Microstructures Formation and Strengthening Mechanism of Ultra-Rapidly Solidified Powder Metallurgy Ti-Si Alloys via Hot Rolling Process

Ti-Si alloys with fin α-Ti grains and Si solutes were fabricated by laser powder bed fusion (LPBF) process and subjected to hot rolling to form ultrafine grains at the submicron level from fine acicular grain structures. The relationship between the microstructures and mechanical properties of each Ti-Si alloy sample was investigated, and the quantitative strengthening analysis was carried out to find the main strengthening factor by using the theoretical models of grain boundary strengthening, solid solution strengthening and precipitation hardening mechanism. Grain refinement was observed with increasing Si content, which was due to the solute drag effect of Si solute atoms as well as Zener pinning by the precipitation of ultrafine Ti3Si particles of about 50 nm in the Ti-0.7%Si material. The 0.2% YS values were 1.5 to 2.2 times higher than those of Ti-0%Si specimens under sufficient ductility of 17–20% elongation. A quantitative analysis using each strengthening model revealed that grain boundary strengthening by grains refinement was the main strengthening factor for all specimens of LPBF Ti-Si alloys.