Hardening (metallurgy)

About: Hardening (metallurgy) is a research topic. Over the lifetime, 25584 publications have been published within this topic receiving 376012 citations.

A modified Johnson–Cook model for tensile flow behaviors of 7050-T7451 aluminum alloy at high strain rates

Abstract: The uniaxial quasi-static and dynamic tensile tests were conducted at different strain rates (10–3 s−1, 800 s−1, 1900 s−1 and 2900 s−1) for 7050-T7451 aluminum alloy. Then, research of the strain rate hardening coefficient in the original Johnson–Cook model at different strains and strain rates showed that the coefficient is a function of strain and strain rate from the tensile experimental results. Furthermore, a modified Johnson–Cook model was proposed to describe the flow behaviors of the studied alloy based on the correction to the strain rate hardening coefficient. Comparisons between the experimental data and predicted results using the original JC model, Khan–Liu (KL) model and the modified JC model showed that a better agreement can be obtained applying the modified model than the other two models. Verifications for predicting three new high strain rates (1500 s−1, 2500 s−1 and 3500 s−1) experimental data demonstrated the modified JC model can provide an accurate description for the dynamic behaviors of the studied alloy.

Effect of heat treatment on mechanical properties of Ti–6Al–4V ELI alloy

Abstract: Ti–6Al–4V alloy of extra low interstitial (ELI) grade has been used in the biomedical applications because of its high strength-to-weight ratio and excellent biocompatibility. However, its relatively poor wear resistance leading to excessive wear and implant loosening requires proper surface hardening. The body implants are also subjected to a variety of loads at varying strain rates. The objective of this study was to evaluate the hardening behavior, strain rate sensitivity and fracture mechanisms with or without hardened surface layer. It was observed that the hardened surface layer had only a small effect on the strength but reduced the ductility. The yield strength (YS) and ultimate tensile strength (UTS) were higher in the water quenching and aging condition while the ductility was lower, when compared to the as-received condition and air cooling and aging condition. As the strain rate increased both YS and UTS increased and ductility decreased. The strain hardening exponent decreased with increasing strain rate. The strain rate sensitivity evaluated via both the common approach and Lindholm approach decreased as the true strain increased. Fractal dimension of fracture surfaces was observed to be associated with the heat treatment condition, ductility, fracture surface characteristics and roughness. The fractal dimension increased with increasing roughness of fracture surfaces.

Penetration of Strain-Hardening Targets With Rigid Spherical-Nose Rods

Abstract: The spherical cavity expansion approximation simplified the target analysis. To verify our models, we conducted terminal-ballistic experiments with three projectile geometries made of maraging steel and 6061-T651 aluminum targets for impact velocities between 0.3 and 1.0 km/s

The Bauschinger effect in precipitation strengthened aluminum alloys

Abstract: The Bauschinger effect in precipitation strengthened Al-Cu-Mg, Al-Zn-Mg and Al-Cu polycrystals was measured as a function of applied strain. Alloys heat treated to contain easily shearable precipitates,i.e., GPB, GP and θ″ exhibited a small Bauschinger effect, on the order of that in pure aluminum. In contrast, alloys with nonshearable precipitates, S′, η and θ′ showed an anomolously large effect. A unique hysteresis loop shape, with a region of convex curvature between sharp inflection points, was observed in the nonshear-able precipitate alloys. The large Bauschinger effect and unusual hysteresis loop shape are due to internal elastic or back stresses exerted by the strong precipitates on the matrix. A nonlinear elastic hardening model is proposed in which the overall work harden-ing is partitioned into an elastic back stress component and a frictional dislocation forest hardening term. Plastic relaxation around the precipitates and inhomogeneous deformation in the polycrystal reduces the level of the internal stresses below that predicted theoretically by the Brown and Stobbs hardening theory.