Synthesis and characterization of Ti2AlC coatings by magnetron sputtering from three elemental targets and ex-situ annealing

Abstract

MAX phase materials have demonstrated great potential applications both as bulk and coating due to their unique properties. Deposition of phase-pure polycrystalline MAX phase coatings often remains a challenge. In this study, Ti-C-Al elemental nanolayer stacks deposited by non-reactive magnetron sputtering followed by ex-situ annealing was adopted to prepare Ti2AlC coatings on two different substrates, Si and SiO2/Si. No Ti2AlC phase was formed on Si substrate due to significant interdiffusion between the coating and the substrate during annealing. Phase-pure, i.e. single-phase Ti2AlC coatings with 3μm thickness on SiO2/Si were obtained after 800°C annealing in argon for 10min. The crystalline transition from the non-MAX competing phases to Ti2AlC MAX phase was found to appear in the region of 600°C–700°C. The microstructural evolution of the coatings during annealing from 600°C to 900°C was systematically investigated by X-Ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM). The reaction path for the formation of Ti2AlC is suggested as follows: first, aluminum reacted with titanium to form a Ti-Al intermetallic phase (i.e. Al3Ti), and the diffusion between the residue titanium and carbon produced non-stoichiometric TiCx; then, the reaction between the Al3Ti intermetallic and TiCx yielded the formation of Ti2AlC MAX phase.