High Temperature Compression Tests Research Articles

Dislocation climb in Mo5SiB2 during high-temperature deformation

During high-temperature compression tests on intermetallic Mo5SiB2, the dislocation microstructures vary with increasing temperature and strain rate. At 1400°C, an increasing tendency exists for slip planes to be of an unexpected type (e.g., {143) and {523)) as a function of the decreasing strain rate and increasing strain that originates from a dislocation climb. As the temperature increases to 1600°C, the internal strain rate of 6.07×10−3s−1 from the dislocation climb at 4% strain exceeds the applied value of 1.67×10−3s−1, and thus, the climb mainly controls the plastic strain, as evidenced by a strength that is lower than that at 1200°C under the same conditions.

Effect of MoSi2 distribution on room and high temperature mechanical properties of aluminum matrix nanocomposites

Abstract

High-temperature deformation resistance and forming behavior of two-step SIMA-processed 6066 alloy

The aims of this study were to investigate the effects of a modified two-step strain-induced melt activation (SIMA) process on the high temperature formability of 6066 Al alloy, and to understand the compressive and tensile properties of the alloy such processed. For these purposes, the forming test which compressed a cylindrical rod into a screw nut was conducted at 550°C, while the compressive and tensile tests were conducted at 550°C and the vicinity. The high-temperature tensile data show that phases on globule boundaries can cause the SIMA-processed alloy to break by integranular fracture, and thus the tensile ductility cannot compete with the alloy in hot-extruded condition to have dynamic recrystallization during tensile deformation. The high-temperature compression test shows that the flow resistance can be decreased by the SIMA process to the level lower than that of the fully annealed alloy. In terms of compressive microstructure, the SIMA-processed alloy is composed of three zones: (1) large deformation zone with flattened structure in specimen center, (2) free deformation zone with globular grain structure near the top and bottom edges, and (3) a transition zone between the above two zones. Finally, the forming test shows that SIMA process can decrease flow resistance by about 25–30%. When a SIMA-processed alloy has sufficient liquid fraction and appropriate globule size, its ability of metal flowing can be significantly increased to have superior high-temperature formability.

Degradation in compressive strength of silica/phenolic composites subjected to thermal and mechanical loading

Reduction to the mechanical properties of fiber-reinforced polymer composites occurs when the material is exposed to radiant heat flux and compressive loading. A thermo-mechanical model was developed to predict the compressive strength and the failure time of silica fiber-reinforced phenolic composites. The coupling heat and mass transfer processes, generation of pyrolysis gases, and their subsequent diffusion process were considered in the model. The thermal softening, thermal decomposition of the matrix material, and phase transition of the reinforced fibers, which reduce the strength of the material, were also taken into account in the formulation of the model. Pyrolysis kinetics of phenolic resin, volume fraction of phase component, temperature profile, compressive strength, and time-to-failure of silica/phenolic composites were predicted using the developed model. The calculated temperature-dependent strength curve was compared with the experimental results measured by a high-temperature compression testing, and the agreement is good. The material fracture morphology was analyzed for silica-phenolic composite specimen after high-temperature compression testing.

Dynamic recrystallization behavior of a biomedical Ti–13Nb–13Zr alloy

The dynamic recrystallization (DRX) behavior of a biomedical titanium Ti–13Nb–13Zr alloy has been investigated using the high temperature compression tests under wide range of strain rates (0.001–1/s) and temperatures 900–1050°C. A constitutive equation represented as a function of temperature, strain rate and true strain is developed and the hot deformation apparent activation energy is calculated about 534kJ/mol. By considering the exponential relationship between work-hardening rate (θ) and stress, a new mathematical model was proposed for predicting flow stress up to the critical strain during hot deformation. The mathematical model for predicting flow stress up to the critical strain exhibits better consistency and accuracy. The DRX kinetic equation of Ti–13Nb–13Zr alloy is described as XDRX=1−exp[−0.32(Ɛ−ƐcƐ*)2.3] . The DRX kinetic model was validated by microstructure observation. It was also found that the process of DRX was promoted by decreasing strain rate and increasing deformation temperature. Eventually, the continuous dynamic recrystallization (CDRX) was identified to be the DRX mechanism using transmission electron microscope (TEM).

