**Yung-I Chen \*, Tso-Shen Lu and Zhi-Ting Zheng**

Institute of Materials Engineering, National Taiwan Ocean University, 2 Pei-Ning Road, Keelung 20224, Taiwan; x76825@gmail.com (T.-S.L.); 10455001@ntou.edu.tw (Z.-T.Z.)

**\*** Correspondence: yichen@mail.ntou.edu.tw; Tel.: +886-2-2462-2192

Academic Editors: Tony Hughes and Russel Varley Received: 20 February 2017; Accepted: 21 March 2017; Published: 23 March 2017

**Abstract:** In this study, equiatomic Ru–Zr coatings were deposited on Si wafers at 400 ◦C by using direct current magnetron cosputtering. The plasma focused on the circular track of the substrate holder and the substrate holder rotated at speeds within 1–30 rpm, resulting in cyclical gradient concentration in the growth direction. The nanoindentation hardness levels of the as-deposited Ru–Zr coatings increased as the stacking periods of the cyclical gradient concentration decreased. After the coatings were annealed in a 1% O2–99% Ar atmosphere at 600 ◦C for 30 min, the internally oxidized coatings shifted their respective structures to a laminated structure, misaligned laminated structure, and nanocomposite, depending on their stacking periods. The effects of the stacking period of the cyclical gradient concentration on the mechanical properties and structural evolution of the annealed Ru–Zr coatings were investigated in this study.

**Keywords:** cyclical gradient concentration; internal oxidation; multilayer coating; nanocomposite coating
