Papers by Keyword: Liquid Structure

Abstract: The liquid local structure of Au₅₀Cu₅₀ solid solution was detected by high-temperature X-ray diffraction experiment and Reverse Monte Carlo (RMC) simulation. The clusters in the liquid Au₅₀Cu₅₀ alloy comprise the 12-coordinated polyhedron with Au center, which was the same as the clusters in the liquid pure Au. In the case of alloying, there was a high population of Au-Au bonds, and the local structure around Cu atoms was changed. In the case of solidification, the 12-coordinated clusters around Au atoms were preserved into the AuCu alloy, forming the disordered solid solution structure. The strong tendency for Cu-Cu bonds was weakened from 2.35 Å in the liquid to 2.81 Å in the solid solution, and the local structure around Cu atoms rearranges. It is shown that the liquid structure of the Au₅₀Cu₅₀ alloy plays a crucial role in the solid solution. Our findings elucidate that the disordered solid solution structure in AuCu alloy stems from the highly dominated 12-coordinated clusters associated with centered Au atom in the melt.

Abstract: The liquid structure of Ni₂Sb₉₈ eutectic alloy is studied with the method of X-ray diffraction and measurements of viscosity in this paper. Covalent bonding structures, which are characterized by the shoulder on the high- Q side of the first peak of structure factors, are observed over the full measuring temperature range. And the split of second peak of the pair correlation function suggests that the chemical short-range order structure exits in the melt. Correspondingly, variation of the viscosity obeys the Arrhenius law except the abrupt point near 1025K and the electrical resistivity changes abnormally at about 1020K. In addition, the coordination numbers prove that the A7-like structure is almost destroyed in liquid Ni₂Sb₉₈ alloy. This research is aim to provide new insight into the structure evolution of liquid alloys during the cooling process.

Abstract: Molecular dynamics (MD) simulations was used to investigate the structures and evolution of atom clusters in liquid Al-Pb alloys. Pair correlation functions and chemical short-rang-order (CSRO) parameters indicate that inhomogeneous atoms are prone to be repulsed while Al-Al and Pb-Pb clusters are easy to emerge. The Voronoi analysis shows that the main coordination number around Al atoms and polyhedron index vary with Pb increasing. The main coordination number abruptly decrease from 11 to 9 when the Pb atomic percentage range from 30% - 40% , proving that Al-Al and Pb-Pb clusters are prone to be separated.

Abstract: Liquid Pb–Bi eutectic alloy has been selected as coolant and neutron spallation source for the development of MYRRHA, an accelerator driven system. The alloy has been characterized in liquid state from melting (125 °C) to 650 °C by mechanical spectroscopy. Experiments have been carried out using hollow reeds of austenitic stainless steel filled with the Pb-Bi alloy and sealed at the extremities. From 350 °C to 520 °C modulus shows a remarkable drop accompanied by a broad internal friction maximum. In the same temperature range radial distribution functions, determined from X-ray diffraction patterns, evidenced variations of the mean distance between the 1st nearest neighbour atoms. The anelastic phenomena have been attributed to a structural re-arrangement of liquid metal. For comparison, other alloys of the Pb-Bi system with hypo-eutectic composition have been investigated.

Abstract: Liquid Pb–Bi eutectic (LBE) alloy has been selected as coolant and neutron spallation source for the development of MYRRHA, an accelerator driven system (ADS). The alloy has been characterized in liquid state from melting (125 °C) to 750 °C by mechanical spectroscopy, i.e. internal friction (IF) and dynamic modulus measurements. The experiments have been carried out using hollow reeds of austenitic stainless steel filled with Pb-Bi alloy and sealed at the extremities. Dynamic modulus showed a remarkable drop in the range 350-520 °C. In the same temperature range radial distribution functions (RDFs), determined from X-ray diffraction patterns, evidenced variations of the mean distance between the 1st nearest neighbour atoms. The phenomenon has been explained as a structural re-arrangement of atoms in the liquid metal.

