Tensile properties of spark plasma sintered AISI 316L stainless steel with unimodal and bimodal grain size distributions

Powder metallurgy associated to spark plasma sintering was used to elaborate near full-dense samples of 316L austenitic stainless steel with unimodal or bimodal grain size distributions. To this aim, two different precursor powders were employed: a ball-milled one giving rise to ultrafine grains and a coarse one, as-received, for grains with conventional size. Sintered specimens were characterized in mechanical tension and their microstructure was revealed using transmission and scanning electron microscopy. Unimodal ultrafine grained samples show a large yield stress and a low ductility with a breakdown in the Hall-Petch relationship. For bimodal samples, a compromise between yield stress and ductility can be found. These features are then discussed in terms of strain mechanisms, grain size distribution and backstress. It is shown in particular that coarse grains contribute to enhance the ductility of the ultrafine grains matrix by modifying both the strain hardening mechanisms and the stress concentration areas.