Effect of a B2/gamma structure on the tensile properties of the cast gamma titanium aluminide Ti48Al2Cr2Nb

Abstract

The gamma titanium aluminides under consideration for engineering applications are in fact multi-phase alloys consisting predominantly of gamma (ordered, face-centered tetragonal) and may contain minor amounts of the ordered hexagonal phase, alpha-two B2 (ordered bcc) or TiB[sub 2]. It is generally believed that the best balance of properties is achieved through a duplex microstructure consisting of equiaxed gamma grains and lamellar colonies of alpha-two and gamma laths. However, the reason for the exceptional performance of the duplex microstructure is as yet inconclusive. The present study is limited to the cast form of alloy Ti-48Al-2Cr-2Nb (at.%), developed by Huang. The microstructure of the nominal Ti-48Al-2Cr-2Nb (48-2-2) consists of alpha-two plus gamma with small amounts of B2. The duplex alpha-two/gamma structure is required to obtain the best balance of properties. However, an investigation of the effects of interstitial content on the tensile properties of 48-2-2 revealed that a B2/gamma structure could be stabilized at room temperature by lowering the oxygen content of the alloy.