IN SITU SYNTHESIS OF CHROMIUM-RICH NITRIDES IN A MECHANICALLY ACTIVATED FE–FECR POWDER SYSTEM

Аннотация

Three Fe–FeCr powders processed in a planetary centrifugal mill for 15, 30, and 60 min were evaluated as precursors for the in situ synthesis of Cr-rich nitrides. The initial mixture contained 82.03 wt.% reduced Fe powder and 17.97 wt.% low-carbon ferrochrome (LC FeCr), corresponding to a nominal Cr content of 13 wt.%. Particle morphology, size distribution, Cr redistribution, BCC structure, and cold compactability were examined using SEM, EDS, XRD, image analysis, and uniaxial pressing. During the first 30 min, plastic deformation and cold welding competed with particle fragmentation, resulting in temporary formation of coarse secondary agglomerates. After 60 min, work hardening promoted fracture and produced finer, predominantly irregular particles. From 15 to 60 min, D50 decreased from approximately 90 to 53 μm, while the apparent BCC crystallite size decreased from 19.8 to 17.1 nm. These structural changes were accompanied by reduced green density and increased susceptibility to cracking. The 60-min compact was sintered at 1150 °C for 1 h in high-purity N₂. Elemental mapping revealed N enrichment within Cr-rich regions. Their local composition was consistent with an M₂N-type phase, provisionally identified as (Cr,Fe)₂N. The results demonstrate that mechanical activation improves precursor dispersion and nitriding reactivity, although excessive processing adversely affects powder compactability.