Erosion and Toughening Mechanisms of Electroless Ni-P-Nano-NiTi Composite Coatings on API X100 Steel under Single Particle Impact

Abstract

The addition of superelastic NiTi to electroless Ni-P coating has been found to toughen the otherwise brittle coatings in static loading conditions, though its effect on erosion behaviour has not yet been explored. In the present study, spherical WC-Co erodent particles were used in single particle impact testing of Ni-P-nano-NiTi composite coatings on API X100 steel substrates at two average velocities-35 m/s and 52 m/s. Erosion tests were performed at impact angles of 30˚, 45˚, 60˚, and 90˚. The effect of NiTi concentration in the coating was also examined. Through examination of the impact craters and material response at various impact conditions, it was found that the presence of superelastic NiTi in the brittle Ni-P matrix hindered the propagation of cracks and provided a barrier to crack growth. The following toughening mechanisms were identified: crack bridging and deflection, micro-cracking, and transformation toughening.