lamellar interface between BCC and MC phase presents a smooth and curvy morphology which exhibits good bonding with no lattice misfit dislocations. As a result, the grain size decreases with increasing TaC addition which improves the yield stress explained by Hall-Petch relationship. The formation of lamellar structure is because at elevated temperature, the decomposition reaction occurs in the MoNbRe0.5W(TaC)x composites: (Mo, Nb, W, Ta)2C → (Mo, Nb, W, Ta) + (Mo, Nb, W, Ta)C in which Re is dissolved in both components to nucleate BCC phase first and MC phase in the following, according to the phase diagrams. In addition, the MC phase also improves the strength of composites, due to its stiffer and more elastic property compared to BCC phase. Wu et al. have also synthesized Ti(C, N)-based cermets with TaC addition with ball-milling and sintering at 1683K. TEM analysis showed that TaC helps dissolution of carbonitride phase and converts to TaC-binder phase. The resulting is a formation of “black-core-white rim” structure with decreasing grain size in the region of 3-5 wt% TaC addition and increasing transverse rupture strength (TRS). 0-3 wt% TaC region showed a decrease in the TRS because the TaC addition decreases the wettability between binder and carbonitride phase and creates pores. Further addition of TaC beyond 5 wt% also decreases TRS because TaC agglomerates during sintering and porosity again forms. The best TRS is found at 5wt% addition where fine grains and homogeneous microstructure are achieved for less grain boundary sliding. Natural occurrence Tantalcarbide is a natural form of tantalum carbide. It is a cubic, extremely rare mineral. See also Tantalum hafnium carbide Hafnium carbide Hafnium carbonitride References Carbides Tantalum compounds Superhard materials Refractory materials Native element minerals Rock salt crystal structure