High Temperature Compression Tests Research Articles

Improvement in the high temperature mechanical properties of additively manufactured Ti–48Al–2Cr–2Nb alloy using heat treatment

Gamma Ti–48Al–2Cr–2Nb (Ti4822) alloy, which is manufactured by an electron beam melting (EBM) process, has excellent ductility but poor high-temperature strength, because it has a near gamma structure. The objective of this study was to control the microstructure of Ti4822 by considering various forms of heat treatment to improve the mechanical properties at room and high temperatures. The heat treatment conditions were varied to create nearly lamellar (NL) and fully-lamellar (FL) structures. First, the EBM-built NL-Ti4822 exhibited a lamellar structure with an average layer thickness of about 92 nm and equiaxed γ-phase particles with a size of several tens of micrometers. On the other hand, the EBM-built FL-Ti4822 had an average lamellar thickness of about 347.2 nm, but in this case the equiaxed γ phase was not observed. The results of the room- and high-temperature compression test showed that the mechanical properties of the two heat-treated materials were significantly superior to those of the as-built Ti4822 across all temperature ranges. Moreover, both materials were highly ductile at room and high temperature despite having a lamellar structure, and exhibited intensified yield stress anomaly and dynamic recrystallization as the fraction of lamellar structure increased. Based on the above results obtained by subjecting the materials to different heat treatment methods, the effects of the microstructures of the two materials on the mechanical properties and deformation mechanisms at room and high temperatures were investigated.

Effect of Initial Microstructure on the High-Temperature Formability of STS 321 Alloy Using a Dynamic Material Model

General austenitic stainless steel has a problem with intergranular corrosion due to volatilizing chromium, which forms chromium carbide in a high temperature environment. By adding titanium as an alloying element, STS 321 stainless steel has excellent creep resistance and intergranular corrosion resistance at high temperatures, because the formation of chromium carbide is suppressed. It is important to find the optimal process conditions for STS 321 stainless steel used in the aerospace field, because high temperature processing is mainly applied, and defects or inhomogeneity of materials that occur during high temperature processing lowers the yield of products. In this study, to investigate the effect of the initial microstructure on the high-temperature deformation behavior of STS 321 stainless steel, a high-temperature compression test was performed on two types of STS321 alloys with different initial microstructures. The temperature range was set at 50°C intervals from 800°C to 1100°C, and the strain rate was set at 10-1/sec intervals from 1 × 100/ sec to 1 × 10-3/sec. Based on the experimental results, the thermal activation energy, which differed depending on differences in the initial microstructure, was calculated. In addition, by deriving flow stress and processing maps, the difference in energy dissipation efficiency depending on temperature and strain rate was explained, along with the initial microstructure and high-temperature deformation mechanism.

Characterization of Hot Workability in AISI 4340 Based on a 3D Processing Map

This study performed high-temperature compression tests at the temperature 900 to 1200 °C and strain rate 0.01 to 10 s−1 to characterize the high-temperature deformation behavior of AISI 4340. The constitutive equation of AISI 4340 was expressed using the Arrhenius model and the Zener–Hollomon (Z) parameter. Dynamic Recrystallization (DRX) behavior was evaluated by observing the compressed specimen with Electron Backscatter Diffraction (EBSD). The processing map is based on the dissipation efficiency of the dynamic material model (DMM) and the plastic instability criterion of Ziegler. At strain 0.4, the power dissipation efficiency value is 0.5 or more, and the instable zones are immediately identified through the processing map. The strain, strain rate and temperature data obtained from the FEM simulation of the hot forging process are displayed on the proposed 3D processing map to avoid the flow instability zones and ensure high power dissipation efficiency zones, allowing the operator to control the process’s temperature and speed.

