Unexpected SiC nanowires growth during spark plasma sintering of WC-10Si: A comparative study on phase formation and microstructure properties against WC-10Co cermet

Abstract In the present work, SiC nanowires were formed unexpectedly during spark plasma sintering of WC-10 wt%Si cermet. The microstructure, hardness, bending strength and fracture toughness of WC-10 wt%Si were compared with conventional WC-10 wt%Co. The sintering temperatures were chosen according to time-temperature-displacement curves to enhance maximum shrinkage of composites containing Si and Co at temperatures of 1850° and 1350 °C, respectively. Thermodynamic investigations showed negative Gibbs free energy of the formation of WSi 2 and SiC compounds during sintering process while the positive amounts of ΔG were calculated for the possible formation of intermetallic compounds in WC-10 wt%Co composite. XRD investigations approved the formation of WSi 2 and SiC compounds while the reaction between WC and Co led to the formation of η phase as expected. The microstructure observations revealed nanowire shapes of SiC particles distributed uniformly. The bending strength of 583 ± 31 MPa and fracture toughness of 6.2 MPa m 1/2 were measured for WC-10 wt%Si composite, these amounts were lower compared to bending strength and fracture toughness of WC-10 wt%Co composite (1032 ± 26 MPa and 16.4 MPa m 1/2 , respectively). Besides, the hardness of 2147 ± 31 and 1622 ± 28 Vickers was obtained for WC-10 wt%Si and WC-10 wt%Co composites, respectively. The weak mechanical properties of WC-10 wt%Si composite were related to the presence of pores between SiC nanowires which acted as crack propagation centers.