Scratch behavior and in situ acoustic emission analysis of PVD chromium nitride coatings on mild steel with electroless nickel interlayers

Reactively sputtered chromium nitride deposits on mild steel were modified with electroless nickel (EN) interlayers. The scratch test was conducted to evaluate the critical load, adhesive and cohesive properties of the coating assemblies. Studies were focused on the failure modes of the single- and multi-layer coatings evaluated on the basis of scratch channels as well as the acoustic activity. Relationships between progressive-, constant-loading, and the in situ acoustic emission signal during scratching are presented. It was demonstrated that the EN coatings with lower phosphorous content (6.2 wt.% P) in both as-deposited and heat-treated states exhibited higher critical load determined by the acoustic emission signal. In addition, effects of heat treatment and interlayer thickness on the scratch behavior of the single and duplex coating assemblies were also analyzed.