Effect of Aging Treatment on the Microstructure and Mechanical Properties of Ti-3Al-8V-6Cr-4Mo-4Zr Alloy

Abstract

The mechanical properties of beta titanium alloys can be improved by precipitating the α phase in the β-phase matrix and controlling the microstructure via appropriate aging treatments. In this study, heat treatment in the range of 400 to 550 °C is performed to optimize the aging of Ti-3Al-8V-6Cr-4Mo-4Zr alloys. The increase in the aging temperature and holding time increases the hardness and compressive yield strength owing to the precipitation of the secondary α phase in the β matrix. The precipitation driving force at 400 °C is low because of the slow diffusion rate, and therefore the improvements in the hardness and strength are small. At temperatures above 500 °C, phase separation occurs rapidly (β → β + β′), and the β′ phase acts as a nucleation site for the secondary α phase. The phase transformation from the β′ to the secondary α phase is promoted at 500 °C, resulting in the highest hardness (406.3 HV) and compressive yield strength (1433.8 MPa) at 24 h. At 550 °C, the secondary α phase grows and the hardness and compressive yield strength degrade. These results can be effectively applied to manufacture springs with excellent formability and mechanical properties.

Keywords

• metastable β-titanium alloy
• aging treatment
• precipitation
• secondary α phase