Reactive Ni/Ti nanolaminates

Nickel/titanium nanolaminates fabricated by sputter deposition exhibited rapid, high-temperature synthesis. When heated locally, self-sustained reactions were produced in freestanding Ni/Ti) multilayer foils characterized by average propagation speeds between similar to 0.1 and 1.4 m/s. The speed of a propagating reaction front was affected by total foil thickness and bilayer thickness (layer periodicity). In contrast to previous work with compacted Ni-Ti powders, no preheating of Ni/Ti foils was required to maintain self-propagating reactions. High-temperature synthesis was also stimulated by rapid global heating demonstrating low ignition temperatures (T-Ig) similar to 300-400 degrees C for nanolaminates. Ignition temperature was influenced by bilayer thickness with more coarse laminate designs exhibiting increased T-Ig, Foils reacted in a vacuum apparatus developed either as single-phase B2 cubic NiTi (austenite) or as a mixed-phase structure that was composed of monoclinic B19' NiTi (martensite), hexagonal NiTi2, and B2 NiTi. Single-phase, cubic B2 NiTi generally formed when the initial bilayer thickness was made small. (C) 2009 American Institute of Physics. [doi:10.1063/1.3253591]