Shock-induced reaction synthesis of isomorphous (Cu-Ni) and immiscible (Cu-Nb) compounds

Abstract

Shock compression of Cu-Ni and Cu-Nb elemental powder mixtures was investigated to study the shock-induced chemical reaction behavior of material systems with very low heats of formation and to synthesize isomorphous, as well as otherwise-immiscible, compounds. Shock loading experiments were performed using a 12-capsule plate-impact recovery fixture, with explosive loading at 0.9 to 1.6 km/s impact velocities. The Cu-Ni powder mixtures revealed formation of an isomorphous Cu-Ni solid-solution alloy with a fine dendritic microstructure, formed via a mechanism involving intense mechanical mixing and melting of elemental reactants. The extent of the reaction was dependent on the shock strength, and the chemistry of the product was observed to depend on the morphology of the powders due to its effect on the crush strength. In the case of Cu-Nb powder mixtures, submicronscale mechanical mixing was observed between the reactants, with possible dissolution of as much as 10 wt pct solute in each component. Complete alloying of copper and niobium was also observed, as indicated by transmission electron microscopy (TEM)/energy-dispersive X-ray (EDS) and X-ray diffraction (XRD) analysis; however, the alloyed region showed the presence of Mo and other impurity elements from the stainless steel capsule. These additives may, in fact, be responsible for stabilizing the ternary compound, in an otherwise immiscible Cu-Nb system.