Changes in High Temperature Deformation Behavior by Differences in Energy Dissipation Efficiency of Ti–6Al–4V Alloy

Ti–6Al–4V alloy is widely used as a system material in high temperature and high pressure environments in various industrial fields and is difficult to mechanically machine. Thus, high temperature processing methods such as hot forging, rolling, and hot forming are usually applied. Among various methods for deriving optimal molding conditions during high-temperature processing, the dynamic material model suggests energy dissipation efficiency according to the flow stress of the material. However, the energy dissipation efficiency merely numerically represents the change in flow stress, not the metallurgical behavior of the material. Therefore, it is necessary to understand the difference in energy dissipation efficiency in relation to the high-temperature deformation mechanism. In this study, high temperature compression tests were performed on the Ti–6Al–4V alloy. The temperature range was set at 800°C∼1200°C at intervals of 50°C, and the strain rate was set at 1 × 100/sec∼1 × 10−3/sec at intervals of 10−1/sec. Based on the results of the experiments, flow stress and processing maps were derived, and the high temperature plastic deformation behaviors of Ti–6Al–4V alloy were analyzed in correlation with the microstructural changes and mechanical properties according to temperature and strain rate. And the prior beta grain size according to the difference in energy dissipation efficiency was explained for each condition.

MoNbV, MoNbVTi and MoNbVTiHf multicomponent refractory alloys—Compositional modulated mechanical properties investigating

In this paper, equiatomic MoNbV, MoNbVTi and MoNbVTiHf refractory multi-component alloys were investigated in comparative style. Single body centered cubic (BCC) structure with increased lattice parameter were determined by X-ray diffraction. Typical dendrite structure was demonstrated by scanning electronic microscope. Mechanical testing shows excellent room temperature compressive mechanical properties of MoNbVTi high entropy alloy (HEA), which exhibited maximum compressive strength beyond 2000 MPa and the fracture strain exceeds 25 %. The high temperature compressive testing shows outstanding high temperature softening resistance of MoNbV medium entropy alloy (MEA), which exhibited compressive strength above 1160 MPa, and plasticity ductility exceeds 18 % at 1273 K. The present study implies MoNbV MEA possesses excellent high temperature strength and plastic ductility,which shed light on the design of high temperature structural material with simple composition.

Microstructural Variation and Evaluation of Formability According to High-Temperature Compression Conditions of AMS4928 Alloy

Ti-6Al-4V alloys are used in various industrial fields such as aircraft parts due to its excellent specific strength and mechanical properties. A high-temperature forming technology has been applied because it is difficult to process complex shapes. During the high-temperature forming process, the microstructure changes significantly due to temperature, strain rate, reduction ratio, and other process variables, and mechanical properties of high-temperature molded products are changed accordingly. Therefore, in this study, a high-temperature compression test was performed on AMS4928, which is one of Ti-6Al-4V alloys used as a material for aircraft parts, and the severe plastic deformation and dead zone were confirmed in connection with the processing map. The changes in microstructure were comparatively analyzed. In addition, it was confirmed that there was a difference in formability due to grain refinement by dynamic recrystallization, and optimal high-temperature forming conditions were derived by linking and analyzing the formability and microstructural factors.

Microstructure evolution and the mechanical properties of in-situ Ti2AlCw-NbC@TiBx/TiAlNb composite with high performance

This manuscript reports an innovative preparation method of TiAl matrix composites. The mixed AlNb powder and B4C powder were put into TiAlNb alloy melt after ball milling. With the help of the reaction in AlNb/B4C powders and the in-situ reaction of various elements in TiAlNb alloy melt, hybrid Ti2AlCw and [email protected] core-shell structure with high dispersion and good interface bonding were synthesized and introduced into TiAlNb alloy. The analysis shows that the NbC/TiBX of the core-shell structure was based on the in-situ reaction on the NbC substrate obtained in high-energy ball milling and was formed by the in situ reaction in the TiAlNb melt. The [email protected] structure and the in-situ Ti2AlC whiskers both have excellent interfacial bonding with TiAl matrix. In this TiAlNb composite with dual-scale reinforcements, the combination of multiple strengthening/toughening mechanisms improves the mechanical properties of TiAlNb alloy matrix. The in-situ Ti2AlCw and [email protected] hybrid reinforced TiAlNb composite was prepared successfully. Room compression tests show that the fracture stress and strain of the composite are increased from 1548 MPa, 20.6% to 2678 MPa, 29.1%. And the high temperature compression tests (at 1073 K) show that the fracture stress and strain of the alloy are increased from 641 MPa, 23.4% to 1012 MPa, 35.9%.

