Preparation, Growth Mechanism And Mechanical Property Of Metallic Glass Films

Metallic glass thin films are both scientifically important and of broad practical applications for their unique properties, such as high hardness, high wear resistance, high corrosion resistance and excellent catalytic properties. However the growth of metallic glass thin film with desired composition by low-cost method is still a challenge and the growth mechanisms and deformation physics of these thin films remain less firmly established as compared with their bulk counterparts.In this thesis, we firstly prepared Pd40Ni40P20 (a classical bulk metallic glass former) metallic glass thin films by electrodeposition. Voltammetric curves and potential-time transient indicate the leading role of Pd in the initial growth stage. Based on compositional, morphological, and electrochemical analyses, the successful electrodeposition of Pd40Ni40P20 is regarded as Pd-induced PdNiP co-deposition accompanying with hydrogen evolution reaction.Then, to quantitatively describe the surface evolution, kinetic surface roughening of electrodeposited metallic glass PdNiP films was investigated by atomic force microscopy combined with electrochemical techniques. Interface width w(l,t) of the films obeys anomalous scaling behavior, with H=0.60±0.06,βloc=0.47±0.03 andβ=0.19±0.03. The results suggest that kinetic roughening of PdNiP films could be controlled by two factors:large overpotential and diffusion instability.Thirdly, kinetic roughening of electrodeposited PdP and NiP metallic glass films during growth was also investigated by atomic force microscopy and synchrotron X-rays phase-contrast radiography. Anomalous scaling of the interface width was observed for PdP system, with H=0.75±0.06,βloc=0.49±0.07 andβ= 0.38±0.08. In contrast, NiP system shows an almost-normal scaling behavior, with H =0.70±0.02,βloc≈0 andβ= 0.16±0.03. The results suggest that surface roughening during film growth is strongly influenced by diffusion instability due to local behaviors like hydrogen evolution reaction (HER), which shifts surface roughening from normal scaling (e.g., in NiP system) to anomalous scaling (e.g., in PdP and PdNiP systems). Finally, we studied the deformation behavior of the PdP metallic glass thin films by bending. The results show that PdP metallic glass thin films deform homogeneously at room temperature under compressive stress when the thickness of the thin film is less than a critical value. This critical value is dependent on the temperature:the higher the temperature, the larger the critical size. During homogeneous deformation, the temperature rise and hardness change can not be found. However, under tensile stress, all the specimens we observed deform by shearing. This indicates that the change of deformation mode in metallic glass is strongly dependent on the stress state.