**1. Introduction**

The nanoscaled internal features, in which two quantities, i.e., the *characteristic length* and the *size parameter* likely overlap, render the conventional deformation mechanisms and size laws often break down and even be reversed in nanostructured (NS) metallic materials, including nanocrystalline (NC) and nanotwinned (NT) materials [1–3]. Indeed, for many purposes, making the crystals as small as possible provides significant advantages in performance, but such materials are often unstable: The crystals tend to merge and grow larger even at room temperature (RT) [4–7]. To suppress the nanograin growth and maintain the nanoscale microstructure, two approaches can be adopted [8–15]: (i) Thermodynamic approach: reduction

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

of the driving force for grain growth by segregation of the solutes at the grain-boundaries (GBs), (ii) Kinetic approach: reduction of the GB mobility, by e.g., porosity, solute atoms, and precipitates at the GBs, which impose drag forces.

In this chapter, first, a brief introduction of mechanical stress-driven grain growth in NS Cu and Ni thin films/foils as well as their mechanical properties will be provided in terms of sizedependent deformation mechanisms. Subsequently, dopants segregation at GBs to hinder grain coarsening and enhance mechanical properties via the alloying method is discussed in three representative binary Cu-based systems, i.e., Cu-Zr, Cu-Al, and Cu-W.
