Deformation Activation Energy Research Articles

Room Temperature Strengthening and High-Temperature Superplasticity of Mg-Li-Al-Sr-Y Alloy Fabricated by Asymmetric Rolling and Friction Stir Processing

Magnesium-lithium alloy is the lightest alloy to date. To explore its room temperature strength and high-temperature ductility, a plate of a new fine-grained Mg-9.13Li-3.74Al-0.31Sr-0.11Y alloy was fabricated by asymmetric rolling, and the rolled plate was subjected to friction stir processing (FSP). The microstructure and mechanical properties at room and elevated temperatures were investigated by optical microscopy, X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and tensile tester. Grain refinement with an average grain size in the α-Mg phase of 1.65 μm and an average grain size in the β-Li phase of 4.24 μm was achieved in the water-cooled FSP alloy. For room temperature behavior, the ultimate tensile strength of 208 ± 4 MPa, yield strength of 193 ± 2 MPa, and elongation of 48.2% were obtained in the water-cooled FSP alloy. XRD and EDS analyses revealed that the present alloy consists of α-Mg and β-Li phases, Al2Y, Al4Sr, MgLi2Al, and AlLi intermetallic compounds. For high-temperature behavior, the maximum superplasticity or ductility of 416% was demonstrated in this fine-grained alloy with an average grain size of 10 μm at 573 K and 1.67 × 10-3 s-1. A power-law constitutive equation was established. The stress exponent was 2.29 (≈2) (strain rate sensitivity 0.44), and the deformation activation energy was 162.02 kJ/mol. This evidence confirmed that the dominant deformation mechanism at elevated temperatures is grain boundary and interphase boundary sliding controlled by lattice diffusion.

Achieving high strain rate superplasticity in an Al-Cu-Li alloy processed by thermo-mechanical processing

In order to obtain high strain rate superplasticity, it is usually necessary to prepare fine-grained aluminum alloy by severe plastic deformation such as equal channel angular pressing. A traditional thermo-mechanical processing was exploited to prepare fine-grained Al-Cu-Li alloy with 3.1 μm grains. A maximum elongation of 1220% was obtained at a high strain rate of 1 × 10−2 s−1 and 490 °C. The high-stain rate superplasticity is attributed to the existence of stabilized fine grains and nano-scaled Al3Zr particles which inhibit the dynamic growth of grain. Furthermore, the calculated deformation activation energy and m values suggest that the grain boundary sliding mechanism is active.

Hot deformation behaviour and microstructure evolution of gold-imitation brass alloy with high corrosion resistance

AbstractThe hot deformation characteristics of Cu−13Zn−1Ni−1Sn−1.5Al gold-imitation brass alloy in a temperature range from 953 to 1123 K and a strain rate range from 0.001 to 1 s−1 were investigated by hot compression tests. The stress−strain curves show that the flow stress decreases with the increase of temperature and the decrease of strain rate. The dynamic recrystallization grains appear while the temperature reaches 1073 K at a constant strain rate of 0.01 s−1. The constitutive equation of the alloy was established and its deformation activation energies were obtained at different strains (ε=0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8). When the strain is 0.8, the constitutive equation of the alloy is = 7.22×109[sinh(0.0187σ)]3.67exp[−227.17/(RT)], and the deformation activation energy is 227.17 kJ/mol. The dissipation power maps and instability maps were established at different strains, which suggested that the recommended processing condition for hot compression was in the temperature range of 1010−1040 K with a strain rate of 1 s−1.

