain, both HCP phase transformation atoms and dislocation length exhibit a trend of initially increasing followed by decreasing, peaking at around 5 % strain. Afterward, the system undergoes dynamic recrystallization, with dislocation movement and grain boundary migration leading to dislocation elimination. When the strain reaches 12.3 %, microvoids initiate at the triple junctions and grow up in an O shape. At a strain level of 12.45 %, there is a sudden drop in system stress, indicating fracture initiation.

Dynamic Mechanical Properties and Modified Johnson-Cook Model Considering Recrystallization Softening for Nickel-Based Powder Metallurgy Superalloys.

The material undergoes high temperature and high strain rate deformation process during the cutting process, which may induce the dynamic recrystallization behavior and result in the evolution of dynamic mechanical properties of the material to be machined. In this paper, the modified Johnson-Cook (J-C) model for nickel-based powder metallurgy superalloy considering dynamic recrystallization behavior in high strain rate and temperature is proposed. The dynamic mechanical properties of the material under different strain rates and temperature conditions are obtained by quasi-static compression test and split Hopkinson pressure bar (SHPB) test. The coefficients of the modified J-C model are obtained by the linear regression method. The modified model is verified by comparison with experimental and model prediction results. The results show that the modified J-C model proposed in this paper can accurately describe the mechanical properties of nickel-based powder metallurgy superalloys at high temperatures and high strain rates. This provides help for studying the cutting mechanism and finite element simulation of nickel-based powder metallurgy superalloy.

Optimization of the Mechanical and Corrosion Resistance of Alloy 625 through Aging Treatments

In the as-annealed condition, the nickel-based Alloy 625 has excellent mechanical and corrosion properties compared to those of common stainless steels. This peculiarity enables its exploitation in several industrial fields at cryogenic and high temperatures and in the presence of severely corrosive atmospheres. However, in this alloy, when high-temperature plastic deformation processes and heat treatments are not carefully optimized, the occurrence of excessive grain coarsening can irremediably deteriorate the mechanical strength, possibly leading to incompatibility with the standard requirements. Therefore, this research work investigated the possibility of adopting single- and double-aging treatments aimed at improving such strength loss. Their optimization involved identifying the best compromise between the hardening effect and the loss in corrosion resistance induced by the simultaneous formation of intergranular chromium-rich carbides during aging. The investigation of the aging treatments was performed using hardness, tensile and intergranular corrosion tests considering different time–temperature combinations in a range from 621 °C to 732 °C. Double aging resulted in a considerable acceleration in the hardening response compared to single aging. However, even after its optimization in terms of both temperature and time, the intergranular corrosion resistance remained a critical aspect. Among all the tested conditions, only single aging at 621 °C for 72 h was acceptable in terms of both mechanical and corrosion properties. The influence of longer exposures will be investigated in a future study.

High-temperature deformation behaviour and processing map of near eutectic Al–Co–Cr–Fe–Ni alloy

The high-temperature deformation behaviour of near-eutectic high entropy alloy was studied at 800–1100 °C and 0.01–10 s−1. The microstructure of the as-cast alloy depicted a proeutectic L12 phase and epitaxially grown eutectic colonies of lamellar L12 and B2. Deformation temperature and strain rate played vital roles in defining the precipitation and deformation behaviour of the alloy. The lower-temperature deformed samples were characterized by extensive deformation twinning and strain accumulation. In contrast, high-temperature deformation led to uniform deformation with dynamic recrystallization, recovery, B2 lamellar fragmentation and B2 precipitation. The microstructure of the deformed samples corresponded well with the processing maps developed via dynamic materials model. The processing zones for the alloy were identified to be 800–950 °C and 10−2 – 10−1.25 s−1 as well as 925–1100 °C and 10−2 – 10−0.5 s−1. The critical material flow parameters displayed a complex relationship with temperature, strain rate and strain. In the studied temperature and strain rate regime, the critical strain rate was determined to be 0.1s−1. At strain rates above and below this value, the critical strain for recrystallization was higher. Within the studied temperature and strain rate regime, the near eutectic alloy displayed superior compressive strength and wider thermos-mechanical processing region than its eutectic counterpart.

