A new viewpoint to the mechanism for the effects of melt overheating on solidification of Pb-Bi alloys

Abstract

The effects of melt overheating treatment on solidification of Pb-Bi alloys were studied from the viewpoint of liquid-liquid structure change (LLSC). Anomalous temperature dependence of internal friction, electrical resistivity, and entropy of liquid Pb-Bi alloys suggested that discontinuous LLSC occurred within about 520–740 °C, based on which the solidification experiments were carried out with different states of Pb-Bi melts. The results revealed that the LLSC affected the solidification behavior and microstructures significantly, that is, the enlarged undercooling, increased nucleation rate, and refined and improved morphologies were brought about when solidifying from the melt experienced LLSC. It is assumed that the LLSC changed the energy constitution of the melt system, and further affected the effective partition coefficient, thermodynamics, and kinetics of crystal growth, then finally altered the solidification behavior and solidified microstructures. This work brings a novel insight into the effect of melt overheating treatment on solidification, by which it could be more effective to manipulate melts.

Can elemental bismuth be a liquid crystal?

“…After all, if Bi forms a liquid crystal over a wide range of temperatures, this type of ordering would not be immediately destroyed by admixture of other elements. In a study [16] of an 80%Bi-20%Pb alloy, an irreversible transformation was observed above 800 K, with a particularly striking signature in the thermopower data (see their Fig. 2).…”

“…Finding a liquid-crystal phase to be thermodynamically stable in an elementary melt, even over only a very limited range in temperature and pressure, would be a revolutionary change in our understanding of the phase diagrams of the elements. If the range of stability of liquid-crystal phases in simple melts is much wider (Sb and Sn are additional candidates [31,32,11,29]), then this could serve as a basis for solving many of the riddles in the field of liquid-liquid transformations, and would likely have significant technological implications as well [16].…”

Influence of melt overheating on microstructure and soldering properties of SnBiCu solder alloy

“…PbSn, InSn, CuSn and SnBi [3][4][5][6][7]. Further works also reveal that the LLSC has significant impact on the solidification process and properties of alloys [8][9][10][11][12]. All of these studies promoted our knowledge about the nature of liquid structure and the correlation of liquid-solid.…”

Change of solidification behaviors in the superheating Sn-40wt.%Bi alloy from the viewpoint of the relaxation of properties

“…More recently, both experimental findings and theoretical predictions have suggested the presence of liquid-liquid structural transitions (LLST) characterized by significant structural changes [13][14][15][16]. Furthermore, according to the known melt structure information, the effect of the LLST on the solidified structures was investigated for some binary alloys, such as Al-Si [2], Pb-Sn [17], Bi-Sb [18] and Pb-Bi [19].…”