Liquid media effect on the abrasion response of WC/Co hardmetal with different cobalt percent

Abstract

Single pass scratch tests were carried out in three different grades of WC/Co, containing 6, 11, 28% of cobalt and in different environmental conditions: dry, distilled water (pH 6), acid (pH 2) and basic (pH 10) solutions in order to analyze its influence on wear and friction coefficient. Tests were conducted with increasing normal load ranging from 2 to 102 N. A drop of liquid was placed between the indenter tip and the sample at the beginning of the test. At the end of the test, sample was cleaned and dried. The total exposure time to liquid is around 200 s in order to minimize corrosion effects. Worn surfaces were analyzed by Scanning Electron Microscopy (SEM) and optical profilometry. Co% has a significant effect on mechanisms transition loads and on friction coefficient. The later increased with Co% due to the larger extent of plastic deformation. Results indicated that at loads inferior to 62 N, liquid nature does not affect friction or critical loads. However, at higher loads, liquid media effect is statistically significant and distilled water presented the lower friction coefficient and fluid wettability. The liquid acted as a lubricant resulting in lower friction when compared to dry conditions. In Rockwell tests, wear is controlled by plastic deformation, whereas, in Vickers tests, brittle-mechanisms such as cracking took place.