Dynamics Properties Of Two Typical Alloy Melts And Their Correlation With Properties Of Solids

As two kinds of advanced materials,amorphous and high entropy alloys have become the research hotspots in the field of materials science in recent decades because of their excellent physical,chemical and mechanical properties.In the case of amorphous alloys,studies on the dynamic behavior of their liquids,as well as structural evolution from liquids to solids,play key roles in revealing the nature of glass transition,improving the glass forming ability and explaining the mechanism of liquid-solid correlation of metallic glasses;in the case of high-entropy alloys,the study of their liquid-to-solid structure evolution and their dynamic behavior of liquids play a key role in explaining the origin of forming solid solution,the relationship between the melt structure and mechanical properties and predicting the mechanical properties.Based on the above background,we first take CuZr and CuZr-based metallic glasses forming liquids as research objects,focus on their abnormal dynamic behavior in different temperature ranges,and explain such anomaly by means of experiments and molecular dynamics simulations.Second,we take AlxCuMnSbSn(x?0.25,0.5,0.75,1,1.5,2.5)high-entropy alloy system as the research objects,and preliminarily probe into the relationship between their dynamic properties and mechanical properties.The research results are as follows:(1)By studies on the viscosity data of CuZrAl and CuZrTiNi alloy melts far higher than the liquidus temperature,we found that the extent of abnormal viscosity drop during cooling in these alloys was related to the content of dopping elements.When the content of doping elements is relatively large,the abnormal viscosity change disappears,which means that the abnormal viscosity change is mainly due to the interaction between Cu and Zr atoms.For CuZr binary alloys,the composition range(27.3%Zr?66.7%Zr)where the dynamic anomaly exists in the melts has been determined by viscosity data combined with the thermodynamic signature.It has been found that the range just accords with the region(30%Zr?70%Zr)where bulk metallic glasses of CuZr can be formed.By using molecular dynamics simulation method on Cu62Zr38,such dynamic anomaly observed in melts during cooling has been explained by the evolution of four typical icosahedron-like clusters which have the largest sensitivity to temperature changes.When cooling approaching 1400K,a more independent dispersion of these clusters compared with that at above 1400K makes the whole system to be more active and the viscosity significantly drop.Then the whole liquid system slows down due to the aggregation and growth of these clusters below 1300K.Therefore,the three-stage tendency of viscosity changes during cooling in CuZr melts has been discovered to own the similar structural origin with what determines the glass-forming ability of this alloys.Such dynamic anomaly in CuZr melts therefore is beneficial to the glass-forming of alloys.This work uncovers how the liquid dynamics influences the properties of glassy solids from the point view of fragile structural units.(2)By studies on the dynamic properties of AlxCuMnSbSn(x=0.25,0.5,0.75,1,1.5,2.5)high-entropy alloys well above the liquidus temperature,we have found that the viscosity of the high temperature melts increases with decreasing temperature over the entire temperature range,and can be fitted by the Arrhenius equation.Using the fragility concept of the superheated melts(depicted by M),it was found that the M change of AlxCuMnSbSn high-entropy alloys with the x value shows a three-stage trend.The change of its Brinell hardness and compressive strength with x also shows a three-stage trend.It is found that there might be a correlation between the dynamic properties of the high-entropy alloy melt and its mechanical properties:the larger the M value is,the greater the strength and hardness.The new discovery in this paper provides a new way to predict the mechanical properties of high entropy alloy in terms of liquid-solid heredity,and helps to develop new high entropy alloy with high hardness and high strength.