Interface Reactions in Bilayers of Aluminum and Nickel-Chromium Alloy

Glancing angle EXAFS and x-ray reflectivity are used to study the interface reaction between nickel-chromium alloys and aluminum. The two metals are found to react independently with Al, with the first reactions taking place at temperatures similar to those found for the pure metals. This means that Ni reacts first with Al to form NiAl₃, leaving behind a Cr-rich region at the interface. In this Cr-rich region some of the Cr transforms to the bcc structure from the fcc form of the alloy. At higher temperatures Cr reacts to form CrAl₇, and there is no evidence for ternary compound formation. Samples were also prepared with a controlled O contamination at the interface, and it inhibits the reaction much the same as for the pure metal cases. The Ni reaction is not identical to the pure sample case, since the presence of Cr slows down the reaction, and inhibits the initial reaction in the as-prepared bilayers.. Authors: Heald, S. M. [Brookhaven National Laboratory (BNL), Upton, NY (United States)]; Tan, Zhengquan [Brookhaven National Laboratory (BNL), Upton, NY (United States)]; Jayanetti, J. D. [Brookhaven National Laboratory (BNL), Upton, NY (United States)]. DOE Contract: AC02-76CH00016; AS05-80ER10742. Subjects: 36 MATERIALS SCIENCE; 360102* -- Metals & Alloys-- Structure & Phase Studies; ALLOYS; ALUMINIUM; CHEMICAL REACTIONS; CHROMIUM ALLOYS; COHERENT SCATTERING; DIFFRACTION; ELEMENTS; FINE STRUCTURE; INTERFACES; INTERMETALLIC COMPOUNDS; METALS; NICKEL ALLOYS; SCATTERING; X-RAY DIFFRACTION