Studies Of Relationship Between Melting Entropy And Melting Point Viscosity Of Zr₂Ni-Ti₂Ni Alloys

Considering the joint roles of the thermodynamics and kinetics on the amorphous formation,the studies on them is remarkably meaningful for exploring amorphous materials.In our studies,a pseudo-binary Zr₂Ni-Ti₂Ni alloy system has been selected,the alloy ingots of different compositions?Zr₂Ni?_x?Ti₂Ni?_1-x?x=0.206,0.44,0.55,0.654,0.71,0.73,0.8 and 0.85?in this system are prepared by arc-melting.In order to get homogenious samples,each ingot was annealed for seventy-two hours in vacuum annealing furnace,and then XRD experiments were performed to determine the uniformity of structure of the ingots with the earlier reports.The ingots subjected to annealing were melt-spun into ribbons by the single-roller melting-spinning technique,x-ray diffraction was carried out to determine the structural feature of each phase.Different wheel velocities were employed to distinguish the amorphous forming ability of the alloys of different compositions in this system.Based on the study,the alloy of?Zr₂Ni?_0.73?Ti₂Ni?_0.27.27 was conformed as the optimal glass forming composition.Three representative compositions?two compositions of eutectic and one intermetallic composition,x=0.206,0.44 and 0.654?in?Zr₂Ni?_x?Ti₂Ni?_1-x system have been chosen for further studies,the melting entropy and the viscosity were taken as the thermodynamic and dynamic representative arguments.The the melting entropies of the alloys were collected on differential scanning calorimeter and viscosities were measured on the torsional oscillation viscometry.The relationship among melting entropy,viscosity at melting temperature and critical cooling rate were explored.For the alloys with x=0.206,0.44 and0.654,the measured values of melting entropy are 7,6.7 and 6.3 J/mol·K,and the measured values of viscosity at melting temperature are:8.17,10.59 and 12.3 mPa?s,respectively.Based on experimental data,we found a linear relationship between melting entropy and the logarithm of viscosity at the melting temperature,low melting entropy corresponds to high melting-point viscosity.The literature data of entropies of fusion and melting-point viscosity of alloys conforms the linear relationship again Through fitting experimental data,we proposed a linear equation log?_m=-0.29?S_m+2.95.This relationship provide a new way for us to look for amorphous system.