The Correlation Between Structures Of Liquid And Solid In Al-Ni Peritectic Alloys

Profound understanding of the mechanism of binary peritectic solidification is very important since peritectic solidifications occur in many kinds of materials. In this paper, the correlation between structures of liquid and solid in Al-Ni peritectic alloys has been studied with an elevated temperature X-ray diffraction as a main means, DSC SEM and electron microscopy as assistant means. This paper presents the variation of the micro-structure of liquid and solid Al-Ni peritectic alloys, on the atomic scale, with the temperature, and component, etc.An investigation about solidification in different component Al- Ni peritectic alloys was taken. Their microscopic structure and micro-area chemical constitution were analyzed using DSC, SEM and Line Scan. The results showed that peritectic reactions in Ni—Al alloys were prevented;Rich-Al segregated at the boundary of peritectic phase.Another investigation shows that Al3Ni alloys with different heat history conditions have different micro-structure. Al3Ni was prepared with Vacuum Arc Furnace, and two Al3Ni samples were cooled in water cooled copper crucible and in Differential Scanning Calorimeter at different cooling velocity. Their microscopic structure and micro-area chemical constitution were analyzed using DSC, SEM and EDS. The results showed that peritectic reactions in Al3Ni alloy was prevented; Compared with microscopic structure in water cooled copper crucible, in Differential Scanning Calorimeter At 20°C/min cooling velocity, the microscopic structure of Al3Ni2 is coarser 14. 72% and the microscopic structure of Al3Ni is finer 31. 21%, this phenomenon is abnormal.In this paper , the author studied the reason of delayed peritectic reaction. The peritectic reaction temperatures of Al-Ni alloys and Sn-Sb alloys were measured with DSC. At the same cooling rate, peritectic reaction temperatures of Al-Ni alloys are serious delayed; but the peritectic reaction temperatures of Sn-Sb alloys nearly equal with their equilibrium reaction temperatures. The research shows that if the crystal structures of primary phase and peritectic phase are different, the peritectic temperature delays; if they are same, the temperature is identical with equilibrium temperature.Using the 6-6 X-ray diffractometer, the liquid structure of Al-Ni peritectic alloys at different composition. As a kind of Al-TM (TM=Mn, Fe, Co, Ni), Al-Ni peritectic alloys have the similar structure to Al-TM. It is found pre-peak in the diffracted intensity cures. The author inferred there are medium-range order structure in the liquid of Al-Ni alloys. The relativity of inter-atomic intensity and liquid structure was analyzed, there is a big attraction between Al and Ni atoms in the Al-Ni alloys melts, which leads to the strong ability of compound formation, and therefore, the formation of the atomic clusters on the medium-range scale comes into being.Through the diffracted intensity cures in liquid state, we can see the nucleation and growth of crystal. The peak positions of the diffracted intensity cures in liquid state and in the solid state is same, At the same time, coordination number of liquid is closer to solid, the author inferred that some compound in solid state is still exist in liquid state, so the author inferred that there are correlation between structure of liquid and solid in Al~Ni alloys.