Tensile creep of textured Ti₂AlC in the 1000–1150°C temperature range

Alumina forming, oxidation and thermal shock resistant MAX phases are of high interest for high temperature applications. Herein we report on the fabrication of a highly textured Ti₂AlC MAX phase and its creep behavior. Creep rates were measured in the temperature range of 1000–1150 °C under a tensile stress range of 15–50 MPa. The minimum creep rate is given by a power law, with stress exponent of 2.5 ± 0.1 and an apparent activation energy of 320 ± 20 kJ/mol. The textured Ti₂AlC samples has significantly lower creep rates than their untextured counterparts, and their times to failure are longer. These enhancements can be partially attributed to the ability of the textured grains, whose basal planes were parallel to the applied load, to form crack bridges. Transmission electron microscopy indicated the defect density before creep was higher than after creep and that the vast majority of grains were defect-free. And while this observation cannot be explained in a dislocation framework, it can in a ripplocation one. We carried out molecular dynamics calculations on graphite showing that ripplocations near a free surface can readily escape, even at 10 K, in principle, solving the mystery.