MICROSTRUCTURE OF A NICKEL-BASE ODS POWDER AFTER MECHANICAL ALLOYING

Mechanical alloying is an important pre-requisite for the manufacturing of heat resistant oxide-dispersion-strengthened superalloys. Though the microstructure of these materials after hot extrusion and recrystallization treatment is well documented, little is known about the microstructural evolution during ball-milling. A method was tested to prepare electron transparent foils and extraction replica from powder particles for TEM investigations. The microstructure was found to consist of a Ni - Cr - Al solid solution in which submicron particles of refractory metals were embedded. The extremely fine grain size of about 50 nm is the consequence of severe plastic deformation. Yttria particles could not be detected in the powder after ball milling, but after a heat treatment at 1000-degrees-C the well-known fine dispersion of oxide particles was evident.