Effect of 20 mol% Al addition on phase formation and mechanical properties of TaCx (x=0.5, 0.55, 0.6 and 0.7) ceramics

TaC x (x = 0.5, 0.55, 0.6 and 0.7) ceramics with 20 mol% Al addition were prepared by hot pressing TaC, Ta and Al powder mixtures. Effects of the overall C:Ta ratios and the Al addition on constituent phases, microstructures and mechanical properties of the consolidated materials were examined. Results showed that O impurity contained in the starting powders was collected in form of Al 2 O 3 due to strong affinity of O with Al. The TaC x -Al composites were easy to densify due to presence of molten Al at its melting point ( T m  = 660 °C) and a transient Al–Ta eutectic liquid at higher temperatures. After densification, the metallic liquids were eliminated ultimately by formation of refractory Ta 4 AlC 3 via reaction of Al, Ta and TaC. Reactions between the remnant Ta and TaC after Ta 4 AlC 3 formation resulted in ζ-Ta 4 C 3-z or h-Ta 2 C depending on the initial C:Ta ratio. The Ta 4 AlC 3 compound was compatible with the tantalum carbides. Microstructures of the TaC x -Al (x = 0.5–0.7) composites were consisted of ζ-Ta 4 C 3-z and Ta 4 AlC 3 fine lamellar grains to benefit the mechanical properties of the composites. The TaC 0.7 –20mol% Al composition had satisfying mechanical properties (flexural strength 613 ± 28 MPa and fracture toughness 11.2 ± 0.8 MPa m 1/2 ). TG-DSC evidenced an increase in oxidation resistance of the TaC x ceramics by the addition of 20 mol% Al.