Nano Mechanical Properties of Flame Sprayed NiCrBSi Coating

To reveal the mechanical properties of thermal spray coating on different scales,flame spray NiCrBSi coating with average thickness 750μm was prepared on 45 carbon steel substrate, the mechanical properties, elastic-plasticity and indentation deformation of coating surface and cross-section were studied by nanoindentation. Results indicate that scale-dependent behaviors of coating mechanical properties were observed as a function of indentation depth for either the coating surface or the cross-section. The nano hardness, modulus and elastic-plasticity of coating decrease with the increasing indentation depth. The coating surface exhibits higher elasticity than the coating cross-section, the ratio of elastic work to the total indentation work, ηIT, of coating surface is 52% at the depth of 500nm, while that of coating cross-section is 40%; moreover, the coating cross-section possesses higher hardness and modulus than the coating surface; the corresponding values of the coating crosssection are 28% and 33% at the depth of 2000nm, higher than those of the coating surface, respectively. The indentation marks show ideal plastic deformation, pile-up and sink-in, and cracks. The difference of ηIT values between coating surface and cross-section decreases with the increasing indentation depth. It reaches about 35% at the depth of 2500nm from the both coating directions. For the coating splat structure,hardness and elastic modulus are the same in different directions,besides, with the increasing indentation depth, larger volume is involved in the indentation. The influence of the surrounding splats (especially the pores, cracks or grain/splat boundaries) on the measured coating properties is enhanced gradually,leading to differences in the appearance between different coating directions, as well as the decrease of coating hardness, elastic modulus.