JOINING OF NICKEL TO MAGNESIA USING NICKEL NICKELOUS OXIDE COMPOSITE

In order to obtain the joints of nickel and magnesia, which have no flat joining interface, a Ni-NiO composite having a stepwise controlled compositional gradient was used for joining fillers. This composite, which was made by the process of powder-metallurgy, was placed between a nickel block and a magnesia block and this set was held at 1 573 K under no pressure in air. In this manner, a good adhesive joint of nickel and magnesia was accomplished. Nickel-concentration distribution on the longitudinal cross section of nickel/composite/magnesia joints smoothly decreased in order of nickel, composite, the solid-solution NiO-MgO, and magnesia. Such a joint has no flat joining interfaces which are weak points against fractures. Thus, bending strength of the joints increased than that of the direct joints of nickel and magnesia. The maximum value in the present work was 128 MPa. Fractures, whose planes became a dome shape, occurred almost in the solid-solution and magnesia in the vicinity of the composite filler. It seems that thermal stress in composite and solid-solution was released by the use of composite filler as compared with the direct joints of nickel and magnesia.