High-pressure high-temperature study of the pressure induced decomposition of the iron nitride γ′-Fe4N

Publication date: 15 September 2019Source: Journal of Alloys and Compounds, Volume 801Author(s): M.H. Wetzel, M.R. Schwarz, A. LeineweberAbstractPre-pressed powder samples of γ′-Fe4N were heat treated at a pressure of 13 GPa and temperatures between 400 and 880 °C in a multi-anvil setup. The phase composition and microstructure, which had emerged at the treatment temperature and pressure, were preserved by rapid quenching and subsequent decompression at room temperature. The recovered samples were investigated by X-ray diffraction as well as by microstructural analysis in a scanning electron microscope. For all applied treatment temperatures the γ′ nitride was found to decompose into other phases. Between 700 °C and 880 °C only single-phase ε nitride had formed whereas for temperatures between 400 °C and 600 °C dual-phase equilibria of low-N solid solutions of N in γ-Fe and partially ordered high-N ε nitrides were observed. The acquired information was cast into a partial Fe–N temperature vs. composition phase diagram valid for 13 GPa, which differs from that at atmospheric pressure by absence of the of γ′ phase and a pronouncedly extended stability region of the γ-type solid solution and of the (ordered) ε-Fe3N1+x nitride. Moreover, the pressure dependent evolution of the phase equilibria related with the pressure-induced decomposition of γ′ nitride is discussed.

Source: Journal of Alloys and Compounds - June 18, 2019 Category: Chemistry Source Type: research