Effects of Si3N4 addition on the microstructure and mechanical properties of binderless tungsten carbides

Abstract

Binderless tungsten carbide (WC) ceramics containing >2.5 mol% Si3N4 were consolidated by resistance-heated hot-pressing over the temperature range of 1500–1700 °C. This sintering condition resulted in the formation of W5Si3. Above 1550 °C, β-Si3N4 was produced, and almost all of the added α-Si3N4 was transformed into β-Si3N4 at 1700 °C. The binderless WC ceramics containing Si3N4 sintered at 1500 °C had an equiaxed, very fine grain microstructure. Their Young's modulus increased from 587 GPa with no Si3N4 addition and sintering at 1700 °C to 677 GPa with the addition of 2.5 mol% Si3N4 and sintering at 1500 °C. The Si3N4-containing ceramics sintered at lower temperatures also had higher Vickers hardness, reaching a maximum of 22.6 GPa at 1500 °C with 5 mol% Si3N4. There was no significant difference in fracture toughness according to the amount of Si3N4 added or sintering temperature; the fracture toughness value ranged from 5.5 to 5.9 MPa m0.5. The addition of Si3N4 to the binderless WC ceramics lowered the sintering temperature by 300 °C while maintaining mechanical properties equivalent to pure WC.