Processing defects in hot extrusion reaction synthesis

Experiments were conducted on a miniature and a larger extrusion press to simultaneously form and extrude nickel aluminides (Ni3Al, NiAl) and nickel aluminide composites from elemental powders using a novel process called hot extrusion reaction synthesis. An overview of macroscopic and microscopic processing defects that can arise in this process is presented as well as strategies for overcoming these defects. Extrusion cracking was found to significantly increase with increased nickel content. Higher extrusion die exit temperatures promoted both a reaction converting elemental powders to the desired intermetallic or intermetallic composites and reduced cracking of NiAl extrusions. Processing defects in the form of matrix micro-cracking and reaction layers between intermetallic matrix and SiC reinforcements were also present in the composite material. The reaction always occurs seconds after the material had been extruded, thus bypassing the consolidation stage of extrusion resulting in the presence of reaction induced porosity. A novel high temperature transient window has been identified for the production of pore-free intermetallic and intermetallic composite rods and wires.