1 - General introduction

Summary

After more than a quarter of a century of active research, composites based on metals are now beginning to make a significant contribution to industrial and engineering practice. This is partly a consequence of developments in processing methods. However, equally important have been advances in the understanding of various structure-property relationships, assisting in the identification of cost effective solutions and highlighting important objectives in the control of microstructure and the design of components. In this first chapter, a brief overview is given of the nature of MMCs and the background to their development.

Types of MMC and general microstructural features

The term metal matrix composite (MMC) encompasses a wide range of scales and microstructures. Common to them all is a contiguous metallic matrix. The reinforcing constituent is normally a ceramic, although occasionally a refractory metal is preferred. The composite microstructures may be subdivided, as depicted in Fig. 1.1, according to whether the reinforcement is in the form of continuous fibres, short fibres or particles. Further distinctions may be drawn on the basis of fibre diameter and orientation distribution. Before looking at particular systems in detail, it is helpful to identify issues relating to the microstructure of the final product. A simplified overview is given in Table 1.1 of the implications for composite performance of the main microstructural features. Whereas some of these microstructural parameters are readily pre-specified, others can be very difficult to control.