Processing defects in hot extrusion reaction synthesis

Experiments were conducted on a miniature and a larger extrusion press to s imultaneously form and extrude nickel aluminides (Ni3Al, NiAl) and nickel a luminide composites from elemental powders using a novel process called hot extrusion reaction synthesis. An overview of macroscopic and microscopic p rocessing defects that can arise in this process is presented as well as st rategies for overcoming these defects. Extrusion cracking was found to sign ificantly 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 N iAl extrusions. Processing defects in the form of matrix micro-cracking and reaction layers between intermetallic matrix and SIC reinforcements were a lso present in the composite material. The reaction always occurs seconds a fter the material had been extruded, thus bypassing the consolidation stage of extrusion resulting in the presence of reaction induced porosity. A nov el high temperature transient window has been identified for the production of pore-free intermetallic and intermetallic composite rods and wires. (C) 2000 Elsevier Science S.A. All rights reserved.