The development of sub-surface damage during high energy solid particle erosion of a thermally sprayed WC-C0-Cr coating

Barber, J., Mellor, B.G. and Wood, R.J.K. (2005) The development of sub-surface damage during high energy solid particle erosion of a thermally sprayed WC-C0-Cr coating. Wear, 259 (1-6), 125-134. (doi:10.1016/j.wear.2005.02.008).

Abstract

The erosion wear performance of a thermally sprayed hard coating has been found to be inferior to that of sintered bulk material of the same composition. The anisotropic microstructure of thermally sprayed WC–Co–Cr coatings, in particular the low fracture toughness in a direction parallel to the substrate, i.e. parallel to the long side of the splats that make up the thermal spray coating has been observed to affect the nature of crack formation both in indentation testing and under high energy solid particle erosion conditions. The present work quantifies the number and length of cracks found, both parallel and transverse to the substrate boundary, in eroded samples of thermally sprayed WC–Co–Cr material. The initiation sites of these cracks are also studied and the importance of voids and other microstructural features (i.e. cobalt lakes, splat boundaries, interfacial inclusions) in the coating as initiation sites is highlighted. Dynamic Hertzian impact theory is used to estimate the elastic contact stresses and sub-surface shear stresses induced by solid particle impacts as well as to infer likely zones of plasticity. These stress fields are related to the location of cracks and to possible mechanisms for crack propagation. The cracks appear in near-surface layers that are likely regions of localised plasticity in the matrix and could result from a mixed mode of ductile fractures driven by plastic strain accumulated after multiple solid impacts as well as fractures driven by elastic stress intensity primarily dominated by sub-surface shear stresses and surface tensile stresses.

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