Mechanochemical synthesis and heating-induced ordering of Ni-Al-Cr-C quaternary solid solutions

Abstract

Nanocrystalline mixed (substitutional/interstitial) solid solutions have been prepared by milling four-component mixtures with the overall compositions (Ni2.8AlCr0.2)C0.5 and (Ni3Al0.8Cr0.2)C0.5. Analysis of X-ray diffraction data indicates that the formation of the solid solutions is accompanied by an increase in deformation stacking fault probability, which is directly related to the amount of dissolved carbon. Our results demonstrate that the heating-induced ordering of the solid solutions occurs in several steps. Nucleation of the antiperovskite phase E21 occurs through spinodal decomposition of the Ni(Al,Cr,C) solid solution starting at 400°C. Heating to higher temperatures leads to partial Cr precipitation from the ordered phase and the formation of the chromium carbide Cr3C2, which reduces the carbon content of the antiperovskite phase.