Characterisation and corrosion performance of HVOF sprayed Ni-10 wt-%Ti coatings

Mechanically alloyed Ni-10 wt-% Ti powders were deposited on 1045 steel substrate using high velocity oxy-fuel (HVOF) thermal spraying process. The microstructure and phase composition of coatings were evaluated by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The results showed that the phase composition of feedstock powders was preserved during spraying and only supersaturated Ni(Ti) solid solution was present in the coatings. The hardness measurements showed that the hardness of coatings was about 510 HV (50 g). Tafel polarisation tests performed after 1 h immersion revealed that the corrosion behaviour of HVOF Ni-Ti coatings was not affected by substrate. However, delamination of air plasma sprayed (APS) Ni-10 wt-% Ti coatings and significant corrosion of substrate was observed in similar conditions. For HVOF Ni-Ti coating and after 24 h of immersion time, the corrosion of underlying substrate was observed after polarisation measurements but no delamination of coating occurred.