Cracking Cause Analysis of GH4099 Alloy Forging

GH4099 alloy forgings were produced by upsetting, punching, machining inner hole and reaming hole. After rough machining, four linear defects of about 10 mm length were found on the outer surface of a forging. Microstructure and chemical composition analysis near the cracks and fracture surface analysis were carried out by optical microscopy (OM) and scanning electron microscopy (SEM) to find out the cracking cause. The results show that the cracking of the GH4099 alloy forging was mainly caused by the segregation of Al element at grain boundaries, leading to hard and harmful β-NiAl phase, which weakened the grain boundaries. The cracks propagated along the grain boundaries. The alloy near the cracks were combined with oxygen to form hard oxide particles at high temperature, leading to fine secondary cracks in the deformation process.