Surface micro-morphology and residual stress formation mechanisms of near-net-shaped blade produced by low-plasticity ultrasonic rolling strengthening process

Abstract

Low surface integrity of near-net–shaped (NNS) blades is the primary problem associated with aero engine performance improvements. This paper proposes a low-plasticity ultrasonic rolling strengthening process (URSP) to improve the surface micro-morphology and residual stress of NNS blades. The surface micro-morphology and residual stress formation mechanisms produced by the low-plasticity URSP were introduced first. Then, the influences of the low-plasticity URSP parameters on the surface micro-morphology and residual stress were analyzed. Furthermore, the feasibility of low-plasticity URSP was analyzed through comparative experiments. Finally, the mechanism of low-plasticity URSP was further demonstrated from two aspects of surface micro-morphology and the residual stress. The results showed that increases in the extrusion depth improved the blade surface micro-morphology and residual stress level. The blade had a surface roughness of Ra 0.2 µm after low-plasticity URSP. A residual compressive stress layer of about 70 µm was formed on the blade surface, and the residual stress first increased and then decreased with the increase in depth. The maximum residual stress was 800 MPa when the residual stress layer depth was 30 µm, and the residual stress was close to that of the base material until the depth reached 70 µm.