Joining ZrB2-SiC composites using glass interlayers

A joining technique, based on the use of a glass powder as a bonding interlayer between two ceramic pieces, is tested for a ZrB2-SiC composite. At the bonding temperature, the glass melts, wets the ceramic and flows through the interface driven by the capillary pressure that builds up between the two contacting ceramic surfaces, promoting their adhesion. The behaviour of three glasses is compared: two in the system Ca-Al-Si-O (melting temperatures 1400 and 1210◦C) and one in the system Y-Al-Si-O (melting temperature 1440◦C). The ceramic-glass interfacial characteristics depend mainly on the temperature, on the composition of the glass and on the phenomena influencing the adhesion, such as the partial dissolution of the ceramic grains when the glass wets them. The 3-point flexural strength values of the joints obtained by the system that resulted with the more homogeneous interface are also reported. C 2005 Springer Science + Business Media, Inc. 1. Introduction Zirconium diboride (ZrB2) is an ultra-refractory material of particular interest because of the excellent and unique combination of high melting point, high electrical and thermal conductivity, chemical inertness against molten metals or non basic slag and superb thermal shock resistance [1]. These properties make it an attractive candidate for high temperature applications where corrosion-wear-oxidation resistance are demanded. Zirconium diboride is currently used as a refractory in foundry or electrical devices (heaters, igniters). Other applications have been recently developed in aerospace for the thermal protection of leading edges or other sharp parts on hypersonic re-entry spacecrafts [2–4]. High density ZrB2-based materials can be obtained through liquid phase sintering at temperatures lower than those necessary for undoped ZrB2 [1, 5–8]. However, the grain boundary phases deriving from the sintering aids sometimes deteriorate the properties of this class of material [6, 8–11], in particular when metal sintering aids (Ni, Fe) are used. Ceramic additives have been tried recently and these improve significantly both the sintering and microstructure of ZrB2 [12–14]. The fracture toughness and strength of monolithic ZrB2 ceramics can be improved by introducing a secondary reinforcing phase [13]. Potential applications of ZrB2-based materials can be widened further by developing reliable joining techniques which would overcome the problems associated with the fabrication of complex shaped components ∗Author to whom all correspondence should be addressed. [