Atom probe tomography investigation of lath boundary segregation and precipitation in a maraging stainless steel

Lath boundaries in a maraging stainless steel of composition 13Cr-8Ni-2Mo-2Cu-1Ti-0.7Al-0.3Mn-0.2Si-0.03C (at%) have been investigated using atom probe tomography following aging at 475 degrees C for up to 100 h. Segregation of Mo, Si and P to the lath boundaries was observed already after 5 min or aging, and the amount or segregation increases with aging time At lath boundaries also precipitation or eta-Ni-3(Ti, Al) and Cu-rich 9R, in contact with each other, takes place. These co-precipitates grow with time and because of coarsening the area number density decreases. After 100 h or aging a similar to 5 nm thick film-like precipitation of a Mo-rich phase was observed at the lath boundaries. From the composition or the film it is suggested that the phase in question is the quasicrystalline R' phase. The film is perforated with Cu-rich OR and eta-Ni-3(Ti, Al) co-precipiLaLes. Not all precipitate types present in the matrix do precipitate at the lath boundaries; the Si-containing G phase and gamma'-Ni-3(Ti, Al, Si) and the Cr-rich alpha' phase were not observed at the lath boundaries. (C) 2012 Elsevier B.V. All rights reserved