Effect of preparation temperature on interfacial reactions and mechanical properties of Nb_f/TiAl composite

TiAl alloys with low density and outstanding high-temperature mechanical property become potential high temperature structural materials, but the inherent brittleness limits their further utilization. In this paper, 10 vol% of tough Nb fiber was introduced into TiAl alloy by powder metallurgy to improve the room temperature properties. Concurrently, the effect of preparation temperature on interfacial reaction between fiber and matrix was explored, as well as mechanical properties of the composites were investigated systematically. The results show that, a Nb_f/TiAl composite without obvious holes and cracks can be synthesized at hot processing conduction of 1150 °C/35 MPa/2 h, whose tensile and bending strength were increased by 36.4% and 24.1%, respectively, compared to those of the monolithic TiAl alloy. The improvement can be attributed to plastic deformation of Nb fiber and weak interfacial debonding resulted from the formation of brittle σ interfacial phase. In addition, more complex interfacial reactions between fiber and matrix occur in the composite prepared at 1200 °C. The phase transition process at the side of TiAl matrix can be described as: γ+Nb → γ/α₂+Nb → B2+α₂ → B2(γ_n)+α₂, and that at the side of Nb fiber is as follows: Nb + Al → Nb + Nbss → Nb + Nbss+σ(α₂) →Nb + Nbss + σ(α₂+O). The thicker brittle reaction layer results in serious micro-cracks at interface and even in the matrix, which significantly reduces macromechanical properties of the composite prepared at 1200 °C dramatically.