Tensile behavior of single-crystal superalloy with different structured cooling holes

Film cooling hole structures significantly influence the mechanical behavior of a single crystal turbine blade. This study investigates the tensile behavior of nickel-based single crystal plate specimens with three different structure holes, including straight, inclined, and diffusive holes, by in-situ tensile tests and crystal plasticity simulation. The results show the cooling holes play a strengthening effect on the single crystal superalloy, and the tensile strengths of the single crystal specimen with holes were increased. At the same time, fracture strains were decreased compared to those without hole. In addition, the cooling hole structure causes the difference in stress concentration and subsequent local plastic deformation around a hole, which further affects the tensile strength, fracture strain, crack initiation and propagation of the single crystal specimens. The asymmetric diffusive cooling hole induces larger resolved shear stresses and localized plastic deformation near the hole, which results in lower tensile strength and decreased fracture strain. Surface microcracks are observed along the acute angle zone for the inclined and diffusive holes, while at an angle of 65° to the loading direction for the straight hole. These orientations are consistent with the maximum accumulated plastic slip in the crystal plasticity simulations. And all the surface microcracks propagated along the direction of the dominant slip system. In addition, the non-uniform distribution of accumulated plastic slips along the hole depth causes the macrocrack initiation on the specimen surface, which propagates along <110> direction, and leads to final failure on {111} plane.