The term "composite materials" encompasses a wide variety of materials from one of the earliest made by man, adobe brick formed from a mixture of mud and straw, to one of the latest, intermetallic rods or platelets grown in a melt of eutectic composition. Others, sometimes referred to as composites, include felted materials, laminates, clad materials, and dispersion-hardened materials.

In recent years, however, the greatest interest has been found in matrix materials reinforced with nonmetallic fibers, either continuous or discontinuous, because of their potentially very high strength and elastic modulus. Research and development in these fiber composites began in earnest about 1960 and reached its peak in perhaps 1971. Extensive investigation has been conducted on both resin-matrix and metal-matrix composites, with some work being done on ceramic matrixes. The present declining interest in metal-matrix fiber reinforced materials is due to a number of factors, but of major importance are the high cost and the difficult fabricability of these materials. Not the least of the fabrication problems is joining.

The subject of this report has been limited to metal-matrix fiber reinforced materials. Other materials, e.g., the dispersion-hardened metals and the resin-matrix composites have not been included because of their different strengthening mechanism, or because they are less appropriate to the functions of the Welding Research Council.

The purpose of this report is to evaluate and summarize, and place in the proper perspective, all of the available information on the joining of the metal-matrix fiber composites. One approach to the production of structures from composites is to start with material containing a single layer of reinforcing fibers with thin matrix material on either side (usually referred to as tapes, although these may be much wider than what is commonly thought of as tapes), assemble sufficient tapes of the proper size and shape in a die, and, by diffusion welding or brazing, produce a completed structure, with the exception of minor finishing work, in one operation. This approach has been applied most often to the fabrication of aircraft gas-turbine engine blades. The fabrication of structures of composite materials, with tapes as the starting material, is somewhat analogous to the fabrication of conventional materials by casting, with melting stock as the starting material. The manufacture of composite material and the production of structures from composite tape are considered to be primary fabrication processes, and the joining aspects of these processes are not a subject of this report.