Effects of superelastic nano-NiTi additions on electroless Ni –P coating properties under bending

Abstract

Electroless Ni –P-nano-NiTi composite coatings have been shown to toughen the brittle Ni –P matrix through transformation toughening, crack bridging and deflection, and micro-cracking. In this study, electroless Ni –P-nano-NiTi composite coatings containing 5.14 wt%, 6.07 wt%, and 7.02 wt % NiTi were subjected to three-point bend testing in order to determine bending properties. Acoustic emission (AE) was monitored during testing to identify fracture events such as delamination and cracking. Monolithic Ni –P coatings experienced major cracking. 5.14 wt% NiTi composite coatings showed delayed onset of cracking and reduction of AE signals indicating reduction in crack severity in comparison to the monolithic coatings. However, coatings containing higher amounts of NiTi showed evidence of coating delamination. Elastic modulus and bend strength decreased with the addition of superelastic NiTi.