Crack generation and propagation mechanism of Mo[sbnd]14Re alloy laser welding

Abstract

This paper investigates the mechanism of crack generation and propagation in laser-welded joints of Mo14Re alloy plates. The study utilized optical microscopy (OM) and scanning electron microscopy (SEM) to examine the microstructure and morphology of the crack area in the Mo14Re laser-welded joint. Additionally, energy dispersive spectroscopy (EDS) was employed to characterize the elements at the crack defect, while electron backscatter diffraction (EBSD) was utilized to analyze the grain boundary and crystal orientation at the crack defect.The analysis of crack formation and propagation considered various factors, including grain boundary segregation, characteristics of grain boundaries and crystal orientation, and the Schmidt factor. The findings revealed that cracks formed in the weld area exhibited distinct characteristics of brittle fracture along the grain. Notably, these cracks displayed evident carbon and oxygen segregation attributed to the presence of a low melting point eutectic liquid film. The segregation, along with high-temperature compounds on the fracture surface, emerged as the primary factors contributing to crack formation.In the proximity of the crack, there exists a concentration of strain, inducing plastic deformation and thereby facilitating crack initiation. Cracks exhibit a tendency to originate along large-angle grain boundaries and deflect along these boundaries. Owing to the difference in atomic slip characteristics on both sides of the crack, the direction of crack propagation is more inclined to deflect towards grains with a smaller Schmidt factor.