Effect of aeration on superficial residual stress level of carburised and quenched gears treated by water cavitation peening

Cavitation impacts, which are generally considered as the dominant factor affecting cavitation erosion of hydraulic machinery, can also be applied to introduce compressive residual stress in the surface layer of mechanical components in a similar way to traditional shot peening. By using a high speed submerged water jet instrument, in which high pressure water is passed through a jet nozzle to the specimen, a uniform cloud of large bubbles can be generated. Bubble collapse on the surface of the specimen will produce an impact effect very similar to shot peening. Therefore, the design of the jet nozzle is very important to obtain the optimum pressure of bubble collapse. In the present study, a new nozzle design with air addition was used, the effect of the air addition flux on the impulse pressure of bubble collapse was investigated, and a comparative study of the residual stress in a carburising quenched gear treated by water cavitation peening with and without air addition was carried out. The results show that after the new nozzle with air addition is adopted, the saturation time of peening is reduced from 30 to 10 min and a superficial compressive residual stress increase of about 30–40% is obtained. The increase in pressure of bubble collapse caused by air addition is responsible for such improvement.