Results of thermal expansion prediction from atomic scale for metastable liquid metals are reported herein. Three pure liquid metals Ni, Fe, and Cu together with ternary Ni60Fe20Cu20 alloy are used as models. The pair distribution functions were em- ployed to monitor the atomic structure. This indicates that the simulated systems are ordered in atomic short range and disor- dered in long range. The thermal expansion coefficient was computed as functions of temperature and atom cutoff radius, which tends to maintain a constant when the cutoff radius increases to approximately 15A. In such a case, slightly more than 1000 atoms are required for liquid Ni, Cu, Fe and Ni60Fe20Cu20 alloy, that is, the macroscopic thermal expansion can be pre- dicted from the volume change of such a tiny cell. Furthermore, the expansion behaviors of the three types of atoms in liquid Ni60Fe20Cu20 alloy are revealed by the calculated partial expansion coefficient. This provides a fundamental method to predict the macroscopic thermal expansion from the atomic scale for liquid alloys, especially in the undercooled regime.
Experimental and computational methods are used to optimize the electrostatic field for levitating metallic materials.The calculated launch voltage increases linearly with the distance between top and bottom electrodes.The combination of a larger top electrode diameter with a smaller bottom diameter may enhance the levitation ability because the electric field intensity near the levitated sample is strengthened.Top convex and bottom concave electrodes can guarantee good levitation stability but decrease the levitation force.The design of bottom electrode is crucial to attain not only a stable levitation state but also a higher levitation capability.As a measure characterizing the intrinsic levitation ability of various materials,the product of density and diameter of levitated samples can be used to determine the launch voltage for counteracting gravity according to a power relationship.
Liquid Fe35Cu35Si30alloy has achievedthemaximum undercooling of 328 K （0.24TL） with glass fluxing method, and it displayed triple solidification mechanisms. A critical undercooling of 24 K was determined for metastable liquid phase separation. At lower undercoolings,α-Fe phase was the primary phase and the solidification microstructure appeared as homogeneous well-defined dendrites. When the undercooling exceeded 24 K, the sample segregated into Fe-rich and Cu-rich zones. In the Fe-rich zone, FeSi intermetallic compound was the primary phase within the undercooling regime below 230 K, while Fe5Si3intermetallic compound replaced FeSi phase as the primary phase at larger undercoolings. The growth velocity of FeSi phase increased whereas that ofFe5Si3 phase decreased with increasing undercooling. For the Cu-rich zone, FeSi intermetallic compound was always the primary phase. Energy-dispersive spectrometry analyses showed that the average compositions of separated zones have deviated substantially from the original alloycomposition.
