Anisotropy of microstructure and tensile properties of Ti–48Al–2Cr–2Nb fabricated by electron beam melting

Abstract

The anisotropy of Ti–48Al–2Cr–2Nb (TiAl-4822) fabricated by electron beam melting (EBM) with 3 different microstructures, namely hot isostatic pressing (HIP), duplex (DP) and fully lamellar (FL) microstructure was investigated. Results show that the HIP material exhibits microstructure with alternating layers of coarse and fine grains. The α2 phase is more concentrated in the layer of fine grains and exhibits a strong texture with (0001) nearly perpendicular to the building direction, which further leads to the preferential orientation of lamellae. Non-uniform distribution of Al results in the selective formation of lamellar colonies in DP microstructure. The variation of critical resolved shear stress (CRSS) for slip activation is believed to cause the anomalous temperature dependence of yield strength at intermediate temperature. For all 3 microstructures, the ductility in Z direction is lower compared with XY direction, which is attributed to the difference in crack initiation mode and preferential orientation of lamellae.