Surface Hardening of Ni Alloys by Means of Plasma Ion Nitriding (PIN) Process (Report 1)(Materials, Metallurgy & Weldability)

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The probability of surface hardening by means of Plasma Ion Nitriding (PIN) process was investigated for pure nickel and commercially used Ni alloys under the conditions of nitriding temperature 773 to 1073K and nitriding time up to 32.4ks in N_2+H_2 mixed gas atmosphere of 800Pa. Remarkable surface hardening more than Hv500 was observed at nitriding temperature 733-1073K for In conel 600, 625, 713C and Udimet 500 which contain chromium, and Hastelloy B which contains molybdenum. On the contrary, Permalloy which contains iron was slightly hardened, and pure Ni and Monel were not hardened. From the result of X-ray diffraction analysis, CrN for Inconel 600, 625, 713C and Udimet 500, MoN and Mo_2N for Hastelloy B were detected as nitrides together with diffraction peaks from the matrix of nitrided layer and base metal beneath it. Diffraction peaks of these nitrides and matrix of nitrided layer were very broad and the half value width of these peaks had a good relationship with surface hardness, which was linearly increased as the increase of the half value width. Therefore, it was considered that hardness increase in PIN Process of Ni alloys was due to ununiform microstrain caused by the precipitation of such nitrides in nitrided layer.
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