Shear banding suppression in Cu/TiZrNb nanolayered composites through dual crystalline/amorphous interfaces

Abstract

Medium/high entropy alloys (M/HEAs)-based nanolayered composites have attracted intense scientific interest due to the improved mechanical properties. However, the shear banding (or shear instability) behavior of the M/HEAs-based nanolayered composites is rarely studied due to the lack of theoretical model to quantify the shear banding-induced strain localization. Herein, the size-dependent strengthening and shear instability behavior of Cu/amorphous TiZrNb nanolayered composites with individual layer thickness (h) of 2–100 nm was systematically investigated by using a combination of nano/microindentations and a detailed theoretical analysis. The results show that the strength of the Cu/TiZrNb composites obeys the trend of “smaller is stronger”. The size-dependent strengthening behavior of the samples with h in the range of 10–100 nm can be well described by the confined layer slip model, while the continuous increase in strength of those with h = 2 and 5 nm is related to the gradually amorphization of the Cu layers. It is intriguingly found that the shear instability of the Cu/TiZrNb composites shows a first-decrease-and-then-increase size dependence, which is apparently different from that of existing face-centered cubic/amorphous nanolayered composites that exhibits a monotonic size dependence. The non-monotonic trend leads to a significantly suppressed shear instability in the sample with h = 50 nm, in which only slight kinks are observed in microindentation. The enhanced resistance to shear banding is attributed to the dual crystalline/amorphous interfaces generated by the layered structure and the amorphous TiZrNb constituent layers that contains crystalline phase at h > 10 nm.