Abstract
There are many research works performed in order to improve the strength and wear resistance of the drill bits in order to prolong their service time and thus reduce the costs and environmental load. Among others, cemented carbide diamond composites are used, including those with WC-Co matrices and various additives. The superior hardness of diamond provides high wear resistance of the composite, while the cemented carbides ensure its high strength and toughness. In this paper, improvement of the cemented carbide diamond composite was reached due to addition of CrB2 and ZrO2 components that inhibited grain growth and promoted the dispersion-driven straightening process. The effect was further enhanced by addition of alumina nanopowder to the sintered powder mixtures. When the Al2O3 powder of the grain size between 20 and 100 nm is added in proportion of 0.2-1.0 wt.% to the Сdiamond–(WC–Co)‒CrB2‒ZrO2 composite, several enhancing mechanisms are promoted, such as transformation toughening, dispersion toughening, and the load transfer mechanism. When the tetragonal phase t-ZrO2 undergoes external stress, it transforms to the monoclinic phase m-ZrO2, generating internal stresses that suppress crack propagation. In turn, dispersion toughening is promoted by the Al2O3 nanoscale reinforcement due to improved sinterability of the powder mixture, reducing the sintering temperature. Finally, the load transfer mechanism appears due to the presence of reinforcing particles that prevent material of the matrix from crack propagation. As a result, the compressive strength of the Сdiamond–(WC–Co)‒CrB2‒ZrO2‒Al2O3 composite increased by 34% from 3.965 GPa up to 5.320 GPa compared to the same composition without alumina nanoadditive. At the same time, the wear rate dropped down by almost 80% from 12.45 to 2.67×10-13 m3·(N∙m)-1.