Korean Institute of Surface Engineering

pISSN : 1225-8024 | eISSN : 3399-8403


한국표면공학회지 (32권1호 67-77)

Effect of the Heat treatment and Boron on the Hot Corrosion Resistance of the Al Diffusion Coating

Al 확산피복층의 고온 내식성에 미치는 후열처리와 B첨가의 영향


창원대학교 공과대학 금속재료공학과;동북공업기술연구소 환경재료 연구실;한국기계연구원;
창원대학교 공과대학 금속재료공학과;동북공업기술연구소 환경재료 연구실;한국기계연구원;


The Ni base superalloy Mar-M247 substrate was aluminized or aluminized after boronizing by the pack cementation under Ar atmosphere. The hot corrosion resistance and after-heat-treatment effect of aluminized specimens were studied by the cyclic hot corrosion test in $Na_2SO_4$-NaCl molten salt. XRD analysis showed that the $Ni_2Al_3$ phase was formed between the coated layer and substrate below 1273K but the NiAl phase above 1273K. The peak of the NiAl phase was developed after heat treatment. Corrosion test showed that corrosion resistance of the specimen with the NiAl phase was better than that with the $Ni_2Al_3$ phase. Corrosion resistance could be improved by heat treatment to form ductile NiAl phase, where cracks were not formed by thermal shock on coating layer. Moreover, it appeared that heat treatment played a role to improve corrosion resistance of Al diffusion coating above 1273K. The existence of boron in the Al diffusion coating layer obstructed outwared diffusion of Cr from the substrate, and it influenced on corrosion resistance of the coating layer by weakening adherence of the oxide scale.