Effect of Bilayer Thickness on Hardness of Ag/Ni Nanoscale Multilayers

Ag/Ni 나노다층박막의 경도에 미치는 Bilayer 두께의 영향

Ag/Ni multilayers with different bilayer thickness between 3 and 100 nm produced by DC magnetron puttering have been studied by cross-sectional TEM and nanoindentation. The micrograph shows perfect layered structure with sharp interfaces between Ag and Ni layers. Absolute hardness is calculated as a reference value to compare hardness of specimens regardless of indent depth. A hardness enhancement of nearly $100\%$ over the rule-of-mixtures values, calculated from the measured hardness of single Ag and Ni thin films, is observed. The hardness increases with decreasing bilayer thickness until 8nm. This enhancement shows a good agreement with Hall-Petch relation using grain size (one half of the bilayer thickness) confined within a layer. The deformation behavior can be explained by dislocation pile-up in smaller grains.