Microstructure evolution and mechanical property of a new multi-component β titanium alloy with ultrahigh strength above 1350 MPa

Abstract

The microstructure evolution and precipitation behavior of a multi-component β titanium alloy (namely TB17) were investigated through various characterization methods. The results show that with the increase of the solution temperature, the coarse lamellar α phase (αl) and fine secondary α phase (αs) existed in the original as-forged TB17 alloy decrease. At the same time, the molybdenum equivalent value of the β matrix also decreases gradually, leading to the increase of αs phase during the following aging process. For the aged samples, the micro-strain accumulated in the β matrix resulted from phase transformation strain exhibits an increasing trend as the solution treatment temperature rises, highly depending on the volume fraction of αs phase. When the alloy is subjected to a solution treatment at temperature of 805 °C plus aging, it can achieve a good combination of high strength of 1375 MPa and considerable ductility due to mixed microstructure of suitable amount of micro-scale αl and nano-scale αs precipitates. The strength is further improved by increasing the solution temperature (from α+β to β field), which is attributed to higher volume fraction of fine αs precipitates formed during aging that can effectively hinder dislocation slip and induce micro-strain. Morphological features of the fracture surfaces are also discussed against the different microstructural morphologies, revealing the fracture mechanism of TB17 alloy under different heat treatment conditions. The current work could contribute to a better understanding of phase transformation behavior and strengthening mechanism in TB17 alloy.