The directed energy deposited (DED) alloys show higher hardness values than the welded alloys due to the finer microstructure following the high cooling rate. However, defects such as microcracks, pores, and the residual stress are remained within the DED alloy. These defects deteriorate the wear behavior so post-processing such as heat treatment and hot isostatic pressing (HIP) are applied to DED alloys to reduce the defects. HIP was chosen in this study because the high pressure and temperature uniformly reduced the defects. The HIP is processed at 1150°C under 100 MPa for 4 hours. After HIP, microcracks are disappeared and porosity is reduced by 86.9%. Carbides are spherodized due to the interdiffusion of Cr and C between the dendrite and interdendrite region. After HIP, the nanohardness (GPa) of carbides increased from 11.1 to 12, and the Co matrix decreased from 8.8 to 7.9. Vickers hardness (HV) decreased by 18.9 % after HIP. The dislocation density (10-2/m2) decreased from 7.34 to 0.34 and the residual stress (MPa) changed from tensile 79 to a compressive -246 by HIP. This study indicates that HIP is effective in reducing defects, and the HIP DED Stellite 6 exhibits a higher HV than welded Stellite 6.

1. Introduction
2. Experimental Procedure
    2.1. 샘플 준비
    2.2. 미세조직 관찰
    2.3. 경도 특성 평가
    2.4. 잔류 응력 측정
3. Results and Discussions
    3.1. 미세조직
    3.2. 경도 평가
    3.3. 전위 밀도 측정
    3.4. 잔류 응력 비교
4. Conclusions
Acknowledgement
References

• 김영도(한양대학교 신소재공학부) | Young Do Kim (Division of Materials Science and Engineering, Hanyang University, Seoul 04763, Republic of Korea)
• 장진성(한국원자력연구원 재료안전기술연구부) | Jinsung Jang (Materials Safety Technology Development Division, Korea Atomic Energy Research Institute, Daejeon 34057, Republic of Korea)
• 강석훈(한국원자력연구원 재료안전기술연구부) | Suk Hoon Kang (Materials Safety Technology Development Division, Korea Atomic Energy Research Institute, Daejeon 34057, Republic of Korea) Corresponding author
• 한흥남(서울대학교 재료공학부) | Heung Nam Han (Department of Materials Science and Engineering & Research Institute of Advanced Materials, Seoul National University, Seoul 08826, Republic of Korea)
• 천영범(한국원자력연구원 재료안전기술연구부) | Young-Bum Chun (Materials Safety Technology Development Division, Korea Atomic Energy Research Institute, Daejeon 34057, Republic of Korea)
• 고재현(한국원자력연구원 재료안전기술연구부, 한양대학교 신소재공학부) | Jae Hyeon Koh (Materials Safety Technology Development Division, Korea Atomic Energy Research Institute, Daejeon 34057, Republic of Korea, Division of Materials Science and Engineering, Hanyang University, Seoul 04763, Republic of Korea)
• 서주원(한국원자력연구원 재료안전기술연구부, 서울대학교 재료공학부) | Joowon Suh (Materials Safety Technology Development Division, Korea Atomic Energy Research Institute, Daejeon 34057, Republic of Korea, Department of Materials Science and Engineering & Research Institute of Advanced Materials, Seoul National University, Seoul 08826, Republic of Korea)