Thermoplastic Micro-formability Of High Entropy Amorphous Alloys And Properties Of Micro-scale Grated Surfaces

In the development of bulk amorphous alloys,people are looking for alloys with high glass forming ability.Applying the high entropy concept of high entropy alloy to amorphous alloy will help to develop amorphous alloy with large glass forming ability,namely high entropy amorphous alloy.At present,high entropy amorphous alloys with high glass forming capacity have been developed,and their mechanical properties,biological and physical properties have been systematically explored.However,as a kind of amorphous material with glass transition and supercooled liquid zone,the thermoplastic micro-formability of high entropy amorphous alloy is still unclear,and studies on micro-patterned high-entropy amorphous surfaces have not been reported.This greatly limits the application of high entropy amorphous in micro-nano scale field.In view of the above background,in this work,TiZrHfNiCuBe high entropy amorphous alloy was selected as the research object,and the following research was carried out:Firstly,high entropy amorphous alloy samples were prepared by copper moulding,and their physical properties were characterized.Through the isothermal crystallization testing,the incubation period of high entropy amorphous alloy at different temperatures was obtained.Based on these results,the Time-Temperature-Transformation(TTT)curve was established,from which the time-temperature window of thermoplastic forming was obtained.The deformation map of high entropy amorphous alloy was constructed through the uniaxial compression experiments.By comparsion with the hot embossing results,it was found that the Newtonian rheology favored the hot forming of the high-entropy amorphous alloy,while when the forming size was reduced to 10 micrometers,the formation of supercooled liquid high entropy amorphous alloys becomes very difficult.Through viscosity measurement and theoretical calculations,it is found that the high viscosity and low fragility(mf=27)of the supercooled liquid high entropy amorphous alloy,are main reasons that hinder the thermoplastic micro-formability.In order to break through this predicament,ultrasonic vibration was introduced and simulated by finite element method,the results revealed that ultrasonic vibration can effectively improve the thermoplastic micro-formability of high entropy amorphous alloys,and the physical origin is probed by molecular dynamics simulation.Owing to the low thermoplastic micro-formability of TiZrHfNiCuBe high entropy amorphous alloys,femtosecond laser processing technology was adopted to process grating structures with different grating sizes on the surface.Compared with the hydrophilic surface of high-entropy alloys,grated surfaces exhibit hydrophobic properties,and the contact angle increases with increasing grating width.Theoretical analysis revealed that the air bag among the micro-gratings of the high entropy amorphous alloy is the main reason for the hydrophobicity.The friction and wear experiments on laser patterned high-entropy amorphous alloy surfaces revealed low friction coefficient compared to smooth surface(friction coefficient=0.5).For surfaces with a groove width of 20 ?m,when the rubbing direction is perpendicular to the grating structure,the friction coefficient is reduced to 0.15;when the rubbing direction is parallel to the grating structure,the friction coefficient is reduced to 0.3.However,when the groove width of the grating structure is increased to 100 ?m,the friction coefficient is larger than the smooth surface,increases to 0.55.Theoretical analysis reveals that the reduction of the friction coefficient mainly originates from the reduction of the contact area between the friction pairs.The TiZrHfNiCuBe high entropy thermoplastic micro-formability and its mechanism were systematically studied,the micro-mechanism was explored,and its micro-forming capability was improved by high-frequency vibration loading.The effect of the microscopic grating structure on surface wettability and friction coefficient were also investigated.This study not only explores the micro-formability and surface properties of high entropy amorphous alloys,but also opens the way for future research and application.