Study On Mechanical Milling And Pressing Billets Of Ti/Al Composite Powders

TiAl alloys are widely used because they possess light quality and excellent elevated temperature properties such as high strength retention, resistance to creep and oxidation. However, the poor ductility and strong resistance to deformation at elevated temperature currently limit their application. In addition, it is difficult to prepare TiAl alloy with fine and homogeneous microstructure by traditional casting and mechanical working processes. Therefore, a new technology, which consists of the preparation of nanocrystalline Ti/Al composite powders with extremely fine lamella microstructure by mechanical milling (MM), the subsequent consolidation and densification of the composite powders by pressing, the composite powders has been put forward to fabricate TiAl alloys with fine and homogeneous microstructure and highly density. Research on the following aspects has been accomplished.The evolution on particle morphology, microstructure, grain size and microstrain of the mixture of Ti and Al elemental powders during MM has been investigated. It was found that the nanocrystalline composite powders with extremely fine Ti/Al alternative lamellar structure (lamella spacing about 0.1~0.5μm) could be prepared by MM using proper processing parameters. Thus forms the theory basis for the preparation of Ti/Al composite powders by MM.In order to consolidate the powder compacts into densified billets, the technique of vacuum degassing, encapsulating and warm pressing was adopted. We can combine the two technique to pressing Ti and Al elemental powders. we analyze the microstrain and density changing of the composite powders during pressing. The density evolution of Ti/Al composite billet became calm when the pressure get to 1000Mp.The technique of vacuum degassing can reduce the content of atmosphere. In the billets. The technique of pressing in low temperature can enhance the interface combine intensity of composite powder. The technique can avoid produce Ti/Al chemical compound in high temperature. The chemical compound would increase the difficulty of pressing. The research on vacuum degassing and temperature of pressing can acquire the ideal composite powders of highly...