General aspects for tribological applications of hard particle coatings

Hard coatings, consisting of WC, TiC or Cr₃C₂ particles with a nickel or cobalt matrix were compared with conventional wear-resistant materials like hardened steel 100 Cr6, Ferro TiC P143, WC-Co hard metal and a widely used thermal spray layer NiCrBSi. The coating procedure was flame spraying and diffusion welding. Some layers were remelted using an electron beam to improve their microstructural properties, porosity and binding to the bulk material.

Wear tests were performed under different degrees of severity to qualify the resistance of the coating, using abrasive, sliding and impact test methods representing different wear mechanisms. It is shown that the benefit of the hard particle content depends on the acting loading situation. Under abrasive and sliding conditions the advantage of a high hardness level, i.e. a high concentration of hard phases, could be demonstrated. For impact loading, causing severe surface fatigue, homogeneous materials with high toughness, such as martensitic steels, are beneficial; followed by coatings with a high concentration of ductile matrix. In some cases, the weaknesses, such as brittleness and limited strength of binding to the bulk, could be improved by electron beam remelting.