Extended elastic region in nanocrystalline HCP and FCC metals under nano-tension loading

Nano-scaled mechanical properties have become important for abundant submicron and nano electronic or mechanical devices. However, the nano-scale mechanical tests have not been developed widely. In this study, a new nano-tension test specimen is designed, using the focused ion beam (FIB) machining. The dimension of the nano-tension gage section can vary from 50 to 1000 nm. The test can be conducted by the widely available nano-indentation facility with a flat tip. The downward applied load from the flat tip onto the central beam (in compression) can be easily transferred to the two-side tension gage sections (in tension). Various pure metals such as face-centered cubic Al and Cu and hexagonal close-packed Mg, Zr, and Ti are selected for the test run. The yield stress and elastic strain are seen to be exceptionally high. The extended elastic region is carefully examined by reproducible experiments and molecule dynamic simulation. It is not considered to be an artifact by FIB machining, but appears to be a common phenomenon for metallic materials in the nano scale when the dislocation activity is difficult to be fully functioned.