Increasing Deformation Temperature Research Articles

Microstructure and Thermal Deformation Behavior of Hot-Pressing Sintered Zr-6Al-0.1B Alloy.

Zr-6Al-0.1B alloy rich in Zr3Al phase is prepared by hot-pressing sintering. The thermal deformation behavior of sintered Zr-6Al-0.1B is analyzed by isothermal compression tests at deformation temperatures of 950, 1050, and 1150 °C with strain rates of 0.01, 0.1, and 1 s−1. The results indicate that at the early stage of thermal deformation, the stress increases rapidly with the increase of strain and then reaches the peak value. Subsequently, the stress decreases with the increase of strain under the softening effect. On the whole, the true stress-strain curve shifts to the high stress area with the increase of strain rate or the decrease of deformation temperature, so the sintered Zr-6Al-0.1B alloy belongs to the temperature and strain rate sensitive material. For the microstructure evolution of sintered Zr-6Al-0.1B during the isothermal compression, the high strain rate can improve the grain refinement. However, because sintered Zr-6Al-0.1B is a low plastic material, too high strain rate will exceed the deformation capacity of the material, resulting in an increase in defects. The increase of deformation temperature also contributes to grain refinement, but when the temperature is too high, due to the decomposition of Zr3Al phase, the deformation coordination of the material decreases, leading to the increase of the probability of the occurrence of defects. This study verified the feasibility of hot-pressing sintering to prepare Zr-6Al-0.1B alloy rich in Zr3Al phase and laid the foundation of “hot-pressing sintering + canning hot-extrusion” process of Zr-6Al-0.1B alloy components.

Hot Deformation Behavior, Processing Maps and Microstructural Evolution of the Mg-2.5Nd-0.5Zn-0.5Zr Alloy.

Isothermal hot compression experiments were conducted on Mg-2.5Nd-0.5Zn-0.5Zr alloy to investigate hot deformation behavior at the temperature range of 573–773 K and the strain rate range of 0.001 s−1–10 s−1 using a Gleeble-3500D thermomechanical simulator. The results showed that the rheological curve showed a typical work hardening stage, and there were three different stages: work hardening, transition and steady state. A strain compensation constitutive model was established to predict the flow stress of the Mg-2.5Nd-0.5Zn-0.5Zr alloy, and the results proved that it had high predictability. The main deformation mechanism of the Mg-2.5Nd-0.5Zn-0.5Zr alloy was dislocation climbing. The processing maps were established to distinguish the unstable region from the working region. The maps showed that the instability generally occurred at high strain rates and low temperatures, and the common forms of instability were cracking and flow localization. The optimum machining range of the alloy was determined to be 592–773 K and 0.001–0.217 s−1. With the increase in deformation temperature, the grain size of the alloy grew slowly at the 573–673 K temperature range and rapidly at the 673–773 K temperature range.

The influence of process parameters on the preparation of closed-cell aluminum foam by friction stir processing

In order to obtain high-quality aluminum foam components, a new preparation method for a 7075 closed-cell aluminum foam based on friction stir processing (FSP) was proposed. The influence of process parameters on microstructures of closed-cell Al foam precursor was investigated by optical metallographic microscope and scanning electronic microscope (OM/SEM). The temperature field and flow field of the Al foam precursor during FSP were simulated by Fluent CFD software. The formability of the Al foam precursor was analyzed by the cupping test. It is found that the rotating speed has great influence on the uniformity and density of the precursor prepared by FSP, but the welding speed has little influence. Numerical simulation shows that the maximum flow velocity of material in the tool shoulder increases by 1.5 times when the rotating speed increases from 800 to 2000 r/min, and the peak temperature at the stirring pin reaches 491 °C, which is consistent with the experimental results. The powder ring is continuous and uniform due to sufficient plastic deformation and flow at travel speed of 50 mm/min and the rotating speed of 2000 r/min. The formability of the precursor increases with the increase of deformation temperature. Especially the cupping test value of precursor is close to that of base metal at 450 °C. In the foaming process, the foam pores first appear at the bottom and then expand upwards with the extension of the foaming time. The expansion rate of the whole foam increases rapidly, and the pores with highly spherical are homogeneously distributed when the foaming time is 110 s at 680 °C.

