Chromium precipitation in B2-ordered NiAl—2 at.% Cr alloys investigated by atom probe field ion microscopy

Abstract

Alloys of the B2-ordered NiAl intermetallic compound of the compositions (numbers indicate at.%) Ni 50Al 48Cr 2, Ni 49Al 49Cr 2, and Ni 48Al 50Cr 2 were studied by atom probe field ion microscopy. Precipitates of α-Cr were detected in the first two compositions ranging from few nanometers as small clusters to several tens of nanometers in size. Due to the relatively low evaporation field strength of Cr atoms, these species cannot be observed directly in field ion micrographs. In Ni 48Al 50Cr 2 samples, different precipitates containing 77 at.% Cr and 23 at.% Al are observed after annealing at 550 °C. In Ni 50Al 48Cr 2, an antiphase boundary was imaged which showed a very high local Cr concentration, where Cr atoms substitute for Al atoms.