Effects Of Silicon Carbide Addition On Microstructure And Mechanical Properties Of Tantalum Carbied Ceramics

TaC/SiC, TaC0.7/SiC and TaC0.5/SiC composites were spark plasma sintered at1700℃-1900℃under40MPa for5min by using staring powders of TaC, Ta and SiC with its concentration varying from5vol%to40vol%. Archimedes method, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, transmission electron microscopy and atomic force microscope were applied to characterize densification the phase compositions and microstructure with mechanical properties including vickers hardness, elastic modulus, flexure strength and fracture toughness measured.(1) The phase compositions of TaC with5-40vol%SiC addition included TaC and SiC. Higher relative density to98.7%and finer grains were achieved when SiC addition increased to40vol%. The SiC functioned as the pinning particles to inhibit the rapid grain growth, thus benefiting the exclusion of residual pores. SiC also served as the reductive agents to remove the harmful oxides from particle surfaces with grain boundaries clean, hence enhancing the sintering driving force. The possible solid solution formed during sintering might also promote the mass transfer. The mechanical properties of hardness, strength and toughness were improved significantly to14.3GPa,437MPa and4.4MPa·m1/2for materials with40vol%SiC While the elastic modulus exhibited a tendency of decrease after a rise when SiC concentration increased.(2) When using5-40vol%SiC sintering raw materials of TaC and Ta with the mole ratio of7:3, SiC tended to react with Ta, thus producing TasSi3. The phase compositions displayed the presence of TaCy, TasSi3and SiC with phase contents and chemistries of TaCy varying when SiC concentration increased. TasSi3might undergo plastic deformation around1300℃, promoting the arrangement of particles and lowering the onset temperature for densification. The coarsening microstructures were observed in all materials, resulting in low strength.(3) The raw materials used here were Ta and TaC with the mole ratio of1:1. The phase compositions of sintered TaC0.5with5-40vol%SiC addition varied starting SiC concentration. The5vol%and10vol%materials were composed of Ta2C, TaCy, ζ-Ta4C3-z and TasSi3. Ta2C dominated in5vol%materials while its concentration decreased sharply in10vol%materials. The5vol%materials possessed the best combination of flexure strength and fracture toughness (714MPa and12.6MPa·m1/2) due to its lamellar microstructure. TaCy, Ta5Si3and SiC were identified in composites with20vol%and40vol%SiC. A drop in flexure strength and fracture toughness was observed with equiaxed microstructures dominating in 20vol%and40vol%composites.