Effect of the ZrO2 Content on the Strength Characteristics of the Matrix Material of Cdiamond–(WC–Co) Composites Synthesized by Spark Plasma Sintering

Abstract—For structurally homotypical specimens different in the ZrO₂ content from the (94WC–6Co) + ZrO₂ matrix material used in diamond-containing С_diamond–(WC–Co) composites formed by spark plasma sintering, the dependences of the relative density ρ_rel, the ultimate strength under compression R_cm and bending R_bm, the microhardness Н_V, and the fracture toughness K_Iс on the zirconia content have been established. The addition of 6 wt % zirconia to the WC–6Co composite leads to an increase in the relative density from 0.948 to 0.990, the ultimate compression strength R_cm from 4950 ± 110 to 5600 ± 120 MPa, the ultimate bending strength R_bm from 1935 ± 80 to 2660 ± 115 MPa, and the fracture toughness K_Iс from 13.8 ± 0.71 to 16.9 ± 0.76 MPa m^0.5 at a slight decrease in hardness (from 15.9 ± 0.72 to 15.1 ± 0.33 GPa). Such values are caused by the decrease of main WC phase grains in size with tetragonal t-ZrO₂ phase transformation and, correspondingly, by the growing role of transformation strengthening mechanism and the active action of inner mechanical compressive microstresses. When the ZrO₂ additive to the WC–6Co composite is increased to 10%, the parameters ρ_rel, R_cm, R_bm, and K_Iс are gradually decreased. At the same time, the material at the indentor imprint edge begins to destruct, and crack propagate in a chaotic way. It has been revealed that the properties ρ_rel, R_cm, R_bm, and K_Ic are worsened at a zirconia nanopowder content above 6 wt % in the WC–Co composite due to the formation of agglomerates during the mixing of components, their separation under sintering, and the formation of micropores and microcracks.