Reinforced Al-Matrix Composites with Ni-Aluminides, Processed by Powders

The paper addresses issues of interest related to the uniform distribution of the reinforcement phase and the continuity of the metal matrix, for two ways of obtaining the powder composites, the hot extrusion and the spark plasma sintering (SPS) respectively. The reinforcement phase is the nickel aluminides obtained by mechanical alloying in ball mills, and the metal matrix is made of aluminum powders. Prior to extrusion, the mixture of aluminum powders and nickel aluminides was pressed and subsequently sintered in environments with high carbon potential, so that in the final product, nickel aluminides, carbide and aluminum oxides were found as reinforcement phases. The obtained results confirmed the hypothesis that, from a blank product with a random distribution of the reinforcement phase, a product with an ordered distribution of the reinforcement phase is obtained after extrusion and that for the same initial proportion of nickel aluminides as reinforcement phase, the composite hardness obtained by hot extrusion is higher compared to that obtained by SPS, the difference being determined by the increase of the proportion of the  reinforcement phase by the appearance of aluminum carbide and aluminum oxides during the sintering operation in the high carbon environment.