Hardening (metallurgy)

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

Laser shock peening of laser additive manufactured Ti6Al4V titanium alloy

Abstract: Laser shock peening is combined with laser additive manufacturing to modify the surface microstructures and mechanical properties of as manufactured Ti6Al4V titanium alloy. Microstructural evolution, microhardness distribution, residual stress distribution and mechanical properties are examined before and after LSP. After peening, the interplanar spacing of lattices of both α and β phases decreases without any new phase formation. Grain refinement is achieved with average grain size of α phase decreasing from 33.6 to 24.3 μm. High density of dislocation lines, tangles, and multi-directional mechanical twins are observed. Residual stress is turned from tensile to compressive state with an affected depth of around 700 μm. The hardening layer reveled by microhardness is around 900 μm in depth. Grain refinement accounts for the yield strength, ultimate tensile strength, and elongation enhancements after peening.

Stabilization of rapid frictional slip on a weakening fault by dilatant hardening

Abstract: Frictional slip is often accompanied by dilatancy due to uplift in sliding over asperities and micro-cracking in the adjacent material. If dilatancy occurs more rapidly than pore fluid can flow into the newly created void space, the local pore pressure is reduced and the effective normal stress is increased in compression, tending to inhibit further slip. This dilatant hardening is analyzed for a simple model. One surface of a slab is loaded by compressive stress and shear displacement and connected to a reservoir of pore fluid held at constant pressure. The other boundary is a frictional surface, assumed to have formed at peak stress, on which the shear stress decreases from a peak value τp to a residual value τr as slip increases from zero to δ0. In the absence of pore fluid effects an instability corresponding to an unbounded slip rate occurs when the slope of the shear stress versus slip relation is more negative than the unloading stiffness of the surrounding material. Dilatant hardening prevents this instability provided that the pore pressure in the reservoir is high enough. If the pressure in the reservoir is too low, the pressure at the fault surface can be reduced to the point at which the pore fluid bulk modulus decreases rapidly, eliminating the stabilizing effect. When the analysis is modified to include normal stress changes simulating those in the axisymmetric compression test, the prediction of the critical pressure in the reservoir agrees to within a factor of 2 or 3 with that observed by Martin in tests on Westerly granite. The predictions are also consistent with the trends observed by Martin of decreasing critical reservoir pore pressure with increasing effective confining stress and decreasing nominal strain rate.