PRINCIPLES AND METHODS OF METAL-CERAMIC BONDING FOR PM APPLICATIONS

Powder metallurgy (PM) offers advantages for both traditional and advanced applications, but often the application requires the combined benefits offered by both a metal and a ceramic when the demands cannot be met by a single material. Metals are ductile with high thermal and electrical conductivity, while ceramics are brittle insulators, refractory, hard, and wear-resistant, with excellent high-temperature properties and a relatively low thermal expansion. Composite components can meet required performance objectives by coupling metals and ceramics that employ the properties of each material. The technological requirements for bonding metals and ceramics in an effective, reliable, and economical manner mandate an understanding of basic bonding principles. These principles are discussed with particular attention given to combining powder materials or joining metal powder to a ceramic part. After discussing the basic scientific and engineering principles that can promote strong (or controlled) metal-ceramic bonding, several relevant joining technologies are reviewed. The first section of the review is a treatment of those general principles that are common to most (if not all) metal-ceramic joining and bonding methods. Factors are presented which affect bond strength, both intrinsic and extrinsic, and methods used in bond evaluation will be provided. The second section provides an overview of processes employed in joining ceramics and metals. Selected successful metal-ceramic composite systems that use powder and melt (liquid-phase joining) metallurgy are discussed with a view to expanding PM applications.