Electropolishing of Kovar Alloy for Vacuum Applications

摘要

Kovar (53% Fe - 29%Ni - 17% Co) is one of the most commonly used materials in high vacuum applications which quite often require electrical insulation(s). Kovar has thermal expansion coefficient close to that of alumina over the range from brazing to cryogenic temperatures. Therefore, joining problems due to difference in thermal expansion coefficients can be minimized when alumina and Kovar alloy are used together (1-4). Besides, Kovar parts should have smooth surfaces to minimize outgas from the surface due to inadequate cleaning, for the applications that require long vacuum life. This paper presents the electrochemical polishing of Kovar alloy in an electrolyte containing acetic acid, chromic acid and water. The primary objectives are to set a proper cell design and determine appropriate electropolishing conditions to attain the minimum surface roughness for Kovar parts in vacuum applications.