The Thermo-Mechanical Properties of novel MAX phase Ceramics

The main focus of this research work was to investigate the high-temperature mechanical performance of the electrically conductive Ti2AlC and Ti3SiC2 MAX phases. Using microscopy techniques, it was found that Ti2AlC had a grain size approximately 4 times larger than the Ti3SiC2 material. Secondary phases were also found to be present in both materials. Electron backscatter diffraction analysis revealed that both materials appeared to have a random texture. A Gleeble 3500 was used to test each materials response to high-strain rate, high-temperature uniaxial compression testing. Ti3SiC2 was found to generally have higher ultimate compressive strengths for each test condition and thereby validating a Hall-Petch relationship. For Ti2AlC, the slower the strain rate, the lower the ultimate compressive stress and also, for each strain rate, the higher the temperature, the lower the ultimate compressive stress. The behaviour of Ti3SiC2 was more incoherent, although generally followed a trend of increasing ductility as the temperature was increased and strain rate decreased. Both MAX phases were thermally shocked while being subjected to a compressive load from either 1000°C or 1200°C. For the 1000°C samples, there was a slight increase in the ultimate compressive stress when the compressive load was increased, while the for the 1200°C samples the change in compressive loads under quenching had no significant effect on the mechanical properties. The microstructure of the thermo-mechanically tested samples revealed substantial deformation in the form of intergranular and transgranular cracking, kinking, delaminations, voids and grain bending. The ductile samples saw a deformation ‘dead zone’ at the edges that had been closest to the compression anvil. The EBSD analysis revealed that the primary phase in samples tested at slower strain rates orientated favourably to the [0001] direction. These samples also showed evidence of low angle grain boundaries. A GND analysis of both materials was also undertaken and revealed higher GND densities with increasing strain rate and temperature for Ti3SiC2 samples, with the opposite being true of Ti2AlC samples