Density Measurement and Atomic Structure Simulation of Metastable Liquid Ti-Ni Alloys
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INTRODUCTION
TO assure that metallic materials can be applied in extreme environments and improved performance, the metal in its liquid state is an important aspect that should be considered. The prime question being put forward is the difference in the thermophysical properties between the solid and liquid states for the same metal. Since the high activity of liquid metals would result in reactions with the container under high-temperature conditions, the traditional methods adopted to measure the properties of solid metals are not suitable for liquid metals. Thus, novel measurement methods including containerless techniques such as electrostatic levitation (ESL), electromagnetic levitation (EML), and aerodynamic levitation[1–3] are developed. Thermophysical properties, such as density, thermal expansion, heat capacity, surface tension, and viscosity,[4–7] have been measured by levitation methods. Density is one of the most fundamental properties of materials; it is a critical parameter for metallurgical processing, casting simulation, heat transition calculation, surface tension, and viscosity determination. While the liquid structure is related to the thermophysical properties, scientists further study the packing of atoms and clusters in liquid alloys by combining the levitation technique with synchrotron radiation.[8,9] At the same P.F. ZOU, H.P. WANG, S.J. YANG, L. HU, and B. WEI are with the Department of Applied Physics, Northwestern Polytechnical University, Xi’an 710072, P. R. China. Contact e-mail: [email protected] Manuscript submitted February 20, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
time, computational simulations are rapidly developed; these are good choices to observe the arrangements of atoms. Using the reverse Monte Carlo, molecular dynamics (MD), and first-principle simulations, investigations of the thermophysical properties and structural information of liquid alloys have been reported, such as for the binary alloy systems Zr-Ni, Al-Au, Fe-Cu, Al-Cu, and Al-Ni.[10–13] Peng et al.[12] measured the densities and viscosities of liquid Al-Au alloys by EML, which agreed with the results achieved from MD simulation. Ding et al.[14] used the MD method to simulate two metallic glass-forming systems. They found that the excess specific heat would increase with the increasing development of structural ordering. The Ti-Ni binary alloy system consists of intermetallic compounds, eutectic alloys, and solid solutions. The Ti50Ni50 alloy is the most famous alloy in Ti-Ni alloy system due to its excellent shape memory effect, good biocompatibility, and mechanical properties,[15–17] which have been studied extensively. In addition, the mechanism of martensitic transformation has attracted much attention.[18,19] To improve the properties and broaden the range of application, research on adding extra elements based on the Ti-Ni alloy is also popular.[20,21] For other Ti-Ni alloys, the work focuses on their glass-forming ability,[22–24] while the final performance is directly related to the solidificat
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