Annealing behavior of mechanically alloyed nanocrystalline NiAl intermetallic under oxidizing and non-oxidizing conditions

In this paper, the phase evolution of nanocrystalline NiAl (n-NiAl) during annealing under both oxidizing and non-oxidizing conditions was investigated. The n-NiAl powders were prepared by mechanical alloying (MA) of Ni and Al elemental powders via a planetary ball mill. The phase evolution during milling and subsequent annealing was studied by X-ray diffraction (XRD) analysis. The microstructure of mechanically alloyed powders consisted of B2-NiAl and martensitic L10-NiAl phases. By annealing under non-oxidizing condition, the microstructure became completely B2-NiAl. Also, the sequence of oxidation observed during annealing under oxidizing condition was explained based on the thermodynamics of oxidation reactions. A very good agreement was observed between thermodynamic calculations and experimental observations.