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.

Shock compression of reactive powder mixtures

“…By avoiding initial contact with the fixture, their carefully designed experiments allowed a highly unidirectional shock wave to be applied to the NizSi mixture, significantly reducing the twodimensional wave focusing effects inherent of the Momma Bear or Sawaoka recovery fixtures. 90,97,99 By performing experiments at several impact velocities and starting densities, the shock energy E deposited in the powder from P-V work was varied (Table 1). Also listed are the thermal energy thresholds for reaction E T , determined through DTA.…”

Preparation of Niobium Aluminium Alloy Based on Shock Compression Method

“…other impurities [16]. To obtain high-quality alloys, model experiments were planned and carried out using a two-stage light-gas gun.…”

“…In the reactionassisted shock consolidation of Nb-Al alloys, the NbAl 3 and Nb 2 Al compounds were identified with X-ray diffraction. Unfortunately, as the plane wave caused by the chemicalinduced shock was not uniform, the products were mixed with other impurities [16]. To obtain high-quality alloys, model experiments were planned and carried out using a two-stage light-gas gun.…”

Particle-level modeling of dynamic consolidation of Ti-SiC powders

“…The Jaumann stress rate is evaluated at the midpoint of the time step for second-order accuracy I A t P (9) an+l/Z = a n + [o"+1/2a.n -anMn+l12 z.n+l/Z = a"+1/2 + a l ( a n + W ;P, p + l / Z ) ~t (10)…”