Liquid phase diffusion welding using Ni-4B alloy thin film as an insert material was investigated in order to obtain precise and high quality joints of very thin sheets. In this study the sheets of Ni, Ni-Fe alloy and Fe-Ni-Cr alloy(SUS304) were used. The thin film was deposited on the specimen (sheet) by magnetron-sputtering after cleaning the specimen surface by bombardment of Ar atom beam. Diffusion phenomena between each base metal and the thin film, and the tensile strength of joints at various thin film thicknesses were investigated. The results were as follows; (1) The melting temperature of Ni-B alloy thin film on the specimen changes by diffusion of boron atoms in heating process. Especially that of the film on Fe-Ni-Cr alloy into which boron atoms remarkably diffuse increases by more than 130°C at heating rate of 10°C per minutes and the thin film thickness of 7μm.
(2) Chromium atoms have a great influence on diffusion of boron atoms in an alloy of Fe-Ni-Cr group, and then boron atoms mainly diffuse through grain boundaries.
(3) Boron atoms activate the grain boundaries of Ni and quicken the movement of grain boundaries and the growth of grains. Ni-B alloy thin film of 1.4μm thickness has a greater effect on quickening them for Ni sheet of 50μm thickness than that of 7μm thickness.
(4) The joint of Ni sheets welded with Ni-B alloy thin film has been almost the same as the base metal in points of the tensile strength and the metallograph at the welding conditions of welding temperature: 1100°C, holding time: 10 minutes, pressure: 9.8×10/Pa and atmosphere: vacuum.
