The effect of tensile stress on oxidation behavior of nickel-base single crystal superalloy

The oxidation behavior of a nickel-based single crystal superalloy at two temperatures (1000 °C/1050 °C) and different stress levels (40 / 60 / 120 MPa) was studied through experimental design. At 1000 °C and 1050 °C, the oxide structures are mainly three layers: the outer layer (Ni, Co) O, the middle layer of complex spinel phases rich in Ni, Co, Cr, Ta and W, the inner layer of α-Al₂O₃. Under the oxide layer forms a γ′ phase disappearing layer due to the selective oxidation of Al. The dynamics of its thickness variation can be fitted by parabola law under different temperatures and stresses. After 400 h of oxidation, the alloy undergoes significant internal nitridation at higher stresses. The oxidation rate increased significantly with the increase of the tensile stress level. The morphologies of the oxide are changed by the applied tensile stress. In the early stage, the tensile stress offsets the self-generated compressive stress in the oxide film, and generates tensile stress in the oxide film, which increases the ion diffusion rate and oxygen vacancy concentration in the oxide layer, thereby improving the oxidation rate of the alloy. In the later stage, the thickness of the oxide layer increases, the interface adhesion decreases, and the effective cross-sectional area of the matrix continues to shrink. The greater tensile stress in the oxide film promotes itself peel off.