Room temperature mechanical behaviour of cast in-situ TiAl matrix composite reinforced with carbide particles

Abstract

Room temperature mechanical behaviour of cast in-situ TiAl matrix composite reinforced with carbide particles was studied using hardness, tensile, compression, and three-point bending tests. The initial microstructure of the in-situ composite consists of TiAl matrix reinforced with coarse primary (HTi2AlC and TiC) and fine secondary (HTi2AlC and PTi3AlC) particles. The in-situ composite shows plastic deformation of TiAl matrix and limited plastic deformation of primary Ti2AlC particles during the compression test. The compressive work hardening behaviour is affected by the plastic deformation of the matrix, plastic deformation of primary carbide particles and formation of cracks. The local equivalent strains in the compression specimens are numerically calculated using finite element analysis (FEA) and related to the size of primary carbide particles. The in-situ composite specimens show brittle fracture behaviour during tensile and three-point bending tests. The numerically calculated critical stress leading to a crack initiation in the notch tip region of three-point bending specimen is comparable with the ultimate tensile strength. The brittle fracture of the in-situ composite includes crack deviation, zone shielding by microcrack toughening, carbide fragmentation, delamination on the matrix-carbide interfaces and pull-out of the carbide particles from the matrix.