Fracture Behavior of Particle Reinforced Metal Matrix Composites

The contributions of the reinforcement volume fraction and annealing temperatures to crack opening force and propagation energy are systematically studied by three point bending tests and by SEM investigations. The bending test data show that for the same reinforcement volume fraction, 2618 and 7075 Al composites require much higher force to open the cracks than 6061 matrix. This relates to the much higher levels of solute elements which causes matrix hardening. Studies reveal that the energy absorption level of the materials during crack propagation depends on both matrix strength and ductility which relates to the reinforcement volume fraction, composition and heat treatment conditions. Large deformation zones are found in front of the crack tip before crack propagation which indicate a ductile failure mode for the composites. Studies also reveal that cracks initiate generally at the particle/matrix interfaces for the low volume fraction reinforced composites. However, for the high volume fraction reinforced composites, crack initiation has been found from both reinforcement/matrix interfaces and broken particles. This indicates that increasing reinforcement volume fraction and matrix strengthening tend to change the fracture mode from interface debonding to particle cleavage cracking.