Relationship among microstructure,mechanical properties and texture of TA32 titanium alloy sheets during hot tensile deformation

The relationship among microstructure,mechanical properties and texture of TA32 titanium alloy sheets during hot tensile deformation at 800℃was investigated.In the test,the original sheet exhibited relatively low flow stress and sound plasticity,and increasing the heat treatment temperature resulted in an increased ultimate tensile strength(UTS)and a decreased elongation(EL).The deformation mechanism of TA32 alloy was dominated by high angle grain boundaries sliding and coordinated by dislocation motion.The coarsening of grains and the annihilation of dislocations in heat-treated specimens weakened the deformation ability of material,which led to the increase in flow stress.Based on the high-temperature creep equation,the quantitative relationship between microstructure and flow stress was established.The grain size exponent andαphase strength constant of TA32 alloy were calculated to be 1.57 and 549.58 MPa,respectively.The flow stress was accurately predicted by combining with the corresponding phase volume fraction and grain size.Besides,the deformation behavior of TA32 alloy was also dependent on the orientation of predominantαphase,and the main slip mode was the activation of prismaticslip system.The decrease of near prism-oriented texture in heat-treated specimens resulted in the enhancement of strength of the material.

Flow behavior modeling of IMI834 titanium alloy during hot tensile deformation

A proper constitutive model was developed to predict the hot tensile flow behavior of IMI834 titanium alloy in α+β region. Hot tensile tests were performed at 800–1025 °C and 0.001–0.1 s−1. The constitutive model was developed through an Arrhenius-type equation at strains of 0.08–0.22 to characterize the hot tension behavior. It was found that the activation energies for hot tensile deformation of IMI834 titanium alloy are in the range of 519–557 kJ/mol at different strain values. The accuracy of predicted flow stress curves was evaluated using standard statistical parameters. These curves are appropriately found to be in good agreement with the experimental ones.

Fracture Behavior and Processing Deformation of C71500 Cupronickel Alloy during Hot Tensile Deformation

The hot tensile deformation properties and microstructure evolution of high purity C71500 cupronickel alloy at 1023-1273 K and 0.0001-0.1 s^(-1)strain rates were studied by uniaxial hot tensile deformation method.Based on the experimental data,the flow behavior,microstructure and fracture characteristics of the alloy were analyzed after considering the influence of different deformation parameters.The relationship between microstructure and high temperature(T≥1023 K)plasticity is discussed,and the fracture mechanism is revealed.The relationship between strain rate sensitivity coefficient and stress index and plastic deformation is discussed.The constitutive equation of the alloy is established by Johnson-Cook model.Based on the dynamic material model,the energy dissipation model is established,and Prasad’s instability criterion based on Ziegler’s expected rheological theory is used to predict the unstable region in the processing map.Processing map in hot tensile is analyzed to provide theoretical basis for different processing technology.

Microstructural evolution and hot tensile behavior of Mg−3Zn−0.5Zr alloy subjected to multi-pass friction stir processing

The microstructures and hot tensile behaviors of ZK30 alloys subjected to single-and multi-pass friction stir processing(FSP)were systematically investigated.Following single-pass FSP(S-FSP),coarse grains underwent refinement to 1−2μm,with a distinct basal texture emerging in the stir zone(SZ).Additionally,second-phase particles were fragmented,dispersed,and partially dissolved.Multi-pass FSP(M-FSP)further enhanced the homogeneity of the microstructure,reduced texture intensity differences,and decreased the fraction of second-phase particles by 50%.Both S-FSP and M-FSP SZs demonstrated superplasticity at strain rates below 1×10^(−3)s^(−1)and at temperatures of 250−350℃.The S-FSP SZ exhibited an elongation of 390%at 250℃and 1×10^(−4)s^(−1),while the M-FSP SZ achieved an elongation of 406%at 350℃and 1×10^(−3)s^(−1).The superplastic deformation of SZ was co-dominated by grain boundary sliding(GBS)and the solute-drag mechanism in S-FSP and mainly by GBS in M-FSP.

Hot tensile deformation behavior and constitutive model of ZK61M high-strength magnesium alloy sheet

Hot deformation behavior of the annealed ZK61 M magnesium alloy sheet was explored using tensile tests with strain rates varying from 0.001 to 0.030 s^(-1) in temperatures range of 423-513 K.The obtained results indicate that the flow stress increased with deformation temperature decreasing and strain rate increasing.Dynamic recrystallization(DRX)occurs when the temperature is higher than 423 K,and the recrystallization volume fraction increases with temperature rising.At a given temperature,the measured DRX volume fraction at a higher strain rate is smaller than that at a lower strain rate.Dimples are observed throughout the tested temperature range.Moreover,they grow larger as temperature increases.An average absolute relative error(AARE)of 2.65%proves that the peak stress predicted by the constitutive model is in good agreement with the experimental results.The correlation coefficient(R’)obtained for the predicted stress and the experimental value considering the strain on the material constant are between 0.9831 and 0.9977.In addition,AARE and root mean square error(RMSE)are less than 6.5%and 8.5 MPa,respectively.This indicates that the deviation of the predicted value from the experimental value is small and the predictions of the proposed model are reliable.

