Microstructure and Properties of γ-TiAl/Ti₂AlC Composites Produced by Reactive Processing from Elemental Powders

Abstract

The γ-TiAI/Ti₂AlC composites with and without impurities, Ni, Cl and P, were prepared by combustion reaction from the elemental powders and homogenized after arc melting. The resulting composition is about 18 vol% Ti₂AlC in the matrix of TiAl with a lamellar structure of Ti₃Al (α₂). In the homogenized specimens, the α₂ phase transforms to the precipitated Ti₂A1C particles in the place of solutionizing lamellar structure. The composite material has a high strength both at ambient and elevated temperatures; about 800 and 400 MPa, respectively, with an ambient temperature ductility of 0.7% at bending test. The fracture toughness test also proves the composite homogenized is better than the as cast and value is 17.8 MPam^1/2. The crack propagation in the homogenized composite is zigzag mode and the precipitated particles are main obstacles for the crack propagation. The composite with impurities shows a marginal improvement in the oxidation resistance over the composites without impurities.