Dynamic recrystallisation and constitutive equation in hot deformed AISI H10 tool steel

ABSTRACT The compression deformation behavior of AISI H10 (DIN 32CrMoV12-28) hot work tool steel was investigated at temperatures ranging from 900°C to 1200°C and strain rates from 0.01 to 1 s−1. True stress-strain curves showed that a decrease in strain rate or increase in deformation temperature can promote the occurrence of DRX. It was found that the characteristic strains and stresses decrease with an increase in temperature or decrease in strain rate. The σc/σp ratio takes an average of 0.94; and the ϵc/ϵp ratio lies in range of 0.48-0.65 (average of 0.53). This suggests that DRV in H10 is not extensive and DRX starts at strains about half of the peak strain. However, the extensive softening by DRX keeps σp close to σc. Using the hyperbolic-sine constitutive equation, the deformation activation energy was calculated to be about 435.76 kJ mol−1.

Optimisation of superplastic processing parameters for a TiZrHfBeCuNi high entropy bulk metallic glass in the supercooled liquid region

In this study, the deformation behavior of Ti20Zr20Hf20Be20(Cu10Ni10) high entropy bulk metallic glass (HE-BMG) in the supercooled liquid region was investigated via uniaxial compression tests. The thermal workability was also investigated to determine the optimal range of processing parameters. The results revealed that the deformation behavior in the supercooled liquid region exhibited two modes: flow deformation and brittle fracture, both of which were significantly affected by temperature and strain rate. The homogeneous flow deformation behavior changed from Newtonian to non-Newtonian with a decrease in temperature and an increase in strain rate. The activation volume of the HE-BMG ranged from 0.146 to 0.304 nm3 based on the transition theory of the free volume model, indicating that the atomic group can migrate (about 12–25 atoms) during high-temperature deformation. The fracture surface analysis of the HE-BMG revealed that the fracture angle increases with increasing deformation temperature, which was primarily due to an increase in cohesive strength. The optimal processing parameters for forming HE-BMG without crystallization were determined by constructing a deformation map based on the deformation behavior and microstructural analysis results.

Effect of Rolling Temperature on the Structural Refinement and Mechanical Properties of Dual-Phase Heterostructured Low-Carbon Steel

Warm rolling at temperatures ranging from 25 °C to 500 °C was conducted on the dual-phase heterostructured low-carbon steel to investigate the effect of deformation temperature on the structural refinement and mechanical properties. Defying our intuition, the grain size and strength of the rolled steels do not deteriorate with the increase in deformation temperature. Warm rolling at 300 °C produces a much finer lamellar structure and higher strength than steels rolled at both room temperature and elevated temperature. It is supposed that the enhanced interactions between carbon atoms and defects (interfaces and dislocations) at 300 °C promote dislocation accumulation and stabilize the nanostructure, thus helping with producing an extremely finer structure and higher strength than other temperatures.

Hot deformation behavior of 60NiTi shape-memory alloy fabricated by hot isostatic pressing

The 60NiTi (Ni60wt%–Ti40wt%) intermetallic is a hard-to-process material. Understanding of hot deformation behavior is crucial for the hot working of 60NiTi. This work studied hot deformation behavior and corresponding microstructure of the hot isostatic pressed 60NiTi in the temperature range of 900 °C–1050 °C and at strain rates of 0.1, 0.01 and 0.001 s−1 through a hot compression test. The flow stress and microstructure were susceptible to the hot deformation parameters. The flow stress decreased with the increase in deformation temperature and decrease in strain rate. Work hardening occurred at a small strain, then followed by softening; finally, near-dynamic equilibrium was achieved between work hardening and softening. A constitutive equation was developed to describe the effects of strain rate and temperature on flow stress. Simulation of hot deformation via the finite element method revealed the workpiece’s inhomogeneous deformation. The deformation occurred mainly in the center area of the cylindrical sample, resulting in high stress and strain concentrations in this region and causing the equiaxial grains to be compressed into prolate grains. This work can provide guidance for the hot working, such as forging and hot rolling, of 60NiTi.