Temperature-dependent size effects on the strength of Ta and W micropillars

The strength of metals increases with decreasing sample size, a trend known as the size effect. In particular, focused ion beam-milled body-centered cubic (BCC) micropillars exhibit a size effect known to scale with the ratio of the test temperature to the critical temperature (Tc) of the BCC metal, a measure of how much the yield stress is governed by the lattice resistance. In this paper, this effect is systematically studied by performing high-temperature compression tests on focused ion beam-manufactured Ta and W single crystal pillars ranging in diameter from 500 nm to 5 μm at temperatures up to 400 °C, and discussed in the context of bulk strength and size dependent stresses. Both metals show larger size effects at higher temperatures, reaching values that are in the range of FCC metals at temperatures near Tc. However, it is demonstrated that size effects can be considerably affected by material parameters such as dislocation density and lattice friction, as well as by the yield criterion used. Furthermore, for W, a change from uniform wavy deformation to localized deformation is observed with increasing temperature and pillar size, further indicating that the temperature ratio strongly influences the relative motion of screw and edge dislocations.

Geomechanical rock properties of a basaltic volcano

In volcanic regions, reliable estimates of mechanical properties for specific volcanic events such as cyclic inflation-deflation cycles by magmatic intrusions, thermal stressing, and high temperatures are crucial for building accurate models of volcanic phenomena. This study focuses on the challenge of characterizing volcanic materials for the numerical analyses of such events. To do this, we evaluated the physical (porosity, permeability) and mechanical (strength) properties of basaltic rocks at Pacaya Volcano (Guatemala) through a variety of laboratory experiments, including: room temperature, high temperature (935 °C), and cyclically-loaded uniaxial compressive strength tests on as-collected and thermally-treated rock samples. Knowledge of the material response to such varied stressing conditions is necessary to analyze potential hazards at Pacaya, whose persistent activity has led to 13 evacuations of towns near the volcano since 1987. The rocks show a non-linear relationship between permeability and porosity, which relates to the importance of the crack network connecting the vesicles in these rocks. Here we show that strength not only decreases with porosity and permeability, but also with prolonged stressing (i.e., at lower strain rates) and upon cooling. Complimentary tests in which cyclic episodes of thermal or load stressing showed no systematic weakening of the material on the scale of our experiments. Most importantly, we show the extremely heterogeneous nature of volcanic edifices that arise from differences in porosity and permeability of the local lithologies, the limited lateral extent of lava flows, and the scars of previous collapse events. Input of these process-specific rock behaviors into slope stability and deformation models can change the resultant hazard analysis. We anticipate that an increased parameterization of rock properties will improve mitigation power.

Effect of high temperature compression deformation strain rate on the microstructure and corrosion behavior of 2205 duplex stainless steel

Purpose – The aim of this paper was to investigate the effect of strain rate on microstructure and corrosion behavior of 2205 duplex stainless steel, after high-temperature compression tests. Design/methodology/approach – The specimens were prepared using a Gleeble3800 thermo-simulation machine over a range of temperatures from 850 to 1,250°C and strain rates from 0.005 to 5 s−1, and the corresponding flow curves and deformation microstructure obtained were further analyzed. To evaluate the effect of strain rate on corrosion behavior, potentiodynamic polarization tests and double-loop electrochemical potentiodynamic reactivation (DL-EPR) were used to characterize the electrochemical performance. Findings – Compared with strain rate of 0.5 s−1, the worst corrosion resistance behavior from the potentiodynamic polarization test results after deformation at 0.005 s−1 was attributed to more austenite (γ) and ferrite (δ) grain boundaries or δ/γ phase interface formation due to the better effect of γ dynamic recrystallization (DRX) or δ dynamic recovery (DRV). Increasing strain rate to 5 s−1 lowered the corrosion resistance, due to the increase in dislocation density. At the low strain rate of 0.005 s−1, the susceptibility to intergranular corrosion (IGC) was comparatively high after deformation at 1050 and 1150°C with more γ/γ grains and δ/γ phase boundary formation, which was lowered with the strain rate increase to 0.5 s−1, due to suppressing effect of γ DRX. Originality/value – The paper provides the scientific basis for the practical application of hot working of 2205 duplex stainless steel.

