Joining of alumina using magnesium- or calcium-aluminosilicate glass–ceramic fillers

Abstract

Magnesium- and calcium-aluminosilicate (MAS and CAS) glass–ceramics were used to join alumina with six different compositions. The fillers were applied onto the alumina by screen-printing, and then joining was performed slightly below and above the filler melting temperature (Tm). The evolution of various intermediate compounds upon heat treatment between the filler itself and at the joining interface was compared. MgAl2O4 and CaO·6Al2O3 was the main crystalline phase presented at the joining interface for the MAS and CAS system, respectively, while more intermediate compounds were observed when only filler was heat-treated. The formation of MgAl2O4 and CaO·6Al2O3 was attributed to the diffusion of Al ions from the alumina base, which is desirable for obtaining a sound joint due to the similar coefficient of thermal expansion to the base alumina. The maximum joint strength of 250 ± 41 and 301 ± 48 MPa was obtained for MAS and CAS filler system, respectively, after joining at T ≥ Tm due to complete interfacial wetting.