Hot deformation behavior of micro-alloyed steel using processing maps developed with different constitutive equations

The hot workability of microalloyed steel was studied in the deformation temperature range of 850?1200?C and strain rate of 0.001-100s-1. The constitutive relation of flow stress with temperature, strain rate and strain was established to construct processing maps of the microalloyed steel. The processing maps were constructed using conventional power law, integral method, and Arrhenius equations. The developed processing maps were used to predict the optimal hot deformation conditions and were validated with metallurgical examinations. The safe regime for hot working of the experimental steel was found to be in the intermediate temperature-strain rate range (1000-1150?C;0.001-10 s-1), where the deformation process was dominated by dynamic recrystallization and dynamic recovery of the austenitic phase. The processing map constructed using Arrhenius equations increased continuously with an increase in deformation temperature and decrease in strain rate and it did not reveal relevant information of hot workability with respect to deformation temperature and strain rate. The dynamic recrystallization behavior of experimental steel was affected by both deformation temperature and strain rate which was explained in detail through microstructural examination.

The Effect of Nb Content on Microstructure Evolution of GH4169 superalloy During Hot Deformation

This research conducted a thermal compression deformation test on two GH4169 alloy samples with 5.40wt% and 5.21wt% Nb contents respectively, under deformation temperatures ranging from 900°C to 1030°C and the strain rates of 0.04s-1, 0.08s-1. Data from the deformation test were used to study the effects of deformation temperature and strain rate on the microstructure, δ phase morphology, and δ phase evolution of both alloy samples, so as to reveal the structural evolution mechanism. The results show that the long needle-like δ phase in the alloy microstructure with high Nb content undergoes deformation fracture and decomposition fracture during deformation and compression under high temperature, with the fracture decomposition temperature being 990°C. Moreover, microstructures of alloys with low Nb content were dominated by granular δ phases; as the deformation temperature increases or the strain rate decreases, the content of the δ phase gradually decreases, causing the alloy’s dynamic recrystallization grain size and dynamic recrystallization volume fraction to gradually increase from deformation twins at low temperatures to complete recrystallization at high temperatures.

Hot-deformation characteristics of Al-alloyed δ-ferritic and martensitic dual-phase steel

The hot working behavior of Al-alloyed δ-ferritic/martensitic dual-phase steel was investigated using a Gleeble-3800 thermomechanical simulator and compression tests at deformation temperatures and strain rates ranging from 800 to 1100 °C and 0.1 to 3 s−1, respectively. The shape of the flow stress curve of the experimental steel resembled that of traditional dynamic recovery (DRV) flow stress curves produced by work hardening, ferritic DRV, ferritic dynamic recrystallization (DRX), and austenitic dynamic phase transformation (DPT). Additionally, constitutive equations were established to predict the steady-state stress. The apparent deformation activation energy of the steel was approximately 264.7 kJ/mol. Moreover, the microstructure following deformation was investigated using electron backscatter diffraction. The primary dynamic restoration mechanisms of δ-ferrite comprised DRV and DRX at temperatures below and above 900 °C, respectively. However, with increasing deformation temperature and strain rate, the primary dynamic restoration mechanism of δ-ferrite shifted from continuous DRX (CDRX) to discontinuous DRX (DDRX). Additionally, the processing maps of the steel were established using the dynamic materials model. Further, based on the microstructure results, it was found that the power dissipation efficiency of ferritic CDRX, ferritic DDRX, ferritic DRV, and austenitic DPT gradually decreased. Additionally, only one domain of flow instability was identified, and it was located at 1025–1075 °C/0.6–3 s−1. Thus, to avoid unstable deformation regions, a two-stage design of the optimal process parameters for industrial processing is highly essential.

