기계적합금화로 제조된 Ni-20Cr-20Fe-5Nb 합금에서 PCA로서 H2O의 역할과 시효석출거동

Abstract

The effect of use of H2O as PCA(process control agent) to prevent the carbon contamination during mechanical alloying process and the precipitation behavior in Ni-20Cr-20Fe-5Nb bulk alloy after aging were investigated. NbC and Cr2O3 were formed during mechanical alloying and consolidation processes in the Ni-20Cr-20Fe-5Nb alloy in which methanol(CH3OH) was added as PCA. Formation of NbC in this alloy decreased the amount of Nb dissolved in the Ni matrix. The use of H2O as PCA in Ni-20Cr-20Fe-5Nb alloy prevented the formation of NbC and increased the hardness. The increase of hardness in this alloy was attributed to the increased amount of Nb dissolved in the Ni matrix. After aging treatment for 20 hours at 600℃ and 720℃ of Ni-20Cr-20Fe-5Nb bulk alloy in which H2O added as PCA, γ'' (Ni3Nb, tetragonal) and δ (Ni3Nb, orthorhombic) precipitates were formed, respectively. The precipitation temperatures of γ'' and δ in this bulk alloy were lower than those in commercial IN 718 alloy. It seemed that the lower precipitation temperatures for γ'' and δ in this bulk alloy than in commercial IN 718 alloy were due to severe plastic deformation during mechanical alloying.