Constitutive Model Parameter Identification Based on Optimization Method and Formability Analysis for Ti6Al4V Alloy.

Titanium alloy is widely applied in aerospace, medical, shipping and other fields due to its high specific strength and low density. The purpose of this study was to analyze the formability of Ti6Al4V alloys at elevated temperatures. An accurate constitutive model is the basic condition for accurately simulating the plastic forming of materials, and it is an important basis for optimizing the parameters of the hot forging forming process. In this study, the optimization algorithm was used to accurately identify the high-temperature constitutive model parameters of Ti6Al4V titanium alloy, and the hot working diagram was established to optimize the hot forming process parameters. The optimal forming conditions of Ti6Al4V titanium alloy are given. Ti6Al4V alloy was subjected to high-temperature compression tests at 800–1000 °C and at strain rates of 0.01–5 s−1 on a Gleeble-1500D thermal/mechanical simulation machine. Each parameter of the Hansel–Spittel constitutive model was taken as an independent variable, and the accumulated error between the stress calculated by the constitutive model and the stress obtained by experimentation was used as an objective function. Based on response surface methodology, an inverse optimization method for identifying the parameters of the high-temperature constitutive model of Ti6Al4V alloy is proposed in this paper. An orthogonal test design was adopted to obtain sample point data, and a third-order response surface approximate model was established. The genetic algorithm (GA) was applied to reversely optimize the parameters of the constitutive model. To verify the accuracy of the optimized constitutive model, the average absolute relative error (AARE) and correlation coefficient (R) were used to evaluate the reliability of optimized constitutive model. The R value of the model was 0.999, and the AARE value was 0.048, respectively, indicating that the established high-temperature constitutive model for Ti6Al4V alloy has good calculation accuracy. The flow stress behavior of the material could be accurately delineated. Meanwhile, in order to study the formability of Ti6Al4V alloy, the hot processing map of the alloy, based on a dynamic material model, was established in this paper. The optimum hot working domains of the Ti6Al4V alloy were determined within 840–920 °C/0.01–0.049 s−1 and 940–980 °C/0.11–1.65 s−1; the hot processing map was verified in combination with the microstructure, and the fine and equiaxed grains and a large amount of β phase could be found at 850 °C/0.01 s−1.

High-temperature compressive creep tests of U3Si2 with spark plasma sintering: Experiments and finite element modeling

This paper reports a systematic high-temperature creep behavior of dense U3Si2 pellets using a spark plasma sintering (SPS) apparatus at elevated temperatures and pressures under vacuum conditions. The stress exponent was subsequently derived to be 3.21 at 1173 K and 2.17 at 1223 K, respectively, indicating a grain boundary sliding creep mechanism. The creep activation energy was determined to be 203.6 ± 19.0 kJ/mol, which agrees well with the literature. Finite element modeling was performed using the creep parameters fitted from the strain-time plot. The results suggest an excellent match with the experimental data, confirming the validity of the experiments. Microstructure characterizations indicate that the main phase of the specimens after creep tests remains to be U3Si2, with a 4 μm thick layer of nano-sized particles induced from the diffusion between U3Si2 and alumina disc used to avoid electric current passing through the sample. The successful conduct of creep experiments demonstrates the great potential of SPS to perform high-temperature mechanical testing of nuclear fuels under vacuum conditions. The subsequent finite element modeling exhibits excellent capabilities for accurately predicting material performance in the creep tests and provides a practical tool in evaluating nuclear fuels’ performance for a much-extended time scale.

