Nitrogen absorption by Fe-1.04at.%Cr alloy: uptake of excess nitrogen

Abstract

By dedicated pre-nitriding (at 580°C in an ammonia/hydrogen gas atmosphere) and de-nitriding (at 470°C in a hydrogen gas atmosphere) experiments, performed on Fe-1.04at.%Cr alloy, it could be demonstrated that the uptake of ''excess'' nitrogen by the nitrided ferritic matrix is not due to the presence of iron in chromiumnitride precipitates, as it was suggested previously. The determination of nitrogen-absorption isotherms for these pre-nitrided and de-nitrided Fe-1.04at.%Cr alloy specimens revealed that the total amount of excess nitrogen in the alloy is composed of two parts: (a) nitrogen adsorbed at the precipitate/matrix interface, and (b) nitrogen dissolved interstitially in the ferrite matrix strained by the misfit between (coherent) the CrN precipitates and the matrix.

Crystal Structure and Morphology of Mixed Cr1–x Al x N Nitride Precipitates: Gaseous Nitriding of a Fe-1.5 Wt Pct Cr-1.5 Wt Pct Al Alloy

“…earlier analyses of nitrogen-absorption isotherms recorded for Fe-1 wt pct Cr (i.e., Fe-1.04 at. pct Cr) [52] and Fe-2 wt pct V (i.e., Fe-2.23 at. pct V), [48] such N is The composition of a Cr 1-x Al x N precipitate with adsorbed excess nitrogen [N] interface can be described as Cr 1-x Al x N y , where…”

Lattice-parameter change induced by accommodation of precipitate/matrix misfit; misfitting nitrides in ferrite

“…It has been demonstrated by previous nitriding/denitriding experiments on FeACr [47] and FeAV [38] alloys that the developing nitrides form with a stoichiometry of N to Me of 1:1, i.e. as CrN and VN nitrides.…”

“…This occurrence of ''excess nitrogen'' is well known and can be ascribed to the (additional) uptake of nitrogen by adsorption of nitrogen at the precipitate-platelet faces and increased ferrite-lattice dilatation due to the hydrostatic stress component of the stress-field induced by the precipitate/matrix misfit [37,38,47,48]. Now, for the denitrided specimens (systems of MeN precipitates in a pure ferrite matrix) the difference of their lattice parameter and that of a single-phase pure ferrite specimen (2.8664 Å [43]) has been plotted in Fig.…”

Normal and excess nitrogen uptake by iron-based Fe–Cr–Al alloys: the role of the Cr/Al atomic ratio

“…Upon nitriding of iron-based binary alloys containing alloying elements with a strong affinity for nitrogen, such as Cr [10][11][12][13][14][15][16][17][18][19][20][21], Al [22][23][24][25][26][27], V [28][29][30][31][32][33] and…”