High tensile ductility and strength in the Ti-42Al-6V-1Cr alloy

Abstract

With the aim of developing a new TiAl alloy with excellent tensile properties, a novel Ti-42Al-6V-1Cr (at. %) alloy was manufactured through casting and hot extrusion in the (α + β) phase region. The microstructure and tensile properties of the as-extruded alloy were investigated. The as-extruded microstructure consisted of fine lamellar colonies and mixtures of γ and B2 grains around the lamellar colony boundaries. The lamellar colony size and spacing of the as-cast alloy were significantly refined by hot extrusion. At room temperature, the tensile strength of the as-extruded alloy was 1113 MPa and the tensile ductility was 2.4%, demonstrating a good combination of high strength and ductility. The as-extruded alloy maintained high tensile strength over 860 MPa up to 800 °C. It was considered that the high lamellar fraction, fine lamellar colony size and fine lamellar spacing in the as-extruded alloy may be responsible for the high strength and improved ductility. A large number of dislocations were observed in the B2 grains. The Burgers vectors of dislocations in B2 grains were determined using the g·b analysis and <110> type dislocations were observed in specimens that had been deformed at room temperature. The {111}<110> slip systems satisfy the von Mises criterion of five independent slip systems that are necessary for a polycrystal to undergo a general homogeneous strain. It is noteworthy that the dislocation emission in the B2 grain occurs at the intersection between the γ twins and the boundary of the γ and B2 grains. This allowed the stress concentration at grain boundaries to be released. The B2 phase is shown to be beneficial to the room-temperature ductility of the present alloy.