Exceptional thermal stability and mechanical properties of dual-phase amorphous-nanocrystalline Al–Mo alloy films

Dual-phase amorphous-nanocrystalline Al-x at.% Mo (x = 20, 26, 30) alloy films prepared in the way of dual-phase co-growth directly through magnetron sputtering were studied in terms of thermally induced microstructural evolution and mechanical properties via annealing at 550 °C. It was observed that, the annealed Al-26 and 30 at.% Mo alloy films maintained stable dual-phase amorphous-nanocrysatlline structure and precipitated Al8Mo3 nano-grains dispersed in amorphous matrix uniformly. After annealing, the surface roughness of Al-26 and 30 at.% Mo alloy films remained unchanged of 7.5 nm and the hardness and elastic modulus of them were as high as 13 and 210 GPa which enhanced about 50 % and 24 % than before, respectively. In contrast, the Al-20 at.% Mo alloy film crystallized completely and mainly contained intermetallic Al12Mo phase along with apparent grain coarsening after annealing, which resulted in significant increase of surface roughness and deterioration of hardness. The excellent thermal stability of dual-phase amorphous-nanocrystalline Al-26 and 30 at.% Mo alloy films stem from the small driving force for precipitated Al8Mo3 nano-grain growth, as well as benefit from effect of diffusion field impingement.