Influence of Al content on diamond nucleation and growth on Fe-Al alloys in CH4-H2 plasma atmosphere

Fe-Al alloys with different Al contents have been exposed to a microwave plasma activated CH4-H2 gas mixture at 670 °C. An intermediate graphite layer formed on Fe-10Al substrate retarded diamond nucleation and deteriorated the interfacial adhesion, and severe metal dusting and carburization occurred. Diamond nucleation on Fe-20Al was enhanced by inhibited graphitization and cementite formation. Only Fe3AlCx-type precipitates were observed. On Fe-27Al and Fe-40Al alloys, graphitization and substrate carburization were completely prevented, producing enhanced nucleation and interfacial adhesion of diamond. The improved carburization resistance and diamond deposition with increasing Al contents is closely related to the formation of an alumina-rich layer on the alloy surface.