Grain Size Effect on Mechanical Behavior of Nanocrystalline Alloy Films

The effect of grain size in nanocrystalline alloys is difficult to analyze because challenges of controlling a number of other microstructure factors. This paper designed and prepared a series of multilayered films with Al-Zr crystalline layers of different thickness but with amorphous layers of identical thickness. In these multilayered films, the heights of columnar crystals in crystalline layers were controlled from 5 to 160 nm and their diameters were kept at 10 to 15 nm, independent of their heights. This design achieved the control of grain size, independent from other microstructure factors. The analysis of mechanical properties of these multilayered films showed that the inverse Hall-Petch phenomenon also exists in Al-Zr nanocrystalline alloys. The critical grain sizes of deviation from the Hall-Petch relationship and the inverse Hall-Petch phenomenon are approximately 40 nm and 10 nm respectively. These mechanical behaviors of nanocrystalline alloys are similar to those reported in pure metals.