Intermetallic compounds of the Cr–Mn system investigated using in situ powder neutron diffraction: The reported order-disorder transformation of the σ phase elucidated. (July 2022)

• Record Type: Journal Article
• Authors: Joubert, Jean-Marc
• Is Part Of: Intermetallics. Volume 146(2022)
• Publication Date: 2022-07
• Subjects: Cr–Mn -- Phase diagram -- Neutron diffraction -- σ phase -- Order-disorder; Intermetallic compounds -- Metallography -- Periodicals; Metallic glasses -- Periodicals; Composés intermétalliques -- Métallographie -- Périodiques; 669.94
• DOI: 10.1016/j.intermet.2022.107580
• Languages: English
• ISSNs: 0966-9795

Abstract

Abstract: Cr–Mn system is very important for many applications. In the present work, the reported intermetallic compounds have been studied using in situ high temperature neutron powder diffraction. For the first time, site occupancies in a σ phase are obtained as a function of temperature by Rietveld analysis. They are compared with calculated data obtained from DFT. The previously reported order-disorder transition in the σ phase around 1000 °C is shown to be in fact a congruent phase transformation to the bcc Cr–Mn solid solution. This solid solution is probably continuous between pure Cr and δ-Mn. The second reported intermetallic α' phase (Cr2 Mn3 ) phase is shown to be in fact a ternary nitride of the Cr–Mn–N system that should not appear in the binary phase diagram. The present work clarifies and explains all the features of the previous literature on this system and brings major revisions to the phase diagram. General conclusions are drawn concerning mistakes that can be done in the evaluations of phase diagrams. Graphical abstract: Image 1 Highlights: Site occupancy determination as a function of temperature for the σ phase. The transformation at 1000 °C previously reported as an order-disorder transition in the σ phase is a transformation to bcc . The α′ phase does not exist: the previously reported phase was probably in fact a ternary nitride.