Effect of ultrasonic shot peening on surface integrity and fatigue performance of single-crystal superalloy

Abstract

• Ultrasonic shot peening applied to improve fatigue performance of single crystal alloys. • Notch fatigue limit after peening increased to higher than the oringinal smooth fatigue limit. • Three anti-fatigue mechanisms: (1) machining marks elimination; (2) surface nanoscale sub-crystalline structure; (3) deformation promotion of casting micro-pores. We investigated the effect of ultrasonic shot peening on the surface integrity and fatigue properties of single-crystal superalloys. The results show that ultrasonic shot peening significantly reduces the surface roughness of single-crystal specimens and improves surface finishing. The surface hardness increases by 49 %, reaching more than HV660. At the same time, the microstructural analysis illustrates that the single-crystal surface layer after ultrasonic shot peening forms a nanoscale refined sub-crystalline structure that rotates along the [110] axis. It significantly improves the mechanical properties of the surface metal. The originally existing round casting micro-pores are elongated along the [001] axis, forming a willow shape - elliptical shapes from the surface inward, reducing the stress concentration of the casting micro-pores perpendicular to the [001] axis. Combining the above three modification effects, the fatigue limit of the single-crystal notched Kt = 3 sample at 650 ℃ strengthened by ultrasonic shot peening is 94.2 % higher than that of the as-received notched sample, and 17.4 % higher than that of the smooth sample.