Effect of abrasive particle size and the influence of microstructure on the wear mechanisms in wear-resistant materials

Downhole drilling operations expose tungsten carbide based sintered (WC-5.7Co-0.3Cr) and sprayed (WC-10Co-4Cr) hardmetals to abrasives of different sizes. Although the effect of abradant size on the abrasive wear of metals has been widely studied, the effect of particle size on the abrasive wear of sintered and sprayed tungsten carbide-based hardmetals has not been examined previously. The abrasion of hardmetal composite surfaces is complex due to the presence of hard and soft phases which respond differently during abrasive wear, where an increase in abrasive size leads to a change in the wear mechanism which significantly affects the overall wear rates. Three different abrasive sizes, 4.5 mu m, 17.5 mu m and 180 mu m, were used in a modified ASTM G65 rubber wheel abrasion test to examine the effects of abrasive size on wear in a sintered WC and a D-gun sprayed WC-based coating. Uniquely, influential parameters affecting the wear mechanisms have been examined and identified with the fundamental material properties of both abrasives and the multi-phase materials. As a unique way of mapping abrasion performance, a parameter previously developed for the micro-abrasion tester, 'severity of contact', has been reworked and plotted against a 'brittleness factor' parameter developed in this work. Plotting these parameters can explain the sharp rise in wear rates associated with the transition from ductile, plastic deformation dominated material removal to a more fracture-related material removal as the size of abrasives increases. This work has developed new insights into how hardmetal composites respond to change in abrasive size and provides a basis for controlling the abrasive particle size. (C) 2011 Elsevier B.V. All rights reserved.