Deformation Mechanisms in Mn+1AXn Phase Ternary Ceramics at High Strain Rates

Abstract

The present study is concerned with understanding the high strain rate deformation mechanisms and the role of microstructural characteristics in Mn+1AXn phase ternary ceramics. These materials crystallize in a Hexagonal Close Packed (HCP) structure with a c/a ratio greater than 1.67 which results in kink band formations when subjected to loading. In this work, we report the high strain rate deformation and fracture mechanisms observed in Ti2AlC, a ternary ceramic, when subjected to dynamic compressive loading (~1,200 s−1) using a Split Hopkinson Pressure Bar (SHPB) technique and 2-D high speed Digital Image Correlation (DIC) to measure in-plane displacements. Specimens with different geometries are tested due to the tendency of these materials to fracture prematurely and also due to lack of established experimental protocols for testing ternary ceramics using SHPB (in comparison to metals, ceramics, polymers), which is another objective of the study. The fractography analysis, done using a Scanning Electron Microscope (SEM), reveals the dominant fracture mechanisms to consist of kink band formations, grain folding and delamination, cavity formation, delamination of the nano-laminates, grain pullout, and tearing etc. These features, though observed under static loading conditions, initiate and propagate in the material by a completely different mechanism. Qualitative and quantitative comparison show dynamic loading leads to more advanced deformation modes.KeywordsMAX phase ternary ceramicsSplit Hopkinson Pressure Bar (SHPB)Digital Image Correlation (DIC)High strain rate