Microscopic Phase-Field Simulation Of Effect Of Temperature On The Precipitation Process Of Ni₇₅Al_xV_25-x Alloy

Microstructure evolution of Ni₇₅Al_xV_25-x alloys was studied with the microscopicphase-field dynamic model. The microstructure along with atomic migration law ofdomain boundaries and the precipitation mechanisms of alternate precipitation of twophases were clarified. The coarsening dynamics was investigated using themicroelasticity theory, and structure function as well as it's scaling behavior wasanalyzed. The simulation results were consistent with the theory and experimentalresults.As the temperature increases, the incubation periods of L1₂ and DO₂₂ are prolonged.The incubation period of L1₂ is shortened as the Al concentration increases, while thatof DO₂₂ is prolonged. As the temperature decreases, the variation of two phasesprecipitation mechanisms as follows: The precipitation mechanisms of DO₂₂transform from spinodal decomposition to congruent ordering+spinodaldecomposition, and those of L1₂ transform from non-classical nucleation to spinodaldecomposition at lower Al concentration regions. At middle Al concentration regions,the precipitation mechanisms of DO₂₂ transform from spinodal decomposition tonon-classical nucleation, and those of L1₂ transform from mixed styles ofnon-classical nucleation and spinodal decomposition to spinodal decomposition. Athigher Al concentration regions, the precipitation mechanisms of L1₂ transform frommixed style to spinodal decomposition, and those of DO₂₂ transform from spinodaldecomposition to non-classical nucleation.There are three styles of domain boundaries between the L1₂ phases, eight betweenDO₂₂ phases, four between L1₂ phase and DO₂₂ phase at early stage of precipitation,respectively. The domain boundaries styles are reduced due to the morphologyarrange along certain direction at coarsening stage, the homophase boundaries ofDO₂₂ are dominated in [100]₍DO₂₂ direction, there exists the orientation relationship of{001}_L12//(001)_DO22 between two phases, and the domain boundaries styles remainedbetween L1₂ phases.The precipitation of L1₂ depends on the orientation and atomic plane matchingstyles at the domain boundaries of DO₂₂. L1₂ precipitates at the domain boundaries formed along [001]_DO22 and [100]_DO22 direction, L1₂ precipitates when(001)_DO22 planes matching at the domain boundaries formed along [100]_DO22 direction,and L1₂ grows along [100]_DO22 direction. When the DO₂₂ substitutes for L1₂ along[100] direction, the Ni atomic planes of DO₂₂ need not change, the substitutionoccurred at the V atomic planes.Due to the elastic interactions between L1₂ and DO₂₂, two phases particles haveobvious orientation at coarsening stage. DO₂₂ is dominated along [100]direction,and L1₂ arrange along <001> directions. The morphology of two-phase is intervaland parallel in space. The growth of particles satisfies the linear law of R³(t)～t atearly stage. As the elastic interactions increases, the particles growth quickly at earlystage and slows down at later stage, and the growth and coarsening predominate atearly stage and later stage, respectively.The scaling behavior of structure function is also applicable for the elasticinteraction systems of Ni₇₅Al_xV_25-x alloys. Despite of the different precipitation orderof L1₂ and DO₂₂, the dynamic scaling behavior of coarsening stage of two phases areconsistent. The peak values of scaling function of DO₂₂ are higher than that of L1₂ athigh temperature, and the peak values of L1₂ are higher than that of DO₂₂ astemperature decreases. The peak values of scaling function are affected byconcentration, and the fluctuation at the right side of scaling function becomesmaller as the concentration increases.