Effects of Current Density on the Mechanical Property of Nickel Base Ceramic Composite Coatings

초록

Mechanical properties of Ni-W-SiC ternary ceramic composite electrodeposits were investigated under different current density and heat treatment condition. The SiC ceramic coated layer was prepared using fine SiC particles of 1 μm in a Ni-W electrolytic solution. Experimental conditions for current density and heat treatment temperature were 2~20 A/dm2 and 500~700oC, respectively. The content of SiC particle in the Ni-W-SiC composite deposit was increased with increasing current density, and reached a maximum value at 10 A/dm2. The surface roughness was also increased with increasing current density, and it showed a same inclination as the case of SiC particle content in the deposits. Therefore it could be said that surface roughness is strongly dependent upon the amount of SiC in the deposits. The hardness of all SiC containing ceramic coatings was higher than that of electrodeposited Ni-W binary metallic coating. The hardness and wear resistance of Ni-W-SiC deposits was increased linearly with increasing current density up to 10 A/dm2, and the hardness obtained maximum value of 1,160 VHN at 10 A/dm2. However, the hardness was decreased as increasing the current density more than 10 A/dm2. It is shown that the hardness of ceramic coated layer is also influenced on the amount of SiC as the case of surface roughness. The hardness was increased in the heat treatment temperature range of 25oC to 600oC, but it was decreased with increasing temperature. Maximum hardness of 1,600 VHN was obtained at 600oC. It is considered that both dispersion-strengthening effect of SiC particles and solid solution hardening effect of soluble tungsten atoms improve mechanical properties of the SiC ceramic composite deposit