Influence of W/Cu Ratio on the Dry Sliding Wear Characteristics of Annealed Nickel-Based Poly Alloy Coatings
摘要
Nickel-phosphorous alloy has wide industrial acceptance for its excellent tribological and electrochemical properties. However, in severe tribological application it needs another reinforcement of hard element like tungsten. Due to addition of hard particle, besides the increase of hardness the coefficient of friction also increased rapidly. This problem can be solved by incorporating self-lubricating soft element like copper. Based on this philosophy, tungsten and copper were incorporated in to nickel-phosphorous alloy by electroless method at different ratios. Microstructural, mechanical and tribological characteristics were investigated. Result showed that the hardness of coating consisting 80:1 W/Cu ratio is 9.32 ± 0.92 GPa which is higher than hardness (8.31 ± 1.21 GPa) of the coating consisting 100:1 W/Cu ratio. Consequently, the wear rate decreased from 4.09 × 10−7 ± 4.63 × 10−8 to 3.47 × 10−7 ± 1.42 × 10−8 mm3/Nm. With further increase of copper within the coating, a gradual increase in wear rate was observed. The inclusion of copper results decreases in coefficient of friction compared to ternary coating containing tungsten due to formation of lubricious CuO layer in the wear track. Minimum coefficient of friction of 0.11 and 0.12 was obtained for coatings consist of 100:1 and 80:1 W/Cu ratio, respectively, which is almost half of the coefficient of friction of ternary coating containing tungsten.