Effects of Fabrication Parameters on Phase Composition, Densification and Mechanical Properties of Aluminum-Alumina Cermets

As a high temperature structural ceramic، cermets exhibit less brittleness than ceramic-ceramic composites or monolithic ceramics owing to the presence of a ductile metal second phase in their microstructure. These cermets can، therefore، be used in applications where the abrasive، creep and thermo-mechanical resistance are required. In the present study، aluminum-alumina cermets with different amounts of aluminum were fabricated at different heat treatment temperatures. In order to evaluate the optimum manufacturing conditions، specimens with different aluminum contents were subjected to DTA and TGA analyses. In addition، microscopic observations، phase analyses، and toughness، strength and hardness measurements were performed using SEM، XRD، three-point bending testing and Vickers hardness testing methods، respectively. The results of DTA and XRD analyses showed that for the oxidizing atmosphere and high amounts of aluminum، there is an exothermic peak corresponding to the oxidation of aluminum and an endothermic peak corresponding to the phase transformation of Al2O3. Higher amounts of aluminum in starting materials caused an increase in the density and toughness، and a decrease in the hardness of the cermet specimens sintered at 1550°C، however، their strength increased when up to 20% aluminum was added. In addition، for the case of 30%Al-Al2O3 cermet، the strength and density increased as the temperature increased up to 1500 ºC، while the toughness increased up to 1550 °C. The oxidation of aluminum phase was also found to be of great importance، hence، it was concluded that the optimized properties may only be obtained using an argon atmosphere.