Ultrasonic impact treatment of CoCrWNi superalloys for surface properties improvement

Abstract The effect of ultrasonic impact treatment (UIT) was studied on the surface microstructure, roughness parameters, micro- and nanoscale mechanical properties, surface residual stress, and nanoscale scratch and friction behavior of L-605 CoCrWNi alloy. According to the results, UIT increased the surface hardness of the L-605 alloy where the hardness of the 1-pass UITed sample (∼690 HV) was higher than that of the annealed alloy by about 120 %. This was attributed to the accumulation of strain, strain-induced martensitic transformation (SIMT), and the formation of ultrafine grains. The UIT also changed the tensile surface residual stress of the as-received L-605 sample to the compressive state. The stylus profilometry showed that applying 3-pass UIT substantially decreased the average roughness R a and resulted in a negative surface skewness with an improved ratio. According to the nanoindentation/nanoscratch results, applying the first pass of UIT increased the nanohardness, H E r −1 ratio, and H 3 E r −2 ratio by 230 %, 200 %, and 280 %, respectively. The UIT reduced the depth/width of the nanoscratch groove, lowered the amount of piled-up material, and substantially decreased the average friction coefficient (AFC).