Elastically Mismatched Interfaces as Related to Glass-to-Metal Seals

The mechanical performance of Glass-to-Metal seals is largely dependent upon the morphology of the oxide interfaces. The interfaces of the glass-to-metal region are transition zones consisting of a metallically bonded base metal with its reduced oxide and progress to interatomic bonds which are a mixture of ionic and covalent in a glass or ceramic base material. Differences in coefficient of thermal expansion, interatomic bonding and overall physical chemistry cause a number of issues in design, manufacture and lifetime serviceability of a G/M seal. To date the primary dimensions of interface assessment are microscopy and analytical chemistry. The purpose of this study is to advance nanomechanical testing as an additional dimension of quality assessment of G/M seals. Nanoindentation makes it possible to quantify intrinsic material properties of highly heterogeneous bulk materials or interfaces on a sub-microscale resolution and upscale the characterization to a continuum mechanics macroscale. To accomplish this transverse 2-D modulus and hardness maps of metallic transition oxides at feedthrough and header interfaces were produced based on material, atmosphere, and heat-treatment. Materials selection arrays were evaluated for a range of materials: a lithia-alumina-silica glass-ceramic and a 9013 alkali barium glass, Hastelloy C-276 and Alloy 52 feedthroughs, and 303 and 304L stainless steel headers. Likewise, electron spectroscopies were correlated to the site of mechanical analysis. Noticeable changes in nanomechanical morphology were observed and found to be dependent upon production parameters