Metastability of epsilon -FeN sub x Solid Solution With Low Nitrogen Content

• Published in: Scripta metallurgica 1986-08, Vol.20 (8), p.1095-1098
• Main Authors: Rochegude, P, Billon, B
• Format: Article
• Language: English
• ISSN: 0036-9748

A crystallographic study of the solid solution epsilon -FeN sub x has shown the high ordering of interstitial atoms on the cell of octahedral holes. This behavior might still be valid in the case of lower nitrogen solutions (from x = 0.19-0.25). However, Mossbauer spectrometry has shown the metastability of these lean solutions after low temperature aging characterized by the formation of the non-stable phase alpha "-Fe sub 16 N sub 2 . This metastability is already well-known in the case of Fe--N martensite. The Mossbauer study already done was complemented by following the crystallographic behavior of lean N solutions and the decomposition of the phases epsilon -FeN sub x for x < 0.25 is discussed. For epsilon nitrides beyond Fe sub 24 N sub 6 no complex reactions occur during aging, gamma '-Fe sub 4 N and a remaining matrix of enriched epsilon phase are obtained directly. Hexagonal solid solutions close to Fe sub 5 N obtained by quenching have a low degree of ordering and are very metastable. Aging of these solutions leads to the appearance of alpha "-Fe sub 16 N sub 2 with a sequence given. Hence, alpha "-Fe sub 16 N sub 2 appears as an intermediate stage not only in the aging of alpha -Fe--N ferrite and the tempering of alpha '-Fe--N martensite, but also in the aging of epsilon -FeN sub x . 6 ref.--AA