Effects of scandium and silicon addition on the microstructure and mechanical properties of Ti-6Al-4V alloy

Abstract

Titanium alloys are excellent candidates for structural components submitted to high temperature owing to their high strength to weight ratio, good corrosion resistance and metallurgical stability. Due to the complex service conditions of spacecraft, the creep property of titanium alloy has been recognized. The microstructural evolution, mechanical properties of Ti-6Al-4V-xSi-ySc alloys have been investigated. Alloys were prepared by three times vacuum arc remelting followed forging, rolling and heat treatment at 950°C/0.5h/AC and 510°C/5h/AC. Then specimens were subjected to uniaxial tensile and creep test. The strengthening and creep resistance mechanism of the alloys were analyzed. The results shown that the grain sizes of alloys were refined significantly by Sc and Si addition. The Si and Sc plays a role in grain refinement and solid solution strengthening. At the same time, the alloy matrix was purified due to the formation of Sc2O3 particles. The Si and Sc addition improve the creep resistance comparing the base alloy. This can be attributed to the strengthening of solid solution of Si and the silicide also have the inhibiting effect on the dislocation movement during creep. Si promote the diffusion of V and suppress the formation of α2 phase. Sc in titanium alloy has three forms, some of which are solid-dissolved, some of which form Sc2O3, and some of which form horseshoe-shaped Al3Sc. The formation of Al3Sc particles is helpful to improve the creep properties of titanium alloy. Sc can inhibit the precipitation of silicide and promote the formation of α2 phase, which are helpful to improve the creep resistance of titanium alloy.