AEM INVESTIGATION OF CERAMIC INCOLOGY-909 DIFFUSIONAL REACTIONS AFTERJOINING BY HIP

Diffusion bonding by hot isostatic pressing (HIP) was performed betwee n Incoloy 909 and five different ceramics. Two of the ceramics were co mposites made from powder mixtures of Si3N4 and either 60 vol % TiN or 50 vol % TiB2, while three were monolithic materials, namely Si3N4 wi th 2.5 Wt% Y2O3 as a sintering additive, Si3 N4 without additives, and Si2 N2O without additives. A diffusion couple geometry was developed to facilitate the preparation of thin-foil specimens for examination b y analytical electron microscopy (AEM). Diffusion bonding was performe d by HIP at 927-degrees-C (1 200 K) and 200 M Pa for 4 h. The formatio n of reaction layers was very limited, being less than 1 mum in total layer thickness. Two reaction products were found by AEM; a continuous , very thin, (less-than-or-equal-to 1 00 nm) layer of fine TiN crystal s at the initial ceramic/metal interface, and larger grains extending about 1 00-500 nm into the superalloy and forming a semi-continuous la yer of a G-phase silicide containing mainly nickel, silicon and niobiu m.