Microscopic Phase Field Study on the Kinetics of Order-Disorder Transition of APDBs Formed between DO22 Phases during Stress Aging

Kinetics of order-disorder transition at antiphase domain boundary (APDB) formed between DO22 (Ni3V) phases during stress aging was investigated using microscopic phase field model. The results demonstrated that whether order-disorder transition happens or not depends on the atomic structure of the APDB. Accompanied with the depletion of V and enrichment of Ni and Al, order-disorder transition happened at the APDB (001)//(002). Whereas at the APDB {100}·1⁄2[100], which remains ordered with temporal evolution, Ni and Al enrich and V depletes. Composition evolution of APDB with order-disorder transition favors the nucleation of the L12 and disordered phase. Some of the grains grew bigger while the others disappeared, accompanying the formation of disordered phase layer during order-disorder transition of APDBs, and the order-disorder transition of APDBs can be considered as accompanying process of coarsening of ordered domain phases and growth of disordered phases.

Simulation of V Atom Substitution Character in Ni-Al-V Alloy

Simulations are performed on atom substitution character in Ni-Al-V alloy based on microscopic phase-field model at 1046K. It was showed that the ordering of both Al and V atoms take place simultaneously during the precipitation process of Ni-Al-V alloy, V atoms substitute the Al sublattice in L12phases, and they prefer β-sites to α-sites. Both of Al and V occupy the β-sites and complex phases Ni3(Al1-xVx)are formed; V atoms substitute the Al sublattice, the D022phases are formed at the boundary of L12phases.

Microscopic Phase-Field Simulation of the Process of Middle Heat Treatment of Ni-Cr-Al Alloy

The effect of the middle heat treatment+aging(1323K+1073K) for the precipitation mechanism and volume fraction of Ni-11at.%Cr-17at.%Al ternary alloy are studied based on microscopic phase-field model. The results show that the precipitation mechanism is non-classical nucleation and growth for the alloy at middle heat treatment, and the congruent ordering and spinodal decomposition mechanism occur at single-stage aging. The larger precipitation strengthening phases are obtained, the volume fraction of ordering phases and the averaged ordering parameter are higher, and the incubation period prolongs after the middle heat treatment.

The Simulation of Stress-Induced Phase Transition of L10 Re-Precipitation Based on Microscopic Phase-Field Model

It is common that the pre-precipitation phase with kinetics advantage is found during non-equilibrium transformation. The continuously changed stress in the transformation increases the complication of precipitation process. The stress induces Ll0pre-precipitation phase in Ni75-Al12.5-V12.5alloy is studied by microscope phase-field model in this paper. It is particularly show that Ll2phase precipitates directly without stress. There is no Ll0phase to be found in the disordered matrix. Oppositely, Ll0phase precipitates firstly with stress, and then it turns into Ll2phase. When stress is less, either or both above situations are observed. While stress is stronger, a large range of Ll0phase precipitates firstly. Then a part of it dissolves. The rest turns into Ll2phase. The precipitation of pre-precipitation phase accelerates the precipitation process. The larger the stress and the more Ll0phase precipitation, the longer it exists and the shorter the induction period is.

Microscopic Phase Field Study on the Site Preference of Al in Ni3V: Coordination Geometry Effect

The site occupation behavior of Al in Ni3V phase with a DO22structure in Ni75AlxV25-xalloy was studied using the microscopic phase-field model which is based on the microscopic diffusion equations. Attribute to the coordination geometry effects, the concentration of Al are non-equal on the two non-equivalent Ni sites, and Al prefers to occupy the NiⅠsites. However, the Al does not prefer to occupy both of the two Ni sites, because the Al concentration on V site is intermediately between that on NiⅠand NiⅡsite. The calculated ordering energies suggest that the site preference of alloying elements are all energetic favorable.