Effect of controlled yttrium oxidation on microstructure, mechanical property and thermal stability of Nb/Y nanometallic multilayer films

Inspired by the ease of oxidation of yttrium (Y) and the excellent thermal stability and mechanical property of its oxides, we propose a method for fabricating Nb/Y multilayer films that exhibit Adjustable performance based on the usage environment by controlling the oxidation of Y in nanometallic multilayer structures. By regulating the oxidation behavior and layer thickness of the Y layer, the Nb/Y nanometallic multilayer can maintain a stable nanolayered structure even at 800 °C. In contrast, multilayer systems reported in recent years typically experience structural degradation at around 400 °C. For the as-deposited samples, as the deposition time of the Y layer increased from 20 s to 80 s, the nanoindentation hardness decreased from 9.39 GPa to 3.65 GPa, exhibiting a reduction of 61 %;the annealed samples with a deposition time of ty = 50 s, as the annealing temperature rose from 400 °C to 800 °C, the nanoindentation hardness increased from 5.73 GPa to 8.95 GPa, demonstrating an increase of 56 %. The results indicate that the oxidation behavior is suppressed with increasing Y layer thickness but enhanced by higher annealing temperatures. And a phase transition from monoclinic to cubic occurs during thermal annealing, which helps to minimize the system's energy. When an equilibrium is established between two phases, thermal stability of the film layer is significantly enhanced, which also demonstrates good mechanical properties.