Effects of carbon nanotubes on crystallisation in amorphous Ni-P electroplating coating

The amorphous nickel-phosphorus coating and its carbon nanotube (CNT) composite coating were prepared by brush electroplating technology. After 1 h heat treatment at 400°C, the coatings translated into the crystalline state, which consists of α-Ni matrix and Ni₃P precipitated phase. The results of energy dispersive X-ray, X-ray diffraction analysis and differential thermal analysis showed that, due to CNTs, the phosphorus content in the coating decreased from 8·42 to 7·34 wt-%. Carbon nanotubes also had an effect on crystallisation kinetics of the amorphous coating. The crystallisation activation energy in Ni-P/2 g CNT composite coating was 25 kJ mol^-1 higher than that in Ni-P coating. The time and temperature of the 50% crystallised were 5 min longer and 29°C higher respectively than that in Ni-P coating. Further study showed that CNTs played a role in obstruction in the crystallisation because CNTs block nucleation and growth of crystallisation for Ni₃P phase.