Fabrications And Properties Of La-based And Zr-based Metallic Glass Thin Films

The primary composition and structure of the material and the test parameters can affect the comprehensive properties.This thesis analyzed the effect of loading rate on the mechanical property of La-Co-Al and Zr-Cu-Ni-Al metallic glass thin film during nanoindentation,and the films of the two components were compared.It was also studied that how substrate temperature impacts structure and property of Zr-Cu-Al-Ti metallic glass thin film for magnetron sputtering.In this paper,the influences of loading rate,composition and substrate temperature on the comprehensive properties of metal-glass films are further revealed,which will be helpful for further research and application of metal-glass films fabricated by magnetron sputtering in the future.During nanoindentation,the limited loading time induced by increased loading rate may cause the relaxation which can't be developed adequately and behind the external deformation,then the plastic deformation isn't sufficient.This makes the P-h curves more steep with a narrower distribution,and gives rise to the increase of creep distance,creep strain rate,hardness and Young's modulus,but the strain rate sensitivity is decreased.The volume and activation energy of shear transformation zone(STZ)which are positive related with loading rate have been obtained by cooperative shear model,and this is consistent with the increase of hardness and modulus.The depressed structural heterogeneity density makes STZ nucleation and deformation mode transition more difficult.Not only the increased STZ volume and activation energy but also the reduced structural heterogeneity density improve hardness and modulus,while decrease the critical size of deformation mode transition.For the adopted loading rate range,La-Co-Al with lower glass transition temperature exhibits larger creep distance,creep strain rate,strain rate sensitivity,STZ volume,and structural heterogeneity density,but shows smaller hardness,modulus and STZ activation energy.At the same loading rate,the distribution of P-h curves is relatively wider for softer La-Co-Al,since the bigger structural heterogeneity density.Furthermore,the influence of loading rate on these parameters is much weaker as compared with that of the material compositions.Substrate temperature plays a significant role in the microstructure and property of Zr-Cu-Al-Ti thin film fabricated by magnetron sputtering\With substrate temperature increasing from 293 K to 673 K,the thin films remain amorphous with improved oxidation resistance ability,hardness,modulus and optical reflectivity.The thin films obtain more ordered structure and denser packing,with substrate temperature increasing from 293 K to 573 K,and no obvious difference is detected with further increased substrate temperature.The columnar size and oxygen content remarkably drop as substrate temperature reaches 573 K and 673 K.The surface roughness exhibits a trend of first rising,then failing and then reascending,with the lowest roughness appearing at 573 K.Overall,the thin film deposited at 573 K is believed to be the most unique one,with big density,smooth surface,uniform structure,good oxidation-resistance stability,mechanical property and reflectivity,meanwhile the surface morphology evolution mode is changed at this temperature.It may be because 573 K is in the range of 0.7?0.8 Tg(Tg?720 K),where the mobility is very doughty and even ultrastable amorphous glass can be fabricated.Too high surface mobility makes the comprehensive property worse a little with further increased substrate temperature.