Oxidation behavior of recast layer of air-film hole machined by EDM technology of Ni-based single crystal blade and its effect on creep strength

High temperature oxidation behavior of recast layer of film cooling hole (made by EDM) of Ni-based single crystal turbine blade was investigated by virtue of XRD, SEM, TEM and EDS. The element redistribution results in the loss of Al element in the recast layer, which inhibits the formation of protective oxide and accelerates the oxidation rate obviously. The concentration gradient of solute elements is large in recast layer. The diffusion path and distance of solute elements at different locations are not consistent. When the solute elements distribution is uneven, they can react with O at different speeds at the same time. The oxidation heat affected layer below the recast layer is significantly thicker than that of the substrate, whose strength is also lower than substrate. The creep behaviors were investigated in particular after oxidation for 0 h, 200 h and 800 h. The oxidation of recast layer significantly promotes creep fracture.