초록 ▼

1. 물리적증착(PVD) 및 확산열처리를 이용한 니켈기초합금의 표면개질 기술개발
· Al의 물리적증착(PVD) 및 확산열처리에 따른 침투거동 분석
· 산화막 및 sublayer의 장기안정성 평가 (900℃)
· 최적 증착조건 및 열처리조건 도출
2. 산화막/금속 계면의 접합성 및 안정성 향상을 위한 복합공정 기술개발
· 물리적증착(PVD) + 화학적증착(CVD) 복합공정을 이용한 보호피막 형성기술
· 물리적증착(PVD) + 레이저빔 표면처리를 이용한 보호피막 형성기술
· 물리적증착(PVD) +

1. 물리적증착(PVD) 및 확산열처리를 이용한 니켈기초합금의 표면개질 기술개발
· Al의 물리적증착(PVD) 및 확산열처리에 따른 침투거동 분석
· 산화막 및 sublayer의 장기안정성 평가 (900℃)
· 최적 증착조건 및 열처리조건 도출
2. 산화막/금속 계면의 접합성 및 안정성 향상을 위한 복합공정 기술개발
· 물리적증착(PVD) + 화학적증착(CVD) 복합공정을 이용한 보호피막 형성기술
· 물리적증착(PVD) + 레이저빔 표면처리를 이용한 보호피막 형성기술
· 물리적증착(PVD) + 전자빔 표면처리를 이용한 보호피막 형성기술
3. 표면개질에 따른 보호피막 성능평가
· 고온부식 특성평가 (900℃, 대기 및 VHTR 조건, SOEC 조건, I-S 공정 조건)
· 산화막/금속간 계면접합성 평가
· 크립하중 하에서 보호피막의 self-healing 효과 평가
4. 표면개질에 따른 후보합금의 인장 및 크립 저항성 평가
· 상온 및 고온인장
· 고온 크립특성 평가 (900℃, 대기 및 VHTR 조건, SOEC 조건)
5. 표면개질에 따른 후보합금의 확산접합 성능평가
· 후보재료의 최적 확산접합 조건 도출 및 성능평가
· 표면개질된 후보재료의 확산접합부 제작
· 확산접합부의 인장 및 크립 특성 평가 (900℃, 대기 조건)
· 확산접합부의 미세조직분석 및 장기안정성 평가 (900℃)

Abstract ▼

Ⅳ. Results
The optimum conditions for physical vapor deposition of Al was derived by controlling various parameters, such as target type, distance between the target and the substrate, pressure of Ar gas in a chamber, and temperature of the substrate. Based on the several tests and analyses, high

Ⅳ. Results
The optimum conditions for physical vapor deposition of Al was derived by controlling various parameters, such as target type, distance between the target and the substrate, pressure of Ar gas in a chamber, and temperature of the substrate. Based on the several tests and analyses, high density Al was deposited under pressure of 7×10^-3 Torr and power of 120W. Those conditions were used to prepare Al layer for the subsequent inter-diffusion heat treatment (IDHT), laser beam (LB) and electron beam (EB) surface treatment processes.
IDHT processes were applied at 600-1150℃ up to 48h. The formation of various intermetallics in Ni-Al binary system was analyzed. By properly controlling the IDHT conditions, two surface intermetallic layers such as β-NiAl formed at 1000℃ and γ’-Ni₃Al formed at 1150℃, were developed and their oxidation resistance was evaluated in air, He, steam, sulfur-iodine (IS) cycle environment. In all cases, stable and protective alumina layer was formed on the surface and the oxidation resistance was significantly improved. Especially, the performance of surface treated specimens in I-S process environments were superior to the other materials for I-S process reactors which showed severe spallation of surface oxides.
Meanwhile, Al-rich micro-alloying zone (4 ~ 5 wt.% Al) was developed using high energy density electron beam on the surface with Al layer. Like IDHT treated specimens, oxidation resistance was greatly improved by forming external oxide layers (spinel, (Cr,Al)₂O₃, Al₂O₃) without internal oxidation which could degrade the mechanical properties of materials.
Tensile and creep-rupture testings were performed to evaluated the effect of the surface treatment. Tensile properties of the surface-treated Alloy 617 were similar to those of the as-received Alloy 617. However, creep-rupture life time is longer for the IDHT treated specimen than the as-received due to the formation of stable oxide (Al₂O₃) in front of the propagating cracks which prevented the formation of deleterious internal oxides. In the case of electron beam surface treated specimen, creep-rupture life time is shorter than the as-received because of the surface defects formed during the surface treatment process. It is expected that the creep property would be improved by minimizing the surface defects through process optimization.
Diffusion bonding was performed for several alloys such as Alloy 617, Haynes 230, and Incoloy 800HT. The optimized diffusion bonding conditions were derived by controlling the bonding parameters, such as temperature, pressure, time, and surface conditions. In addition, by applying the post-bond heat treatments, tensile property of diffusion bond was somewhat recovered to the values similar to those of base materials. As results, tensile ductility of the diffusion-bonded is greater than 50% and creep-rupture time is greater than 90% of the parent materials at 900℃, which are excellent performance for the diffusion bonding. Basec on the diffusion bonding conditions of the parent materials, diffusion-bonding was performed for the surface-treated Alloy 617 (1050-1100℃/10MPa for inter-diffusion heat treatment and 1180℃/15MPa for electron beam treatment). Due to the high contents of Al near the interface, Al-rich oxide particles are formed along the bond-line, so Ni foil was inserted between the surface-treated specimens and the post-bond heat treatment was applied to enhance the performance of the diffusion bonding. As results, tensile ductility was recovered to some extent by post-bond heat treatment.