Correlation Between Structures Of Liquid And Solid In Some Metals

In this paper, the correlation between structures of liquid and solid in some metals has been studied with an elevated temperature X-ray diffraction as a main means, DSC and electron microscopy as assistant means. In order to adapt the X-ray diffraction equipment for the research work, some improvements have been done. The "liquid micro-multi-phase structure mold"based on an eutectic alloy system in which the solid solubility is limited. The idea of this model is also suit to the unlimited intersolubility solid solution system. Because there is a difference of the bond forces between congeneric atoms and heterogeneous atoms in the two system alloys, the liquid of unlimited intersolubility solid solution system consists of multi-phase clusters in which different atoms are randomly displaced each other. The clusters with different ingredient are statistically distributed about the alloy ingredient. And the boundaries of the distrbution are the maximum solubility of solid and liquid of this alloy ingredient. In the region between liquidus and solidus, multi-phase clusters polarize to two points, which are the intersection points of temperature line and liquidus, solidus. In this case, the liquid is made of two type clusters that their ingredient change along the liquidus and solidus, and the ratio of the two type clusters coincides with level rule. The clusters which ingredient change along solidus will move to crystal phase to make it grow, and the clusters their ingredient change along liquidus will still stay in liquid. It is of significance to develop the "liquid micro-multi-phase structure model"to suit to the liquid alloys which are unlimited solubility solid solution system. First, to explain why there is no segregation in rapid and undercooled solidification, it is the theory fundament for the new technology to prepare material without segregation. Second, to indicate the quantitative relationship between phase diagram and structure of liquid and solid. Third, to improve the understanding on the usage of "liquid micro-multi-phase structure mold"to solid solution region of the eutectic alloy system. It is the first time and elementary to prove it is right that the "liquid micro-multi-phase structure model"is suit to unlimited solubility solid solution system by the structure analysis of liquid metal X-ray diffraction and theory calculation on Cu70Ni30 alloy liquid and undercooled liquid between its liquidus and solidus. Because the difficulty of the experiment, the proving work is not done for other unlimited solubility solid solution alloys and this is future work for us. By analyzing the structures of liquid, undercooled liquid and solid of Cu₇₀Ni₃₀ alloy, it is indicated that this alloy melt is of a short order structure of fcc which is its solid structure. And it is discovered that the cluster correlation radius and atom number of cluster in the alloy melt do not significantly change in the temperature range from 1250 to 1400℃, they are 1.125 nm and 457. But they significantly increase in the undercooled liquid (1200℃), they are 1.3 nm and 704. This shows that the fcc short order structure of liquid cluster is retained to the solid by cluster size increasing and nucleation in undercooled. Analyzing on the structure of Al65Cu20Fe15 alloy melt illustrates that its melt is consist of clusters with icosahedral short order structure, then the correctness is proved for "There exist a lot of icosahedral clusters in liquid", the judgment of Frank. The micro-inhomogeneous structure region is discovered in the melt of icosahedral quasicrystal Al65Cu20Fe15 alloy during heating process. In this region the structure is icosahedral short order cluster and undisintegration icosahedral quasicrystal phase, the temperature range of this region is from 1056 to 1250℃. In the liquid above 1400℃, the structure is homogeneous, it is only consisted of icosahedral short order clusters. Then there exist a correlation between liquid structure and solid structure of icosahedral quasicrystal Al65Cu20Fe15 alloy. The correlation radius and atom number of clusters in liquid of Al65Cu20Fe15 alloy at 1150℃are about 1.2 nm and 400, and its coordination number is 10.3. After analyzing the structures of liquid, supercooled liquid and solid of amorphous Zr41Ti14Ni10Cu12.5Be22.5 alloy, it is discovered that the amorphous structure at solid is directly kept from its liquid structure, but the degree of order at solid is higher than that at liquid. And the amorphous structure in supercooled liquid region is still the same structure as in liquid and solid, but it is of a tendency to crystallizing. When the amorphous alloy is crystallizing, it will crystallize to CuZr2, Be2Zr and an unknown phase. The melting temperature range of intermetallic compounds made from amorphous alloy component elements is 650 to 728℃, it is far lower than melting point temperatures of their pure elements. Using the technology of computer numerical calculation of temperature distribution, the amorphous cooling process can be simulated. According to the simulation cooling rate, it can be predicated wether the amorphous can be formed in the alloy.