Effect of isothermal forging strain rate on microstructures and mechanical properties of BT25y titanium alloy

In order to confirm the optimal isothermal forging process for BT25y alloy, the effect of strain rate on the microstructure and mechanical properties was studied. Quantitative relationships between microstructure characteristics and mechanical properties were obtained. Results showed that as the strain rate decreased, the lamellar α coarsened, the β grain boundary connected by small recrystallized grains disappeared, and the microstructure became much more uniform. Tensile strength for the three processes all maintained at a high level, but the elongation tended to first increase and then decrease with dropping strain rate. The tensile fracture changed from quasi-cleavage fracture to complete ductile fracture, and finally transformed into a mixture of ductile fracture and brittle fracture at lower strain rate. Fracture toughness improved with increased strain rate, but the thermal stability deteriorated gradually.