Simulation And Temperature Field Measurement During Solidification Of Metallic Glass

The solidification process of metallic glass is different from that of crystalline alloy.Crystallization does not occur during solidification of metallic glass because the cooling rate of metallic glass is rapid and melt atoms do not have enough time to diffuse and rearrange.There is no latent heat release during solidification of the metallic glass and no platform in the solidification cooling curve.The disappearance mechanism of latent heat during solidification of metallic glass is not clear.Therefore,it is necessary to explore the solidification law of metallic glass.In this thesis,Zr₄₁Ti₁₄Ni₁₀Cu_12.5Be_22.5 bulk metallic glass was made by water quenching method and copper mold casting method,respectively.The temperature field data of the solidification process were collected by EM9104 C multi-channel data acquisition instrument.Based on the temperature data obtained,the interfacial heat transfer coefficient between metallic glass and different heat transfer mediums was calculated as well as the expression of liquid-solid interface propulsion rate in different coordinate systems was presented.Through application of numerical simulation software ProCAST,the solidification process of Zr₄₁Ti₁₄Ni₁₀Cu_12.5Be_22.5 bulk metallic glass made by copper mold casting method was simulated as well as the maximum theoretical diameter of Zr₄₁Ti₁₄Ni₁₀Cu_12.5Be_22.5 bulk metallic glass was predicted.The results of calculation and simulation indicate that when the surface temperature of alloy made by water quenching method is cooled from 920℃ to 100℃,the cooling time of Zr₄₁Ti₁₄Ni₁₀Cu_12.5Be_22.5 bulk metallic glass with diameter of 16 mm is 26.5s.The average interface heat transfer coefficient between the alloy and the quartz tube is about 1300W/（m2?K）,which is obtained by finite difference equation.When Zr₄₁Ti₁₄Ni₁₀Cu_12.5Be_22.5 bulk metallic glass is made by copper mold casting method,the interface heat transfer coefficient between the alloy and the copper mold increased with the increase of the alloy temperature,but it is not a linear proportional relationship.The cooling curves of Zr₄₁Ti₁₄Ni₁₀Cu_12.5Be_22.5 bulk metallic glass with diameter of 8mm obtained from both the simulated and measured results are basically in agreement with each other.When the pouring temperature is 840℃,the maximum theoretical diameter of Zr₄₁Ti₁₄Ni₁₀Cu_12.5Be_22.5 bulk metallic glass made by copper mold casting method is about 125¹30mm.There are some larger limitations in the temperature field measurement of metallic glass by water quenching method which is not suitable to study the solidification process of metallic glass.When alloy melt solidify in amorphous form compared with crystalline form,the specific heat capacity of alloy step near the glass transition point,and the disappearance of latent heat have connection with the change of specific heat capacity.