Properties of ceramics in the system ZrB₂–Ta₅Si₃

Abstract

Ceramics in the system ZrB 2 -Ta 5 Si 3 were studied as candidates for the development of new ultra high-temperature ceramic materials. The ceramics were prepared by hot pressing at 1900-2200°C in He. Mutual additions of ZrB 2 and Ta 5 Si 3 even in small amounts had significant densifying effects due to chemical interactions and solid solubility between the components, which have not been reported in the literature. Materials containing between 8 and 30 vol% Ta 5 Si 3 exhibited less oxidation than pure ZrB 2 , which is the result of phase separation in surface borosilicate glass induced by Ta 2 O 5 . For higher concentrations, oxidation resistance substantially decreased with increasing Ta 5 Si 3 content. The trend in the oxidation behavior of the materials showed significant dependence on the volume of oxidation products. Ceramics containing up to 10 mol% (30 vol%) Ta 5 Si 3 , which showed the highest oxidation resistance, also had the highest strength and hardness in the system, and are of interest for high-temperature structural applications in oxidizing environments.

Oxidation of TaSi2-Containing ZrB2-SiC Ultra-High Temperature Materials~!2009-09-08~!2009-12-23~!2010-04-20~!

“…( 6). This solution phase has been previously observed [8,10] and is reasonable since both ZrB2 and TaB2 have a hexagonal crystal structure. XRD results showed that the (100), (101), and (111) peaks for ZrB2 all exhibited shoulders displaced by 0.1 to 0.5 degrees 2theta higher indicating reduction of the lattice parameters of the hexagonal ZrB2 structure with the introduction of TaB2…”

“…(3). Talmy et al [7][8][9] attribute similar observations of glass immiscibility to Ta additions to the system. EDS analysis [10] of the immiscible phases in Fig.…”

“…Talmy et al showed that two to twenty mol% TaB2 additions to ZrB2-SiC resulted in improved oxidation resistance at temperatures between 1200 and 1400C [7]. Similarly, Ta5Si3 and TaSi2 additions in the amounts of 8-31 v% showed improved oxidation resistance relative to ZrB 2 at temperatures between 1100 and 1400C in air for times of two to three hours [8,9]. In all cases, Talmy showed evidence for immiscible glass formation in the oxidation products and attributed the improved oxidation resistance to the steeply rising liquidus temperatures, increased viscosity, and decreased oxygen diffusivity [7] of the phase-separated glasses.…”

Thermochemical and Mechanical Stabilities of the Oxide Scale of ZrB2+SiC and Oxygen Transport Mechanisms

“…SiO 2 ðlÞ þ COðgÞ (2) respectively. Intense research is ongoing to characterize and enhance this scale as a barrier against oxygen [11][12][13][14][15][16][17][18][19][20][21][22][23] (the scale microstructure can be seen in, for example, Fig. 4 of Opila et al 15 ), which apparently is superior to that of either monolithic diboride or SiC at the intended high temperatures (see Fig.…”

Toward Oxidation-Resistant ZrB2-SiC Ultra High Temperature Ceramics

“…Ta 5 Si 3 provides the tantalum to induce glass immiscibility and silicon to form the protective borosilicate glass in the oxidized layer. [39] ZrB 2 -and HfB 2 -TaSi 2 composites have been formed by hot pressing, [40] resulting in formation of a solid solution as the tantalum entered the boride matrix. The HfB 2 -TaSi 2 displayed superior mechanical properties to the ZrB 2 -based material.…”