Effect of melt flow on microstructure formation from undercooled Ni-B alloys---a comparative study based on EBSP

摘要

A grain refined microstructure is of great interest in industrial applications because of the improved mechanical properties and enhanced homogeneous features. A large melt undercooling can lead to the formation of metastable phases and refined microstructures in the single-phase solid solution alloys. Using an electromagnetic levitator (EML) or glass flux method by rf heating, a grain-refined microstructure has been found in many alloys, e.g., Ni-Cu. In the meanwhile, the microstructure transition as a function of melt undercooling can be well interpreted by using the fragmentation model developed by Karma. In the model, Karma only considered two factors of solute and capillarity effects as driving force for fragmentation. However, when a sample is processed by the EML or heated by rf method in glass slag, the melt flow induced by the magnetic field imposed onto the metallic sample is unavoidable. In the present study, we employed an electrostatic levitator (ESL) and an electromagnetic levitator (EML) to investigate the microstructure and microtexture formation from undercooled Ni_(99)B_1 alloys.