Fabrication, microstructure and mechanical properties of multi-phase tantalum carbide based (TaCz-Ta5Si3) ceramics

Abstract

Three multi-phase tantalum carbide composites (TaCz-Ta5Si3) were fabricated by Spark plasma Sintering (SPS) using Ta, TaC and SiC powders. SiC was added to control the C:Ta ratio (z = 0.6, 0.74, 1.0), regulating the phase composition and grain morphology while also serving as a deoxidizer. Composite TaC0.6-Ta5Si3 had Ta2C as the major phase and contained Ta4C3−x, TaC and Ta5Si3. It exhibited an excellent combination of high flexure strength (714 ± 21 MPa) and toughness (13.9 ± 0.2 MPa·m1/2), despite a low Ta4C3−x fraction, a phase known to have very high toughness. The outstanding performance was attributed to the elongated Ta2C grain morphology, highly laminated intra-granular Ta4C3−x laths, and the refined Ta2C grain size. Composite TaC0.74-Ta5Si3, characterised by equiaxed grain morphology, exhibited good flexure strength (571 ± 36 Mpa) and toughness (7.6 ± 1.1 MPa·m1/2) due to the presence of Ta4C3−x laths in the c-TaC. Lastly, composite TaC1.0-Ta5Si3, composed of c-TaC and Ta5Si3, exhibited moderate strength (545 ± 25 MPa) and toughness (5.3 ± 0.1 MPa·m1/2).