Effect of W/B atomic ratio on the microstructure and mechanical properties of WCoB-TiC ceramic composites: first-principles calculations and experiment

The thermodynamic stability, mechanical properties and electronic properties of the WCoB and W2CoB2 hard phases in WCoB-TiC ceramic composites are analyzed by the first-principles calculations. The microstructure, hardness, transverse rupture strength (TRS) and fracture toughness (KIC) of WCoB-TiC ceramic composites with various W/B atomic ratios are measured by experiments. First-principles calculations indicate that W2CoB2 has better thermodynamic stability and comprehensive mechanical properties than WCoB. The poor mechanical properties of WCoB are due to the heterogeneous nature of Co-W anti-bonds. The better mechanical properties of W2CoB2 are mainly derived from the stronger BB covalent bonds. Experimental results show that the density of WCoB-TiC ceramic composites increases rapidly with increasing of W/B atomic ratio initially and then gradually stabilized. Hardness, TRS and KIC of WCoB-TiC ceramic composites increases firstly and then decreases with the increase of W/B atomic ratio. When W/B atomic ratio is 0.6, hardness is the highest at 92.3 ± 0.3 HRA. When the W/B atomic ratio is 0.5, the WCoB-TiC ceramic composite has the highest TRS and KIC, which are 853.6 ± 30.3 MPa and 11.48 ± 0.33 MPa m1/2, respectively.