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

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 (alpha vertical bar beta) 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 gamma 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 degrees 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 gamma twins and the boundary of the gamma 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. (C) 2016 Elsevier B.V. All rights reserved.