Assessment of Metallurgical Slags as Solar Heat Absorber Particles

The use of ceramic solid particle technology in TES-integrated CSP plants offers a high solar-to-electricity ratio and enhanced storage densities, thanks to their high operational temperatures and wide temperature ranges. Metallurgical slags with composition similar to that of the state-of-art bauxite particles can be used as a sustainable and economical secondary raw material to prepare solid particles. In this study, the as-received state and the high-temperature phase and microstructural changes of two fayalite slags from copper and lead production were elucidated by XRD and SEM/EDS methods in a comparative manner. Solid particles were prepared from slags by the oil dropping method, with subsequent heat treatment. Solar-thermal-application-related functional properties of slag particles, such as heat capacity, absorptance, and thermophysical properties, were evaluated by differential scanning calorimetry (DSC), spectrophotometer, heating microscope, and high-temperature compressive tests, respectively. Owing to the formation of more stable Fe-rich phase components and less amount of glassy phase, copper slag is found to be a more promising secondary resource than lead slag in terms of material and functional properties.

Characterization and Calculation of the Dynamic Recrystallization Texture in Fe-3.0 Wt.% Si Alloy.

High-temperature plane-strain compression tests were performed on Fe-3.0 wt.% Si alloy from 900 °C to 1150 °C at strain rates of 5 s−1 to 1 s−1, and the texture development from different initial textures was investigated by means of electron backscattered diffraction. Dynamic recrystallization occurs by strain-induced boundary migration, and the evolutions of the microstructure and different texture components vary with the initial texture. The critical orientation boundary separating the weakened and enhanced texture components moves with the initial texture, and a quantitative relationship is established to represent the dependence of the critical Taylor factor on the instantaneous texture. A model is proposed to describe the dynamic recrystallization texture by incorporating the oriented nucleation probability with a variable critical Taylor factor. The present work could improve the accuracy of hot deformation texture prediction based on strain-induced boundary migration.

Properties of both Chinese silica brick and silica raw material

ABSTRACT The phase and morphology changes of both Chinese silica brick and silica raw material after high-temperature heat treatment, as well as the high-temperature compressive creep behaviour of silica bricks were investigated. The results show that silica raw materials presented a dense structure at room temperature, but cracks and pores appeared after heating treatment. With the crushing of silica particles, silica brick was transformed into homogeneous structure, and final homogeneous degree of the silica brick made of crystalline silica is higher than that of cemented silica. The final creep results of the silica bricks showed expansion after high-temperature compressive creep testing (1550 °C, 50 h), and the expansion of silica brick made of crystalline silica was larger. Compared with the Chinese standard GB/T 5073 - 2005, setting L0 as the original height of the silica brick can more fully reflect the expansion creep characteristics of silica brick.

The Mechanism of Fracture and Damage Evolution of Granite in Thermal Environment.

In the study of rock mechanics, the variation of rock mechanical characteristics in high-temperature environments is always a major issue. The discrete element method and Voronoi modeling method were used to study the mechanical characteristics and crack evolution of granite specimens subjected to the high temperature and uniaxial compression test in order to study the internal crack evolution process of granite under the influence of high temperatures. Meanwhile, dependable findings were acquired when compared to experimental outcomes. A modified failure criterion was devised, and a Fish function was built to examine the evolution behavior of tensile and shear cracks during uniaxial compression, in order to better understand the evolution process of micro-cracks in granite specimens. Shear contacts occurred first, and the number of shear cracks reached its maximum value earliest, according to the findings. The number of tensile contacts then rapidly grew, whereas the number of shear cracks steadily declined. Furthermore, it was found that when temperature rises, the number of early tensile cracks grows. This study develops a fracture prediction system for rock engineering in high-temperature conditions.

