Molecular Dynamics Simulation And Experimental Investigation On Heat Capacities Of Liquid Metals

As an advanced processing technique for metallic materials, rapid solidification of supercooled liquid metals offer a promising way for preparing bulk amorphous metal, which is not expected for traditional rapid quenching techniques. To control the solidification process, the specific heat capacity of supercooled liquid metal is of particular importance. However, the specific heat capacity of supercooled metallic liquids is difficult to be completely determined by experiment, for the supercooled liquid metals are metastable and inaccessible for direct-contact measurement.Molecular dynamics simulation provides an available way to study the thermal properties of supercooled liquid metals numerically. The main purpose of this thesis is to investigate the heat capacities of two pure metals and three series of binary alloys numerically and experimentally.The average heat capacities of the a series undercooled Cu-Ni melts were derived by using glass fluxing technique. The undercoolings of these alloys were 381, 380, 349 and 431K respectively, which exceed the critical undercooling of the classical nucleation theory. A detailed analysis of the heat transfer condition during the solidification process was carried out, which suggested a linear relationship between the time duration of thermal arrest t_a and the undercooling ΔT. The hypercooling points of the alloys, derived from the relationship between t_a and ΔT, were determined to be 457.7, 461.1,448.4 and 528.3K respectively.Molecular dynamics simulations based on embedded-atom method and an effective pair potential are carried out to predict the specific heat of liquid copper and silver. The relationship between the specific heat of liquid metal and the undercooling are investigated. The simulations predict the specific heat of liquid copper and silver quite well and show that the specific heat of copper decreases slightly with the temperature decreasing linearly above and below the melting point, while the specific heat of silver behaves non-monotonously.A discussion about the influence of interatomic potential on the calculation of specific heat is given. The simulation results show that the bulk module has little influence on the simulation of heat capacity, while the cohesive energy and share stress module influence the heat capacity obviously.The simulation of heat capacities of Cu-25%Ni, Cu-33%Ag and Fe-33%Ni are carried out. The comparison between the predicted heat capacity of Cu-25%Ni alloy and the experiment showed reasonable agreement. The heat capacity of Cu-25%Ni behaves non-monotony, while the heat capacities of Cu-33%Ag and Fe-33%Ni keep constant in a rather large region.