Porosity nucleation in metal-matrix composites

The mechanism of porosity nucleation in pressure infiltration casting of metal-matrix composites (MMCs) is investigated. Five interfacial configurations are investigated for a variety of matrix/reinforcement systems. Interfaces with negative curvature such as cavity are found to be potential sites for porosity formation. The Al/Al2O3 system is most susceptible to porosity nucleation for the systems considered. Appropriate matrix alloying such as Mg in the Al/Al2O3 system and Mg and Cu in the Al/SiC system and reinforcement coatings such as Cu coating on SiC significantly reduce the contact angle, enhance wettability at the interface, and could be effective for suppressing porosity formation. Other effective methods include careful control of the cooling condition as well as the applied pressure.