Research on persistent fracture mechanism of laser forming repaired GH4169 superalloy

The microstructure and persistent properties of the wrought samples and the laser forming repaired (LFR) samples of GH4149 alloy are investigated. The results show that the microstructure of wrought substrate is characteristic of equiaxed grains, and there are grainess and short rod like δ phase distributes in and along boundaries of the grains, which can effectively prevent dislocation motion and reduce the rate of crack propagation. Compared with as-deposited samples, the microstructure of laser repaired GH4169 alloy with double aged (DA) treatment changes little and still is characteristic of columnardendrites which grow epitaxially along the deposition direction of the substrate. There are still masses of Laves phase precipitations between dendrites. Laves phase is a brittle phase which provides a favorable position for the initialization and expansion of the cracks. The fracture mechanism of wrought sample suffering from high temperature is due to microvoid coalescence fracture, and the MC, δ phase are nucleation centers of micropores which form dimples with different shapes and sizes after fracture. The break of the repaired samples suffering from high temperature lood occurs in the repaired zone. The interdendritic Laves phase, MC are nucleation centers of the dimples, thus leaving the dimples of recognizing interdendritic region as dimple center and dendrite dry region as torn edges.