A New Ternary Al-Ti-N Alloy Prepared by Reaction Sintering (V)

Formation of L1₂-Al₃ Ti Phase by the Addition of Cu

Abstract

The mechanism of the crystal structure transformation of Al₃Ti from DO₂₂ to a high symmetry Ll₂ by the addition of Cu was investigated using the DV-X α molecular orbital calculation. The calculation suggested that Ti atoms were able to locate at the 2nd neighbor sites of Ti atoms by substitution of Cu atoms for a part of Al atoms, namely, the 1st neighbor sites of Ti atoms. This atomic configuration is the mechanism for the stabilization of the Ll₂ crystal structure of Al₃Ti by the addition of Cu. Therefore, Cu was added to improve the ductility of a new reaction sintered Al-Ti-N alloy which consists of Al₃Ti and AlN phases. The added Cu transformed the crystal structure of Al₃Ti from DO₂₂ to a high symmetry Ll₂, and as a result, decreased the hardness of the alloy.