Research On The Solidification Of High-entropy Alloy In High Magnetic Field

High-entropy alloys(HEAs) is a new kind of alloys with bright future. In this thesis,CuAgAlFeNi HEA with lower melting point was synthesized by the arc-melting furnace.Subsequently, the effects of high magnetic field on the CuAgAlFeNi alloy duringundirectional solidification were studied,too. The conclusions are listed as follows:(1)The as-cast CuAgAlFeNi alloy was seen to be divided into hypoeutectic layer andsolid solution layer because of the gravity segregation. The hypoeutectic layer, whichwas determined to have hypoeutectic Ag-Cu composition and trace Al, had lowerhardness and lower melting point. In contrast, the solid solution layer was composed ofsolid solution phase, which had multi-element mixture of Al, Fe, Ni and few Cu, andwas investigated to have higher hardness and melting point. Within the majoritydendrite, it was found that there was special structure which was named of “eutecticglobe”, and its composition was similar to that of the hypoeutectic layer.(2)The structure of eutectic globe was transferred from the mixture of primary crystalof Ag and (Ag-Cu) eutectic into divorced eutectic after refusion.(3)High magnetic field could cause eutectic refinement and promote the irregulargrowth of precipitation phase which was determined to have predominantly Fe.Analysis shows that the melt convection during solidification was effectivelysuppressed in high magnetic field, and the length of the solute transfer was reduced, too.As a result, the microstructure of eutectic was refined. Furthermore, high magnetic fieldcould increase the diffusion coefficient of the atom, and eventually facilitate thediffusion But the mechanism and the effects of a high magnetic field on the size ofprecipitates still need for further research.