Hardening (metallurgy)

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

Effects of heat treatment on microstructure and tensile deformation of Mg AZ80 alloy at room temperature

Abstract: The plasticity of coarse and grain-refined Mg AZ80 alloys in the as-cast, γ-dissolved and homogenized states was investigated by specialized tensile testing at room temperature. Results indicate that microstructural parameters such as the activation volume and mean free path are important descriptors for these materials and capture the nature of the solute and second phase effect on strength and ductility. The as-cast alloys contain a microstructure consisting of α-Mg matrix, and divorced eutectic α-Mg/γ-Mg17Al12 phase with non-uniform Al solute content in the α-Mg. Dissolution of the majority of γ-phase occurs after annealing 5 h at 420 °C, and an almost uniform solid solution is obtained after 20 h at 420 °C. The yield strength is dependent upon the volume fraction of γ-phase and grain size. All alloys yield initially by basal slip and they exhibit different work hardening behaviour. The as-cast alloys show the fastest initial hardening and earliest saturation, and ultimately the lowest ductility. In contrast the solutionized alloys show a lower initial work hardening rate that is sustained, and enhanced ductility. The flow stress dependence of the strain rate sensitivity indicates that dynamical recovery processes associated with the dislocation–dislocation interactions, which develop in the as-cast alloys after small amount of deformation, lead to strain localizations and early failure. Results reveal that reducing the grain size and dissolving the γ-phase will enhance the ductility of AZ80 at room temperature.

Hardness trends in micron scale indentation

Abstract: A continuum theory for elastic-plastic solids that accounts for the size-dependence of strain hardening is employed to analyze trends in the indentation hardness test. Strain gradient plasticity theory incorporates an elevation of flow stress when non-uniform plastic deformations occur at the micron scale. Extensive experimental data exists for size-dependence of indentation hardness in the micron range for conical (pyramidal) indenters, and recent data delineates trends for spherical indenters. Deformation induced by rigid conical and spherical indenters is analyzed in two ways: by exploiting an approximation based on spherically symmetric void expansion and by finite element computations. Trends are presented for hardness as a function of the most important variables in the indentation test, including the size of the indent relative to the material length parameters, the strain hardening exponent, the ratio of initial yield stress to Young's modulus, and the geometry of the indenter. The theory rationalizes seemingly different trends for conical and spherical indenters and accurately simulates hardness data presented recently for iridium, a low yield strain/high hardening material. The dominant role of one of the material length parameters is revealed, and it is suggested that the indentation test may the best means of measuring this parameter.