Evaluation of Ni-Cr Coatings: An Approach towards True Property Assessment

Properties of thermal sprayed coatings are unique owing to the presence of defects (cracks/pores), intersplat/interpass interfaces, oxides and secondary phases (as a result of feedstock undergoing phase transformations during in-flight and solidification). For this reason, interpretation of properties usually encounters limitations due to the concurrent effect of all these variables. Moreover, the process induced residual stresses affects as well the mechanical behavior of the coatings. In this study, the mechanical, thermal, electrical and physical properties of Ni-20Cr coatings sprayed under various thermal history conditions (low/high oxidation, molten/partially molten/unmolten particle states, high/medium/low kinetic energies) are evaluated in as sprayed and heat treated conditions (stress relief and sintering). Mechanical properties are found highly dependent on the residual stress state, whereas thermo/electrical properties are predominantly dependent on the character of the intersplat interfaces. An extensive discussion of the true interpretation of property evaluation in metallic coatings is to be presented.