Ultrafine-grained twinning-induced plasticity steel prepared by mechanical alloying and spark plasma sintering

A twinning-induced plasticity (TWIP) steel was prepared by mechanical alloying and spark plasma sintering (SPS), and its microstructure and mechanical behavior were examined. The ultrahigh microhardness and considerable tensile strength of the sintered bulk sample were mainly attributed to grain-size strengthening and particle strengthening by numerous Mn-rich particles dispersed in the matrix. Micropores coupled with large internal inclusions easily produced cracks in the bulk sample under uniaxial tensile stress, resulting in poor ductility with rapid intergranular brittle fracture. The ductility of the material showed significant improvement with the elongation increased from 4% to 13% after annealing the bulk sample at 850 °C for 1 h. The size of the inclusions in the annealed sample dramatically reduced and several small dimples with high densities and depths were formed, presenting a mixed fracture mode in which intergranular fracture was the dominant mechanism, whereas transgranular fracture was the supplementary mechanism.