Post-dynamic recrystallization behavior of a powder metallurgy Ni-Co-Cr based superalloy under different deformation conditions

The post-dynamic recrystallization (PDRX) behavior of a powder metallurgy (PM) Ni-Co-Cr based superalloy was researched by thermal compression tests at the temperature range of 1020–1080 °C within the strain rates of 0.01–1 s−1, followed by heat preservation for 0–45 s after deformed to 10%−50%. Electron backscatter diffraction (EBSD) and Transmission Electron Microscope (TEM) techniques were employed to investigate the effect of the deformation conditions on PDRX behavior. The results show that the deformation conditions (strain rate, temperature, degree of deformation and holding time) have great impact on the PDRX kinetics. Increasing deformation temperature, strain or holding time can result in the effective release of residual deformation stored energy, promoting the PDRX course. The irregular energy storage release of the superalloy deformed at different strain rates is mainly concerned with the various microstructure evolution during heat preservation. The evolution of twin boundary (Σ3) during PDRX exhibits the similar regularity with that of recrystallization fraction. The formation of Σ3 boundary induces the recrystallized nucleation, leading to further release of deformation storage energy. Meta-dynamic recrystallization (MDRX) and static recrystallization (SRX) are the dominant mechanisms of PDRX, and the nucleation induced by undissolved γ′ precipitates or assisted by twins also play certain roles in microstructure evolution during heat preservation of the deformed superalloy.

Microstructure and flow behaviour of a quenching and partitioning steel at elevated temperatures

ABSTRACT Hot compression tests were carried out on a quench and partitioning steel in the temperature range of 850-1050 °C and strain rates of 10-3- 1 s-1. The single-peak flow curves were appeared at high strain rates and low temperatures and the multi-peaks at the opposite condition. It was found that the mechanism of dynamic recrystallization (DRX) changes by passing from 950 °C due to dynamic precipitation of carbide particles. The microstructural characterizations using optical microscopy and electron back scattered diffraction (EBSD) techniques revealed various mechanisms of DRX in different deformation conditions. EBSD results showed opposite variations of high and low angle grain boundaries with increasing deformation temperature and decreasing strain rate. By using the hyperbolic sine constitutive equation, the value of apparent activation energy at the typical strain of 0.5 was determined as 297.67 kJ/mol.

A study of hot compression behavior of an as-cast FeCrCuNi2Mn2 high-entropy alloy

In this study, hot deformation behavior of an as-cast FeCrCuNi2Mn2 high-entropy alloy (HEA) was evaluated. For this purpose, hot compression tests were carried out in the temperature range of 600–1000 oC and initial strain rate range of 0.001–0.1 s-1. Flow stresses under different deformation conditions were then friction-corrected. Work hardening rate analysis was used to evaluate the occurrence of dynamic recrystallization. Microstructures of the hot compressed specimens were characterized using optical microscopy. Strain-dependent constitutive equations were developed using the data obtained from the Sellars–Tegart–Garofalo equation. The critical and peak strain and the critical and peak stress, as dynamic recrystallization parameters, were extracted from the work hardening rate versus stress curves. The results indicated that the modeled flow stresses were generally lower than the measured ones, which could be attributed to the impact of friction on the flow stress. Microstructural observations after hot compression tests as well as evaluation of work hardening rate versus stress curves showed typical dynamic recrystallization characteristics under different deformation conditions. In addition, with increase in deformation temperature and decrease in strain rate, more DRX grains were formed along grain boundaries and shear bands, resulting in a decrease in the flow stress. The size of the DRX grains was strongly affected by deformation temperature and increased with increase in temperature. The normalized critical stress and strain for the initiation of DRX were calculated as εc/εp = 0.60 and σc/σp = 0.86, respectively. The activation energy of hot deformation was determined to be 708 kJ/mol. It was noticed that the developed constitutive equations could accurately predict the flow stress behavior of the studied alloy over a wide range of experimental conditions.

