Bonding of Si sub 3 N sub 4 Ceramics and an Fe--26Cr Alloy Using Titanium Foils and a Nickel Interlayer

A silicon nitride ceramic and an Fe--26 mass.% Cr alloy were bonded in an argon gas stream using a Ti-foil (20 mu ) and Ni plate (1 mm). The fracture strength, obtained by bending tests at room temperature, was approximately 70 MPa for the bondings as-made at 1423K for 3.6 ksec. By increasing the diffusion-annealing times the strengths were reduced rapidly, resulting in 40 MPa for 32 ksec, and then increased gradually up to 80 MPa for the bondings diffusion-annealed at 1373K for 360 ksec. The bonding layer was composed of two layers: One of them is an intermediate layer consisting of the TiN, Ti(Si, Ni), and oxides contained in the ceramics as the binder. The others are is the intermetallic compounds such as TiNi, TiNi sub 3 , and their mixture, as well as the Ni--Ti solid solution layers. With the diffusion-annealing at high temperatures the TiNi layer was decomposed to the TiNi sub 3 and then to the Ni(Ti). In accordance with the decrement of the alloy layer thickness the fracture strengths were increased, in particular when the TiNi layer was thinned less than a few micronmeters. It was found that the high fracture strengths were obtained for the surface-polished bondings, and were more than 200 MPa. This indicates that the surface flaws reduced significantly the fracture strength of the as-bonded specimens. 6 ref.--AA