The reaction mechanism and mechanical properties of the composites fabricated in an Al–ZrO2–C system

The in situ composites with the reinforcement volume fraction of 30 vol.% and the C/ZrO2 mole ratio of 0, 0.5 and 1.0 have been fabricated by using exothermic dispersion synthesis in an Al–ZrO2–C system. The reaction mechanism and mechanical properties of the composites have also been studied. When the reinforcement volume fraction of the composites is 30 vol.% and the C/ZrO2 mole ratio is zero, the Al first reacts with ZrO2 to produce the α-Al2O3 particles and the active Zr atoms, and then the Zr atoms react with Al to form the Al3Zr blocks, which are distributed uniformly throughout the aluminum matrix. The ultimate tensile strength and elongation of the composites at room temperature are 215.2 MPa and 3.0%, respectively. The fracture mechanism of the composite can be characterized by a crack nucleus initiating in the Al3Zr blocks and then propagating to the interface because of the poor properties of Al3Zr. With increasing the C/ZrO2 mole ratios, the ZrC is formed previous to the Al3Zr due to its lower Gibbs free energy, and its formation peak becomes bigger in the DSC curve. The amount of the Al3Zr blocks decreases, which leads to the improvement in the tensile properties of the composites. When the C/ZrO2 mole ratio is up to 1, the Al3Zr blocks have almost disappeared in the composites. The reinforcements are composed of α-Al2O3 and ZrC. At the same time, the ultimate tensile strength and elongation increase to 245.4 MPa and 8.0%, respectively. The tensile fracture surface is composed of fine ductile dimples.