Zhong-Yue Huang

A new understanding of melt overheating treatment of Sn-20 wt-%Sb from viewpoint of TI-LLST

Abstract Investigations of the electrical resistivity of liquid Sn–20 wt-%Sb alloy as a function of temperature were carried out by dc four probe method. An abnormal change on the resistivity–temperature curve was observed in temperature interval of 850–980°C, which indicated that temperature induced liquid–liquid structure transitions (TI-LLST) occurred with temperature rising. Further explorations of effects of TI-LLST on solidification showed that the undercooling for primary or peritectic phase crystallisation increased for the samples solidified from the melt experienced the TI-LLST, and the size of primary phase decreased markedly.

Different solidification behaviours of Bi–10wt%Te alloy induced by liquid structural change

By means of DC four-probe technique, the temperature dependence of the electrical resistivity (ρ–T) of liquid Bi–10wt%Te alloy has been measured. Two abnormal changes on the ρ–T curve within the temperature ranges of 497–550°C and 639–708°C suggested that two irreversible liquid–liquid structural changes (LLSC) occurred. To explore the effects of the LLSC on the solidification behaviour of the alloy, solidification experiments were carried out. The results show that after experiencing LLSC, there will be enlarged undercooling, much finer microstructures and larger quality of Bi2Te phase. Moreover, the morphology of solidified Bi2Te is changed from dendrite to equiaxed.

Electrical resistivity of Sn–3.5Ag–xBi solder melts

This article reported the temperature dependence of the electrical resistivity (ρ) of liquid Sn–3.5Ag lead-free solder alloy in continuous heating and cooling processes with varying Bi content in the range of 0, 2, 3.5, 5, and 7 wt.% Abnormal transitions can be observed on ρ–T curves, which indicate liquid–liquid structure transition (LLST) occurs in Sn–3.5Ag–xBi melts. Interestingly, unlike the pattern at first heating cycle, the LLST is reversible during subsequent cooling and heating cycles. Sn may play an important role on the reversibility, and Bi has a noticeable influence on the turning temperatures and characteristics during first heating cycle. The transition mechanism is analyzed from the viewpoint of short-range orders.

Effects of liquid–liquid transition on solidification of Sb–10 wt-%Cu alloy

Abstract The electrical resistivity of the liquid Sb–10 wt-%Cu alloy as a function of temperature was measured using direct current four probe technique. In a relatively high temperature zone above the liquidus, the resistivity–temperature (ρ – T ) curves of the melt change abnormally; moreover, the changing pattern in the first heating process is completely different from the ones in the subsequent heating and cooling cycles. Since resistivity is a structural sensitive parameter, these abnormal changes of ρ – T curves indicate that the temperature-induced liquid–liquid structure transitions (L-LSTs) probably occur in Sb–10 wt-%Cu melt, with some reversible characters. To explore the effects of the L-LST on the solidification behaviours and solidified microstructures of this alloy, solidification experiments were further carried out according to the temperature ranges with anomalous changes on ρ – T curves. Results show that after the melt experienced the L-LST, larger undercooling, shorter solidified time and much finer microstructures with differently microscopic patterns could be obtained.

Temperature dependences of structure and physical properties of eutectic InSn49.1 melt

The temperature dependences of structure and some physical properties of eutectic InSn49.1 (wt%) melt were investigated by means of high temperature X-ray diffractometer, internal friction and DC four-probe method. In the heating procedure of the melt, a discontinuous temperature induced liquid–liquid structure change was observed within the temperature range of 620–850°C. The X-ray diffraction results show that both mean nearest neighbour distance and coordination number altered anomalously within 650–800°C; in addition, the size of the ordering domain and ordering degree of the melt all decreased evidently at the end of the structure change. It is presumed that this structure change resulted from the adjustment of the atomic bonds of Sn–Sn and In–In. A theoretical discussion on the correlation between structure and physical properties of InSn49.1 melt was also given.

Structural order and anomaly of liquid gallium–indium during isothermal dissolution of indium in liquid gallium

The behaviour of the excess entropy of the isothermal dissolution of indium in liquid gallium is examined in this article. We show the presence of a structural anomaly using the pair distribution function and excess entropy analysis when particles move from a far distance to the first coordination shell with increasing indium content, indicating that the structural anomaly depends only on what happens up to the local shell. These findings are in agreement with results of earlier studies. Moreover, the translational order parameter is introduced to quantify the disorder in liquid gallium–indium. The order mapped together with the two-body excess entropy shows that with an increase in indium content, the ‘true’ liquid changes to the liquid containing solid-like clusters.

Exploration of crystallization behavior of Cu_(36)Zr_(48)Al_8Ag_8 amorphous alloy and melt overheating on its GFA and thermal stability by electrical resistivity measurement

The crystallization behavior of Cu36Zr48Al8Ag8 amorphous alloy and the melt overheating on its glass-forming ability(GFA) and thermal stability are explored by the high-temperature four-electrode electrical resistivity method. The results show that this amorphous alloy has a high-temperature crystallization stage which has not been revealed in the previous literatures besides the lowtemperature crystallization stage. The crystallization products of the first stage are AgZr and Cu10Zr7 metastable phases by using differential scanning calorimetry(DSC) and X-ray diffractometry(XRD). They transform into equilibrium phases CuZr2, AlCu2Zr and CuAl2 in the second stage crystallization. On one hand, when the overheating temperature is greater than 430 K, the thermal stability of Cu36Zr48Al8Ag8 amorphous alloy decreases significantly, and the first stage crystallization behavior changes and the quasicrystals precipitate firstly. On the other hand, its glass-forming ability firstly increases and then decreases with the melt overheat increasing.The effect of the melt overheating on the glass-forming ability and the thermal stability of amorphous are analyzed and discussed from two aspects of melt structure homogeneity and the degree of oxidation.

Electrical resistivity of liquid Sb–Zn alloys

Using the DC four-probe method, temperature dependence of the electrical resistivity (ρ − T) of Sb100− x Zn x (x = 25, 40, 50, 57, 61, 80 at%) alloys was investigated in the temperature range of 500–860°C. The results showed that resistivity of each liquid alloy decreased non-linearly with temperature increasing above their liquidus (T L) until reaching critical temperature, at which the resistivity–temperature coefficients dρ/dT–T converts from negative into positive. The phenomena of liquid phase transformation might relate with the dissociation of covalent bonds, chemical orders and associations in Sb–Zn melts.

Influence of temperature-induced liquid–liquid structure transition on directional solidification microstructure of Sn–Bi40wt-% alloy

Prior investigation suggested that a temperature-induced liquid–liquid structure transition (TI-LLST) could occur in Sn–Bi40wt-% alloy around 879°C. Based on the results of TI-LLST, the Sn–Bi40wt-% alloys are melted and held at the temperature above and below TI-LLST, respectively, and then solidified from the same temperature. The aim of this work was to explore the influence of TI-LLST on directional solidification microstructure by using the Bridgman method. The results show that dendritic arm spacing decreases and the microstructure is refined markedly for the samples solidified from the melt which experienced the TI-LLST.