Elevated Temperature Deposition of Metal (Nb, Ti) – Max (Ti2alc) Phase Nanolaminates: Synthesis, Microstructure and Micro-Mechanical Characterization

Abstract

We utilize elevated temperature physical vapor deposition techniques to design metal/MAX multilayered nanocomposite thin films with alternating nanoscale metallic (Nb, Ti) and MAX phase (Ti2AlC) layer thicknesses. These metal/MAX nanolaminate architectures attempt to exploit a unique hierarchical topology – as interfaces between the layers are expected to be in direct competition with the internal interfaces within the MAX layers, to drive their tunable macroscopic mechanical behavior. Our first deposition attempt with the Nb/Ti2AlC metal/MAX system showed highly diffused layer interfaces with distinct Ti rich and Nb-Al  rich layers, with the presence of MAX phase alongside TiC and other Ti-Al and Nb-Al intermetallic phases. The Nb/Ti2AlC system possessed a layered architecture, though the MAX phases were not found to be continuously present in each alternating layer. The second Ti/Ti2AlC system showed a non-lamellar nanocomposite microstructure and the formation of mixed Tin+1AlCn phases (a mix of n = 1, 2), and no indication of layering. Diffusion occurring between the metal/MAX layers in both cases, likely due to the elevated temperatures during the deposition process, is speculated as the likely cause of these resultant microstructures. The mechanical properties of both systems were evaluated using micromechanical (nanoindentation and micro-pillar compression) techniques, and were found to be within the bounds predicted by composite theory for the Nb system (yield and instability strengths of 4.88±0.1 GPa and 5.57±0.03 GPa ) and just short of expectations for the Ti system (yield and instability strength of 5.61±0.28 GPa and 6.21±0.25 GPa). This work provides important insights for future depositions, such as the need to effectively block/mitigate interlayer diffusion by either lowering the deposition temperature or adding a third layer that can act as a diffusion barrier.

Keywords: Multilayers, Nanocomposite, Max phase, PVD, Microcompression, nanoindentation, TEM