Effects of Ru content on phase transformation and compression property of cast TiAl alloys

Abstract

Ruthenium (Ru) is a promising element to heighten the comprehensive mechanical properties of TiAl alloys. In the present study, the phase transformation during the cooling of Ti-47Al-2Cr-2Nb-xRu (x=0, 0.1, 0.5, 1.0, at.%) alloys was investigated. The results show that Ru tends to segregate in the interdendritic region during solidification, and therefore, refines the as-cast microstructure of the alloys. As a β-stabilizer, Ru does not induce a novel solidification reaction but maintains the peritectic reaction of L+β→α. An excessive Ru content would cause the formation of (γ+τ1+B2) and (α+γ+τ1+B2) phase regions below 1,250 °C. The precipitation of τ1-containing mixture is attributed to the Ru-segregation, which inhibits the reaction of α→γ and facilitates the formation of B2 phase. The discontinuous coarsening of γ phase and block τ1 phase formed alternately in a manner of analogous eutectoid decomposition within B2 phase. In addition, the effect of Ru content on compression property of the alloys was studied. The yield strength increases up to 427 MPa at 800 °C with the addition of 1.0at.% Ru, which is mainly due to the solution strengthening effect of Ru.