Distribution of Ion-Implanted Nitrogen in Iron Alloys Investigated by AES

Abstract.

 The depth distribution and the lateral distribution of nitrogen after implantation by means of plasma immersion ion implantation (PIII) in ferritic alloys with 0.3 wt.-% Al and 3.6 wt.-% Cr has been studied by scanning Auger electron spectrometry (AES). To get information about the chemical state of nitrogen and to improve the detection limit methods of data analysis (factor analysis, LLS) have been applied to depth and line profiles, respectively. Thereby the detection limit for nitrogen was reduced from 6% to 1%.

The nitrogen distribution is laterally homogeneous in the near surface region only. Depth profiles obtained at several points within the sputter crater showed that the in-depth distribution of nitrogen varies markedly between different points on the sample and from sample to sample. The nitrogen concentration in the implantation maximum corresponds to Fe₂N_1−x (x ≈ 0.04 ⃛ 0.18).

A remarkable feature are grains having a 10 μm wide seam rich in N and a nearly nitrogen-free grain’s interior. The N/Fe ratio determined from line profiles show that the outer layer of the grains has almost the exact composition Fe₄N and the transition to the nearly nitrogen-free grain's interior (c_N ≤ 1%) occurs within 1 ⃛ 4 μm. The same shape of the N(KLL) peak was found in depth profiles and line scans, respectively, and it corresponds to gasnitrided samples γ ′–Fe₄N and ɛ–Fe₂N_1−x.