Effect of Phosphorus on Mechanical Properties of Ni-P Electrodeposit

초록

The effects of P and heat-treatment on the mechanical properties of Ni-P alloy deposits were investigated. Electrodepositions were performed in the sulfamate bath. The content of P in Ni-P deposits gradually increased from 0.2 to 0.9wt.% with increasing H3PO3 concentration from 0.007M to 0.018M in the bath. The hardness of Ni-P deposits increased with increasing P content and then reached 495VHN (Vickers hardness) at Ni-0.9 wt.% P while the hardness of pure Ni deposit was 150VHN. From result of XRD analysis, the grain size was linearly decreased with increasing phosphorus content and it was 15nm at 0.9wt%P, while pure Ni was about 25nm. It seemed that the increase of hardness with increasing P content was due to the decrease of grain size and solution hardening of solute. The hardness of Ni-P deposits was increased with increasing heat-treating temperature and reached the maximum hardness at 300℃ and then decreased in all Ni-P alloy deposits. The grain size was not significantly changed from the initial value of 5nm in the as-plated material, but grain growth was started from 350℃. It is considered that the increase in hardness of deposit up to 300℃ was due to P segregations in the grain boundary, and decrease in hardness above 300℃ was caused by the formation of Ni3P precipitates and substantial growth of Ni3P.