Deformation-Controlled Design of Metallic Nanocomposites.

Achieving the theoretical strength of a metallic alloy material is a demanding task that usually requires utilizing one or more of the well-established routes: i. decreasing the grain size to stop or slow down the dislocation mobility, ii. adding external barriers to dislocation pathways, iii. altering the crystal structure, or iv. combining two of the previous discrete strategies, i.e., implementing crystal seeds into an amorphous matrix. Each of the outlined methods has clear limitations, hence further improvements are required. We present a unique approach that envelops all the different strength-building strategies together with a new phenomenon - phase transition. We simulated the plastic deformation of a Zr-Nb nanolayered alloy using molecular dynamics and ab initio methods, and observed the transition of Zr from HCP to FCC, and then to BCC during compression. The alloy, which was prepared by magnetron sputtering, exhibited near-theoretical hardness (10.8 GPa) and the predicted transition of the Zr structure was confirmed. Therefore, we have identified a new route for improving the hardness of metallic alloys.