Dynamic recrystallization behavior and nucleation mechanism of dual-scale SiCp/A356 composites processed by P/M method

Abstract Thermal deformation can improve the properties of aluminum matrix composites (AMCs) prepared by powder metallurgy (P/M) due to the dense and uniform microstructures. And the final microstructure of the AMCs is related to the dynamic recrystallization (DRX) behavior and nucleation mechanism in the thermal forming process. In this regard, the hot compression tests of dual-scale SiC particles reinforced A356 (SiCp/A356) composites prepared by P/M method were carried out at temperatures of 460–520°C and strain rates of 0.01–5 s−1 on a thermal simulation tester. The corresponding microstructure evolution was analyzed by electron back-scattered diffraction and transmission electron microscopy. The results indicated that the stress–strain curve was a typical DRX unimodal stress curve. The comprehensive influences of the strain rate and deformation temperature on the stress were investigated using the Zener–Hollomon parameter (Z), where the deformation activation energy was 443.204 kJ/mol. The DRX critical strain model and DRX volume fraction model were established. DRX behavior of the SiCp/A356 composites was sensitive to the deformation temperatures and strain rates. The micro and nano SiCp can promote the DRX nucleation of Al matrix due to the particle-stimulated nucleation.

Room-Temperature Strengthening, Portevin-Le Chatelier Effect, High-Temperature Tensile Deformation Behavior, and Constitutive Modeling in a Lightweight Mg-Gd-Al-Zn Alloy

To explore room-temperature strengthening and high-temperature ductility, a lightweight novel Mg-1.85Gd-0.64Al-0.62Zn alloy was fabricated by innovative multidirectional forging and a hot-rolling technique. Microstructures and mechanical properties were studied at room and elevated temperatures with an optical microscope, an X-ray diffractometer, and a tensile tester. An ultimate tensile strength of 260 MPa, yield strength of 171 MPa, and elongation of 20.4% were demonstrated at room temperature. The room-temperature strengthening mechanisms were identified by strengthening the model estimation. A type C Portevin-Le Chatelier effect was discovered and elucidated in this alloy. X-ray diffraction analysis revealed that the phase composition is α-Mg solid solution and (Mg, Al)3Gd, Al7Zn3, and Al2Gd intermetallic compounds. Examination of the microstructure at elevated temperatures revealed that dynamic recrystallization and dynamic grain growth occur. In particular, it was discovered that bimodal microstructures or incomplete dynamic recrystallization microstructures exist in high-temperature deformation. A maximum quasi-superplasticity of 228.4% was demonstrated in this alloy at 673 K and 5.0 × 10-4 s-1. Flow stress curves showed that the present alloy exhibits Sotoudeh-Bate curves or a long intermediate strain-hardening stage followed by a strain-softening stage. A modified Zerilli-Armstrong constitutive equation incorporating the number of dislocations was established. The power-law constitutive equation was established to identify the deformation mechanism. Both constitutive models had good predictability. At 673 K and 5.0 × 10-4 s-1, the stress exponent was 4, and the average deformation activation energy was 104.42 kJ/mol. The number of dislocations inside a grain was 146. This characteristic evidence confirmed that dislocation motion controlled by pipe diffusion dominates the rate-controlling process under this condition.

Hot tensile deformation behavior and microstructure evolution of 7075 aluminum alloy sheet

The hot tensile deformation behavior of 7075 aluminum alloy sheet was studied using Gleeble-3800 thermal simulation machine at deformation temperatures of 400–475 °C and strain rates of 0.001∼1s−1. Microstructure evolution and fracture morphology were observed by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The hyperbolic sine model is used to establish the constitutive equation of the relationship between peak stress and Z parameter. The results show that the hyperbolic sine Arrhenius constitutive equation can well characterize the flow behavior of the studied alloy, and the hot deformation activation energy is 132.52 kJ/mol. The average relative error between the predicted and experimental values is only 4.58%, and r2 is as high as 0.988, indicating that there is good consistency between the experimental value and the predicted value. When the strain rate keeps unchanged, the elongation of the studied alloy shows an upward trend in the lower deformation temperature range (400–425 °C). When the deformation temperature continued to rise to 475 °C, the elongation of the studied alloy decreased sharply. Based on the analysis of fracture morphology, a large number of dimples can be observed at 450 °C/0.001s−1, which is a typical ductile fracture. With increasing of deformation temperatures, the fracture mechanism gradually changes from ductile fracture to brittle fracture. Under the condition of 425 °C/0.01s−1, there are a lot of dislocations in the alloy, and the dislocation walls are formed. With the increase of deformation temperatures or the decrease of strain rates, the dislocation density gradually decreases and dynamic recrystallization occurs. The softening mechanism of the studied alloy changes from dynamic recovery to dynamic recrystallization.

