Evolution of microstructure and residual stress during annealing of austenitic and ferritic steels

International audienceIn this work the recovery and recrystallization processes occurring in ferritic and austenitic steels were studied. To determine the evolution of residual stresses during material annealing the nonlinear sin 2 ψ diffraction method was used and an important relaxation of the macrostresses as well as the microstresses was found in the cold rolled samples subjected to heat treatment. Such relaxation occurs at the beginning of recovery, when any changes of microstructure cannot be detected using other experimental techniques. Stress evolution in the annealed steel samples was correlated with the progress of recovery process, which significantly depends on the value of stacking fault energy

Texture-Governed Cell Response to Severely Deformed Titanium

The phenomenon of superior biological behavior , r it observed in titanium processed by an unconventional severe plastic deformation method, that is, hydrostatic extrusion, has been described within the present study. In doing so, specimens varying significantly in the crystallographic orientation of grains, yet exhibiting comparable grain refinement, were meticulously investigated. The aim was to find the clear origin of enhanced biocompatibility of titanium-based materials, having microstructures scaled down to the submicron range. Texture, microstructure, and surface characteristics, that is, wettability, roughness, and chemical composition, were examined as well as protein adsorption tests and cell response studies were carried out. It has been concluded that, irrespective of surface properties and mean grain size, the (10 (1) over bar0) crystallographic plane favors endothelial cell attachment on the surface of the severely deformed titanium. Interestingly, an enhanced albumin, fibronectin, and serum adsorption as well as dearly directional growth of the cells with preferentially oriented cell nuclei have been observed on the surfaces having (0001) planes exposed predominantly. Overall, the biological response of titanium fabricated by severe plastic deformation techniques is derived from the synergistic effect of surface irregularities, being the effect of refined microstructures, surface chemistry, and crystallographic orientation of grains rather than grain refinement itself

Evolution of microstructure and residual stress during annealing of austenitic and ferritic steels

In this work the recovery and recrystallization processes occurring in ferritic and austenitic steels were studied. To determine the evolution of residual stresses during material annealing the nonlinear sin 2 ψ diffraction method was used and an important relaxation of the macrostresses as well as the microstresses was found in the cold rolled samples subjected to heat treatment. Such relaxation occurs at the beginning of recovery, when any changes of microstructure cannot be detected using other experimental techniques. Stress evolution in the annealed steel samples was correlated with the progress of recovery process, which significantly depends on the value of stacking fault energy

Texture-Based Optimization of Crystal Plasticity Parameters: Application to Zinc and Its Alloy

Evolutionary algorithms have become an extensively used tool for identification of crystalplasticity parameters of hexagonal close packed metals and alloys. However, the fitnessfunctions were usually built using the experimentally measured stress–strain curves. Here, thefitness function is built by means of numerical comparison of the simulated and experimentaltextures. Namely, the normalized texture difference index is minimized. The evolutionaryalgorithm with the newly developed fitness function is tested by performing crystal plasticityparameter optimization for both pure zinc and zinc-magnesium alloy. These materials arepromising candidates for bioabsorbable implants due to good biocompatibility and optimalcorrosion rate. Although their mechanical properties in the as-cast state do not fulfill therequirements, they can be increased by means of hydrostatic extrusion. The developed modelingapproach enabled acquisition of the crystal plasticity parameters and analysis of the activedeformation mechanisms in zinc and zinc-magnesium alloy subjected to hydrostatic extrusion. Itwas shown that although slip systems are the main deformation carrier, compressive twinningplays an important role in texture evolution. However, the texture is also partially affected bydynamic recrystallization which is not considered within the developed framework