Heterogeneous Microstructure Enhanced Comprehensive Mechanical Properties in Titanium Alloys

The design of materials with good strength and ductility is still a challenge to current materials science. Here, we propose a two-step aging method to balance the comprehensive mechanical properties in near-β titanium alloys by designing multiscale α precipitate distribution. Phase-field calculations in Ti-V binary alloys are used to screen the heat treatment process by changing the microstructure. Our calculations show that the coarse α precipitates nucleate near grain boundaries at 650°C first and grow and nucleate to the grain interior with the increase of aging time. The fine α precipitates nucleate and grow in grain after subsequent aging at 550°C, and the whole system shows four different microstructures in grain by changing the aging time, i.e., homogeneous fine α precipitates, coarse α precipitates surrounded by fine α precipitates, fine α precipitates surrounded by coarse α precipitates, and homogeneous coarse α precipitates. Based on this strategy, we design a hierarchical α precipitate microstructure in Ti55531 alloy by two-step aging at 650°C/60 min plus 550°C/180 min, which shows enhanced mechanical properties with the ultimate tensile strength of 1.38 GPa and total elongation of 6%. Our work sheds light on the design of novel Ti alloys with comprehensive strength and ductility properties by heterogeneous microstructure.