Identification and characterization of a novel Mn–N nitride formed in Fe–Mn–N alloy

Abstract

An unexpected phase, formed throughout the ferritic matrix of an Fe–Mn (1.62 wt% Mn) alloy during a nitriding treatment at 843 K for 8 h, is analysed. This new phase, labelled θ′, is a metastable Mn nitride. It adopts the form of plates, with length 200 nm and width 20 nm. Its crystal structure is established by electron microdiffraction in conjunction with group-theory analysis. This nitride crystallizes in the tetragonal system and belongs to the space groupP 42/m 2/m 2/cwith the following lattice parameters: a_{\theta'} = 2.876 Å and c_{\theta'} = 5.752 Å. The θ′-phase crystal lattice is oriented with respect to the surrounding ferritic matrix according to the cube-on-cube orientation relationship, namely: (100)_{\theta'} || (200)_\alpha, (010)_{\theta'} || (020)_\alpha and (002)_{\theta'} || (002)_\alpha.