Tailoring mechanical properties of Mo-SiC composites through controlled phase formation during reactive spark plasma sintering

Abstract

The present study investigates the sintering behavior of Mo-xSiC reactive composites (x= 10–40 vol%) using reactive spark plasma sintering (RSPS) at 1700°C for 5 min. The microstructure, phase formation, and mechanical properties of the fabricated composites were evaluated. X-ray diffraction (XRD) analysis reveals the formation of various compounds, including Mo2C, Mo3Si, and Mo4.8Si3C0.6, which increase in intensity with increasing SiC content. It was found that composites with 10 vol% and 15 vol% SiC still contained unreacted Mo phase, whereas larger amounts of SiC resulted in no remaining Mo. Conversely, unreacted SiC particles were detected in all composites. Field-emission scanning electron microscopy (FESEM) and energy-dispersive spectroscopy (EDS) analysis confirm the presence of multiple phases. The flexural strength of the composites exhibits complex relationships with SiC content, with Mo-10 vol% SiC and Mo-15 vol% SiC composites showing superior strength (585±32 MPa and 618±21 MPa) due to the presence of unreacted Mo phase. The strength decreased with increasing SiC content, likely due to the formation of brittle intermetallic phases. Hardness increased with SiC content, with a significant improvement in Mo-20 vol% SiC composite (12.88 ± 0.21 GPa), but decreased thereafter. Fracture toughness followed a different trend, decreasing with increasing SiC content due to the elimination of ductile Mo phase and the formation of brittle phases. Therefore Mo-10 vol% SiC and Mo-15 vol% SiC composites exhibited the highest fracture toughness values of 8.34±0.68 MPa.m1/2 and 7.99±0.37 MPa.m1/2, respectively.