Formation of NiAI/SiC_p Composites by Simultaneous Hot Extrusion and Reaction Synthesis

摘要

Nickel aluminide intermetallics, e.g. NiAl, have been formed in the past using Hot Extrusion Reaction Synthesis (HERS) from elemental powder mixtures of nickel and aluminium. However, excessive heat generated during the process caused the NiAl compound to melt on formation. The addition of high melting point inert powder (e.g. ceramics) to the original mixture of nickel and aluminium while primarily acting as reinforcement can also serve to buffer the reaction. This paper reports small scale HERS experiments to form NLAl/SiC_p composites. The effect of extrusion temperature and 4-5 μm SiC_p volume content on the developed microstructures and on the peak extrusion pressure has been investigated. The addition of SiC_p powder buffered the reaction during HERS of the intermetallic composites and a volume content of 15% SiC_p was sufficient to produce solid extrudates and prevent melting. The highest extrusion temperatures resulted in the highest peak extrusion pressures; owing to the formation of hard Al-rich intermetallics in the pellet immediately prior to extrusion. Porosity was also reduced at 15vol. % SiCp loading. However, considerable levels of porosity were still generally present in the extrusions. This was due to the fact that all reactions in this study commenced after the consolidation stage of extrusion resulting in typical porosity associated with conventional reaction synthesis. A novel method of reacting the powder mixture inside the container immediately prior to extrusion is under investigation. This should eliminate porosity formed during reaction synthesis and promote fully dense extruded intermetallics.