Bonding glass ceramics to high temperature alloys

Abstract

Scanning and transmission electron microscopy and energy dispersive X-ray analysis have been used to determine the interactions occuring at the interface during the coating of a Nimonic alloy and titanium metal by lithium silicate glass ceramics. The fast diffusion of chromium from the substrate into the glass is shown to have a major influence on the microstructure and phase composition of the resulting glass ceramic. It is observed that a layer of adhering metal oxide on Nimonic plays an important role in achieving the desired bonding between the alloy and the glass ceramic coating. Lack of such an oxide, in the case of titanium metal, leads to direct contact and reaction of silicates with the metal. This severe reaction between the glass coating and titanium gives rise to a porous structure. It is shown that adherence oxides are needed to control the reaction. Alternatively some form of barrier layer may be necessary.