니켈 초내열합금의 표면경화층 형성을 위한 초음파 나노표면개질 공정 최적화

Abstract

This study aimed to optimize the ultrasonic nanocrystal surface modification process for forming a hardened surface layer on Nimonic 80A by applying different process conditions and analyzing their effects on microstructure and mechanical properties. Electron backscatter diffraction analysis revealed that ultrasonic nanocrystal surface modification created a nanocrystalline layer near the surface, beneath which a hardened layer with an orientation gradient was observed. The characteristics of this hardened layer were significantly influenced by process parameters. Reducing feed rate, spindle speed and increasing load enhanced impact density, resulting in a nanocrystalline layer thickness of about 61.8 ± 6.7 μm. These optimized conditions improved surface hardness to 479.3 ± 7.3 HV and increased the depth of the hardened layer to 480 ± 50 μm. After aging at 700 °C for 16 hr., the nanocrystalline layer exhibited less than 5 % reduction in thickness, indicating excellent thermal stability. As a result, this study suggests that optimizing ultrasonic nanocrystal surface modification parameters is important for forming a hardened surface layer with improved hardness and depth. In addition, the excellent thermal stability of the nanocrystalline layer after heat treatment indicates the potential applicability of ultrasonic nanocrystal surface modification in high-temperature environments.