Improvement in mechanical properties and fretting wear of Inconel 718 superalloy by ultrasonic nanocrystal surface modification

Abstract

Inconel 718 (IN718) superalloy specimens were treated with ultrasonic nanocrystal surface modification (UNSM) at room and high temperatures (RT and HTs). The purpose of this work is to investigate the UNSM temperature dependence of the microstructure, fretting wear resistance and mechanical properties such as surface hardness, yield strength, ultimate tensile strength and ductility. A nanocrystalline surface layer with a certain depth was generated on the surface and in the near-surface region of the UNSM-treated specimens. Results revealed that the surface hardness of the specimen subjected to UNSM at RT was increased by 35% compared with that of the untreated ones, and the hardness was further increased of the specimen subjected to UNSM at HTs of 400 and 600 °C compared with the UNSM at RT. The friction and wear performance of IN718 superalloy was evaluated using a ball-on-disk tribometer fretted against SAE52100 bearing steel. The friction coefficient of the UNSM-treated specimens at RT, HTs of 400 and 600 °C was reduced from 0.68 to 0.65, 0.10 to 0.08 and 0.077 to 0.03 at fretting testing temperatures of 25 and 400 °C, respectively. The fretting wear resistance of the UNSM-treated specimens at RT, HTs of 400 and 600 °C was enhanced compared with that of the untreated specimen. The fretting wear resistance of the specimens was further enhanced by increasing the fretting wear testing temperature. It was concluded that the UNSM temperature played a vital role in further increasing the fretting wear resistance, surface hardness, yield and ultimate tensile strengths of IN718 superalloy for nuclear applications.