In situ Al2O3 particle-reinforced Al and Cu matrix composites synthesized by displacement reactions

An innovative in situ reaction technique is developed for the synthesis of Al2O3/Al and Al2O3/Cu composites. This technique provides a new approach overcoming the problems of loss and agglomeration of reinforcement particles when the particles are added directly into their matrixes by a conventional ex situ technique. The experimental results have shown that the presence of network Al(Cu)-CuAl2 eutectic, which is detrimental not only to the fracture toughness, but also to the stability of the microstructure, can be reduced from the final product by introducing two or more oxides into the synthesis. Moreover, the network CuAl2 phase can be eliminated entirely only by changing Al matrix into Cu matrix when Al amount is not excess in the Al-CuO preforms. The mechanisms of formation or absence of Al(Cu)-CuAl2 eutectic in the Al2O3/Al and Al2O3/Cu composites are explained based upon thermodynamics of the systems. The modification of the microstructures in the in situ synthesis Al2O3/Al, Al2O3/Al-Si-Cu, Al2O3/Al-Si-Cu-Mn and Al2O3/Cu composites can be understood in the light of thermodynamics.