Study On Phases Formation And Crystallization Kinetics Of Non-equilibrium Solidified Alloys

Compared with conventional crystalline alloys, non-equilibrium solidified alloys show outstanding mechanical properties due to their special microstructure. The rapidly solidified Al-based alloys, especially the Al-based amorphous alloys, are highlighted because of their specific strength, tunable corrosion resistance and high fracture strength. It makes Al-based glasses to be very promising materials for potential aerospace applications. The crystallization kinetic model has been used to improve the analysis result accuracy and get the correct conclusion about crystallization process, which is very important for studying the formation mechanism of amorphous alloys and their thermal stability.This thesis mainly focus on the contents below: the solidification behavior of Al-Fe-Si-(Zr) alloy under sub-rapid or rapid solidification, such as the influence of cooling rate on the microstructural evolution of alloy (Chapters 2 and 3); the effect of cooling rate and the composition of alloy on the crystallization of amorphous phase, which formed during the rapid solidification (Chapter 4); the formation and crystallization of nano/amorphous Al-Fe-Si-Zr alloy (Chapter 5); improvement of isochronal crystallization kinetics model and its application to the amorphous alloy (Chapters 6 and 7); establishment of multi-peak transformation kinetics model and incubation kinetics model and the study on their validity in the practical application in chapter 8. The results indicate that:The cooling rate and components of alloy agents influence the microstructure of alloy under non-equilibrium condition. In the sub-equilibrium condition, the cooling rate affects no only the phase selection, but also the volume fraction, shape and size of the intermetallic compounds. The increase of cooling rate and component of Fe or Zr in Al-Fe-Si-(Zr) both contribute to the formation of amorphous phase.In the as-spun Al89Fe8Si2Zr ribbons, a composite nanocrystalline/amorphous structure formed companied with the average size of nano Al particles of about 10 nm and the crystallization of as-spun composite Al89Fe8Si2Zr was investigated by the continuous heating annealing DSC analysis. The result showed that the crystallization process two progresses, which with the approximately same reaction rates.An improved analytical model for isochronal transformation kinetics has been developed. The proposed treatment for the temperature integral and the consequent analytical model for isochronal transformation kinetics have been proved to be more effective than the previous model especially in a narrow temperature interval by numerical method. Moreover, both the multi-peak transformation kinetics model and incubation kinetics model established here show the validity and precision during their practical applications.