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-beta titanium alloys by designing multiscale alpha 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 alpha precipitates nucleate near grain boundaries at 650 degrees C first and grow and nucleate to the grain interior with the increase of aging time. The fine alpha precipitates nucleate and grow in grain after subsequent aging at 550 degrees C, and the whole system shows four different microstructures in grain by changing the aging time, i.e., homogeneous fine alpha precipitates, coarse alpha precipitates surrounded by fine alpha precipitates, fine alpha precipitates surrounded by coarse alpha precipitates, and homogeneous coarse alpha precipitates. Based on this strategy, we design a hierarchical alpha precipitate microstructure in Ti55531 alloy by two-step aging at 650 degrees C/60 min plus 550 degrees 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.

Automated summary

The study proposes a method to design titanium alloys with comprehensive mechanical properties by balancing the distribution of multiscale alpha precipitates. By utilizing a two-step aging approach, a Ti55531 alloy is successfully designed with enhanced mechanical properties, showing an ultimate tensile strength of 1.38 GPa and total elongation of 6%.