Hot Deformation Behavior and Processing Map of GH901 Superalloy

During the forging process GH901 superalloys easily produce cracks and defects, such as coarse crystals in tissues, which affect the performance of the alloy. Using GH901 nickel-based alloy, high-temperature compression tests at deformation temperatures of 990, 1040, 1090 and 1140 °C were carried out in a Thermecmastor-Z thermal simulator, with strain rates 0.001, 0.01, 0.1 and 1 s−1. Next, the isothermal forging process of a GH901 disc was simulated using DEFORM finite element simulation software. The results showed that with the increase in deformation temperatures and the decrease in strain rates, the flow stress clearly decreased. The flow stress constitutive model of GH901 superalloy under ε0.3 and the flow stress constitutive model for strain compensation were obtained. The processing map was built, and a reasonable range of thermal processing was obtained. Meanwhile, the isothermal forging simulation verified the reliability of the thermal processing range of the alloy.

Mechanical behavior at elevated temperatures of an Al–Mn–Mg–Sc–Zr alloy manufactured by selective laser melting

A high temperature compression and compression creep study was undertaken performed on Al–Mn–Mg–Sc–Zr alloy produced by selective laser melting (SLM). High temperature compression tests in the temperature range from 150 to 300 °C were conducted for the as-fabricated (AF) and aged (HT) SLM specimens. The 0.2% proof stress (σ0.2) showed comparable values at different loading directions, which reveal an isotropic mechanical behavior. σ0.2 of the HT samples exceeded that of the AF at temperatures up to 200 °C. At 250 °C, σ0.2 of AF surpasses that of HT, due to the interaction of solid solution strengthening above 0.5 of the homologous temperature and the formation of new precipitates in this temperature range. For AF and HT σ0.2 becomes similar again at 300 °C. Creep tests were conducted at 250 °C in a stress range of 100–150 MPa. The Norton stress exponent was determined to (5.1 ± 0.2) indicating that creep is dislocation climb controlled. An activation energy for creep of (198 ± 11) kJ/mol was found. It is suggested that solid solution strengthening in conjunction with a dispersed L12 Al3Sc precipitates improved the creep resistance compared to conventionally cast-manufactured Al–Sc–Zr alloys.

Hot Deformation Behavior of Ultralight Dual-Phase Mg-6li Alloy: Constitutive Model and Hot Processing Maps

High-temperature compression tests with dual-phase Mg-6Li alloy were conducted on the Gleeble-3500 thermal-mechanical simulator. Flow stress and micro-structure evolution were analyzed for temperatures (T = 423, 473,523 and 573 K) and strain rates (ε˙=0.001, 0.01, 0.1 and 1 s−1). On this basis, the constitutive model and hot processing maps were established. Besides, the dynamic re-crystallization (DRX) of α-Mg phase, grain orientation and texture composition under different deformation conditions were analyzed by EBSD technology. The experimental results show that the flow stress of Mg-6Li alloy increased with decreasing deformation temperature and increasing strain rate. In addition, the range of instability zone expanded with the increase of strain. The optimal thermal processing temperature was found to be in the range of 500 K–573 K, and the optimal strain rates were between 0.01 s−1–1 s−1. Model-predicted stress values were compared with experimental values for model verification. The 0.9954 correlation coefficient and the 5.48% average absolute relative error shown by the calculation indicate an acceptable accuracy of the model in predicting thermal deformation behavior of Mg-6Li alloy. Moreover, based on our EBSD data and maps analysis, the DRX proportion of α-Mg phase in Mg-6Li alloy was relatively low, and α-Mg phase formed <0001>//CD basal texture.

Research on static recrystallization behaviour of pure molybdenum rods during forging

In this work, thermal compression experiment of pure molybdenum rods with sintered density of 9.7–9.8 g cm−3 were performed on the Gleeble-1500D thermal simulator. The double-pass vacuum high-temperature compression test was carried out in a deformation temperature of 1200 °C–1350 °C, a strain rate of 3 s−1 and an interval time of 10–500 s. The stress-strain curve was obtained and analysed. The static softening rate was calculated by the 2% compensation method of yield stress, and the curve of that was fitted. The results show that the softening rate is proportional to the interval time and the deformation temperature. The static recrystallization activation energy and critical temperature of pure molybdenum rod is 583.79 kJ mol−1 and 1365 °C, respectively. Besides, the static recrystallization kinetics model and grain growth model of pure molybdenum rod was established and microstructure evolution of molybdenum was analysed during the deformation process.

