Application of a low pressure infiltration process to produce particle-reinforced metal matrix composites

Abstract

Process parameters to control the microstructure of particle-reinforced MMC in the low pressure infiltration process were investigated. In the experiment, the mixed powder of reinforcement particle and metal particle in various volume fraction was employed to control volume fraction of reinforcement particles in PRMMC. Mixed powder and Al-Cu alloy or cast iron were placed in the silica tube having a small nozzle at the bottom. Then, the upper alloy was melted by induction heating and the alloy melt was forced to infiltrate into the lower mixed powder layer by applying a certain pressure on the melt surface. As for the particle size dependence of the infiltration pressure, the pressure increased exponentially with a decrease in the particle size of the reinforcement in the case where the metal particle was not used, indicating that the pressure at the advancing melt surface decreased due to capillary pressure and friction between melt and particles. On the contrary, when the mixed powder was employed, lower pressures were required because of an increase in the permeability of mixed powder layer attributed to the metal particle acting as a void. In the microstructure of PRMMC obtained, the reinforcement particles were homogeneously distributed and a linear relationship was obtained between volume fraction of reinforcement particle in the mixed powder and the observed area ratio. It was concluded that homogeneous particle distribution and accurate control of the fraction of reinforcement particle could be attained by the LPI process.

Keywords:

• low pressure infiltration process
• particle reinforced metal matrix composite
• cast iron
• microstructure control