Reactive Sintering of NiAl-Al2O3 and NiAl-SiC Composites

摘要

In this work we have recognized the possibilities to obtain "in-situ" near net-shape composites of NiAl-SiC and NiAl-Al_2O_3, by combustion synthesis technique, starting from mixtures of Nickel-Aluminum metallic powders and ceramic reinforcement of Al_2O_3 and SiC. These composites cannot be shaped due to their limited ductility and are difficult to cast due to their high melting point and reactivity. The reactive sintering is performed at temperatures of 890-910 K in tubular furnace under argon pressure. The compacts of the Ni-Al intermetallic compound and ceramic reinforcement (Al_2O_3 and SiC) have been obtained, below aluminum melting point, due to the large amount of exothermic heat liberated during the formation of NiAl compound. The most significant disadvantage of the intermetallic NiAl phase is the brittleness at room temperature; in this work we show that it is possible to obtain a reduction of the hardness values by grain refinement with the utilization of the reactive sintering in the powder-metallurgy technique as well as with the addition of a third alloying element, such as iron, to Aluminum and Nickel powders before the reactive process. The results of the composites NiAl-SiC are very interesting as well; these present a significant raising of the Vickers microhardness values of the intermetallic matrix (from 300 HV_(0,2) to 750 HV_(0,2)) compared to those measured in NiAl-Al_2O_3 composites, caused by the presence of Si and C in the NiAl phase.