Effect of Deformation Conditions on Dynamic Recrystallization of As-Cast GH625 Alloy

High temperature compression tests at a deformation temperature range of 1273K~1473K with various strain rates of 0.01s-1~0.1s-1 on as-cast GH625 alloy were carried out, aiming at the current research status that the deformation process of cogging and the recrystallization behavior of ingot are still in the study. The results indicated that the recrystallization nuclei of ingot formed not only along the original grain boundaries, but also in the interdendrite. Dynamic recrystallization volume percent increased with the increase of temperature and the decrease of strain rate. When the temperature was high and strain rate was low, the dynamic recrystallization behavior of as-cast GH625 alloy was dominated by discontinuous recrystallization. However, when the temperature was low and strain rate was high, continuous recrystallization also existed. These results can provide some reliable experimental support for the cogging process design.

Comparison of thermomechanical stresses produced in work rolls during hot and cold rolling of Cartridge Brass 1101

Thermomechanical stresses play an important role in defining the life of the work roll used in hot rolling process. In this research temperature dependent mechanical properties of cartridge brass are determined experimentally using high temperature compression tests at different temperatures and strain rates. Real life measurements are made from a brass rolling mill as input data for the simulation boundary conditions. Hot rolls are made of AISI H11 hot work tool steel. Temperature dependent mechanical properties of AISI H11 steel are used. Thermal and mechanical stresses produced in the work rolls during hot rolling process are predicted using a thermoplastic finite element approach in the ABAQUS Standard software. Hot rolling is compared with cold rolling to determine the effects produced on the work rolls. A criterion is introduced to compare the severity of stresses produced on the rolling surfaces in case of hot rolling and cold rolling based on the yield stress of the roller material for different temperatures. A method for separating thermal and mechanical stresses in the simulation is also described.

Effects of cryomilling on the microstructures and high temperature mechanical properties of oxide dispersion strengthened steel

The effects of cryomilling on the microstructures and high temperature mechanical properties of oxide dispersion-strengthened (ODS) steel were examined. Cryomilling was newly tried on this ODS steel to control oxides, grains, and dislocation microstructures. Fe–14Cr–3W–0.4Ti (wt.%) alloy powder and 0.3wt.%Y2O3 powder were mixed and were mechanically alloyed (MA) through ball milling at each of room temperature (RT) and −150°C and then hot isostatic pressing (HIP), hot rolling, and annealing processes were implemented to manufacture two types of ODS ferritic steel, K1 (RT) and K4 (−150°C). Oxide particles were shown to be finer and more uniformly distributed in K4 (5–10nm size distribution) than in K1 (average size 30nm). The two alloys were subjected to high temperature compression (RT∼900°C) tests. K4 represented higher yield strength under all temperature conditions. However, K4 showed rapid strength decreases at high temperatures exceeding 700°C and showed similar levels of strengths to K1 at 900°C. This is considered attributable to the fact that although cryomilling increased the number density of oxide particles, it simultaneously reduced grain sizes too much, so that grain boundary weakening at high temperatures could not be sufficiently prevented.

Study on Backpressure Forming Process of Scroll

As for the high thickness ratio and small wall thickness and uneven structure characteristics of automotive air condition scroll, the scroll forming process is studied using back pressure forming process by the DEFORM software. The forming principle for backpressure deformation, the metal flowing rules and the force situation are analyzed, the material of scroll is 4032 aluminum alloy whose true stress-strain curve is obtained by high temperature compression test. Set 10 measuring points in the vortex, the effect laws of backpressure and backpressure distance on scroll forming quality are compared by simulation. Four factors and four levels orthogonal experiment is numerically simulated while billet temperature, mold temperature, backpressure and backpressure distance are independent variables, the data of the maximum forming load, height difference and flatness are acquired by the orthogonal experiment. The grey system theory was used in the parameters optimization of backpressure forming of scroll, the experiment is done on the self-designed molding machine, the results which meet the requirement of the scroll size and verify the feasibility of the forming process and the grey system theory.

High Temperature Behavior of the EN AW-2618A Piston Alloy Containing 0.12wt% Zr: Influence of Heat Treatment

This study compares the conventional T6 (“solution-quenching-aging”) treatment with an innovative one, in terms of high temperature response of the EN AW-2618A alloy, containing 0.12wt% Zr. The new treatment is aimed to stimulate Zr-based precipitates with optimal size, shape and distribution, in order to completely take advantage of Zr anti-recrystallization effect. To assess alloy's thermal stability, samples subjected to both heat treatments were soaked at 250°C, up to 50h. Hardness measurements, microstructural characterization and high temperature compression tests have been carried out, giving evidence of significant improvements connected to controlled formation of Zr-based precipitates.

