Nitrogen concentration and hardness profiles are shown in Fig. 1.
The relative uncertainties for nitrogen concentration are estimated to
be around ±5%. The vertical scales were adjusted to show the match
of the two profiles in the third region.
Three regions can be discriminated in the profiles:①fromthe surface
down to 8 μm; ② from 8 μm to 45 μm, and ③ from 45 μm to 80 μm. In
region ①, with nitrogen concentration above 10 at.%, a compound layer
was observed by SEMand confirmed by GIXRD. In region②the nitrogen
content decreased from 11 to 6 at.%, while hardness was roughly
constant. In region ③, nitrogen content and hardness show the same
trend with depth, decaying to bulk levels below 80 μm.
The last two regions comprise the diffusion layer, where it is generally
observed that hardness correlates linearly with the nitrogen
concentration [9,12–14]. This was also observed for region ③ of the
present work, where N concentration is below 6 at.%. In this concentration
range the curves superpose well [11,12,16]. However, in region ②
the nitrogen concentration and hardness do not correlate.
In order to clarify the origin of the deviation fromlinear relationship
between nitrogen content and hardness in region ②, the set of diffraction
patterns obtained with the first sample preparation procedure
outlined above, is shown in Fig. 2, starting at the surface down to the
Nitrogen concentration and hardness profiles are shown in Fig. 1.The relative uncertainties for nitrogen concentration are estimated tobe around ±5%. The vertical scales were adjusted to show the matchof the two profiles in the third region.Three regions can be discriminated in the profiles:①fromthe surfacedown to 8 μm; ② from 8 μm to 45 μm, and ③ from 45 μm to 80 μm. Inregion ①, with nitrogen concentration above 10 at.%, a compound layerwas observed by SEMand confirmed by GIXRD. In region②the nitrogencontent decreased from 11 to 6 at.%, while hardness was roughlyconstant. In region ③, nitrogen content and hardness show the sametrend with depth, decaying to bulk levels below 80 μm.The last two regions comprise the diffusion layer, where it is generallyobserved that hardness correlates linearly with the nitrogenconcentration [9,12–14]. This was also observed for region ③ of thepresent work, where N concentration is below 6 at.%. In this concentrationrange the curves superpose well [11,12,16]. However, in region ②the nitrogen concentration and hardness do not correlate.In order to clarify the origin of the deviation fromlinear relationshipbetween nitrogen content and hardness in region ②, the set of diffractionpatterns obtained with the first sample preparation procedureoutlined above, is shown in Fig. 2, starting at the surface down to the
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