Mechanical damping in porous Ti3SiC2 Original Research Article

The ternary compound Ti3SiC2 is the most studied of a family of machinable ternary carbides and nitrides, the so-called MAX phases. Those compounds, in turn, belong to a larger class of recently classified solids, kinking nonlinear elastic solids, because they deform mainly by the formation of regular and incipient kink bands. This kinking leads to exceptionally high damping properties, which are influenced by porosity. We report on a systematic study of the effect of porosity levels – ranging from 0 to 55 vol.% – on the damping properties of Ti3SiC2. The major effects of porosity are, first, a reduction in the threshold stress needed for kink band formation, a reduction that stems mostly from concomitant reductions in the shear moduli; and, second, a reduction in the ultimate compressive stresses. The presence of porosity does not greatly affect the specific damping capacity, which hovers around 0.15, at near the maximal stresses. It follows that porosity level, like grain size, becomes a useful microstructural variable that can be used to tune the stress level over which the damping is required.