PHYSICAL SIMULATION OF INTERFACIAL CONDITIONS IN HOT FORMING OF STEELS

In the last few years,substantial experimental simulation and mumerical modelling hare been carried out in IMMPETUS to characterise the interfacial heat transfer and friction conditions during hot forging and rolling of steels. Emphasis has been placed on the influence of the oxide scale which forms on the steel workpiece. In the present paper, the experimental methods used for investigating interfacial heat transfer and friction conditions are described. Theses include hot flat rolling of steel slabs and hot axi- symmetric forging of steel cylinders and rings.Temperature measurements and computations demon- strate that for similar conditions, similar conditions, the effective interfacial heat transfer coefficients (IHTC) derived for hot rolling are significantly higher than those for forging, mainly due to the contribution of scale cracking during rolling. On the basis of experimental observations and numerical analysis,physical models for interfacial heat transfer in forging and rolling have been established. In addition, hot' sandwich' rolling and hot tensile tests with finite element modelling have been carried out to evaluate the hot ductility of the oxide scale.The results indicate that the defomation, cracking and decohesion behaviour of the oxide scale depend on deformation temperature, strain and relative strengths of the scale layer and scale - steel interface.Finaly, friction results from hot ring compression tests and from hot rolling with forward/backward slip measurements are reported.

Flow stress prediction of Hastelloy C-276 alloy using modified Zerilli−Armstrong,Johnson−Cook and Arrhenius-type constitutive models

To better understand the hot deformation behaviors of Hastelloy C-276 alloy under elevated temperatures,hot tensile tests were carried out in the temperature range of 1223−1423 K and the strain rate range of 0.01−10 s^−1,respectively.Based on the modified Zerilli−Armstrong,modified Johnson-Cook,and strain-compensated Arrheniustype models,three constitutive equations were established to describe the high-temperature flow stress of this alloy.Meanwhile,the predictability of the obtained models was evaluated by the calculation of correlation coefficients(r)and absolute errors(Δ),where the values of r for the modified Zerilli−Armstrong,Johnson−Cook,and Arrhenius-type constitutive models were computed to be 0.935,0.968 and 0.984,and the values ofΔwere calculated to be 13.4%,10.5%and 6.7%,respectively.Moreover,the experimental and predicted flow stresses were compared in the strain range of 0.1−0.5,the results further indicated that the obtained modified Arrhenius-type model possessed better predictability on hot flow behavior of Hastelloy C-276.

Superplastic deformation of commercial OOCr22Ni5Mo3N0.17 duplex stainless steel

The superplastic behavior of a commercial duplex stainless steel has beenstudied by means of isothermal hot tensile test at temperatures of 850-1050 deg C for the initialstrain rates ranging from 3X10^(-4) s^(-1) to 5X10^(-2) s^(-1). At 960 deg C, the best superplasticdeformation that caused the maximum elongation greater than 840 percent was obtained for an initialstrain rate of 1.2X10^(-3) s^(-1). At 850 deg C, the best elongation 500 percent was achieved for aninitial strain rate of 2.5X10^(-3) s^(-1) During the deformation in higher temperature region,coarse gamma grains formed during the prior treatments were broken into spherical particles,resulting in a homogeneous dispersion of gamma particles within the delta-ferrite matrix. However,at lower temperatures between 800 and 950 deg C, the sigma phase was formed through the eutectoiddecomposition of delta->gamma+sigma, resulting finally in the stable equiaxed micro-duplexstructures with delta/gamma and gamma/sigma respectively. The precipitation of the sigma phaseplayed an important role in improving the superplasticity at 850 deg C. The strain-rate sensitivitycoefficient, m-values, were also determined by the strain rate change tests. The microstructurestudies show that the superplastic process occurs mainly by the local work hardening and thesubsequent dynamic recrystallization and a grain boundary sliding and grain switching mechanism.

Hot Ductility of Severe Plastic Deformed AA6061 Aluminum Alloy

The hot ductility of 6061 aluminum alloy,which was subjected to two different severe plastic deformations（SPD）,was studied at different temperatures and strain rates.The tensile tests were carried out at the temperature range of 300-500 ℃ and at the strain rates of 0.0005-0.01 s^（-1）.The microstructure evolution was characterized using optical microscopy,transmission electron microscopy and X-ray diffraction technique.The influences of the microstructure after SPD,thermomechanical parameters（temperature and strain rate） and specimen size on the hot formability of this alloy were then analyzed.The results show that a decrease in grains/subgrains exhibited significant effect on the hot ductility of SPDed samples.The constitutive equations were then developed to model the hot formability of the studied alloy.The developed model can be represented by Zener-Hollomon parameter in a hyperbolic sinusoidal equation form.Both the changes of elongation to failure and Zener-Hollomon parameter indicate that the hot ductility of the alloy is more sensitive to the temperature rather than to the strain rate.The uniform elongation is independent of the specimen size,but the postnecking elongation increases dramatically as the ratio of l/A^（1/2） decreases.