Large volume of Fe-Ga magnetostrictive alloy solidification undercooled

Title: Large volume of Fe-Ga magnetostrictive alloy solidification undercooled Author: Zhou Jiankun Degree-granting units: Shanghai Jiao Tong University Key words: magnetostriction;; Fe-Ga;; undercooling;; directional solidification;; magnetic domain;; texture Abstract: Magnetostrictive alloys are important materials, sensors and micro-drive, in the sonar transducer, the field of weapons systems and robotics widely used. Now more commonly used to Tb-Dy-Fe as the representative of a strain of giant magnetostrictive materials, while large, high Curie temperature of excellent performance, but with brittle, disadvantages of higher raw material costs. And in recent years the Department of magnetostrictive Fe-Ga alloy with high strength, good toughness and low cost, and in single crystal materials [100] direction for nearly 400 ppm to neodymium magnets obtain the large magnetostriction, excellent performance, thus making with a wide range of applications and commercial value. Department of magnetostrictive Fe-Ga alloys show a large number of research results: the proper alloy, rapid solidification and oriented growth is the preparation of high performance Fe-Ga material prerequisites. Therefore, to find a large volume can grow, can obtain good orientation and structure of rapidly solidified metastable solidification control technology has become the preparation of high performance Fe-Ga magnetostrictive material like one of the key issues. Undercooling rapid solidification in these areas will undoubtedly have a unique advantage. Undercooling technology is developing rapidly in recent years a new type of rapid solidification technology, in the deep cold conditions, when excited by the nucleation, melt up to several meters per second high-speed growth, crystal growth by artificially controlling alloy when the nucleation conditions, can be prepared by a homogeneous orientation materials, is considered to be potential development of new rapid directional solidification technology. Therefore, this combined cycle using hot molten glass cleaning method carried out the first glass cleaning agent composition and other factors on Fe_ (81) Ga_ (19) alloy purifying effect of the study; for the effective application of rapid solidification of undercooled technology, and carried out under conditions of high undercooling solidification Fe_ (81) Ga_ (19) alloy and its magnetic force microscope evolution research; and on this basis, the introduction of the technology orientation of Fe-Ga alloy material preparation. In addition, the prepared Fe_ (81) Ga_ (19) alloy rods in the preferred orientation of crystal growth, microstructure and magnetic properties were analyzed; Finally, under different undercooling get excited Fe_ undercooled melt (81) Ga_ (19) alloy rod texture and magnetostrictive properties are http://www.chinamagnets.biz/Neodymium/Ball-Neodymium-Magnets.php discussed. Main research results obtained in the following aspects: Through the glass fluxing combined cycle thermal method of B_2O_3, NaSiCa + B_2O_3 (referred to as Na-Si-Ca-Al-B) and Na-Si-Ca-Al-B + Na_2B_4O_7 glass as cleaning agents for Fe_ (81) Ga_ ( 19) the effect of cold melt were analyzed. Glass cleaning mechanisms found B_2O_3 just physical adsorption, can only get smaller too cold; Na-Si-Ca-Al-B glass integrated physical and chemical purification, to obtain large undercooling, but its viscosity is too large, resulting in access to cold degree of instability; Na-Si-Ca-Al-B + Na_2B_4O_7 glass retains the physical and chemical synthesis purification mechanism, while effectively reducing the Na-Si-Ca-Al-B glass viscosity. And analysis of the sample weight, superheat, holding time and other factors on the impact of undercooling, cooling experiments to determine the specific process: the use of 70% Na-Si-Ca-Al-10B +30% Na_2B_4O_7 glass as clean agent, the heating process should be fully in the exhaust temperature below 400 ℃ two minutes at about 200 K superheat, heat 1.5 min, the heat cycle in which Fe_ (81) Ga_ (19) successfully melt up to 300 K undercooling above. Through the cold Fe_ (81) Ga_ (19) alloy microstructure evolution and magnetic domain structures found: 0 ~ 315 K in a wide range of undercooling, Fe_ (81) Ga_ (19) alloy solidification can be divided into three categories: the low undercooling (ΔT ≤ 50 K) the Fusing dendrites, intermediate undercooling range (50 K <ΔT <200 K) of the small and large equiaxed undercooling (ΔT> 200 K) when the recrystallization; and its own formation mechanism was discussed. It is noteworthy that, in the undercooling of 150 ~ 200 K range, solidification in the growth of small granular grains with a certain direction, thus selected as the cold zone directional solidification of undercooled too cold to stimulate degree range. In addition, samples of cold magnetic force microscope studies show, Fe_ (81) Ga_ (19) alloy surface magnetic domain structure on undercooling are also very sensitive to the changes. Based on the above two studies, the use of genetic undercooling, in the 200 K undercooling, the surface through the points to stimulate and inspire the undercooled melt and successfully achieved Fe_ (81) Ga_ (19) alloy undercooled rapid directional solidification. By 200 K undercooling point of excitation under preparation Fe_ (81) Ga_ (19) alloy rods of orientation analysis of directional solidification found some samples of columnar crystals with strong [100] texture of the bar [100] with the specimen axis preferred orientation angle of 10 ° or so, the result is better than the best previous results reported in the literature; by XRD, DSC, TEM samples by means of the microstructure of the bars found undercooling rapid directional solidification of Fe_ (81) Ga_ (19) alloy is not uniform within a fully disordered A2 structure, but in the micro pervaded many of the Ga atom clusters form by the occurrence of lattice distortion of the DO3 structure, and some nano-scale with [111] orientation of the structure of the embedded domain; through the magnetic properties of the sample found in the axial direction of the sample received more than 800 ppm of large magnetostrictive properties, which is almost in the block previously reported Fe -Ga magnetostrictive materials for maximum performance twice, we believe that stimulate the undercooled melt prepared Fe_ (81) Ga_ (19) along the axial direction of the polycrystalline rod height [100] texture as well as rapid solidification process appear in clusters of Ga lattice distortion DO3 structure and composition of non-uniform microstructure is greatly enhanced magnetostrictive properties of the main factors. Finally, to stimulate undercooling on solidification Fe_ (81) Ga_ (19) solidified alloy bars, texture, and its performance was studied and found to stimulate the organization can be directed undercooling range With increased undercooling, stimulate, get bar [100] orientation of a gradual increase in the saturation magnetostrictive properties also increased, from 150 K to stimulate undercooling 210 K 750 ppm to 885 ppm when . In addition, because the sample [100] preferred orientation there is a certain angle with the rod axis, the magnetic field causes the magnetostrictive properties with increasing emergence of the phenomenon first increases and then decreases. Degree Year: 2009