Computer simulation of the early stage of precipitation of L1₂-Ni₃ (Al, Cr) using microscopic phase-field method

Based on the microscopic phase-field model, the evolution of atom morphology of Ni₈₀Al₇Cr₁₃ ternary alloy is simulated at 873 K during the aging process. The early stage effect of precipitation is studied and discussed through analysising the changes of microstructure, composition and order parameter with the time. The study shows that the ordering of atom is happened earlier than the clustering of atom in the early time of precipitation, firstly forming the nonstoicheometric L1₀ ordered domain with very low order parameter, then the order parameter increasing with the increase of the aging time. At the same time, the ordered domain expands toward the nonordered domain, and the nonstoicheometric L1₀ ordered domain gradually transforms to the nonstoicheometric L1₂ structure when the order parameter of L1₀ increases to some degree. At last, the composition and the order parameter of nonstoicheometric L1₂ ordered domain attain to that of the stoicheometric L1₂ ordered domain. In the stoicheometric L1₂ ordered domain, Al priority occupies the α_I antisite, Cr priority occupies the α_II antisite.