iCHORD-SI combination as an alternative to EDS-EBSD coupling for the characterization of γ-γ′ nickel-based superalloy microstructures

• Published in: Materials characterization 2018-08, Vol.142, p.492-503
• Main Authors: Vernier, Suzanne, Franchet, Jean-Michel, Lesne, Maxime, Douillard, Thierry, Silvent, Jérémie, Langlois, Cyril, Bozzolo, Nathalie
• Format: Article
• Language: English
• Subjects: BACKSCATTERING; COMPARATIVE EVALUATIONS; CRYSTALLOGRAPHY; EDS-EBSD coupling; ELECTRON DIFFRACTION; Engineering Sciences; Focused ion beam; Gamma - gamma prime nickel-based superalloy; HEAT RESISTING ALLOYS; ION BEAMS; ION CHANNELING; Materials; MATERIALS SCIENCE; MICROSCOPES; MICROSTRUCTURE; NICKEL ALLOYS; PRECIPITATION; Secondary ions; SPATIAL RESOLUTION
• ISSN: 1044-5803; 1873-4189
• DOI: 10.1016/j.matchar.2018.06.015

Because they exhibit very similar diffraction patterns, the γ and γ′ phases of nickel-based superalloys cannot be distinguished by the conventional EBSD technique alone. This paper presents an original method which discriminates those phases on an orientation map by exploiting their chemical differences. Performed with a Focused Ion Beam (FIB) microscope, the method is the combination of the ion CHanneling ORientation Determination technique (iCHORD) – recently developed by Langlois et al. [1] – with the chemical information obtained from Secondary Ion (SI) images. The performances of the method are compared to the EDS-EBSD coupling which also discriminates phases based on their chemical compositions. Applied filters, angular resolution, spatial resolution of the phase discrimination and acquisition time are discussed. It results that the iCHORD–SI combination offers an orientation map with an angular resolution slightly decreased compared to that of the EBSD technique, but with a good phase resolution (down to 150 nm) and within a reasonable acquisition time. Thus, the iCHORD–SI combination appears to be an interesting method for the crystallographic systems where phases are difficult to discriminate by the EBSD technique alone but present a significant chemical contrast. •A new method to get orientation maps discriminating the gamma and gamma’ phases of Ni superalloys is described.•The method combines the iCHORD technique with secondary ion imaging.•The new method resolves precipitates down to 150 nm within a reasonable acquisition time.