High strain-rate response and deformation mechanisms in polycrystalline Ti2AlC

Ti2AlC is a representative member of MAX phase materials, which are known to exhibit a unique combination of properties observed in conventional ceramics and metals. In this paper, experimental protocols for the high strain-rate compressive response (up to ~4700 s−1) using a Split Hopkinson Pressure Bar (SHPB) is developed. The optimized specimen geometry for Ti2AlC, derived in this work, ensures dynamic equilibrium and minimizes dispersion in the transmitted pulse. A modification of the conventional SHPB experimental set-up involves in situ high speed imaging, which facilitates identification of real strains free of macroscopic crack artifacts. Characteristics of the high strain-rate response of polycrystalline Ti2AlC, associated deformation mechanisms and micro-scale origins are presented. The results show that Ti2AlC shows significant inelastic deformation and strain softening before fracture, even at very high strain-rates. Post-fracture microstructures are analyzed to determine dominant deformation mechanisms which reveal simultaneous coexistence of kink bands and delamination, grain-pullouts and trans-granular cracks induced by high strain-rate loading. These deformation characteristics – also active under quasi-static loading, are responsible for the exceptional damage tolerance of Ti2 AlC and provide experimental evidence for high rate kink banding in MAX phases.