화학공학소재연구정보센터
Journal of the American Ceramic Society, Vol.92, No.10, 2404-2407, 2009
Phase Constitution and Mechanical Properties of Carbides in the Ta-C System
Carbides in the Ta-C system were prepared by hot-pressing mixed powders of TaC and Ta in C/Ta atomic ratios of 1.0, 0.9, 0.8, 0.7, and 0.6 at 1800 degrees C for 2 h. The compositions, 1.0, 0.9, and 0.8, produced single face-centered-cubic (fcc) TaCy phase with C/Ta ratios essentially the same as the starting compositions and densities exceeding 96.5% of theoretical. Grain size decreased with increasing carbon deficiency with a corresponding increase in Vickers hardness from 13.5 to 20 GPa. The flexural strength, however, decreased from 650 to 500 MPa due to a decrease in fracture toughness from 5.3 to 3.8 MPa root m. The compositions 0.7 and 0.6 produced two carbide phases, fcc TaCy and rhombohedral zeta-Ta4C3-x phase in the 0.7 composition and zeta-Ta4C3-x and hexagonal-close-packed (hcp) alpha-Ta2C phase in the 0.6 composition. Fracture toughness measured by single-edge-precracked-beam technique was exceptionally high (12.7 +/-0.7 MPa root m) for the 0.6 composition with a high weight percent of the zeta-Ta4C3-x phase (similar to 83 wt%). The fracture surface was highly faceted with multiple cleavage crack planes and steps.