Synthesis of Metallic and Intermetallic Matrix Composites Reinforced by Alumina by Reaction in NiO/Al Mixtures

Present study concerns a reduction of nickel oxide by aluminum via mechanical alloying. Essentially, the reaction products depend on two parameters: the milling time and the molar ratio of elementary powders. This reaction between the starting NiO–Al powders, which takes place during the high-energy ball milling, makes it possible to produce nickel matrix composites reinforced by alumina particles. For the NiO/Al molar ratio of 3/2, the synthesis reaction begins after 4 h of milling time while for a ratio of 3/3, it ends after 2 h forming Ni–Al2O3 composite. Furthermore, changing the NiO/Al ratio to 3/4 and 3/5, allows generation of different phases, where the excess Al reacts with Ni already produced to form NixAly intermetallic matrix reinforced with Al2O3 particles. Due the low apparent density of the green compact, a sintering treatment is necessary to densify the material. This process has been carried out at 800 and 1200 °C under argon atmosphere. Experimental results show that the milling time and starting ratio of NiO/Al powders have an important effect on the reduction reaction of NiO by Al.