This first chapter of the volume largely serves to set the scene for an appraisal of the current status of metal matrix composite (MMCs), with relatively little in the way of detailed information, but extensive cross-referencing to other chapters of the volume, in addition to conventional citation of the literature. The chapter also includes a brief survey of both scientific issues and technological usage of various types of MMC, with some indications of how the landscape has changed since publication of the first issue of Comprehensive Composite Materials in 2000. Particular attention is paid to cermets, which are highly successful in technological terms and are in widespread commercial use: while they should certainly be considered to be type of MMC, they are not specifically covered elsewhere in this volume. Other “special category” MMCs mentioned here include highly porous metals, intermetallic matrix MMCs and graded structure MMCs, although all of these are treated in some detail in other chapters. Finally, there is mention at certain points of the effects of using very fine reinforcement, which is covered elsewhere in the volume only in terms of the processing challenges presented when the fibers or particles concerned are ultra-fine (nanoscale). In fact, while there has been extensive study over the past couple of decades of the potential offered by such reinforcement (in both MMCs and other types of composite system), caveats are identified here concerning expected property combinations, particularly in terms of the toughness of such composites.
Ceramic matrix composites (CMCs) are widely used in aerospace sector (gas turbines, structural re-entry thermal protection) and energy sector (heat exchangers, fusion reactor walls). These applications require a joint either permanent or temporary between CMC components with surrounding materials. Therefore, this chapter throws a light on different modes of joining and problem associated with them. This chapter mainly focuses on the joining of CMC–CMC joints, CMC–Metal joints, and non-permanent joints. As new CMCs are developed to meet the high temperature applications there is every scope for refining the existing techniques and for the development of new methods for joining the CMCs. This chapter also deals with machining of CMCs. The extent of machining varies depending on the application; however, CMCs are machined to ensure the dimensional accuracy. This chapter has also given insight on machining techniques like abrasive jet machining, laser machining, ultrasonic machining, abrasive water jet machining, and electrical discharge machining (EDM). It is observed that techniques like EDM and ultrasonic machining offers the ability to machine intricate profiles with a relatively low metal removal rate, whereas conventional abrasive grinding offers good material removal rates and surface finish.
Ceramicists define fatigue as the process (or processes) that leads to degradation of mechanical properties with time. Failure can occur under static loads (static fatigue), monotonically increasing or decreasing loads (dynamic fatigue), or under mechanical repetition of loads (cyclic fatigue). This chapter focuses mainly on cyclic mechanical fatigue.
