Reaction-assisted shock consolidation of RSR Ti–Al alloys

Abstract

A new method for the shock consolidation of hard metallic powders has been successfully tested. This method extends the process developed by Sawaoka and Akashi for the processing of ceramics (U.S. Patent 4,655,830) to metallic powders. Shock-activated reactions between elemental mixtures of niobium and aluminum powders were used to chemically induce bonding between difficult-to-consolidate intermetallic TiAl compound powder particles. The highly exothermic reactions activated by the passage of shock waves form an intermetallic binder phase which assists in the consolidation of the very hard TiAl alloy powders. Shock impact experiments were carried out utilizing a twelve-capsule shock recovery system in which a plane wave generating lens is used for accelerating a flyer plate to velocities of 1.7 and 2.3 km/s. With these impact velocities, sufficient shock pressures are generated in the powders, contained in capsules, to result in shock-induced reactions between the elemental powders of the mix. Fully dense compacts were successfully recovered and were subsequently characterized by optical, transmission, and scanning electron microscopy, x-ray diffraction, and microhardness testing. Transmission electron microscopy revealed both microcrystalline and amorphous regions in the reaction zone. In one instance, the amorphous material crystallized under the heating effect of the electron beam. Shock induced reaction between elemental powders and with the TiAl powders, producing ternary compounds, was also observed.