Experimental and Numerical Studies on Hot Compressive Deformation Behavior of a Cu-Ni-Sn-Mn-Zn Alloy.

Cu-9Ni-6Sn alloys have received widespread attention due to their good mechanical properties and resistance to stress relaxation in the electronic and electrical industries. The hot compression deformation behaviors of the Cu-9Ni-6Sn-0.3Mn-0.2Zn alloy were investigated using the Gleeble-3500 thermal simulator at a temperature range of 700-900 °C and a strain rate range of 0.001-1 s-1. The microstructural evolution of the Cu-9Ni-6Sn alloy during hot compression was studied by means of an optical microscope and a scanning electron microscope. The constitutive equation of hot compression of the alloy was constructed by peak flow stress, and the corresponding 3D hot processing maps were plotted. The results showed that the peak flow stress decreased with the increase in the compression temperature and the decrease in the strain rate. The hot deformation activation energy was calculated as 243.67 kJ/mol by the Arrhenius equation, and the optimum deformation parameters for the alloy were 740-760 °C and 840-900 °C with a strain rate of 0.001~0.01 s-1. According to Deform-3D finite element simulation results, the distribution of the equivalent strain field in the hot deformation samples was inhomogeneous. The alloy was more sensitive to the deformation rate than to the temperature. The simulation results can provide a guideline for the optimization of the microstructure and hot deformation parameters of the Cu-9Ni-6Sn-0.3Mn-0.2Zn alloy.

Hot deformation behavior and microstructure of Ni-Cu rich Al-Si AA4032 alloy

The Al-Si alloy family is among the most widely used nonferrous alloys, in both cast and wrought products. The alloys have undergone a continuous progress toward improvement of various properties. The present research investigated the hot deformation behavior of AA4032 alloy, modified with addition of 3.5 %wt of Ni and 3%wt of Cu. The study was carried out using constitutive equations at the temperature range of 693–823 K (420–550 °C) alongside the strain rates of 0.001–1 s−1. The processing maps were determined by superimposing the instability maps on power dissipation maps. Moreover, the effect of extra copper and nickel on the microstructure and phase formation was studied via optical microscopy, SEM and TEM. The hot deformation activation energy of the Ni-Cu rich alloy is also calculated to be 338 KJ/mol (at ε = 0.1) which is notably higher than that of the self-diffusion of pure Al. It is found that the best hot working condition is the temperature range of 720–780 K with a strain rate of 0.001–0.03 s−1. The microstructure of the alloy at the calculated safe zone was uniform, while it showed cracking at the unsafe region of deformation parameters.

Effect of Zr and Er Addition on the Microstructural Evolution of a Novel Al-Mg-Zn-Er-Zr Alloy during Hot Compression.

The hot compression experiment of homogenized Al-5.2Mg-0.6Mn-0.29Zn-0.16Er-0.12Zr alloy was carried out by the Gleeble-3500 thermal simulation testing system. The deformation behavior in temperatures of 350~500 ℃ and deformation rates of 0.01~10 s-1 was studied. The relationship between stress and strain rate and deformation temperature was analyzed. The constitutive equation of alloy high-temperature deformation was constructed by the Zener-Hollomon method, and the hot working diagram with the true strain of 0.2 and 0.5 was constructed according to the dynamic material model. The research results show that flow stress has a positive correlation with strain rate and a negative correlation with temperature. The steady flow stress during deformation can be described by a hyperbolic sinusoidal constitutive equation. Adding Er and Zr into Al-Mg alloy can not only refine grains and strengthen precipitation but also form a core-shell Al3(Er, Zr) phase. In the deformation process, Al3(Er, Zr) precipitates can pin dislocations and inhibit dynamic recrystallization (DRX). Dynamic recovery (DRV) is dominant during hot deformation. The mechanism of dynamic recovery is dislocation motion. At high temperatures, Al3(Er, Zr) can also inhibit grain coarsening. The average hot deformation activation energy of the alloy is 203.7 kJ/mol. This high activation energy can be due to the pinning effect of Er and Zr precipitates. The processing map of the alloy was analyzed and combined with the observation of microstructure, the hot deformation instability zone of the alloy was determined, and the suitable process parameters for hot deformation were obtained, which were 450~480 °C, and the strain rate is 0.01~0.09 s-1.

