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

The mechanical properties of beta titanium alloys can be improved by precipitating the alpha phase in the beta-phase matrix and controlling the microstructure via appropriate aging treatments. In this study, heat treatment in the range of 400 to 550 degrees 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 alpha phase in the beta matrix. The precipitation driving force at 400 degrees C is low because of the slow diffusion rate, and therefore the improvements in the hardness and strength are small. At temperatures above 500 degrees C, phase separation occurs rapidly (beta -> beta + beta '), and the beta ' phase acts as a nucleation site for the secondary alpha phase. The phase transformation from the beta ' to the secondary alpha phase is promoted at 500 degrees C, resulting in the highest hardness (406.3 HV) and compressive yield strength (1433.8 MPa) at 24 h. At 550 degrees C, the secondary alpha 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.