The Parameters Identification of High-Temperature Constitutive Model Based on Inverse Optimization Method and 3D Processing Map of Cr8 Alloy Steel.

As a novel kind of cold roller steel, Cr8 alloy steel has the characteristics of high hardness, high wear resistance and good toughness, which can effectively prolong the service life of the roller that is an important part of the steel rolling mill. How to accurately define the constitutive model parameters of metal materials is the major problem, because it seriously affects the accuracy of numerical simulation results of the roller hot forming process. In the study of Cr8 alloy steel’s thermal deformation behavior of the present paper, the high temperature compression test was done on a Gleebel-1500D thermal/force simulation testing machine. A novel method of parameter identification was proposed based on inverse optimization. The Hansel–Spittel constitutive model was established by using the inverse optimization method. To carry out the verification on the accuracy of the established constitutive model, the predicted flow-stress of constitutive model was made a contrast to the experimental flow-stress, and the standard statistical parameters were also applied to further evaluation. The results showed a relatively high prediction accuracy of the Hansel–Spittel constitutive model based on the inverse optimization algorithm. Meanwhile, to obtain optimal parameters of Cr8 alloy steel in the thermal processing, 3D thermal processing maps concerning strain-rate, strain and temperature were built based on the dynamic material model. According to the 3D processing map, the most adequate thermal processing parameters of Cr8 alloy steel were obtianed as follows: strain 0.2–0.4, strain-rate 0.05–0.005 s−1, temperature 1100–1150 °C.

Rheological behaviour of a La-based bulk metallic glass (BMG) used in 3D printing

ABSTRACT To be used as a new kind of three-dimensional printing material, rheological behaviour of a La-based bulk metallic glass (BMG) was studied over a wide range of high temperatures and strain rates by uniaxial compression experiments. The variations in peak stress and steady stress with temperature and strain rate were analysed. Three rheological regions were revealed for the BMG: a non-Newtonian, a Newtonian and an abnormal region which are determined by the temperature and strain rate. The variation on viscosity further indicates that the rheological mode transforms from Newtonian fluid to non-Newtonian fluid with the increase of strain rates at the same temperature. The results from scanning electron microscope test also confirm the microstructural changes that occurred at three different rheological modes. The crystallisation kinetics of La55Al25Ni5Cu10Co5 was studied by thermal analysis and the result show that the crystallisation process of La55Al25Ni5Cu10Co5 glassy alloy is the diffusion-controlled growth. The relationship among steady-state stress, strain rates and temperatures are determined by using hyperbolic function under high-temperature compression test. The curve shows that the logarithmic relationship between the steady-state stress and strain rates satisfies the linear relationship. Besides, the activation energy Q of this amorphous alloy in Newtonian rheological region is 131.31 kJ/mol.

Effect of La-Ce Mixed Rare Earth on High Temperature Deformation Behavior of 685 Armor Steel and Its Mathematical Model

A thermal simulation test machine was used to conduct high-temperature compression tests on two sets of 685 test steels with and without rare earths. Through linear fitting analysis and microstructure observation, the effect of rare earths on the high-temperature deformation behavior of 685 armored steel was studied. The results show that when the deformation temperature is 1000°C, La-Ce mixed rare earth can increase the deformation resistance of steel, and the influence varies with the amount of compression deformation, while at 1100°C, the rare earth has no obvious influence on the deformation resistance of steel. After adding rare earth, the recrystallization activation energy of steel is increased by 6.78%. Mixed rare earth (La-Ce) has an inhibitory effect on the recrystallization of steel. Using Origin8.0 software for regression analysis, a mathematical model of armored steel containing rare earths is established. The model has good curve fitting characteristics, and the calculated values are basically in agreement with the experimental values.