Unveiling effects of Zr alloying on structure and properties of nanocrystalline Cu-Zr films

• Nanocrystalline Cu-Zr thin-film materials with low Zr content. • Significant structural refinement and texture weakening induced by Zr alloying. • Extended Zr solubility in the FCC Cu crystal lattice. • Surface roughness tuned by Zr alloying. • Balance between enhanced hardness and good electrical conductivity. Nanocrystalline Cu-Zr films with Zr content in the range of 0.3–2.7 at.% were deposited by direct current magnetron sputter deposition. Effects of Zr alloying on the structure, surface, mechanical, and electrical properties were systematically investigated using X-ray diffraction, electron microscopy, atomic force microscopy, indentation, and the four-point probe method. The experimental results revealed that the Zr content significantly affects the structural and functional characteristics of the films, with the most notable changes observed between 0.3 and ≈1.5 at.% Zr. Beyond this range, further increase in the Zr content results in only minor changes in the microstructure and mechanical properties, while the solubility, electrical resistivity, and surface roughness continue to rise. The alloyed Cu-Zr films exhibit hardness values between 3.2 and 4.2 GPa, exceeding 2.5 GPa measured for the unalloyed Cu film, which is attributed to the combined effect of grain boundary strengthening due to structural refinement and Zr segregation, along with solid solution strengthening.