1 Department of Photonics Engineering, Technical University of Denmark2 Department of Wind Energy, Technical University of Denmark3 Materials science and characterization, Department of Wind Energy, Technical University of Denmark4 Center for Electron Nanoscopy, Technical University of Denmark5 Department of Mechanical Engineering, Technical University of Denmark6 Materials and Surface Engineering, Department of Mechanical Engineering, Technical University of Denmark7 Centre for oil and gas – DTU, Center, Technical University of Denmark
According to classical theories precipitate interfaces are described by their degree of coherency with the matrix, which affects their strengthening contribution. Investigations of nitride precipitate interfaces in 12% Cr steels with transmission electron microscopy have shown the nitrides to be enveloped in an amorphous shell a few nm thick, thus leaving them without any coherency with the matrix. The amorphous nature of the shells could be ascertained with high resolution microscopy and dark field techniques. When extracted from the ferrite matrix the amorphous shells were observed to crystallize during electron beam exposure. The amorphous shells were observed around Ta- and Nb-based nitrides, which are considered to have a high interfacial energy with the ferrite matrix. They were not observed around V-based nitrides which have a Baker–Nutting relationship with low-misfit to the matrix.