Flow Stress Behavior and Microstructure Evolution of Austenitic Stainless Steel with Low Copper Content during Hot Compression Deformation

In order to study the microstructure evolution and flow stress behavior of as cast antibacterial austenitic stainless steel containing 1.52 wt.% copper, Gleeble 3800 was used for thermal compression simulation test. Through OM and EBSD analysis, it is found that the dynamic recrystallization mechanism of thermal deformation is mainly discontinuous dynamic recrystallization. With the increase of deformation temperature and deformation rate, the proportion of recrystallization nucleation gradually increases. The growth of twins relies on recrystallization and, at the same time, promotes dynamic recrystallization. Considering the influence of strain on flow stress, the strain compensation Arrhenius model is established according to the obtained stress-strain curve, and high accuracy is obtained. The correlation coefficient and average relative absolute error are 0.979 and 7.066% respectively. These results provide basic guidance for the technology of microstructure control and excellent mechanical properties of antibacterial stainless steel.

Formability Difference between TC4 Titanium Alloy Hollow Shaft and AISI 1045 Steel Hollow Shaft Formed by Cross Wedge Rolling with a Mandrel

Production of TC4 alloy hollow shaft formed by cross wedge rolling (CWR) can meet the needs of the lightweight structures in aviation field. Different from the steel, the formability of TC4 alloy is sensitive to deformation temperature. In this work, the formability difference of TC4 alloy hollow shaft and AISI 1045 steel hollow shaft formed by CWR with a mandrel was studied numerically and experimentally. The results show that the influence of temperature on TC4 alloy flow stress is larger than that of 1045 steel, and the peak stress of TC4 alloy at 900 °C is close to that of 1045 steel at 1050 °C. For the hollow shafts of two materials, the ellipticity increases with increasing the inner hole diameter. For the same size of thin-walled billets, the forming quality of TC4 alloy at 900 °C is better than that of 1045 steel at 1050 °C. The CWR temperature range of TC4 alloy is narrower than 1045 steel. The increase of the initial deformation temperature can significantly increase the ellipticity of TC4 alloy and the appropriate forming temperature range of CWR TC4 alloy hollow shaft should be lower than 950 °C. Moreover, the rolling force and torque of TC4 alloy hollow shaft are smaller than that of 1045 steel when CWR hollow billet with the same dimensions.

The dynamic compressive behavior and constitutive models of a near α TA23 titanium alloy

The dynamic impact tests were carried out for a near α TA23 titanium alloy in deformation temperature range 293 K–773 K and strain rate range 0.001 s−1-4000 s−1. The test results show that as deformation temperature increases, the flow stress decreases significantly, and the temperature and strain rate have an interactive effect in the dynamic impact compression process. The original Johnson-Cook (J-C) model and its modified model were established. The model verification results show that the relative error of the modified model is 3.28%, while the relative error of the original model is 5.32%, which indicates that the modified model has higher accuracy and applicability in predicting the dynamic impact deformation behavior of TA23 alloy.

Optimization of volume fraction and microstructure evolution during thermal deformation of nano-SiCp/Al–7Si composites

Abstract This paper takes nano-SiCp/Al–7Si matrix composites prepared by powder metallurgy as the research object. With the help of advanced microstructure characterization techniques and performance analysis methods, the effect of nano-SiCp volume fraction on the microstructure and properties of composites is systematically studied. Based on optimizing the volume fraction of nano-SiCp, the thermal deformation behavior of the composites is investigated. It was found that with an increase of nano-SiCp content, the distribution uniformity of nano-SiCp decreases gradually. And because the surface of nano-SiCp is easy to adsorb gas and the aggregated distribution of nano-SiCp is not conducive to the sintering process, the density of the composites shows a gradually decreasing trend. The hardness of the composites tends increasing gradually, and the increase in amplitude gradually decreases. Due to the addition of nano-SiCp, there are many interfaces between SiCp and Al matrix, and cracks are prone to initiation and expansion at the interface. Therefore, as the volume fraction of nano-SiCp increases, the elongation of nano-SiCp/Al–7Si composites gradually decreases. When the volume fraction of nano-SiCp is 2%, the strength of the composites reaches the maximum value of 217 MPa. Compared with the Al–Si alloy without adding nano-SiCp, the results increased by 37.3%. In addition, with the decrease of strain rate and the increase of deformation temperature, the dislocation density in the composites gradually decreases, and the dynamic softening progresses more fully. The dynamic recrystallization nucleation mechanism mainly includes the subcrystal merging mechanism and the grain boundary bowing mechanism.

