Friction stir welding of WC-12Co cermet / SC45 steel with a Ni interlayer.
By Marie-noëlle Avettand-fenoel (Université de Lille), Toru Nagaoka (Osaka Research Institute of Industrial Science and Technology), Hidetoshi Fujii (Joining and Welding Research Institute, Osaka University), Roland Taillard (Université de Lille)

WC-12Co cermet was friction stir lap welded with SC45 steel with or without different thicknesses of a Ni interlayer. The material flow was first characterized. Various out of equilibrium phases were then identified in the steel nugget. Some interdiffusion was noticed at the steel-cermet, steel-Ni and Ni-cermet interfaces, leading to the formation of oversaturated Co solid solutions in Fe or in Ni. Besides, the increase in the Ni interlayer thickness gave rise to a more pronounced wear of the Si3N4 tool and to a larger amount of retained austenite in the nugget. The mechanical tests finally suggest the better quality of the interface of the Ni bearing joints compared to the Ni-free joint case.