Influence Of High Magnetic Field On The Growth Behavior Of Intermetallic Compound Layers At Sn-Cu Interface

Very recently, technology on manufacturing superconducting magnets has shown great progress, and it is possible to use high magnetic field for controlling physics chemical process and materials processing. High magnetic field has several effects on the materials. A magnetic field with enough density can beome an independent parameter out of temperature and press, and then it hopes to prepare new materials with high magnetic field. The application of high magnetic field on the materials processing technologies is therefore becoming one of the vital areas in materials science, and several interesting results have been found, most of which have been focused on the microstructure and thermodynamic stability of the alloys. However, less research has been found on the diffusion and interface migration in high magnetic field. And then it is difficult for understanding the processinges related to kinetics in high magnetic field, for example, the diffusion phase transformation and electrochemical deposition. Since the growth of interfacial intermetallic compound (IMC) layers lardgely involves the diffusion and interface migration, it is interesting to observe the growth behaviors of IMC layer in high magnetic field for understanding the diffusion and interface migration. Unfortunately the influence mechinsm of high magnetic field on the IMC layer has still not been interpreted clearly whether in solid-solid couples or in solid-liquid couples.Up to now, many reports have been found on the growth behaviors IMC layer at Sn-Cu interface without magnetic field. Much information about the IMC layer growth can be provided for studing on the effect of high magnetic field. However, some issues about the IMC layer growth at Sn-Cu interface also need to be conducted, such as, the effect of liquid bath on the IMC layer growth, the changes of IMC layer growth induced by the element additions and the substrate structures.Several couples prepared from three Sn-based alloys, and two types of Cu substrate, namely pure Sn, Sn1.5Cu, Sn0.3Ni, Cu foils and single crystal Cu, were shosen in our work to investigate the growth of IMC layer in high magnetic field. The cross sections and growth kinetics, morphology evolutions, crystal orientations and components'concentration of IMC layer in high magnetic field were observed by using scanning electronic microscopy (SEM), X-ray diffraction (XRD), and electronic probe microanalysis (EPMA). Based on the experimental results, the influence of high magnetic field on the atomic diffusion and interface migration was tired to be analyzed from magnetization free energy and Lorentz force view points, and the main foundings were presented as follows: (1) From the cross sections and growth kinetics of IMC layer, it was found that the applied magnetic field had promted the IMC layer growth. The thickness of scallop-type IMC crystals had a linear relationship with aging time t 1/2 in Sn/Cu couples.This result suggested that the IMC layer growth was controlled by the diffusion during aging, and the growth activation energy without magnetic field was calculated as 116kJ/mol. However at liquid-solid Sn/Cu and Snl.5Cu/Cu interface, a linear relationship between the thickness and t1/3 was found, which meant a ripening process for IMC growth. High magnetic field increased the growth coefficient of IMC layer at Sn-Cu interface, while decreased the dissolution of Cu. After a relative long time reaction, two areas of IMC layer were found at Sn0.3Ni/Cu and Sn0.3Ni/single crystal Cu interface, and the application of high magnetic field promoted the formation of the stick-type IMC in the outer area near Sn substrate. This effect of magnetic field decreased with inceasing temperature. When the temperature was higher than 350℃, high magnetic field inhibited the detachment of IMC layer from the interface.(2) From the morphology of IMC layer, two effects of high magnetic field could be found on the morphology of IMC grains. The one was that high magnetic field enhanced the average size of IMC crystals during IMC layer growth. The average size of scallop-type IMC grains in Sn/Cu and Sn1.5Cu/Cu was increased by high magnetic field. High magnetic field promoted the formation of scallop-type IMC by increasing IMC layer thickness in Sn/single crystal Cu. And the other was that high magnetic field changed the morphology of IMC layer. In the case of Sn0.3Ni/Cu and Sn0.3Ni/single crystal Cu couples, high magnetic field also increased the stick-type IMC in the outer area near Sn substrate.(3) The crystal orientations of IMC layer were observed from the XRD plots, and it was found that high magnetic field changed the crystal orientation of IMC layer. A 2T magnetic field slightly changed the crystal orientation of interfacial Cu6Sn5 in Snl.5Cu/Cu couples. From the XRD plots for IMC layers in Sn0.3Ni/Cu couples under various magnetic field conditions, high magnetic field obviously changed the crystal orientations of the (Cu, Ni)6Sn5 IMC layer, and leaded to the appearance of new peaks. The magnetic field changed the crystal orientations of IMC layer on the single crystal Cu substrates. This effect of magnetic field also decreased with increasing temperature.(4) The solute distributions as well as the content of IMC components at the liquid-solid interface front were investigated by using EPMA. The results showed that high magnetic field inhibited the dissolution of Cu in the liquid bath and decreased the content of Cu solute at the interface front. The concentration of Ni solute for the facted-type or stick-type IMC grains in the outer IMC area near Sn substrate was higher than that for round-type IMC grains at Sn0.3Ni/Cu interface, while magnetic field transformed the morphologies of IMC grains in Sn0.3Ni/Cu couples by changing the content of Ni solute. (5) According to the experimental results, the influence of high magnetic field on the growth behaviors of IMC layer were analyzed based on magnetization free energy and Lorentz force. From the growth kinetics of IMC layers, the Lorentz force inhibited the intrinsic convection in the liquid bath, and thus decreased the dissolution of Cu into the liquid Sn and retarded the detachment of interfacial IMC layer. The magnetization free energy promoted the ripening process of IMC layer and decreased the dissolution of Cu by decreasing the equilibrium concentration of Cu in liquid Sn bath. From the morphology evolutions of IMC layer, the average size of IMC crystals in high magnetic field could be increased by promoting the ripening process of IMC layer. Moreover, the magnetization free energy could also change the content of the solute in IMC layer and thus modified the morphology and crystal orientations of IMC layer.