Electronic Transport Properties And Solidification Behaviors Of Binary Sb-based Alloy Melts

Researches show that the thermal history of parent alloy melt has an importantinfluence on structures and properties of solid materials. So the further study ofstructures and properties about liquid metals can contribute to the improvement ofquality, the modification of materials as well as the development of new materials,etc. While the discovery of liquid polymorphism, polymorphism structuraltransition and Liquid-Liquid Structural Transition (L-LST) can help us to explorethe law and nature of crystallization through melt thermal history more effectively,which opens a new entry point to research the behavior of solidification. But untilnow, the cognition of intrinsic nature, related law and correlation of solidificationabout L-LST are far from enough. So it is important to study the structures andproperties of liquid melts as well as its effects on solidification more systematicallyand deep.The melt states of Sn-Sb15, Cu-Sb90and In-Sb90alloys as well as itsinfluences on solidification are explored in this paper. The main details andmethods are as follows: First, DC four-electrode method was used to get theresistivity-temperature curves of the alloys above, and the possibility of L-LST,temperature ranges, reversibility and transition rules were then investigated. Next,design suitable melt overheating treatment procedures and solidification conditionsaccording to the characteristics of L-LST and then explore the effects of differentmelt states on solidification behavior, size and distribution of microstructures,crystal morphology, growth pattern and crystallographic anisotropy by heatanalysis, observation of microstructures, SEM and XRD. The main innovations ofthis paper are as follows: First, the correlation of melt state and anisotropy ofCu-Sb90was explored for the first time. Second, the reversibility of L-LST and theeffects of different cooling conditions on solidification behavior and microstructurewere revealed clearly. The main conclusions are summarized as follows:(1) Nonlinear changes occurred in resistivity-temperature curves of Sn-Sb15melts in three heating and cooling cycles suggest the appearance of temperatureinduced L-LST. Moreover, the L-LST in first heating process is irreversible but it isreversible in the new melt after first heating process. Analysis believes that thereversibility is related to the generation and broken of tetrahedral shot-range ordersin Sn. Besides, there are obvious dynamic characteristics of reversible L-LST in the cooling processes. With the increment of cooling rate, the start temperature pointsand end points are moved to the low temperature ranges and the transition intervaldecreases.(2) Results reveal that L-LST can affect the solidification behaviors andmicrostructures significantly, i.e. the enlarged undercooling of primary andperitectic phases, increased solidification time of primary phase and decreasedsolidification time of peritectic phase, refined microstructures. In addition, thereversion of reversible L-LST or not can also affect the solidification behaviors andmicrostructures. The reversible L-LST is suppressed under the condition of fastcooling rate, and the increasing extent of undercooling and refining effect are moreobvious. Besides, the crystal morphology is also altered.(3) Different melt states can significantly change the crystal morphology andgrowth pattern of primary Sb in Cu-Sb90alloy. Specifically, the two-dimensionalcrystal morphology changes from large block with obvious edges and corners tospherical and long strips after L-LST, and the three-dimensional crystalmorphology changes from block to cylinder by deep etching. The growth patternalso changes from facet to non-facet. Besides, part eutectic Sb changes fromirregular lamellar to fibrous. The results of X-ray diffraction show that thepreferential growth crystal face shifts from {104} to {003}. The alteration ofcrystal morphology, growth pattern and crystallographic orientation indicate thechange of melt states can reduce the crystallographic anisotropy of Sb. Analysisbelieves that reasons for the above phenomenon are the increasing of solid-liquiddiffusion degree and the weakening of energy anisotropy.(4) The phenomenon of temperature induced L-LST is also found in In-Sb90melts. It is different from last two Sb-based alloys because of its irreversibility. Infurnace cooling, air cooling, iron mold cooling and copper mold cooling, L-LSTcan refine microstructures of Cu-Sb90more or less but the effect of latter twoconditions is very weak, which indicates that the refining effect is weakened withthe increment of cooling rate. Meanwhile, the crystallographic anisotropy of Sbalso declines under the condition of air cooling. Analysis believes that the stabilityof solid-liquid interface reduces due to the change of melt states and the cellularcrystal interface evolves into the equiaxial grain interface.(5) Finally, the mechanism of the revealed phenomenons and related results isdiscussed by relevant liquid physics theory and basic principle of solidification.