Atom-probe study of Cu and NiAl nanoscale precipitation and interfacial segregation in a nanoparticle-strengthened steel

The Cu and NiAl nanoscale precipitation and interfacial segregation in the martensite and austenite phases within a high-strength steel were studied by atom-probe tomography (APT). In the martensite phase, APT reveals the precipitation of isolated NiAl nanoparticles and NiAl/Cu co-precipitates, indicating that NiAl nanoparticles form first in the precipitation sequence. In comparison, the austenite phase contains only Cu nanoparticles with Ni segregation at the particle/matrix interface, in which the Ni segregation reduces the Cu nanoparticle interfacial energy. In addition, Mn and C exhibit an enrichment at the martensite/austenite interface, and the mechanism for the interfacial segregation was also discussed.