Microscale abrasion–corrosion behaviour of WC–Co hardmetals and HVOF sprayed coatings

Abstract

WC–Co hardmetals are employed as wear resistant materials in a wide variety of applications, some of which require resistance to abrasive wear. In some instances, sintered materials are employed, whilst in other situations, WC–Co coatings are deposited onto a component by thermal spraying. WC–Co materials, be they sintered materials or coatings, usually contain WC particles of less than 10 μm in size. When assessing the abrasive wear performance of such materials, tests such as those described in the ASTM standards G65 and B611 are commonly used which employ abrasive particles significantly larger than the size of the carbides in the hardmetals. However, when the abrasive particle size is of the same order of magnitude as the carbide size (or less), then the mechanism of wear changes as the abrasive particles are able to interact with the carbides and matrix phase separately. In certain conditions of use, abrasion of WC–Co materials may primarily be due to small abrasive particles and thus conventional abrasion tests may not be appropriate. In this work, microscale abrasive wear testing of WC–Co sintered hardmetals and coatings was examined. Coatings were thermally sprayed by both liquid-fuelled and gas-fuelled high velocity oxy-fuel (HVOF) systems. The microscale abrasion testing employed abrasive particles in a size range 2–10 μm in both acid and neutral slurries. Generally, it has been observed that microscale abrasion of both the sintered and coating materials occurs predominantly by preferential removal of the binder phase followed by pullout of the carbide. Binder phase removal is accelerated by corrosion in acid media. The wear behaviour of the various materials examined was related to the microstructure and the conditions of the abrasive wear test.