In situ investigation of the tensile deformation of laser welded Ti2AlNb joints

Abstract

The tensile deformation behavior of laser welded Ti2AlNb joints was investigated using in situ analysis methods. The fracture mode of the single-B2-phase fusion zone was quasi-cleavage at room temperature and intergranular at 650°C, while that of base metal was microvoid coalescence at both room temperature and 650°C. Tensile deformation at room temperature was observed using in situ SEM tensile testing. In base metal, microcracks nucleated and propagated mainly within the O phase or along O/B2 phase boundaries. While both the cross- and multi-slips were found in the single-B2-phase fusion zone, a confocal laser scanning microscopy was used to observe the crack initiation and propagation process in situ at 650°C. Cracks mainly formed along the B2/O phase boundaries in base metal, along the fragile grain boundaries of B2 phase in the fusion zone. The thermal simulation experiment and following TEM analysis indicated that the precipitation of continuous O-phase films along the B2 grain boundaries resulted in the high temperature brittleness of laser welded Ti2AlNb joints.