鋳造法によって作製された ZrC 添加 Mo-Si-B 合金のミクロ組織と機械的性質

ZrC-added Mo-Si-B alloys were prepared by arc-melting. After heat-treatment at 1800℃ for 24 h, their density and elastic moduli were measured, and their microstructure was evaluated. Moreover, high-temperature compression tests at 1400℃ and four-point bending tests with a Chevron notch at room temperature were conducted to investigate their mechanical properties. The primary phase was Mo solid solution (Moss) or ZrC depending on Mo/ZrC compositional ratio. After the primary phase crystallization, Mo2B, Mo5SiB2 (T2), Moss+ZrC eutectic, Moss+T2 eutectic and/or Moss+Mo3Si+T2 eutectic were crystallized out during solidification. Mo2B and/or Mo3Si dissolved during the heat treatment in some alloys. The ZrC-added Mo-Si-B alloys had higher high-temperature strength compared with the ternary Mo-Si-B alloys even though ZrC-added Mo-Si-B alloys contained less volume fraction of the T2. Besides, the ZrC-added Mo-Si-B alloys exhibited better fracture toughness than that of ternary Mo-Si-B alloys, reaching 20.2 MPa(m)1/2. Therefore, this study found that ZrC plays a significant role in improving high-temperature strength and fracture toughness in Mo-Si-B alloys.

Constitutive Modeling During Simultaneous Forming and Quenching of a Boron Bearing Steel at High Temperatures

Simulation of hot stamping process needs reliable material data, especially at high temperatures where plastic deformation takes place in austenitic microstructure. In the current study, high-temperature non-isothermal compression tests (NICT) at different ranges of temperature, strain and strain rate as well as constitutive modeling of the flow curves were carried out. The Johnson-Cook and the Nemat-Nasser phenomenological models for isothermal deformation conditions were revised and applied to fit the flow curves during high-temperature NICT. It was shown that the models can satisfactorily predict the material flow stress at the mentioned conditions. Furthermore, the models were employed in order to describe the work-hardening behavior of the material. The results indicated that the fitted work-hardening rate can successfully follow the experimental data during deformation till no strain-induced phase transformation is initiated.

A comparative study of microstructure and high temperature mechanical properties of a β-stabilized TiAl alloy modified by lanthanum and erbium

Abstract The effect of rare earth (RE) elements addition on the microstructure and high temperature mechanical properties of a β-stabilized TiAl alloy was investigated by scanning electron microscopy (SEM) and high temperature compression tests. SEM and EDS results showed that RE-added alloys contained dispersed particles. Most particles were rich in RE-elements and oxygen, thereby suggesting that solute oxygen atoms in the matrix of alloys were scavenged by RE-elements. However, less than 10% of particles contained oxide phase in proximity to aluminide phase. With increasing RE-content, mean size of particles was increased; however, the number of particles reached to the maximum values at 0.2% RE, corresponding to minimum interparticle spacing. Afterwards, as a result of increasing growth rate, the number of particles was declined to the lower values. Fine and closely spaced particles in the microstructure of TNM+0.2La and TNM+0.2Er alloys led to retarding dynamic recrystallization and higher peak flow stresses at 900 and 1000 °C. Also, the results showed that Er-containing alloys possessed a higher flow stress, particularly at 1000 °C, since the particle size of Er-containing alloys was less than that of La-containing alloys.

Deformation behavior of Mo5SiB2 at elevated temperatures

Abstract During high-temperature compression tests on Mo 5 SiB 2 , the deformed microstructure varies with the temperature, strain rate and strain, and their changes have profound effects on the deformation behavior. At 1200 °C, the plastic deformation is provided by dislocation glide on potential slip planes, such as {1 1 0} and {0 0 1}. Due to the limitation of less activated slip systems, the specimens rupture when compressed to the strain of ~3% at 1200 °C and 1.67×10 −4 s −1 . With temperature increasing to 1400 °C, the activation of more independent slip systems increases the deformation capability of the alloy. However, there is an increasing tendency for slip planes to be of an unexpected type (e.g. {1 4 3} and {5 2 3}) as a function of decreasing strain rate and increasing temperature, which is related to dislocation climb. Moreover, dynamic recovery or recrystallization is easy to occur under the conditions of heavy deformation (like 25% strain) and slow strain rate (like 1.67×10 −4 s −1 ), showing the decrease in the dislocation density and flow stress.

