Improvement mechanism of fretting fatigue lifetime of turbine dovetail tenon by shot peening combined with CuNiIn coating at 500 °C

In this study, turbine dovetail tenon specimens made of iron-based superalloy were composite treated by shot peening and CuNiIn coating, and the fretting fatigue performance at room temperature and 500 °C high temperature was investigated. The surface integrity of the composite-treated dovetail specimens and the wear, fracture morphology, and microstructure after the fretting fatigue tests were characterized. The results showed that the composite treatment of shot peening and CuNiIn coating made the surface roughness of iron-based superalloy from 0.405 μm to 11.279 μm, 46 % reduction in surface hardness and the residual compressive stress layer of about 100 μm was introduced. Compared with the as-received (AS) specimens, the fretting fatigue lifetime of shot peening and CuNiIn coating composite treatment (SC) specimens was increased by 437 % at room temperature, and the fretting fatigue lifetime of SC specimens at high temperature was reduced by 54 % compared with that at room temperature. The cracks in SC specimens were still initiated by multiple fatigue sources, but the number of crack sources decreased and the position of crack sources moved down. At room temperature, CuNiIn coating first underwent shear grinding and then entered delamination wear, while at high temperature, the presence of a large number of coating oxides would lead to serious abrasive wear of CuNiIn coating. Fretting fatigue resulted in obvious orientation differences in the contact region, and the formation and propagation of cracks were related to the plastic deformation and dislocation accumulation of the contact region. The good plasticity of CuNiIn coating is an important reason why it can improve the fretting fatigue performance. The surface hardening caused by shot peening and the introduction of residual compressive stress layer can effectively inhibit crack initiation and propagation. The composite treatment of shot peening and CuNiIn coating can effectively improve the fretting fatigue performance of the dovetail structure of superalloy.