The aim of this study was development of new composite coatings based on Co-W-Si ternary system which has good oxidation resistance in high temperature. For this, first, Co (ss) /CoWSi-WSi 2 nanocomposite powder was synthesized by mechanical alloying and subsequent heat treatment. The synthesized powder was precipitated on Ni substrate and cladded by laser. Different laser cladding parameters were investigated and optimized parameters were obtained for having coating with almost 15at% Ni. After optimization of parameters such as beam power, scanning rate and overlapping, the microstructure and hardness of coating were characterized. To clarify oxidation resistance, the coating was cyclically oxidized at 900, 1100 and 1300 ?C. The results showed that WSi 2 and CoWSi were formed after 30 h and 50 h ball milling, respectively. Heat treatment was done on 30 h ball milled powder at 1100 ?C for 4 h and Co (ss) /CoWSi-WSi 2 nanocomposite was produced. The produced powder was precipitated on Ni substrate with 1 mm thickness and laser cladding parameters including beam power: 450 W, scanning rate: 2.5 mm.s -1 and overlapping; 50% was obtained as optimized parameters. After laser cladding, phase investigation showed that using the thermal stabilized powder caused Co (ss) /CoWSi-WSi 2 coating without any unexpected phases. The microstructure of coating was dense, crack-free and formed from three different zones with equiax, dendritic and eqiax structures. The microhardness result showed that the hardness of coating was 950 HV and distributed uniformly to substrate. The oxidation results confirmed diffusion-control mechanism at three temperatures. The oxide scale was dense, without any cracks and SiO 2 -rich at 900 ?C, while at 1100 ?C, the oxide scale was thicker, dense and mixture of tungsten, cobalt and silica oxides. At 1300 ?C, the double scale was formed; outer layer was SiO 2 -rich and inner layer was enrichment of tungsten and cobalt with alittle oxygen concentration. At initial stage of oxidation at 1300 ?C, spinel phases were formed by solid state reaction between parent metal oxides. The spinels spalled and separated from the scale. After that, SiO 2 -rich layer covered the surface and reduced oxidation rate. Based on these results, inward diffusion of oxygen controlled the oxidation reactions at three temperatures. Keywords: Oxidation resistance, laser cladding, Co (ss) /CoWSi-WSi 2 , mechanical alloying, microstructure
