Comparison of Four Different Methods to Determine the Hardness of Plasma-sprayed Cr3C2–NiCr Coating by Nano-indentation

Abstract A Cr3C2–NiCr coating with a thickness of 200 μm was deposited on an AISI 1045 steel substrate using a supersonic plasma-spray technique. The hardness of the Cr3C2–NiCr coating was characterized by a nano-indenter equipped with an atomic force microscope (AFM). The AFM images indicated that the nano-indents on the Cr3C2–NiCr coating exhibited significant “pile-up” deformation. Such pile-up behavior needs to be taken into account in hardness determination because the pile-up height accounts for a large proportion of the indentation depth. In this paper, four different methods are compared to determine the hardness of the Cr3C2–NiCr coating: the Oliver–Pharr method, two work-of-indentation methods (total work of indentation and plastic work of indentation), and an AFM analysis method. The results show that the Oliver–Pharr and work-of-indentation methods overestimated the hardness, and the AFM analysis method is considered as a more accurate method for determining the hardness of the Cr3C2–NiCr coating.