Abstract
Nanosized alloy nitrides or alloying element (M)–Nitrogen(N) cluster formed in plasma nitriding of Fe–M binary alloys were investigated by means of high resolution TEM. Specimen surface of the Fe–Cr alloys was hardened by the formation of disk shaped CrN of NaCl structure, which is ∼2 nm thick and 10 nm in diameter. In nitrided Fe–Al specimen, two kinds of AlN nitrides of metastable NaCl type and stable wurtzite type were formed near the specimen surface. Both of these were much larger than CrN. Contrasting to these specimens, in nitrided Fe–Ti and Fe–V alloys, high density M–N clusters of few nanometres diameter, many of which were monolayered lying on {001} α , were formed, leading to larger hardness increase than that in Fe–Cr and Fe–Al alloys. The formation of M–N clusters in nitriding is explained by the thermodynamical analysis of phase separation between M/N poor and M/N rich bcc phases.
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