Abstract

In the last two decades, a new class of ceramics has emerged that has challenged their typical description as materials that are hard, difficult to machine, and susceptible to damage and thermal shock. This class of 160+ members – known as the MAX phases – share common unique chemical formula Mn+1AXn, (where n = 1, 2 or 3, M is and early transition metal, A is an mostly group 13-16 elements, and X is either C or N) and naonolayered crystal structure in which strongly bonded MX layers are interleaved by weakly bonded A layers. The main reason for growing interest in MAX phases lies in their unusual mechanical properties in general, and high damage tolerance in particular. In general, MAX phases are elastically stiff, good thermal and electrical conductors, resistant to chemical attack, and have relatively low thermal expansion coefficients, but also relatively soft and most readily machinable, thermal shock resistant and damage tolerant. Moreover, some of them – notably Ti2AlC and Ti3SiC2 – are fatigue, creep, and oxidation resistant. Therefore, MAX phases are considered to be a good candidate materials, especially for high temperature structural applications in extreme environments. This seminar lecture provides an overview of the current understanding of mechanical behavior of MAX phases, with the special focused on their deformation by kinking that can be traced back to their naolaminated crystal structure. Deformation and failure mechanisms below and above brittle to plastic transition temperature in MAX phases are reviewed, as well as effect of microstructure (i.e. grain size and secondary phases) on the observed mechanical behavior of polycrystalline MAX phases. Furthermore, anisotropic deformation and failure mechanisms in MAX single crystals, micropillars and cantilevers is discussed in more details. Possibilities for further improvements in mechanical properties of MAX phases by tailoring their composition and microstructure are also briefly discussed in this presentation.