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.
Highlights
Multilayer nitride coatings with nanoscale layer thickness have exhibited extremely high mechanical hardness due to dislocation blocking by layer interfaces and Hall–Petch strengthening [1].By contrast, the hardness enhancement in the Y2 O3 /ZrO2 superlattice has been limited because oxides are brittle materials that are deformed by fracture mechanisms [2]
Our previous studies [12,13,14,15] investigated the internal oxidation of Ru-based alloy multilayer coatings annealed at 600 ◦ C in oxygen-containing atmospheres for the application of protective coatings on glass molding dies
The specific cosputtering processes, which were performed using a substrate holder rotating at a slow speed of one to seven revolutions per minute, have been examined in detail for fabricating Ru–Ta coatings [14]; the fabricated coatings had exposed substrates alternately to the sputter sources without shutter shielding, forming a multilayer structure with a cyclical gradient concentration period at a nanometer scale
Summary
Multilayer nitride coatings with nanoscale layer thickness have exhibited extremely high mechanical hardness due to dislocation blocking by layer interfaces and Hall–Petch strengthening [1].By contrast, the hardness enhancement in the Y2 O3 /ZrO2 superlattice has been limited because oxides are brittle materials that are deformed by fracture mechanisms [2]. Our previous studies [12,13,14,15] investigated the internal oxidation of Ru-based alloy multilayer coatings annealed at 600 ◦ C in oxygen-containing atmospheres for the application of protective coatings on glass molding dies. An oxidized laminated structure formed because of the inward diffusion of oxygen during the annealing process; this structure comprised alternating oxygen-rich and oxygen-deficient sublayers stacked adjacent to the surface. Because the elements were stacked on the substrate with an alternating gradient concentration, the O atoms could diffuse through the paths in the transverse direction, thereby forming oxide sublayers. After the oxygen content in the oxide sublayers reached a saturation level, the grainboundary diffusion along the original columnar structure drove oxygen
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