Production and microstructural investigation of TRIP matrix composites reinforced by nano-sized reinforcement particles via mechanical alloying method

In this thesis, TRIP matrix composites produced via mechanically alloying which is a powder metallurgy method and cold pressing process; and investigated the transformations of matrix and reinforcement phases, deformation mechanisms. As a matrix phase 304L stainless steel which have lower Ni content have been chosed as well as the Y2O3 stabilised ZrO2 nano particles. The samples of TRIP matrix composites were subjected to plastic deformation by mechanical alloys and pressing processes and this ratio was further increased by compression test. In matrix, the austenite phase transforms to αʹ martensite as a result of stress during plastic deformation and the strain caused by plastic deformation induce the transformation of twinning to αʹ martensite. In this thesis, high compressive strength of TRIP matrix composites was obtained by strengthening and deformation mechanisms. Deformation mechanisms provide ductility the TRIP matrix composite samples by volume expansion cause to elongation. In microstructural images of the samples shows that the TRIP matrix composite samples have αʹ martensite, ε martensite, twinning, deformation (shear) bands, stacking fault tetrahedron and these microstructures occur due to transformations caused by plastic deformation. αʹ martensites provide ductility by volume expansion cause to elongation and strength by deformation hardening. TRIP matrix composites that are produced have higher hardness but lower density as the weight fraction of reinforcement increased. Increased weight fraction of reinforcement provide % strain at the same stress. The fracture images of the samples shows that the TRIP matrix composite samples have dimples, so which can be associated to ductility of the composite. In this thesis, TRIP matrix composite have higher strength and ductiliy by deformation and strengthening mechanisms; also the addition of nano sized reinforcement particles contributed to higher strength by strengthening mechanisms that occured only nanoscale materials.