An isothermal section of the equilibrium phase diagram in the ternary Ni-Cr-N system was experimentally determined at 1 273 K. Binary Ni-Cr alloys with chromium concentration from 20 to 79 mass% were nitrided in pure nitrogen gas under various pressures between 10 and 96 kPa at 1 423 or 1 523 K. The ternary Ni-Cr-N alloys prepared by the nitriding were equilibrated at 1 273 K for time varying between 2.0 × 10
6 and 3.7 × 10
7 s. The concentration of nickel and chromium of each phase in the equilibrated alloys was determined by conventional electron probe microanalysis. Nitrogen in solid solution phases and nitrides was analyzed by a refined method of electron probe microanalysis, which has been recently established by the present authors.
A nitride with the metal-atom arrangement of
β manganese, which is designated as a
π phase, was found to be in equilibrium with a nickel-rich fcc-
γ phase, a chromium-rich bcc-
α phase, and a di-chromium nitride, which is designated as an
ε phase. The chemical compositions of the
π and
ε phases observed in the present work led to the formulae of Cr
12(Ni
0.94-0.97 Cr
0.06-0.25)
8 N
3.9-4.2 and (Cr
0.99 Ni
0.1)
2 N
0.80-0.97, respectively. The
π phase became unstable above 1 473 K. This explains a previous unsuccessful attempt to make the Ni-Cr-N ternary
π phase by replacing molybdenum in Mo
12Ni
8N
4 with chromium.
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