Hot Tensile Deformation Behavior of Mg-4Li-1Al-0.5Y Alloy

The microstructure evolution and deformation mechanism of the as-extruded-annealed Mg-4Li-1Al-0.5Y alloy (denoted as LAY410) were investigated during the hot tensile deformation at the temperatures between 150°C and 300°C with strains from 8 × 10−5 s−1 to 1.6 × 10−3 s−1. The results show that when the strain rate decreases and/or the deformation temperature increases, the peak stress of the alloy gradually decreases, and the elongations to fracture gradually increases. The true stress–strain curves show typical dynamic recrystallization (DRX) softening characteristics. It is observed that the microstructure in the magnesium (Mg) alloy deformed at 150°C is mainly composed of the deformed grains and a few recrystallized grains. The microstructures in the Mg alloy deformed at 200°C consisted of substructures and a slightly increasing number of dynamic recrystallized grains. When the deformation temperature reaches 250°C, the number of recrystallized grains increases significantly, and the microstructures are dominated by recrystallized grains. Moreover, through theoretical calculation and result analysis, the activation energy was about 99.3 kJ/mol, and the hot tensile deformation mechanism was the alternate coordinated deformation mechanism among grain boundary slip (GBS), intragranular slip, and DRX.

Thermal Processing Map and Microstructure Evolution of Inconel 625 Alloy Sheet Based on Plane Strain Compression Deformation.

Plane strain compression tests were used to study the deformation behavior of an Inconel 625 alloy sheet at various temperatures and strain rates. The peak stress was selected to establish the constitutive equation, and the processing maps under different strains were drawn. The results show that the effective stress–strain curve of Inconel 625 has typical dynamic recrystallization (DRX) characteristics. With the increasing deformation temperature and the decreasing strain rate, the softening effect is significantly enhanced. The parameters of the constitutive equation are calculated, and the average error of the constitutive equation is 5.68%. Through the analysis of the processing map, a deformation temperature of 950–960 °C with a strain rate of 0.007–0.05 s−1 were determined as the unstable region, and obvious local plastic-rheological zones were found in the unstable region. The optimum deformation condition was found to be 1020–1060 °C/0.005–0.03 s−1. Through electron backscattered diffraction (EBSD) characterization, it was found that both the increase of temperature and the decrease of strain rate significantly promote the recrystallization process. At a low strain rate, the main recrystallization mechanism is discontinuous dynamic recrystallization (DDRX). It is expected that the above results can provide references for the optimization of the rolling process and microstructure control of an Inconel 625 alloy sheet.

The temperature effect on the plastic deformation of the Mg88Zn7Y5 alloy with LPSO phase studied by in-situ synchrotron radiation diffraction

The temperature dependence of the compressive deformation behavior of the Mg88Zn7Y5 alloy with a high volume fraction (~85%) of the long-period stacking-ordered (LPSO) phase was studied by in-situ synchrotron radiation diffraction. The as-extruded microstructure exhibits a fully recrystallized α-Mg phase with a nearly random texture. The LPSO phase, identified as the 18R polytype, is represented by wavy lamellae elongated along the extrusion direction and has an intensive basal texture. The alloy compressed along the extrusion direction at room temperature shows a superior yield strength of 480 MPa. With increasing deformation temperature, the yield strength is reduced by 15% at 200 °C and by 46% at 300 °C, respectively. At all tested temperatures, the basal slip is activated in the α-Mg matrix far below the yield strength. The macroscopic yielding of the alloy is controlled by the activation of deformation kinking in the LPSO phase. The synchrotron radiation diffraction data indicate the stress localization at kinks with respect to the grains having the same orientation.