Mechanism of reheat cracking in electron beam welded Ti2AlNb alloys

Abstract

Abstract In order to clarify the characteristics and formation mechanism of the reheat cracking in Ti2AlNb weldments, a series of heat treatment conditions were performed to the circular joints welded by electron beam, and then the macrostructures and microstructures were investigated using optical microscopy, scanning electron microscopy, X-ray diffractometry, and transmission electron microscopy. The results show that the reheat cracking occurs primarily along the grain boundaries in the weld when the Ti2AlNb circular welded joints are heated up to about 700 °C. During the heat treatment, an almost complete transformation of B2→O happens while the temperature goes up through the O single-phase region. Then, O→B2+O phase transformation occurs primarily along the grain boundaries as the weld metal continues to heat up to the B2+O dual-phase region. Under the high tension stress consisting of welding residual stress and phase transformation stress, reheat cracking occurs at the interface between the B2+O dual-phase layer and the O-phase matrix.