Hot Tensile Deformation Behavior and Constitutive Models of GH3230 Superalloy Double-Sheet.

In this paper, the hot tensile deformation of a GH3230 superalloy double-sheet was conducted under deformation temperatures ranging from 1123~1273 K and strain rates ranging from 0.001~0.2 s-1. The flow behavior of the GH3230 superalloy double-sheet was analyzed in detail. The hot tensile deformation process of the GH3230 superalloy double-sheet includes four stages of elastic deformation, strain hardening, steady state and fracture. The true stress decreases with the increasing deformation temperature and decreasing strain rate. The variation of the strain rate sensitivity index and strain hardening index with processing parameters were discussed. The average apparent activation energy for hot tensile deformation is 408.53 ± 46.96 kJ·mol-1. A combined Johnson-Cook and Hensel-Spittle model considering the couple effect of strain hardening, strain rate hardening and thermal softening was established to describe the hot tensile behavior of the GH3230 alloy double-sheet. Compared to Johnson-Cook model and Hensel-Spittle model, this model has the highest predicting accuracy. The average absolute relative error of true stress between the experimental and the predicted is only 2.35%.

Hot Workability of the Multi-Size SiC Particle-Reinforced 6013 Aluminum Matrix Composites.

The size and distribution of ceramic particles in aluminum matrix composites have been reported to remarkably influence their properties. For a single ceramic particle, the particle size is too small and prone to agglomeration, which makes the mechanical properties of the composites worse. When the ceramic particle size is too large, the particles and alloy at the interface are not firmly bonded, and the effect of dispersion distribution is not achieved, which will also reduce the mechanical properties of the composites. The multi-size ceramic particles are expected to improve this situation, while their effect on hot workability is less studied. In this study, the hot deformation behavior, constitutive model, processing map and SEM microstructure were investigated to evaluate the hot workability of multi-size SiC particle-reinforced 6013 aluminum matrix composites. The results showed that the increased deformation temperature and decreased strain rate could decrease flow stresses. The flow stress behaviors of the composites can be described by the sine-hyperbolic Arrhenius equation with the deformation activation energy of Q = 205.863 kJ/mol. The constitutive equation of the composites is ε ˙=3.11592×1013sinh0.024909σ4.12413exp-205863RT. Then, the hot processing map of the SiCp/6013 composites was constructed and verified by SEM observations. The rheological instability zone was in the region of a high strain rate. The optimal processing zone for composites was 450~500 °C and 0.03~0.25 s-1. In addition, the strain level was found to increase both the Q value and the area of the instability zone.

Characterisation of tensile deformation behaviour of Fe–25Cr–35Ni-based alloy at high temperature

Fe–25Cr–35Ni-based alloy tensile deformation behaviour was studied through tensile test at strain rates of 5 × 10−4, 10−3, 5 × 10−3 and 10−2 s−1 from 900 to 1023°C in this paper. The flow stress has a good correlation with testing temperature and strain rate. TEM and SEM were used to analyse the microstructure evolution. The results show that DRV and DRX are the important factors for reducing the flow stress during hot tensile deformation. The occurrence of DRV and DRX was confirmed by TEM micrographs in high temperature tensile deformation. The hyperbolic sine-type equation with deformation activation energy and temperature describes Fe–25Cr–35Ni-based alloy hot tensile deformation, and the deformation activation energy is 5.24 × 102 kJ mol–1.

