Research On The Microstructure,Properties And Formation Mechanism Of Ni₆₀Nb₄₀ Ultra-stable Glass

Ultra-stable glasses(USGs)have a unique structure and excellent properties,such as high thermodynamic and dynamic stability,excellent mechanical properties,corrosion resistance and optoelectronic properties.The application in the field of coating,micro-processing and electronic devices has received extensive attention.At present,USGs have been successfully prepared by adjusting a single factor substrate temperature or deposition rate,and controlling the film thickness can adjust its thermodynamic and mechanical properties.However,the research on microstructure evolution mechanism and plastic deformation model of USGs is not systematic enough,which is based on process parameters such as deposition time,substrate temperature and deposition rate.As potential coating materials,USGs have a lack of research on oxidation mechanism during natural aging.The paper uses Ni₆₀Nb₄₀ USGs as the research object,the microstructure of USGs prepared at different deposition times,substrate temperatures and deposition rates is observed,the mechanism of structure evolution and studies the relationship between mechanical properties and microstructure based on the cooperative shear model are analyzed.The oxidation resistancemechanism of USGs during the natural aging process is studied,which provides a theoretical basis for the structure,performance control and application of the metallic glass thin films.By adjusting the deposition times,Ni₆₀Nb₄₀ USGs were prepared by magnetron sputtering technology.The T_g values of the films prepared at deposition times of 1h,2h and 3h are 627?,617?and 612?,respectively,indicating that the shorter the deposition time,the higher the temperature required to break away from the amorphous structure.The free volume content of the films prepared at different deposition times are4.27%,3.88%and 3.59%,respectively.The longer the deposition time,the lower the free volume content and the stronger the stability.With the extension of the deposition time,the elastic modulus and hardness of the film gradually increase.The upper boundary of the relationship between elastic modulus and hardness increases from E=32.3+26.6×H for 1 h to E=44.1+21.9×H for 2 h,then increased to E=44.4+21.6×H for 3 h;the maximum indentation depth and maximum creep displacement of the film gradually decreased,and the shear transition zone(STZ)volume increased from 0.145nm³ to 0.273 nm³;the activation energy of STZ increased from 14.1 k J/mol to 26.6k J/mol,indicating the plastic deformation resistance,creep resistance and stability gradually increased.When the substrate temperature is from room temperature to 300?,the average particle size,root mean square roughness,T_g and?T of USGs gradually increase,the elastic modulus and hardness of USGs increase,and the maximum indentation depth and maximum creep displacement gradually decrease;the strain rate sensitivity index m decreased from 0.2072 to 0.1578,the STZ volume increased from 0.116 nm³ to 0.221nm³,and the activation energy of STZ increased from 11.3 k J/mol to 21.5 k J/mol,indicating the number of atoms inside the island structure gradually increased and the surface was rough,the plastic deformation resistance and creep resistance are enhanced,and the film stability is further enhanced.When the deposition rate gradually increases from 6.8 nm/min to 20.4 nm/min,the average particle size and root mean square roughness of the film first increased and then decreased,and the T_g and T_x first decreased and then increased,indicating that the thermodynamic stability first decreased and then increased.When the deposition rate is lower than the critical value q_c,the film structure is mainly affected by surface relaxation;when the deposition rate is greater than q_c and less than q_m,the film structure is mainly affected by sputtering shadows;when the deposition rate increases to the critical value q_m,the film structure is mainly affected by the film temperature and atomic diffusion.As the deposition rate increases,the elastic modulus and hardness of the film first decrease and then increase;the maximum indentation depth and maximum creep displacement first increase and then decrease;the m value increases from 0.4722to 0.8971,and then decreases to 0.6998;STZ volume first decreased from 0.163 nm³ to0.145 nm³,and then increased to 0.151 nm³;the activation energy of STZ decreased from 15.8 k J/mol to 14.1 k J/mol,and then increased to 14.7 k J/mol,indicating stability,plastic deformation resistance and creep resistance performance decreases first and then increases.Based on the first principles calculation,the oxidation mechanism of USGs during the natural aging process was analyzed,which the substrate temperature is 400?and the sputtering power is 40W.Ni Nb₂O₆ oxide is formed at the boundary of amorphous island structure during the natural aging process,and its lattice constant is a=14.022,b=5.675 and c=5.015 nm,and the boundary of the amorphous island structure can provide conditions for the formation and growth of oxides,such as energy,oxygen atoms and the formation of space for growth.Ni Nb₂O₆ grows along the growth direction of the amorphous Ni Nb matrix with an island-like mechanism.The elastic modulus of the amorphous matrix is 115.0 GPa,and the hardness is 3.60 GPa;the Young's modulus of Ni Nb₂O₆ is 153.0 GPa,and the hardness is 5.60 GPa;the Young's modulus of Ni Nb₂O₆ is calculated by first-principles as 139.64 GPa,and the hardness is6.11 GPa,the formation of oxides in the Ni₆₀Nb₄₀ metallic glass thin film during the natural aging process can increase the elastic modulus and hardness of the amorphous alloy film,and further improve the service performance of the amorphous film.