Microstructure and properties of borided Monel 400 alloy

Despite its good corrosion resistance, Monel 400 alloy has limited wear resistance due to its low hardness. In this study, boriding thermochemical treatment was carried out to improve the tribological behavior of this alloy under dry sliding conditions. Commercial boriding powder, with SiC as diluents was used. Microstructural characterization (x-ray diffraction, confocal and scanning electron microscopy) and mechanical properties (Vickers microhardness, adhesion resistance and sliding wear resistance) were conducted. Silicides/borides layer up to 91 mu m was formed on Monel 400 alloy after 6 h boriding at 900 degrees C. The surface layer consisted of three distinct regions: (I) an exterior dense nickel silicide layer, (II) a needle-like boride layer located below the silicide layer and (III) the matrix. There was an increase up to five times in the surface hardness value and an improvement up to 58% in the wear resistance due to the formation of a hard silicide/boride layer. A transition from severe plastic deformation to crack formation and spalling of silicides/borides layer was observed after the boriding treatment.