Erosion-corrosion behavior and mechanism of heated electroless NiP coating under flow

Abstract

To study on erosion-corrosion behavior and mechanism of NiP coating (NiP) and NiP coating after heat treatment at 400°C (h-NiP) in liquid flow and solid-liquid flow, the numerical simulation, microstructure, and electrochemical methods were applied. It could be seen that the spherical structure of the coating surface was no longer dense, and the coating changed from amorphous to crystalline after heat treatment at 400°C. Numerical simulation showed that the coating possessed a higher velocity and a small static pressure at the edge in the straight pipe. The electrochemical analysis showed that the icorr of NiP and h-NiP became larger and the Rp became smaller as the solution speed increased, the icorr of h-NiP was larger than that of NiP, the Rp of NiP was larger than that of h-NiP. In addition, the both coating had a higher icorr in the solid-liquid flow than that of the liquid flow at the same speed. The results indicated that the corrosion resistance of NiP coating was reduced because it had become the crystal after heat treatment at 400°C. The numerical simulation was helpful to reveal the local stress information of NiP coating under flow.