DESIGN OF THE MICROSTRUCTURAL SCALE FOR OPTIMUM TOUGHENING IN METALLIC COMPOSITES

The role of the microstructural scale in toughening of composites cont aining a metallic constituent is described by invoking a dislocation p ile-up mechanism for debonding at metal ceramic (intermetallic) interf aces. Below a certain size of the metal phase, the pile-up length beco mes subcritical precluding debonding. The toughening effect below and above this critical size separates into two kinds of behavior leading to a maximum toughness when plotted against the characteristic length of the metal phase. The position of this maximum defines the optimum m icrostructural scale. The concept is applied successfully to metal-cer amic and metal-intermetallic composites with a microstructural length scale of less than about 10 mum. Metal matrix composites where the met al forms a continuous network through the microstructure are shown to have much higher toughness than the case where the same volume of the metal phase is distributed as discrete particles in the composite.