On the elastic properties and mechanical damping of Ti3SiC2, Ti3GeC2, Ti3Si0.5Al0.5C2 and Ti2AlC in the 300–1573 K temperature range

In this paper we report on the temperature dependencies of Young’s, E, and shear moduli, μ, of polycrystalline Ti3SiC2, Ti2AlC, Ti3GeC2 and Ti3Si0.5Al0.5C2 samples determined by resonant ultrasound spectroscopy in the 300–1573 K temperature range. For the isostructural 312 phases, both the longitudinal and shear sound velocities decrease in the following order: Ti3SiC2 > Ti3Si0.5Al0.5C2 > Ti3AlC2 > Ti3GeC2. Like other phases in the same family, these solids are relatively stiff and lightweight. The room temperature E values range between 340 and 277 GPa for Ti2AlC to 340 GPa for Ti3SiC2; the corresponding μ values range between 119 and 144 GPa. Poisson’s ratio is around 0.19. Both E and μ decrease linearly and slowly with increasing temperature for all compositions examined. The loss factor, Q−1, is found to be relatively high and a weak function of grain size and temperature up to a critical temperature, after which it increases significantly. Modest (4% strain) pre-deformation of Ti3SiC2 at elevated temperatures results in roughly an order of magnitude increase in Q−1 as compared to as-sintered samples, which led us to the conclusion that the damping is due to the interaction of dislocation segments with the ultrasound waves. That Q−1 decreases with increasing strain amplitude is consistent with such an interpretation. The loss factors of the deformed Ti3SiC2 sample are orders of magnitude higher than those of typical structural ceramics. The technological implications of having readily machinable solids that have stiffnesses comparable to Si3N4 and damping capabilities comparable to some woods are obvious and are discussed.