The mechanical behavior of nanoscale Al-TiN multilayered composites was studied using micropillar compression experiments, which were compared with previously performed nanoindentation experiments, and the microstructure was investigated using scanning and transmission electron microscopy. It was found that at extremely small layer thicknesses (<5 nm) the nanoscale multilayers acquire remarkable hardness (∼6 GPa), high flow strengths (∼4.5 GPa maximum) and high compressive deformability (5-7% plastic strain). These high strengths were accompanied by extraordinarily high strain-hardening rates in the Al layers, which were of the order of 16-35 GPa (∼E/4-E/2) in "regime II" of the stress-strain curve of the compression tests in the 2-4 nm layered films and 5-9 GPa in the Al-18 nm-TiN-2 nm layered films, where Al layers deform plastically and TiN layers are deformed elastically. The high strengths and high work-hardening rates are discussed and analyzed using the concepts of dislocation motion and interactions within the confined nanoscale Al layers.
Bibliographical noteFunding Information:
The authors wish to thank J. K. Baldwin at LANL for assistance with magnetron sputtering of Al/TiN multilayers. The very fruitful discussions with Prof. J. P. Hirth and Prof. W. D. Nix are gratefully acknowledged. This work was funded by the Office of Basic Energy Sciences (BES) of the Office of Science, Department of Energy of the United States Government. The Center for Integrated Nanotechnologies, a BES user facility, is acknowledged for nanoindentation access through an approved user proposal with N. A. Mara.
- Compression test
- Plastic deformation