Effect of particle size and volume fraction on hot extrusion reaction synthesis of SiC particle reinforced NiAl

Hot extrusion reaction synthesis (HERS) was used to fabricate nickel alumin ide/SiCp composites from elemental powder mixtures of nickel, aluminum, and silicon carbide. The effect of extrusion temperature, silicon carbide part icle size, and volume content on the developed microstructures and on the p eak extrusion pressure was investigated using a miniature extrusion rig, Ma trix microcracking and loss of aluminum were observed in the final microstr uctures. The large surface area to volume ratio of the miniature extrudate "wires" in conjunction with a shorter reaction time at temperature reduced the reaction between the matrix and the SIC reinforcements. Although extrus ion should have eliminated reaction synthesis related porosity, considerabl e levels of porosity were still generally present in the final extrudates, because all the elemental powder extrusions reacted after emerging from the die exit instead of before, thus by-passing the consolidation stage of ext rusion, A novel two stage extrusion method has been identified to overcome this problem.