This study was carried out to investigate the effect of W substitution on the precipitation behavior of χ and σ phases in super duplex stainless steel. The χ phase was precipitated at the interface of ferrite / austenite phases and inside the ferrite phase at the initial stage of aging. With an increase in the aging time, the volume fraction of the χ phase increased, and then decreased with the transformation from the χ phase to the σ phase. The σ phase was precipitated later than the χ phase, and the volume fraction of x phase increased with the increase in the aging time. The ferrite phase was decomposed into the new austenite (γ2) and σ phases by aging treatment. The decomposition of the ferrite phase into the γ2 and σ phases was retarded by W substitution for Mo. The volume fraction of the χ phase increased and that of the σ phase decreased due to W substitution. The χ and σ phases were intermetallic compounds, which had lower nickel concentration, and higher chromium, molybdenum, and tungsten concentrations. The χ phase has higher molybdenum and tungsten concentrations than those of the σ phase. The amounts of chromium and nickel in the χ and σ phases did not change, but these phases have higher concentrations of molybdenum and tungsten due to W substitution for Mo.

HIP처리가 가스터빈 고정익 등 고온부품에 적용되는 열차폐 코팅층의 접착강도 및 고온특성에 미치는 영향을 조사하였다. 시편은 IN738LC 초합금 표면에 8wt%Y2O3-ZrO2분말을 플라즈마 용사법으로 코팅한 후 1200˚C, 100MPa의 고온, 고압에서 4시간 동안 HIP 처리하여 준비하였다. 실험결과 HIP 처리된 코팅의 경우 미세균열과 기공이 상당량 감소하였으며 EDX분석을 통해 계면에서 원자간 상호확산이 발생한 것을 확인하였다. 이러한 코팅층의 치밀화 및 상호확산으로 인해 HIP처리된 코팅층의 접착강도는 48% 이상 크게 증가하였으며 조직 또한 균질화 되었다. 반면 가열과 냉각이 반복되는 환경에서 코팅층의 내구력은 HIP 처리된 경우가 다소 저하되었다. 이는 코팅과 모재와의 열팽창 차이로 인한 변형을 완화시켜주는 기공과 미세균열이 감소되었기 때문으로 판단된다.