HOT TENSILE PROPERTIES OF INCONEL 706 ALLOY

INCONEL 706 is a high-strength nickel-based super alloy that is commonly used in high-temperature applications such as gas turbines and nuclear reactors. In this study, the hot tensile properties of Inconel 706 were investigated to better understand the material's behavior under high-temperature and high-stress conditions. Tensile tests were conducted at temperatures ranging from 740°, 860°, 940°, 1020°1080°and strain rates ranging from 0.001/s to 1/s. The results showed that the ultimate tensile strength and yield strength of Inconel 706 decreased with increasing temperature, while the elongation increased. The strain rate had a negligible effect on the mechanical properties. Microstructural analysis revealed that the deformation mechanism changed from dislocation slip to dynamic recrystallization as the temperature increased. The activation energy for deformation was calculated to be 421 kJ/mol, indicating that diffusion-controlled mechanisms play an important role in the deformation process. Overall, the hot tensile properties of Inconel 706 were found to be highly dependent on temperature and microstructure, which should be considered in the design and operation of high-temperature components made of this alloy. The output from the tensile testing machine is used for the data in analysis software like MATLAB, Ansys. The aim of investigations conducted in this project is to study the change of the mechanical properties, especially the high temperature mechanical properties of HTPI, at elevated temperatures.

Microstructure evolution, deformation behavior and manufacture design of TiAl matrix composites reinforced with in-situ borides precipitation

Phase transformation and borides precipitation caused by boron addition influence microstructure evolution and deformation behavior of in-situ TiAl matrix composites. Dynamic recrystallization mechanism and dynamic recovery mechanism were investigated by isothermal compression tests, scanning electron microscopy and transmission electron microscopy, etc. The value of apparent deformation activation energy (Q) of present composites is calculated to be 691.506 kJ/mol. In the temperature range of 1100−1200 °C, nucleation and growth of recrystallized γ and α grains promoted by TiB obstacles dominate the deformation below or above Tα2→α. The dynamic recovery of α phase dominates the deformation in condition with low strain rates at 1250 °C. Boron addition increases the fraction of α phase and decreases the transformation temperatures of γ→α and α2→α, which promotes the nucleation and growth of recovered α grains during the loading. Deformation mechanisms and processing performance were also clarified based on the reestablished constitutive model.

Hot compressive deformation and microstructural evolution of 60NiTi alloy

Hot deformation behavior and microstructure of 60NiTi alloy during hot compressive deformation were investigated using Gleeble−3500 thermal simulation test machine in the temperature range of 500−650 °C and strain rate range of 0.001−1 s−1. The constitutive equation of hot compression was constructed and the hot processing maps were plotted. When the compression temperature rose or the strain rate declined, the peak stress reduced. The hot deformation activation energy was calculated as 327.89 kJ/mol, and the proper hot working parameters of compression temperature of 600−650 °C and strain rate of 0.005−0.05 s−1 were obtained. The recrystallization degree increased with increasing compression temperature. When the strain rate increased, both dislocation density and number of twins were improved, and the Ni3Ti phase tended to aggregate. Ni3Ti precipitation phase was beneficial to inducing dynamic recrystallization of the 60NiTi alloy. The dynamic recovery, dynamic recrystallization and twinning took place during hot compressive deformation of the 60NiTi alloy.

Hot Deformation Behavior of TA1 Prepared by Electron Beam Cold Hearth Melting with a Single Pass

The Gleeble-3800 thermal simulator was used for hot compression simulation to understand the hot deformation performance of TA1 prepared by the single-pass electron beam cold hearth (EB) process. The deformation degree is 50% on a thermal simulator when the temperature range is 700-900 °C, with a strain rate of 0.01-10-1 s. According to the thermal deformation data, the true stress-strain curve of TA1 was studied. Meanwhile, the constitutive model and processing map were established through the experimental data. These results indicate that the deformation temperature negatively affects strain rate and flow stress. The heat deformation activation energy of EB produced TA1 sample was lower than that of VAR produced TA1 sample in the studied range. The best processing areas of EB-produced TA1 were strain rates of 0.05-0.01 s-1, within 700-770 °C; or strain rates of 0.01-0.15 s-1; 840-900 °C. The results of this paper enrich the fundamental knowledge of the thermal deformation behavior of TA1 prepared by EB furnaces.