Effect of Sr addition on the high temperature deformation behavior and processing maps of Mg-7Sn alloy

The effect of strontium (Sr) addition (1 wt%) on the hot deformation behavior of Mg-7Sn (wt%) was investigated by performing high temperature compression tests in the temperature range of 300–450 °C and at strain rates of 0.05 s−1 – 5 s−1. The flow stress curves suggested the occurrence of dynamic recrystallization (DRX). The constitutive equation was developed using an Arrhenius-type hyperbolic sine equation. The addition of Sr to Mg-7Sn led to a decrease in the activation energy value, suggesting easy hot working as compared to Mg-7Sn alloy. The processing maps were further generated for both alloys at 0.2 strain (strain near peak stress). For both alloys, the high-efficiency domain appeared in the high temperature and high strain rate ranges. However, it was observed that the safe working region increased for Sr-added Mg-7Sn compared to Mg-7Sn alloy. The deformed microstructures from the safe region characterized using electron backscatter diffraction (EBSD) showed faster development of recrystallized grain in Mg-7Sn-1Sr alloy. Further, the EBSD maps depicted the occurrence of particle stimulated nucleation (PSN) in Mg-7Sn-1Sr alloy which was absent in Mg-7Sn alloy. The PSN occurrence with the addition of Sr is predicted to cause easy deformation and increase the recrystallization fraction in the Mg-7Sn-1Sr alloy. The unstable regions showed the presence of voids in both the alloys.

Dynamic Constitutive Relationship of Mg–Gd–Y–Zr–Ag Alloy during High Temperature Deformation Process

The thermal deformation behavior of the Mg-Gd-Y-Zr-Ag alloy was studied by isothermal hot compression tests at high temperatures. The flow stress increased with increased strain rates and decreased temperatures, first increasing and finally remaining stable with increased strain. A hot processing map was built. Using the processing map and microstructural analysis, the temperature should remain at 673-773 K for this alloy to ensure the deformation quality. The primary softening mechanism is discontinuous dynamic recrystallization (DDRX). Rising temperatures and declining strain rates facilitated the emergence and growth of Dynamic recrystallization (DRX) grains. An original JC (O-JC) model and a modified JC (M-JC) model were established. The M-JC model indicated a better prediction than the O-JC model. Still, it was deficient in predicting flow stresses with insufficient coupling effects. Hence, based on the M-JC model, a newly modified JC (NM-JC) model, which further enhances the interaction between strain and strain rate as well as strain and temperature, is proposed. Its projected values can better align with the tested values.

High Temperature Deformation Behavior and Processing Maps of FeCoNiCrAlTi Dual Phase High Entropy Alloy

High Temperature Deformation Behavior and Processing Maps of FeCoNiCrAlTi Dual Phase High Entropy Alloy

Comparative study on high temperature deformation behavior and processing maps of Mg-4Zn-1RE-0.5Zr alloy with and without in-situ sub-micron sized TiB2 reinforcement

Mg-4Zn-1RE-0.5Zr (ZE41) Mg alloy is extensively used in the aerospace and automobile industries. In order to improve the applicability and performance, this alloy was engineered with in-situ TiB 2 reinforcement to form TiB 2 /ZE41 composite. The high temperature deformation behavior and manufacturability of the newly developed TiB 2 /ZE41 composite and the parent ZE41 Mg alloy were studied via establishing constitutive modeling of flow stress, deformation activation energy and processing map over a temperature range of 250 °C - 450 °C and strain rate range of 0.001 s −1 - 10 s −1 . The predicted flow stress behavior of both materials were found to be well consistent with the experimental values. A significant improvement in activation energy was found in TiB 2 /ZE41 composite (171.54 kJ/mol) as compared to the ZE41 alloy (148.15 kJ/mol) due to the dispersed strengthening of in-situ TiB 2 particles. The processing maps were developed via dynamic material modeling. A wider workability domain and higher peak efficiency (45%) were observed in TiB 2 /ZE41 composite as compared to ZE41 alloy (41%). The Dynamic recrystallization is found to be the dominating deformation mechanism for both materials; however, particle stimulated nucleation was found to be an additional mode of deformation in TiB 2 /ZE41 composite. The twinning and stress induced cracks were observed in both the materials at low temperature and high strain rate. A narrow range of instability zone is found in the present TiB 2 /ZE41 composite among the existing published literature on Mg based composites. The detailed microstructural characterization was carried out in both workability and instability domains to establish the governing deformation mechanisms.

