The Fabrication By EBPVD And Characterization Of Al/Ni Multilayer Foils

The Al/Ni multilayer foils can act as local heat sources to melt the solders or act as ‘special solders’ and thereby join components rapidly. This ‘special solders’ can be applicable especially in the deep sea and space. The Al/Ni multilayer foils usually were fabricated by magnetron sputtering or cold-roll. The Al/Ni multilayer foils with total thicknesses of tens of microns, fabricated by magnetron sputtering which has a low deposition rates, are expensive. The cold-rolled foils are low cost, but the nonuniform morphology and the easily contaminated interface prevent them from widely applying. High rate electron beam physical vapor deposition(EBPVD) method based on the Piercegun, allows the minimization of the process time and cuts costs of the Al/Ni multilayer foils with high quality. Compared with the cold-rolled foils, the microstructures of the Al/Ni multilayer foils fabricated by EBPVD are uniform and the interface is pure.In order to deposite the Al/Ni multilayer foils with controlled compositions and microstructures, the L5 EBPVD was remoulded including crucibles, partition of deposite space and special mechanism. The microstructures of Al/Ni multilayer foils fabricated by EBPVD with typical technological parameter were characterized. The DSC curves and the sequence of intermediate phase formation in the Al/Ni multilayer foils fabricated by EBPVD with slow heating were acquired to explore reaction mechanism. The reaction velocities were measured usuing electrooptical technology.The boron nitride pot is fit for holding Al ingot which a focused high energy electron beam is directed to melt in EBPVD. The two crucibles have been partitioned off by a screen in order to prevent a mixture of Al vapor and Ni vapor. With the thermal storage capacity of substrate increasing, the heating rate of substrate decreases in preparation process and finally the Al/Ni multilayer foils were fabricated by EBPVD successfully.The phase composition of the Al/Ni multilayer foils fabricated by EBPVD depends on the process time and the thermal property of substrate. The current intensity of electron beam, thermal conductivity and surface topography of the substrate have an significant effect on layer microstructures of the Al/Ni multilayer foils fabricated by EBPVD. With the current intensity of electron beam and thermal conductivity of substrate increasing, deposition rate increases. The surface roughness of substrate has an significant effect on the surface morphology of the Al/Ni multilayer foils. The holes widely observed in the Al/Ni multilayer foils is due to insufficient surface diffusion of adatoms caused by low substrate temperature.The DSC traces at a heating rate of 40°C/min show the presence of two exothermic peaks for the two-stage formation of the single phase Al3 Ni, maybe referring to nucleation and the growth of such Al3 Ni layers. When the heating rate falls to 20°C/min, the two-stage becomes one. The peak temperatures shift to higher values for higher heating rate. In this article, the sequence of phase transformations in the Al/Ni multilayer foils during the reaction in the case of slow heating: Al+Ni â†' Al3Ni+Al+Ni â†' Al3Ni+Al1.1Ni0.9+Al3Ni2, and the first phase to form is Al3 Ni. The reaction velocity of the Al/Ni multilayer foils in this paper is much lower than the Al/Ni multilayer foils fabricated by magnetron sputtering, but higher than the cold-rolled foils.