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

Abstract In this paper we report on the temperature dependencies of Young’s, E , and shear moduli, μ , of polycrystalline Ti 3 SiC 2 , Ti 2 AlC, Ti 3 GeC 2 and Ti 3 Si 0.5 Al 0.5 C 2 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: Ti 3 SiC 2 > Ti 3 Si 0.5 Al 0.5 C 2 > Ti 3 AlC 2 > Ti 3 GeC 2 . 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 Ti 2 AlC to 340 GPa for Ti 3 SiC 2 ; 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 Ti 3 SiC 2 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 Ti 3 SiC 2 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 Si 3 N 4 and damping capabilities comparable to some woods are obvious and are discussed.