Application of Four Different Models for Predicting the High-Temperature Flow Behavior of 1420 Al–Li Alloy

In this paper, the high-temperature rheological behavior of 1420 aluminum–lithium alloy under experimental conditions (temperatures of 350–475 °C and strain rates of 0.01–10 s−1) was systematically investigated using a Gleeble-3500 thermal simulation tester (temperature 350~475 °C, strain rate of 0.01~10 s−1). Based on the flow stress curves of this alloy, four different types of high-temperature constitutive models of the alloy were constructed: the Arrhenius (AR) model, the Modified Johnson–Cook (MJC) model, the Modified Zerilli–Armstrong (MZA) model, and the VOCE model. The prediction accuracy of the four constitutive models was compared, and the response of the accuracy of the four constitutive models to the deformation parameters (temperature, deformation rate, and strain) was analyzed. The results showed that the VOCE, AR, and MZA models had high overall prediction accuracy with average absolute relative error (AARE) of 1.8933%, 3.9912%, and 7.8422%, respectively. The VOCE model could achieve the prediction of large strain deformation resistance under small strain with small batch experimental conditions for the corresponding conditions. The AR model had optimal prediction accuracy for the high-rate deformation process. The MJC model had the optimal prediction accuracy for the low-temperature low-rate deformation process. The MZA model had better prediction accuracy for the low-rate high-temperature deformation process. The 1420 aluminum–lithium alloy process parameters selection area constitutive model matching diagram was constructed.

Enhanced viscous glide creep in disordered β (Cu17Sn13) intermetallic phase with coarse grains

High-temperature deformation mechanisms and processing maps of the coarse-grained A2 (disordered BCC) β (Cu17Sn13) intermetallic phase alloy (with the chemical composition of Cu-24.6 wt %Sn) were examined in compression in the temperature range of 843–993 K and strain rate range of 10−3-10 s−1. The β phase exhibited a stress exponent (n1) of nearly 3 over almost the entire strain-rate range at these temperatures. Limited subgrain formation occurred during hot compression. This microstructural feature and the observation of n1 = 3 strongly suggest that solute drag creep is the main high-temperature deformation mechanism. A comparison of the high-temperature deformation mechanisms and behaviors of the BCC β phase and FCC α-solid solution phase (with the composition of Cu–10Sn alloy studied in previous work) shows that both β and α phases exhibit solute drag creep, but β is considerably weaker in strength, and the upper limit of strain rate for solute drag creep is much higher (over 100 times). Solute drag creep at high strain rates in the β phase can be attributed to the high breakaway stresses for dislocations from the solute atmosphere in the presence of a high concentration of Sn solutes in the matrix. The β phase exhibits superior hot workability compared with the α phase according to the processing maps, especially at high strain rates. This is because there is no flow instability regime for the β phase under the investigated testing conditions and the power dissipation efficiency at high strain rates is higher in the β phase compared with the α phase.

Predicting microstructural evolution based on deformation history of A230 alloy using a finite element method-assisted generative model

Data-driven methods for predicting and evaluating microstructural characteristics have attracted significant attention owing to recent developments in artificial intelligence (AI). In high-temperature deformation processes, the microstructure changes nonlinearly, according to the causal relationship with the deformation history in the form of time series. This makes it difficult to predict the microstructural evolution using existing AI generative models, in which time-series data are not used as an input. Therefore, herein we proposed a novel method to establish a connection between the time series deformation history and the latent vector of the AI generative model. To this end, the dynamic recrystallization (DRX) fraction and DRX grain size of a microstructure were calculated based on the deformation history, which included the temperature, strain, and strain rate, using the finite element method (FEM) combined with a DRX kinetic model. By applying the calculated DRX fraction and DRX grain size as label data, a conditional deep convolutional generative adversarial network was trained to generate microstructures. It was confirmed that the microstructural evolution due to the deformation history can be realistically reproduced. Furthermore, by comparing the average grain size and grain size distribution of the synthetic and actual microstructures, it was proven that the proposed model can be used to accurately predicts not only the shapes but also the quantitative features of microstructures. The results of this study demonstrate that FEM and AI technologies can be used sequentially to simulate the microstructural evolution as photorealistic images.

Dynamic recrystallization behavior of a Mo-2.0%ZrO2 alloy during hot deformation

The high-temperature deformation process of molybdenum alloy reinforced by 2.0%ZrO2 was tested in the temperature range of 1100–1400 °C and strain rate range of 0.005–1 s−1 in a vacuum environment, and the microstructure evolution during the high-temperature deformation process was investigated. Based on the Arrhenius model, the transient equation of the Mo-2.0%ZrO2 alloy was established, and the relationship between deformation temperature, strain rate and flow stresses was described. The flow stresses of the Mo-2.0%ZrO2 alloy were characterized by dynamic recovery and recrystallization in the deformation process. Dynamic recrystallization of the Mo-2.0%ZrO2 alloy mostly occurs at high temperatures and low strain rates. At higher strain rates (0.1–1 s−1) and low temperatures (1100–1200 °C), chain-like fine crystals and fine equiaxed grains were found, indicating that partial dynamic recrystallization occurred. At low strain (0.005 s−1) and low temperatures (1100–1200 °C), equiaxed grains were found to demonstrate continuous dynamic recrystallization. Coarse equiaxed grains were found at low strain (0.005–0.1 s−1) and high temperature (1300–1400 °C), indicating a dominance of grain growth. The Mo-2.0%ZrO2 alloy have low activation energy compared with Mo-Al2O3 alloy, which is beneficial to hot working. The Mo-2.0%ZrO2 alloy has two typical textures, 〈100〉//ND and 〈111〉//ND, after high temperature deformation. As the strain decreases, there is enough kinetic energy to reduce the basal plane deviation in TD and RD directions, and the texture of Mo-2.0%ZrO2 alloy is dominated by 〈100〉//ND.

