Mechanical alloying as method for introducing carbon in Ni3Al intermetallide

The method for the mechanical alloying of Ni-Al-C and Ni₃Al-C mixtures was used to obtain nonequilibrium solid Ni(Al,C) solutions in which the carbon content varies from 2.9 to 8.5 at %. The relationship between carbon dissolution and the probability of appearance of deformation-induced stacking faults (SFs) in the formation of mixed (substitutional and interstitial) solid Ni(Al,C) solutions has been found based on an analysis of the diffraction spectra. SFs are assumed to serve as pathways of carbon penetration in nickel-based solid solutions. The effective carbon radius was found to be about 0.0616 nm in the formation of an antiperovskite phase Ni₃AlC _x . The method of calculating the amount of interstitial carbon was proposed based on the experimental lattice parameters of fcc solid Ni(Al,C) solutions and ordered phases L1₂ Ni₃Al and E2₁ (Ni₃AlC _x ). The temperature stability of the nonequilibrium solid Ni(Al,C) solutions was established. It was shown that the decomposition of the solid solutions proceeded according to a spinodal mechanism at a temperature of 400°C with separation into two phases, i.e., an antiperovskite carbide (Ni₃AlC _x ) and Ni(Al,C). At higher temperatures (600?C800°C), carbon precipitates from these phases with the formation of an antiperovskite Ni₃AlC_0.16, solid Ni(Al) solution, and nanocrystalline graphite.