The role of the ω phase on the microstructure evolution of precipitation and mechanical property in Ti–3Al–5Mo–4Cr–2Zr–1Fe

Abstract

This study investigates the effect of the ω phase on the microstructure evolution and mechanical properties of the Ti–3Al–5Mo–4Cr–2Zr–1Fe (Ti-35421) near β titanium alloy. The study employed a solution treatment at 850 °C followed by two aging treatments, namely, Double Aging (DA) and Isothermal Annealing (IA). The results show that the DA alloy had finer precipitation and fewer Precipitation-Free Zones (PFZs) than the IA alloy. While the Ultimate Tensile Strength (UTS) of the DA alloy was higher (1376 MPa) than that of the IA alloy (1272 MPa), its plasticity was lower. On the other hand, the IA alloy exhibited a better balance between UTS (1272 MPa) and ductility (8.12%). The nucleation mechanism of DA was attributed to the presence of the α stable element Al, which diffused in the microstructure and aggregated in the ω phase, creating favorable nucleation sites for the precipitation of the secondary α phase during low temperature aging. As a result, the PFZs decreased, and the dispersion distribution strengthened the β matrix structure. Conversely, the high aging temperature during IA made it difficult to form the ω phase, resulting in coarser precipitation and increased PFZs as the temperature increased. This paper revealed the influence of ω on the relative precipitation during the phase transition, the microstructure and properties of the Ti–3Al–5Mo–4Cr–2Zr–1Fe, providing valuable insights for optimizing its heat treatment process.

Keywords

• Near β titanium alloy
• ω phase
• Phase transformation
• Double aging
• Mechanical properties