High-temperature deformation behavior and processing maps of a novel AlNbTi3VZr1.5 refractory high entropy alloy

High-temperature deformation behaviors of a nonequiatomic novel AlNbTi 3 VZr 1.5 refractory high entropy alloy were studied. Hot compression tests were carried out at different temperatures ranging from 1100 to 1250 ℃ and various strain rates from 0.001 to 1 s −1 . The true stress-true strain curves indicated obvious sharp drops in the flow stress after reaching peak stress. This may be caused by either dislocation unlocking from a substitutional solute atmosphere or destroying short-range ordered structures. Flow stress analysis was investigated by introducing the Arrhenius constitutive relation. The apparent activation energy ( Q ) for high-temperature deformation was calculated to be 228.1 kJ/mol. The processing maps show that the best processing window was determined at 1200–1250 °C and 10 −0.75 to 1 s −1 . Detailed microstructure evolution characterization with EBSD analysis shows that the occurrence of discontinuous dynamic recrystallization along grain boundaries is the main softening mechanism of the AlNbTi 3 VZr 1.5 RHEA during the hot compression deformation. The size and volume percentage of dynamically recrystallized grains increase as the Z parameter decreases. • The high-temperature behavior of novel AlNbTi 3 VZr 1.5 refractory high entropy alloy is investigated. • The apparent activation energy was 228.1 kJ/mol. • The best processing window is determined at 1200–1250 °C and 10–0.75–1 s −1 . • Discontinuous dynamic recrystallization along grain boundaries is the main softening mechanism of the AlNbTi 3 VZr 1.5 RHEA during the hot compression deformation.

High-temperature deformation processes in migmatites from the Atuba Complex, southern Ribeira Belt: Constrains from microstructures and EBSD analyses

The Atuba Complex occurs in the southern region of the Ribeira Belt, in the eastern Paraná State. It comprises part of the Curitiba Terrane and is mainly composed of stromatic metatexites and migmatites subject to varying degrees of mylonitisation. The present work aims to perform microstructural analyses on ductile tectonites, as well as assess the prevailing deformation mechanisms by characterizing quartz crystallographic textures and microstructures, in order to understand in a more accurate way the structural and tectonic evolution of the Atuba Complex and of the Curitiba Terrane. The rocks have two phases of migmatization (granodiorite-tonalitic and granitic leucosomes) and constitute two deformation phases (Dn-1 and Dn), represented by the Sn-1 and Sn foliations, generated by ductile shear. Sn-1 foliation may be associated with Paleoproterozoic overthrusting tectonics and Sn foliation may be the result of Neoproterozoic sinistral transpressive tectonics. The electron backscatter diffraction (EBSD) results related to foliation Sn show that the deformation was accommodated by dislocation creep achieving dynamic recrystallization in quartz. Microscopically, the quartz may exhibit lobate grain boundaries, suggesting grain boundary migration (GBM), and may also show microstructures indicative of recrystallization by subgrain rotation (SGR) and, as very fine grains developed along grain boundaries, suggesting dynamic recrystallization by bulging (BLG), pointing to deformation superposition under greenschist facies conditions. The feldspar crystals show undulose extinction, subgrains and new grains, formed mainly by bulging and subgrain rotation. The domain comprised by the Sn foliation show activation of the basal slip with rhombohedral component or rhombohedral slip system for quartz, which indicate the deformation occurred at low temperature conditions (<500 °C) and may be associated with retrometamorphism that occurred in the Atuba Complex.

