AEM investigation of ceramic/Incoloy 909 diffusional reactions after joining by HIP

Diffusion bonding by hot isostatic pressing (HIP) was performed between incoloy 909 and five different ceramics. Two of the ceramics were composites made from powder mixtures of Si sub 3 N sub 4 and either 60 vol.% titanium nitride or 50 vol.% TiB sub 2 , while three were monolithic materials, namely Si sub 4 N sub 4 with 2.5 wt.% Y sub 2 O sub 3 as a sintering additives, Si sub 3 N sub 4 without additives, and Si sub 2 N sub 2 O without additives. A diffusion couple geometry was developed to facilitate the preparation of thin-foil specimens for examination by analytical electron microscopy (AEM). Diffusion bonding was performed by HIP at 927 deg C (1200K) and 200 MPa for 4 h. The formation of reaction layers was very limited, being < 1 mu m in total layer thicknes. Two reaction products were found by AEM; a continuous, very thin, ( < + 100 nm) layer of fine TiN crystals at the initial ceramic/metal interface, and larger grains extending approx 100-500 nm into the superalloy and forming a semi-continuous layer of a G-phase silicide containing mainly nickle, silicon and niobium.