REACTIVE INFILTRATION PROCESSING OF ALUMINUM-NICKEL INTERMETALLIC COMPOUNDS

Aligned nickel wire bundles 4 to 5 cm in length and up to 2.5 cm in di ameter are infiltrated by pure aluminum using gas-assisted infiltratio n, to produce samples having global compositions in the range of 40 to 76 at, pet nickel. As-reacted sample macrostructures feature a large single-phase region of NiAl independent of applied pressure and nickel preform volume fractions in the ranges of 0.15 to 0.3 MPa and 0.23 to 0.44, respectively. These macrostructures also contain, in some cases , either an aluminum-rich zone on top, or nickel-rich phases at the bo ttom of the sample, depending on the global stoichiometry of the mater ial. Two high-speed digital cameras are used to record the infiltratio n and reaction processes. The acquired images show that infiltration a nd reaction are decoupled in time. Infiltration proceeds initially und er partial preform saturation, at a rate on the order of 50 cm.s(-1). The sample then self-heats for 2 to 3 seconds due to exothermic reacti on between aluminum and nickel. Thereafter, a spontaneous combustion f ront ignites due to local melting of nickel and propagates at an avera ge rate on the order of 5 cm.s(-1). Macrostructures and process kineti cs are explained by the combined influences of capillarity during infi ltration, heat evolved during the reaction, and gravity.