Enhanced mechanical properties of machinable Si3N4/BN composites by spark plasma sintering

Si3N4/BN composites were fabricated by spark plasma sintering (SPS) through traditional powder mixing process and by a chemical route to Si3N4/BN composite powder, respectively. The SPS-processed Si3N4/BN composites maintain a considerably high bending strength, exhibiting some gradual decrease though with increasing BN content. Given the BN content, the bending strength is enhanced for the composites prepared by powder mixing relative to the chemical route counterparts. Differences in the α → β phase transformation of Si3N4 and grain growth during the SPS process play a key role in the variation of strength. Regardless of the preparation method, the Si3N4/BN composites with a BN content up to 30 vol.% can be well machined with WC tools.