Correlative study of lattice imperfections in long-range ordered, nano-scale domains in a Fe-Co-Mo alloy

F. Theska, A.V. Ceguerra, A.J. Breen, Ch. Turk, S.P. Ringer, S. Primig
Ultramicroscopy 204 (2019) 91-100.

This paper concerns the development of novel data mining methods in atom probe microscopy.

We aim to study the precision of spatial distribution maps that have been developed to enable visualization of the local lattice occupation in crystals.

We present a correlative study of atom probe microscopy, neutron diffraction and microstructural modelling of B2 long-range ordered, nano-scale domains in a Fe-Co-Mo Maraging-type steel. Our previous research has shown that under slow cooling conditions, the steel matrix partially decomposes into nano-scale B2 long-range ordered domains surrounded by disordered regions, resulting in reduced toughness.

Usually, a long-range order parameter S referring to ideal B2 long-range order is assumed within such domains according to neutron diffraction. However, our new atom probe microscopy and modelling results presented here indicate lattice imperfections with a partial substitution of atoms on the Fe- and Co-sublattices. We consider preferential retention effects and present a model unit cell to define the observed imperfect B2 long-range order.

Extending our understanding of the relationship between processing, nano-scale order and materials properties may help to guide future improvements in materials design.