Study On The Crystal Orientation And The Microstructure Control Of TbDyFe Alloy

Solidification characteristics of TbDyFe alloy (Tb_0.27Dy_0.73Fe_1.8 and Tb_0.27Dy_0.73Fe_1.95) and influence of the solidification conditions and microstructure configuration on the preferred orientation were studied by the way of directional solidification process and solidification parameter control in this paperInvestigation of the crystal orientation indicated that when temperature gradient G₁≥800K/cm, and the crystal growth velocity V≤43μm/s, there existed <110> oriented crystal in Tb_0.27Dy_0.73Fe_1.8. And following with the increase of V and G_L, the <110> orientation crystal could be get easier.For Tb_0.27Dy_0.73Fe_1.8 alloy, Terfenol-D crystal with a <110> orientation could be obtained if 800K/cm≤G_L≤900K/cm and 150μm/s≤V≤200μm/s, the same with < 112> orientation crystal could be gained when 500K/cm≤G_L≤700K/cm and 180μm/s≤V≤220μm/s respectively.The observation of microstructure change indicated that the solid-liquid interface characteristic of Tb_0.27Dy_0.73Fe_x alloy changed along with the solidification condition and crystal growth velocity. Under the condition of G_L=500K/cm, when growth velocity V=111μm/s, the solid-liquid interface characteristic of Tb_0.27Dy_0.73Fe_1.8 would be unshaped interface microstructure character, which belonged to Non-faceted growth; when V≤50μm/s, the solid-liquid interface microstructure had changed, the crystal were co-growing in non-faceted and faceted; when 10μm/s≤V≤24.41μm/s, Terfenol-D crystal grew in non-faceted entirely.When V=50μm/s, 500K/cm≤G_L≤700K/cm and V=80μm/s, G_L =900K/cm, only part of the RFe₂ phase present piece shape microstructure, which should be compound state of non-faceted and faceted; when V=50μm/s, G_L=800K/cm and 900K/cm, RFe₂ phase were all piece shape microstructure. When V=102μm/s, G_L= 900K/cm, non-faceted morphologies appeared. The RFe₂ phase of Tb_0.27Dy_0.73Fe_1.95 alloy were all piece shape microstructure when G_L=900K/cm, 700K/cm and 500K/cm, and 12μm/s≤V≤333.3μm/s, which belong to lubricity interface character, and the crystal grew in non-faceted morphologies.Study of orientation and microstructure control of TbDyFe alloy indicated that when solid-liquid interface grew in cellular morphology, Terfenol-D crystal with <110> orientation could be obtained easily; when the interface grew in dendrite, <112> orientation crystal would appear. It always happened to be cellular-dendrite morphology or unstable solid-liquid interface when crystal developed as multi-orientations. Zhou Meizheng (Material Science) Supervised by professor: Ji Chengchang...