Research On Solidification Microstructure And Property Of Fe-Sn Alloy And Cu-Fe Alloy Imposed By High Magnetic Field

In recent years, superconducting magnetic field has been widely applied in various branches of material science. And it is playing an increasing role in the fundamental research. Many new ideas and technology are being gestated by using high magnetic field during the fabrication and application of materials. So the field is being widely concerned. This paper is financially supported by National Natural Science Foundation of China (No.50574027) and National high-tech R&D Program of China (863 Project) (No.2007AA03Z519). Firstly, solidification microstructure and properties of Fe-Sn alloys under high magnetic field are investigated. The aim is to decrease its problems of the density difference in two components to obtain dispersed microstructure. Secondly, solidification microstructure, processing, heat treatment and properties of high-strength, high conductivity Cu-Fe alloy under high magnetic field are presented. The aim is to solve its problems of the contradictory relationship between the tensile strength and the conductivity to develop the novel method to improve the alloy performance.The research results of solidification structure and magnetic properties of Fe-49%Sn (weight percent) monotectic alloys show that, the primary dendrites forα-Fe phase in the Fe-Sn alloy have a tendency to align along the parallel direction of high magnetic field. The alignment degree ofα-Fe phase is increased with the magnetic flux density, since the easy magnetization<100> crystallographic direction ofα-Fe phases is not only the direction of the lowest internal energy, but also a preferential growth direction ofα-Fe dendrites. XRD analysis shows that the diffraction intensity of (110) crystal plane ofα-Fe phases parallel to the direction of the high magnetic field gradually increases with the increase of magnetic flux density, indicating that the alignment ofα-Fe phase induced by the magnetic field increases. It is caused by the significant increasing preferential growth ofα-Fe phase. The measurement of magnetic property show that the magnetic anisotropy energy of Fe-49% Sn alloys is gradually increased with the magnetic flux density which indicated that the magnetic anisotropy of the alloys is enhanced by imposition of high magnetic field. In the experimental conditions used, the cooling rate has a small effect on the microstructure and magnetic properties of Fe-49% Sn alloys, but the holding time has greater impact since the enhanced alignment of a-Fe phases induced by high magnetic field is increased with the holding time, and thereby increasing its magnetic anisotropy.The migration of Fe-rich phase in Cu-Fe alloys induced by high magnetic field is investigated. It is shown that the Fe-rich particles are homogeneously distributed in the Cu-rich melt. With the increasing of the magnetic flux density, the Fe-rich particles have the tendency of floating up. However, the Fe-rich particles migrate down when imposed by the negative gradient magnetic field. The macrostructure and the alignment microstructure are analyzed. The theory on melt migration induced by the magnetic flux density and magnetization force is proposed.The solution and aging treatments of Cu-Fe casting alloys under high magnetic field are investigated. It is shown that the solubility of Fe element in Cu matrix ofCu-15%Fe (weight percent) alloy reduce 0.39% when treated at 1000℃temperature with 10T magnetic field. It indicates that high magnetic field can promote the precipitation of Fe in Cu matrix in a certain extent, which is similar to the effect of slow cooling. Moreover, the speciems after solution treatment were aged in the 500℃and 800℃temperature under 10T high magnetic field. The results show that solubility of Fe in Cu matrix is up to the minimum value at the aging temperature of 500℃. The analysis results show that the activation energy of atoms is changed by imposition of high magnetic field, so that the diffusion behavior of atoms is affected. The relationship of diffusion coefficient with high magnetic field is satisfied with the formula DM=Dexp(U/kT).The results of XRD and EDS analysis on Cu-Fe casting alloys of precipitation treatments under high magnetic field show that more Fe element are precipitated under the aging temperature of 500℃with 10T high magnetic field, the solubility of Fe in Cu matrix is decreased and the precipitation of Fe is slightly increased by prolonging treatment time. The measurement results of solubility, microhardness and lattice constant show that the crystal lattice distortion, coherency relation between precipitation phase and matrix are changed by imposition of high magnetic field. The optimized temperature of treatment is 500℃.The research of microstructure and mechanical/conductivity properties in Cu-14.5%Fe (volume percent) composites show that the curled ribbon-like Fe fiber is formed in the cross-sectional with the increasing of drawing ratio, and the density and uniformity of Fe fibers are also increased. The averaged spacing of the fibers and drawing ratio is satisfied the relationship ofλ=32exp(-0.42η). The measurement of mechanical properties shows that the tensile strength gradually increases with the increase of drawing deformation, and the excess strength of Cu-Fe micro-composites overestimated the rule of strength mixture has the relationship with the average inter-fiber spacing as the formula of△σD=-188+465λ-1/2. The measurement of conductivity properties shows the conductivity is stabilized in the range of 49.54-56.89%IACS with the increasing of the drawing ratio, and the resistivity and drawing ratio of the alloy has the linear relationship as the drawing ratio is in the range of 4.91 to 8.23.Effect of annealing on mechanical/conductivity properties of the deformed in situ Cu-14.5% Fe alloys is investigated. It is shown that the tensile strength and microhardness are gradually reduced with the annealing temperature, while the conductivity firstly increases and then decreases due to the influence of matrix and fiber morphology. The optimized annealing temperature is 450℃at which the alloy has the good tensile strength and conductivity. With the increase of the holding time, the tensile strength and microhardness sharply is lowered firstly, then gradually stabilized. However, the conductivity is just the opposite. The optimized holding time is 1h; The investigation of different cooling conditions such as furnace cooling, air cooling and water quench reveals that air cooling is optimized cooling way.Effect of magnetic field annealing on mechanical/conductivity properties of the deformed in situ Cu-14.5%Fe alloys is investigated. It is shown that when the annealing temperature is 300℃, the tensile strength is rapidly increased at first, and then slightly declined. Moreover, the tensile strength is linear with magnetic flux density when the magnetic flux density is further increased. When the magnetic flux density is up to 10T, the tensile strength is increased by 11%. However, the conductivity has a rapid decline. At the annealing temperature of 500℃, with the increase of magnetic flux density, the tensile strength has a rapid decline and then slight increase, and as the magnetic flux density is up to 10T, the tensile strength increased by 2.8%. While the magnetic flux density is up to 5T, the conductivity is reached to 58.7%IACS. When At the annealing temperature of 800℃, the tensile strength and conductivity have a significant increase with the magnetic flux density, which can partially solve the contradictory between them. The whole distribution of tensile strength and conductivity shows that the magnetic field annealing can slightly changed their distribution. The figure of merit analysis shows that the better annealing temperature is 300℃, which make the general evaluation index of the alloy up to 5786.