Abstract: The liquid structure of two lead-free solder molten alloys, Sn-0.5Cu and Sn-1.8Cu (wt.%), have been investigated using X-ray diffraction method. The main peak for liquid structure of Sn-0.5Cu is similar to that of pure Sn. A pre-peak has been found in the low Q part on the structure factor S(Q) of Sn-1.8Cu tested under 320°C and the pre-peak decreases its intensity with increasing temperature, but it disappeared finally when the testing temperature reached 350°C. The microstructure of the solder matrix as well as interfacial reaction between liquid solders and Cu substrate was also studied. The structural unit size corresponding to the pre-peak almost equals to magnitude of crystal planar distance of Cu6Sn5 phase. The appearance of a pre-peak may be due to existence of clusters with Cu6Sn5-phase-like structure in the melt. Quantity and size of clusters increases with decreasing temperature but their structural unit size remains constant. Cu6Sn5 phases develop from incorporating and growing of the clusters during solidification, thus result in the correlation between liquid structure and solid microstructure.

Abstract: In the present work, the resistivity of Ga36.5Sb63.5 alloy during cooling process was studied by the method of DC Four electrodes . The result of the experiment showed that there is an anomalous point at 710°C－735°C on the resistivity-temperature curve of Ga36.5Sb63.5 melt. At the same time, The relevance of the resistivity and the liquid structure of the alloy was analyzed. The physical properties of Ga36.5Sb63.5 alloy melt was discussed.

Abstract: The liquid structure of two lead-free solder Molten alloys, Sn-0.5Cu and Sn-1.8Cu (wt.%), has been examined using X-ray diffraction method. The main peak for liquid structure of Sn-0.5Cu is similar to that of pure Sn. A pre-peak has been found in the low Q part on the structure factor S(Q) of Sn-1.8Cu tested under 320°C, but it disappeared finally when the testing temperature reached 350°C. The both viscosity was measured using a torsional oscillation viscometer. It was found that the anomalous variations of viscosity had a direct relation with the transition of the liquid structure, which is consonant with the results of high temperature X-ray diffraction. The microstructure of the solder matrixes as well as interfacial reaction between liquid solders and Cu substrates was also studied. The results show that particle-like Cu6Sn5 intermetallic compounds (IMCs) emerge in Sn-1.8Cu solder matrix. The IMC layer at Sn-1.8Cu/Cu joint is thicker than that at Sn-0.5Cu/Cu interface. The correlative effect of liquid structure on phase evolution in the solder joints is analyzed.

Abstract: In order to obtain an insight into the high glass-forming ability of bulk metallic glasses, we have analyzed liquid structures of the Zr-Cu and the Zr-Ni binary alloys with different compositions. High-energy (E = 113 keV) x-ray diffraction experiments were carried out for the liquid alloys levitated by a conical nozzle levitation (CNL) technique. While a peculiar shoulder on the second peak was observed in the structure factors of the Zr-Cu liquid alloys, those of the Zr70Ni30 and the Zr50Ni50 liquids exhibit an asymmetric shape of the second peak. In addition, it was found that the effect of concentration variation in the liquid Zr-Ni alloys was significantly different from that of the liquid Zr-Cu alloys. The liquid structure analyses using the reverse Monte Carlo (RMC) simulation have clarified that a degree of the short-range correlation between the constituents in the liquids affects substantially the glass-forming ability of the binary Zr alloys.

Abstract: The effect of melt treatment on the microstructure and creep-rupture behavior of M963 superalloy at 1248K under 225MPa has been investigated. The microstructure of the as-cast superalloy without melt treatment consists of γ solid solution matrix, γ´precipitate, coarse blocky MC carbide and (γ+γ´)eutectic. The striking difference in microstructure is that the melt treatment changes the MC carbide from the coarse blocky morphology into the fine script-like morphology. After heat-treated at 1483K for 4h followed by air-cooling, both the creep life and rupture elongation of the melt-treated alloy are all doubled those of the alloy without melt treatment. The mechanism of the melt treatment on the creep-rupture behavior of the M963 superalloy is discussed.