Corrosive wear of multi-layer Fe-based coatings laser cladded from amorphous powders

Since amorphous alloys exhibit good wear and corrosion resistance, they are supposed to be applied as a candidate implant material. In this work, using laser cladding, Multi-layer Fe-based alloy coatings were fabricated from amorphous powders on 316L stainless steel (SS) substrate. When the number of cladding layers increases, the microstructure of the coating was mainly composed of gamma-Fe firstly, then evolved to gamma-Fe and alpha-Fe solid solutions, and then to a composite of amorphous and crystalline phases. The surface hardness of the coating was also enhanced consequently to over 1200 HV. During reciprocate sliding against an Alumina ball in a simulated body fluid (Ringer's solution), the volume loss and the coefficient of friction (COF) of the coatings generally decreased firstly and then increased with the number of cladding layers. During sliding at open circuit, the drop in open circuit potential (OCP) of all the Fe-based coatings, except for the 1-layer one, was not as significant as that of the 316 SS substrate. Moreover, when applying a cathodic potential during sliding, no obvious protective effect was obtained for the coatings, which indicates that the multi-layer Fe-based coatings possess a good corrosion-induced wear resistance in comparison to 316L SS. Because of the formation of an electric double layer, the fixed potential of 100 mV(SCE) or -600 mV(SCE) was beneficial to reduce the COF, especially for 316L SS. The tribocorrosion at OCP showed that the 2-layer coating possessed the best corrosive wear resistance, and its COF and volume loss were about 3 and 5.6 times lower than those of the substrate. The material loss in Ringer's solution at OCP is mainly controlled by the mechanical wear for the coatings and the synergism between corrosion and wear for the substrate. Furthermore, this work provides a way to optimize the tribology system by adjusting the number of cladding layers to reduce COF and wear in a simulated body fluid.