Synthesis and characterization of Ti₃SiC₂

Tamer S. El-Raghy

doi:10.17918/00000715

For the first time, bulk, single phase, fully dense Ti₃SiC₂ samples were fabricated by hot pressing or hot isostatic pressing of Ti, SiC, and C powders. This compound is as readily machinable as graphite, has a Young's modulus of 325 GPa and a hardness of 4 GPa. Its electrical conductivity is 4.5x10^6 [Omega]^-1 m^-1. The thermal expansion coefficient in the temperature range 25 to 1000[degrees]C, the room temperature thermal conductivity, and heat capacity are, respectively, 9.2x10^-6 [degrees]C^-1, 43 W/m. K and 588 J/kg K. By controlling the process, the final grain size fabricated was fine (3-5 [mu]m) or coarse (100-200 [mu]m). For both microstructures the failure is brittle at room temperature, but above 1200[degrees]C the failure is ductile. At 1300[degrees]C, both microstructures exhibited high levels of plasticity (>20%). Both the fine and the coarse grained materials were found to be damage tolerant. Although the coarse grains material is not susceptible to thermal shock up to 1400[degrees]C, the fine grains material was found to thermal shock between 750 and 1000[degrees]C. Oriented macro-grains (1-4 mm) of Ti₃SiC₂ were fabricated to study the deformation mechanism. We have shown conclusively that there is an active slip system (across the basal planes) at room temperature which results in the room temperature plasticity. It was found that grain buckling and cavities formation are two mechanisms by which the material accommodates the strain. The oxidation was parabolic with parabolic rate constants, kp, that increased from 1x10^-9 to 1x10^-4 kg^2 m^-4 s^-1 as the temperature increased from 900 to 1400[degrees]C, respectively, which yielded an activation energy of 370 +/- 20 kJ/mol. The scale that forms was dense, adhesive, resistant to thermal cycling and layered. Carburization, nitridation and siliconization resulted in the formation of, respectively, TiCx, TiN-TiCx-SiC and TiSi2-SiC surface layers. In general the surface treatments resulted in hardnesses of 12-20 GPa. The siliconization also enhanced the oxidation resistance by more than 3 orders of magnitude. Activation energies of 370 and 130 kJ/mol were measured in carburization and siliconization, respectively.

Synthesis and characterization of Ti₃SiC₂

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Synthesis and characterization of Ti₃SiC₂

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