The dynamic softening identification and constitutive equation establishment of Ti–6.5Al–2Sn–4Zr–4Mo–1W–0.2Si alloy with initial lamellar microstructure

Abstract The high-temperature deformation behavior of Ti–6.5Al–2Sn–4Zr–4Mo–1W–0.2Si alloy with initial lamellar microstructure was investigated through performing hot compression experiments at temperatures of 940–1,030°C and strain rates of 0.001–10 s−1 on the Gleeble-3500 simulator. Three kinds of typical flow curves corresponding to different strain rates were distinguished. The deformation activation energy and Zener–Hollomon parameter were obtained through kinetic analysis. By comparing saturated dislocation density with the critical density for dynamic recrystallization, dynamic softening behaviors were identified and verified by the Poliak–Jonas criterion. Furthermore, a piecewise physical-based constitutive model incorporating dynamic softening behaviors was constructed. Finally, microstructures deformed under different deformation conditions were analyzed to further verify the softening behaviors determined by identification criterions.

Hot deformation behavior of FeCrCuMnNi high entropy alloy

The hot deformation behavior of FeCrCuMnNi high entropy alloy (HEA) was investigated using hot compression test within the temperature range of 500–970 °C at the strain rate of 0.1, 0.01, and 0.001 s−1 up to the strain of 0.6. An Arrhenius-type equation was used to evaluate the hot deformation behavior of the alloy and propose the constitutive equation. FeCrCuMnNi HEA revealed a typical hot deformation behavior with almost 250 kJ/mol deformation activation energy, which was mostly governed by the lattice diffusion of Cu. Discontinuous dynamic recrystallization (dDRX) was the main restoration phenomenon during hot deformation in which the grain boundary sliding and dislocation sliding were suggested as the main active mechanisms. The processing maps were plotted based on the efficiency of energy consumption (η) and flow instability (ξ). It was revealed that the instability region between 750 and 850 °C at different strain rates might be directly related to the formation of a hard sigma phase within this temperature range.

Creep properties and deformation mechanisms of a Ni2Co1Fe1V0.5Mo0.2 medium-entropy alloy

The creep properties of a Ni2Co1Fe1V0.5Mo0.2 medium-entropy alloy (MEA) in the temperature range 973–1073 K, and under the stresses 150–200 MPa, have been investigated in detail. The Ni2Co1Fe1V0.5Mo0.2 MEA possesses excellent creep properties at 973 K/150 MPa and 973 K/175 MPa. The stress exponent n was calculated to be 3.1 at 973 K, suggesting the dominance of viscous dislocation glide mechanism in creep deformation. The activation energy for creep deformation was measured to be 456.3kJ·mol−1, which is comparable to the activation energy for self-diffusion of Mo, indicating a strong effect of Mo diffusion on viscous dislocation glide. Detailed transmission electron microscopy analysis reveals: (1) increased stress and strain can alter the dislocation configurations and promote dislocation climb, and thus to increase the creep rate; (2) increased temperature and strain can lead to active recovery and recrystallisation, and thus to cause grain refinement.

Research on hot deformation behaviour of as-cast W12Cr4V5Co5 steel

ABSTRACT Hot working response of as-cast W12Cr4V5Co5 steel was investigated by isothermal compression testing in the temperature range of 1000-1150°C and strain rate range of 0.01-10 s−1. Experimental results showed that the flow stress and microstructure evolution were susceptible to the hot deformation parameters. Work hardening first occurred at a small strain, followed by softening, and finally, an approximate dynamic equilibrium was achieved between work hardening and softening. The activation energy of deformation was calculated to be 557.33 kJ mol−1, and constitutive equations compensated with strain were proposed to describe the flow stress as a function of deformation parameters. Microstructure analysis indicated that the average grain size decreased with the increase in strain rate and the decrease in deformation temperature. Additionally, the simulation of hot deformation via Deform-3D software revealed the sample's inhomogeneous deformation during hot compression. This study may provide guidance for hot working of as-cast W12Cr4V5Co5 steel.