Preparation and characterization of tantalum carbide (TaC) ceramics

Synthesis, properties and thermal decomposition of the Ta4AlC3 MAX phase

“…Since -Ta4AlC3 was the only phase present in samples made by HP at 1500C and 1600°C, the measured density can be compared to the theoretical density (TD) of -Ta4AlC3 (TD = 12.92 g/cm 3 [1]) or mixtures of -Ta4AlC3, β-Ta4AlC3 (TD = 13.36 g/cm 3 [1]), Ta2AlC (TD = 11.82 g/cm 3 [1]) and TaC (TD = 14.49 g/cm 3 [28]). The densities of the samples produced by HP at 1500°C and by SPS at 1600°C were all lower than the theoretical density of - Ta4AlC3 (Table 2), due to the presence of limited residual porosity and a roughly estimated 1 ± 2 wt% amount of Al2O3 (TD = 3.98 g/cm 3 [29]). The weight percent of Al2O3 could not be accurately estimated by Rietveld refinement, because its amount was close to the XRD detection limit and several diffraction peaks overlapped with those of the MAX phases, i.e., planes (012) and (008) in 413 and (004) in 211.…”

Mechanical properties of tantalum carbide from high-pressure/high-temperature synthesis and first-principles calculations

“…4,5 Its melting point reaches an extremely high 3983 1C and TaC has therefore attracted great research interest. [6][7][8] Up to now, mostly fully dense TaC has been synthesized, with Vickers hardness about 11.1-15.7 GPa, [9][10][11] thus limiting extended engineering applications. To fully exploit TaC's potential and to extend the application range of TaC-based ceramic materials it is of crucial importance to understand the origin of TaC's mechanical properties and the underlying deformation mechanisms in the structural failure process at an atomic level.…”

“…High-densification monolithic TaC ceramics were prepared by the hot pressing method, leading to a Vickers hardness between 11.1 and 15.7 GPa. [9][10][11]19 TaC synthesized using spark plasma sintering (SPS) 20,21 is reported to have a hardness of 13.9 GPa, 22 while high-pressure high-temperature (HPHT) synthesis of TaC yielded a hardness of 19.2 GPa. 23 This leads to the question, what is the underlying mechanism behind those different hardnesses in the same TaC system?…”

Microstructure and mechanical properties of TaC ceramics with 1–7.5 mol% Si as sintering aid

“…Addition of small particles, such as SiC, TaB 2 , TaSi 2 , Si 3 N 4 , and short fibers could increase UHTCs densification. Using ultrafine TaC powders as starting material also facilitated densification . Oxygen in the powder causes exaggerated growth of TaC grains at high temperatures to trap residual pores.…”

“…Using ultrafine TaC powders as starting material also facilitated densification. [19][20][21][22][23] Oxygen in the powder causes exaggerated growth of TaC grains 9,10 at high temperatures to trap residual pores. Accordingly, reductive agents such as B 4 C 15 and C 6 were added to TaC and were effective in increasing TaC densification because of elimination of the oxide impurities.…”