Effects of surface oxidation behavior of NiTi shape memory alloy on adhesion of epoxy resin/polytetrafluoroethylene composite coating

The nickel-titanium (NiTi) shape memory alloy (SMA) substrates were firstly subjected to different high-temperature oxidation treatments. Then they were sprayed by the polymer coating (epoxy resin (EP): polytetrafluoroethylene (PTFE) in a mass ratio of 3:1). Effects of the surface chemical composition, morphology, roughness and oxide thickness on adhesion between the NiTi SMA substrate and the coating were studied. The results demonstrated that the adhesion of the oxidized samples could be improved significantly as compared with that of the untreated sample. A heating temperature of 600 °C was determined to be optimal in the range of 300–700 °C for preparing the composite coating for NiTi SMA substrates. The highest adhesion strength was 6.76 MPa for the oxidized sample with a duration time of 30 min under 600 °C. It has been found that the adhesion was strongly depended on the high surface oxygen content, uniform morphology, appropriate roughness and oxide thickness.