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 diameter are infiltrated by pure aluminum using gas-assisted infiltration, 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 bottom of the sample, depending on the global stoichiometry of the material. Two high-speed digital cameras are used to record the infiltration and reaction processes. The acquired images show that infiltration and reaction are decoupled in time. Infiltration proceeds initially under 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 reaction between aluminum and nickel. Thereafter, a spontaneous combustion front ignites due to local melting of nickel and propagates at an average rate on the order of 5 cm.s(-1). Macrostructures and process kinetics are explained by the combined influences of capillarity during infiltration, heat evolved during the reaction, and gravity.