Strengthening mechanism and effect of Al2O3 particle on high-temperature tensile properties and microstructure evolution of W–Al2O3 alloys

The W–Al2O3 alloy rods were successfully fabricated by the powder metallurgy process and hot swaging. Subsequently, the high-temperature tensile tests were conducted to characterize the mechanical properties of the W–Al2O3 alloy. At 800 °C, the ultimate tensile strength of W-0.25 wt% Al2O3 alloy is 611.1 MPa, which is 18% higher than that of pure W. After tension, the microstructure evolution was evaluated using metallographic microscope and transmission electron microscopy. For the pure W undergoing deformation at 1000 °C, dynamic recrystallization occurs, leading to the sharp decrease of the strength. However, the microstructure of the W-0.25 wt% Al2O3 alloy contains a large number of sub-grain and low-angle grain boundaries, which does not significantly change in the temperature range of 800–1200 oC, and the work hardening plays a leading role during the high-temperature deformation process. Due to high hardness, the dispersed Al2O3 particles effectively prevent the dislocation movement, displaying a significant strengthening effect.

Deformation beneath Gakkel Ridge, Arctic Ocean: From mantle flow to mantle shear in a sparsely magmatic spreading zone

Mantle deformation processes leading to seafloor spreading are often difficult to infer due to the highly serpentinized and weathered state of most abyssal peridotites. We investigated the development of high-temperature crystal-plastic deformation and lower temperature mylonitization processes in relatively fresh (<50% modal serpentine) and ultra-fresh (<1% serpentine) mantle peridotites derived from the heterogeneous mantle in the sparsely magmatic zone of ultraslow-spreading Gakkel Ridge system by analyzing 12 peridotites from two dredge sites (<1 km apart). Microstructurally, these 12 peridotites consist of seven high-T deformed samples and five mylonites. Modally, the 12 samples include harzburgites, lherzolites, an olivine websterite, and a plagioclase-bearing lherzolite. Based on their mineral major and trace element compositions, the lherzolites, harzburgites, and olivine websterite are residual peridotites. The lherzolites containing clinopyroxenes with flat REE patterns likely underwent refertilization with a high influx of melt. The plagioclase-bearing lherzolites probably formed by subsolidus reaction after the partial melting process. Microstructural observations support that high-T crystal-plastic deformation (most likely at temperatures exceeding 1000 °C) was active in the peridotites of the high-T deformation group, accommodating mantle flow beneath the Gakkel Ridge. The identified melt refertilization process may have contributed to the formation of [010]-fiber olivine fabrics in these peridotites. Mylonitic microstructures, decreasing fabric strength and grain-size reduction of olivine suggest that mylonitization occurred under relatively low-temperature mantle conditions (~800 °C) and probably accommodated strain localization. Water did not greatly affect the peridotites during the development of the shear zones, although amphibole with “dusty” zones developed in one mylonitic peridotite after mylonitization, indicating that late-stage metasomatism occurred locally within the shear zone. This low-T mylonitization is likely to have affected mantle peridotites of this region independently of petrogenetic processes. The development of these deformation processes in Gakkel Ridge suggests a shift from flow in the uppermost mantle to shear zone formation in the rift valley walls.

Modelling and physical analysis of the high-temperature rheological behavior of a metallic glass

The high-temperature rheological behavior, around the glass transition temperature, of a Zr48Cu34Ag8Al8Pd2 metallic glass was investigated by strain rate jump experiments. The results show that the plastic deformation behavior and apparent viscosity strongly depend on temperature and strain rate. The high temperature rheology can be interpreted within the framework of the free volume model. The relative defect concentration deduced from the free volume model depends on temperature and strain rate and it explains the evolution of apparent viscosity within testing conditions, which is inversely correlated with the defect concentration. The stress overshoot is found to be a characteristic feature of the high-temperature rheological behavior. The origin of the stress overshoot is analyzed based on the physical meaning of the parameters in the free volume model. The results demonstrate that the strength of the stress overshoot is determined by the time of change from non-equilibrium to equilibrium defect concentrations. This study highlights the link between the stress overshoot phenomenon and the initial structural state, examining the influence of physical aging and stress relaxation on the high-temperature deformation process of metallic glasses.

Effect of strain rate on formability of 22MnB5 steel during hot stamping process

Hot stamping is a high temperature and high strain rate deformation process, which is widely used in automotive industries because of the advantages associated with the process like higher formability, no spring back, higher specific strength to weight ratio etc. When strain rate increases, the formability of materials decreases but in some conditions reversal behavior was also observed, therefore in this work, the focus is to find the effect of strain rate on thickness distribution, thickness gradient evolution and formability of 22MnB5 Steel. To capture the effect of strain rate, a wide range of high-temperature tensile tests were conducted in the thermomechanical simulator (Gleeble-3800) for different strain rates (0.01, 0.1, 1/s) under uniaxial and plain strain conditions. It is found that formability of 22MnB5 steel increases with increase in strain rate in the drawing region.