Effect Of Ultrasonic Vibration-Assisted Micro-Compression On The Properties Of Zr-Based Bulk Amorphous Alloy At Room Temperature

As a new type of material with excellent mechanical and physical properties,bulk amorphous alloys have a wide range of application prospects in such fields as mechanics,acoustic,biology,optics,and so on.Different from traditional metal materials,amorphous alloys show brittleness similar that of glass at room temperature,so it is difficult to perform plastic processing by conventional methods.Casting and thermoplastic forming are typical forming methods at present.However,casting can only produce limited geometry,and thermoplastic forming may leads to the hot brittleness of the amorphous alloy and then degrade the mechanical properties of the material.In view of the defects on the typical forming methods of bulk amorphous alloys,a series of different amplitudes and strain rates of ultrasonic vibration-assisted micro-compression(UVMC)treatment were carried out on the Zr-based bulk amorphous alloy at room temperature.The effect of ultrasonic vibration load on the mechanical properties of bulk amorphous alloy at room temperature was studied.A hot compression experiment was set as a control to study the thermal effects of ultrasonic vibration on amorphous alloy.The X-ray diffraction(XRD),thermodynamic analysis,and microstructural photographs show that UVMC results in the appearance of nanocrystals with periodic atomic arrangement in the disordered structure of amorphous alloys.With the increase of ultrasonic amplitude,the volume fraction of the nanocrystals is increased from 5%to about 15%.By comparison with the hot compression experiment,it is found that this kind of nanocrystalline is not caused by temperature rise.The strain rate of the UVMC load has a certain influence on the hardness of the amorphous alloy.Under the low strain rate,its hardness is not much changed.At the moderate strain rate,the hardness value is obviously reduced.And under the high strain rate,the change of the hardness is disordered,and it is hard to find the rule.With the increase of the amplitude in the process of the UVMC,the crystallization temperature(T_x)of the alloy is slightly fluctuating,while the glass transition temperature(T_g)decreases gradually.It indicates that the ultrasonic vibration load with higher amplitude can reduce the T_g of amorphous alloy,and expand the scope of its supercooled liquid phase region.The bulk amorphous alloy treated with UVMC exhibits plastic strain under quasi-static compression test,with the increase of ultrasonic amplitude,the yield strength decreases and the plasticity increases.Its forming properties will be improved more obviously when the bulk amorphous alloy is treated with ultrasonic vibration load with higher amplitude and lower strain rate.However,hot compression treatment has limited lifting effect on the alloy’s plasticity.The experimental results and theoretical analysis prove that ultrasonic loading leads to the formation of nanocrystals,the increase in free volume and the decrease in the volume of flow units,which make the propagation range of shear bands wider,and the spatial and temporal distribution of flow units more uniform.The material exhibits better fluidity in quasi-static compression process.Under the combined action of these factors,the plastic forming ability of Zr-based bulk amorphous alloy at room temperature has been largely improved.