A Comparative Study of Decomposition Kinetics in MAX Phases at Elevated Temperature

Abstract

The role of pore microstructures on the susceptibility of MAX phases (Ti3SiC2, Ti3AlC2, Ti2AlC, Ti2AlN2, Ti4AlN3) to thermal dissociation at 1300-1550 °C in high vacuum has been studied using in-situ neutron diffraction. Above 1400 °C, MAX phases decomposed to binary carbide (e.g. TiCx) or binary nitride (e.g. TiNx), primarily through the sublimation of Aelements such as Al or Si, forming in a porous surface layer of MXx. Positive activation energies were determined for decomposed MAX phases with coarse pores but a negative activation energy when the pore size was less than 1.0 µm. The role of pore microstructures on the decomposition kinetics is discussed.