Enhanced tribological performance of shot peened nickel-based single crystal superalloy with heterogeneous gradient nanostructure at elevated temperature

The dry-sliding wear behaviors of nickel-based single crystal (NBSC) superalloy under different shot peening (SP) intensities and sliding times are investigated and compared with those of non-SP NBSC superalloy. The surface roughness of SP superalloy is 82.9 %–388.1 % higher than that of non-SP superalloy, and the surface microhardness is 8.7 %–50.4 % higher than that of non-SP superalloy. However, at the initial stage of abrasion, due to the large surface roughness, the coefficient of friction (COF) and wear rate of SP superalloy are higher than those of non-SP superalloy. After long-term abrasion, the COF and wear rate of SP superalloy are lower than those of non-SP superalloy, which is attributed to the SP-induced gradient-hardening layer and gradient-nanograined microstructure. Under cyclic friction load, a five-layer heterogeneous gradient nanostructure is generated on the worn surface of SP superalloy, including ultrafine nanograined glaze layer, nanocrystal layer, sub-grain layer, rotated γ′ layer and distorted γ′ layer. While non-SP superalloy has a thicker heterogeneous gradient nanostructure with larger grain sizes, and there is no rotated γ’ layer. SP-induced high-density dislocations strengthen the wear resistance. These findings provide new insights into the strengthening mechanism of SP on wear and highlight the potential of SP in the design of wear-resistant NBSC superalloy.