Fabrication of a Glass-Ceramic-to-Metal Seal Between Ti–6Al–4V and a Strontium Boroaluminate Glass

Abstract

Glass-ceramics are widely utilized in the electronics industry to provide electrical insulation and to form leak-tight joints with a range of metals. The coefficient of thermal expansion (CTE) of the glass-ceramic can be controlled by the extent of crystallization to reduce detrimental tensile stresses in the joint. In recent years, there has been interest in using titanium alloys, in place of stainless steels, due to their lower density and superior specific strength. In this study, the heat treatment of a strontium boroaluminate glass has been tailored to create glass-ceramics with mean CTEs ranging from 5.7 ± 0.1 × 10−6/K to 9.7 ± 0.1 × 10−6/K over the temperature range 303–693 K. The resultant glass-ceramic consists of three crystalline phases and residual glass. A glass-ceramic with a mean CTE of 6.9 ± 0.1 × 10−6/K was subsequently fabricated to form a compression seal with a Ti–6Al–4V housing and a preoxidized Kovar pin. Single pin assemblies were shown to be reproducible in terms of microstructure and all passed a standard helium leak test, indicating that a successful seal had been produced.