Dynamic Recrystallization Behavior of GCr15SiMn Bearing Steel during Hot Deformation

The hot deformation behavior of GCr15SiMn steel was studied through high temperature compression tests on the Gleeble-1500 thermal-mechanical simulator. The initiation and evolution of dynamic recrystallization (DRX) were investigated with microstructural analysis and then the process variables were derived from flow curves. In the present deformation conditions, the curves of strain hardening exponent (n) and the true strain (ɛ) at the deformation temperature of 1423 K and strain rates of 0.1, 1 and 10 s−1 exhibit single peak and single valley. According to Zener-Hollomon and Ludwik equation, the experimental data have been regressed by using linear method. An expression of Z parameter and hot deformation equation of the tested steel were established. Moreover, the Q values of GCr15SiMn and GCr15 steels were compared. In order to determine the recrystallization fraction under different conditions, the volume fraction of DRX as a function of process variables, such as strain rate (ɛ), temperature (T), and strain (ɛ), was established. It was found that the calculated results agreed with the microstructure of the steel at any deformation conditions.

Evolution of the Laves Phase in Ferritic Heat-Resistant Steels During Long-term Annealing and its Influence on the High-Temperature Strength

Heat-resistant ferritic steels containing Laves phase precipitates were designed supported by thermodynamic modeling. High-temperature compression tests at 1173.15 K (900 °C) and a detailed characterization of the microstructural evolution during annealing at 1173.15 K (900 °C) were carried out to investigate the effect of Laves phase formation on the high-temperature strength. Due to the addition of W/Mo and/or Nb, the high-temperature strength of the newly designed alloys is significantly higher than that of the reference steels. However, the high-temperature strength of all investigated steels decreases slightly as the annealing time is increased up to 1440 hours. To determine the influence of Laves phase formation and coarsening on the high-temperature strength during long-term annealing, the precipitates were extracted from the ferritic matrix in different annealing states. The phases in the powder residue were determined by XRD, and the chemical composition of the Laves phase in dependence of the annealing time was analyzed by EDS measurements. During annealing, steel Fe18CrMoW forms Nb(C,N), Ti(C,N), Laves phase (Fe2Nb) and Fe3Nb3C, whereas alloy Fe19CrWAl forms Nb(C,N), Ti(C,N), and Laves phase (Fe2Nb). The Laves phase within the alloys Fe18CrMoW and Fe19CrWAl differs in its morphology as well as its chemical composition. The Laves phase in steel Fe18CrMoW attains its chemical equilibrium after 192 hours, whereas alloy Fe19CrWAl required 24 hours. Overall, the formation of the Laves phase prevents significant grain growth during high-temperature annealing, thus preserving the high-temperature strength over a long time period.

HOT DEFORMATION BEHAVIOR OF BLADES STEEL 10Cr12Ni3Mo2VN FOR ULTRA- SUPERCRITICAL UNITS

10Cr12Ni3Mo2VN steel is mainly made by forging and usually used to make last stage blades of ultra-supercritical unit,demanding strict standards of microstructure property because of its hard service environment,so it is necessary to conduct deep research on its hot deformation behavior.The hot deformation behavior of10Cr12Ni3Mo2 VN steel was investigated through high temperature compression tests on the Gleeble-1500 thermal-mechanical simulator at 850~1200 ℃ and strain rate range of 0.01~10 s-1.The results show that dynamic recrystallization becomes more prone to happen and recrystallized grain size increases with increasing temperature and decreasing strain rate.Isometric crystal and mixed structure appear after compressed 60% at 1200 ℃ with high and low strain rate respectively.A new method of establishing the hot deformation hyperbolic sine constitutive equation by Levenberg-Marquardt algorithm is proposed.Parameters of the constitutive equations established by traditional linear fitting and Levenberg-Marquardt algorithm have a similar value,and both of the constitutive equations have a high prediction precision,so the method of establishing constitutive equation by Levenberg-Marquardt algorithm is credible.However,Levenberg-Marquardt algorithm can get all parameters at the same time with fewer and simpler steps compared to traditional linear fitting.In addition,the values of critical strain for dynamic recrystallization initiation are determined from the work hardening rate-strain curves and a model related to Zener-Hollomon parameter for predicting critical and peak strain under different deformation paraments is established.