The Effect of Heat Treatment Process on Microstructure and Mechanical Property of Large-sized TC18 Titanium Alloy Bar

摘要

The effect of three temperature stages of two step heat treatment process on microstructure and mechanical property of near-β Ti-5Al-5Mo-5V-lCr-lFe (TC18) titanium alloy was investigated systematically. The experiment results showed that with the increasing of low-stage temperature, the volume fraction and shape of primary α phase in alloy matrix almost were unchangeable, while the quantity of secondary a phase reduced and its shape was changed from cross acicular to coarse parallel strip. At the same time, the room temperature tensile strength decreased, while the plasticity, impact toughness and fracture toughness increased With the increasing of middlestage temperature, the volume fraction and size of primary α phase decreased, while the volume fraction of secondary α phase obviously increased The tensile strength obviously increased, while the plasticity, impact toughness and fracture toughness decreased slightly. With the increasing of high-stage temperature, the volume fraction of primary α phase decreased and the shape of α phase was changed from equiaxial to polygonal, while the volume fraction of secondary α phase slightly increased The tensile strength and fracture toughness of alloy slightly increased while the plasticity and impact toughness almost kept unchangeable. The optimal heat treatment processing was 840°C for 2 hours and furnace coolaJ to 750°C for 2 hours and air cooled, then annealed at 620°C for 6 hours.