Microstructure and strengthening mechanism of ultrastrong and ductile Ti-xSn alloy processed by powder metallurgy

Dynamic recrystallization, grain refinement and strengthening mechanism were investigated in the ultrastrong and ductile α Ti-xSn alloy processed by spark plasma sintering (SPS) and hot extrusion. Compared with pure Ti, the yielding and ultimate tensile strength of Ti-xSn alloy were greatly increased by 140% (993.88 MPa) and 92% (1086.76 MPa). The alloyed solutes dragged nucleation and grains growth of the recrystallization process. The bimodal microstructure was occurred and the average grain size was refined with increasing the alloyed contents. The fraction of deformed strips was increased but the fraction of the recrystallized grains was decreased. Brittle Ti3Sn compound (∼100 μm) was formed in the high Sn content samples. The quantitative analysis of the relationship between the fraction of recrystallized grain, low angle grain boundary fraction, activation energy for grain growth and solid solute atoms indicated either a linear or parabolic relationship. Quantitative analysis of strengthening effects pointed out that solid-solution strengthening effect, strain hardening and boundary strengthening were the main contributors to the great strength enhancement. The toughening mechanism was discussed by the compatible uniform strain and postponed necking. Rapid cracks initiation and propagation after uniform strain led to gradual ductility sacrifice. The present work may provide a new understanding on the relationship among the mechanical properties, microstructure and processing of Ti alloy.