Natural aging of Ni60Nb40 metallic glass thin film: Evolution of microstructure and mechanical properties

Abstract

Since metallic glass thin films (MGTFs) are commonly used in the atmosphere of air, the study on the evolution of structure, morphology, and mechanical properties of MGTFs exposed to air is of great significance for the practical application of MGTFs. The oxide formation mechanisms are investigated by experimental and calculation methods in this work. The results indicated that the crystalline oxide NiNb2O6 can be formed when exposed to air. The crystal structure of the oxide is orthorhombic, and the lattice constants can be calculated as: a = 14.022, b = 5.675 and c = 5.015 nm. The oxide NiNb2O6 was initiated around the amorphous island-like boundary during natural aging. The island boundary of amorphous matrix can provide the formation condition of nucleation and growth for crystalline oxide. The averaged Young's modulus and hardness of NiNb2O6 oxide are much higher than that of the amorphous matrix based on the results of experiments and first-principle calculations, indicating that the presence of crystalline oxides might improve the wear-resistance performance of the films.