Two different numerical schemes, the standard explicit scheme and the
time-elimination relaxation one, in the framework of phase-field model with
finite interface dissipation were employed to investigate the solute trapping
effect in a Si-4.5 at.% As alloy during rapid solidification. With the
equivalent input, a unique solute distribution under the steady state can be
obtained by using the two schemes without restriction to numerical length
scale and interface velocity. By adjusting interface width and interface
permeability, the experimental solute segregation coefficients can be well
reproduced. The comparative analysis of advantages and disadvantages in the
two numerical schemes indicates that the time-elimination relaxation scheme
is preferable in one-dimensional phase-field simulation, while the standard
explicit scheme seems to be the only choice for two- or three dimensional
phase-field simulation. Furthermore, the kinetic phase diagrams in the Si-As
system were predicted by using the phase-field simulation with the
time-elimination relaxation scheme.
Grain refinement of 01420 Al-Li alloy through particle stimulated nucleation(PSN) of
recrystallization is reported. The results showed that the rolling in the overaged 01420 Al-Li alloy
resulted in the formation of the deformation zones associated with the second phase particles larger
than 0.80 μm which can act as the nucleation sites for recrystallized grains. The precipitates larger
than 0.80 μm are sticked shaped S-phase(Al2MgLi) and globular β-phase(Mg2Al3), and the density of
β-phase particles is approximately as two to three times as the S-phase particles. The S-phase
particles can’t be as PSN sites since they were broken to small dispersoid particles during rolling. The
average grain size of 01420 Al-Li alloy solutioned at 470°C for 2h, aged at 300 °C for 48h, 81% rolled
at 300 °C and finally recrystallized at 500 °C for 10min is approximately 10 μm.
Nickel-based super alloys are the main candidate materials for aero-engines, gas turbine blades etc. This paper focuses on the simulation of nucleation and growth kinetics of γ' phase, and stress response mechanism of γ' phase particles during their preferential coarsening (rafting) in elastic inhomogeneous system. A phase-field model is employed in the present study, which incorporates chemical, interfacial, and elastic energies, and it couples essentially to externally imposed mechanical field. Due to the limitations of the 2D model on analyzing the shape and size of the precipitate particles, the process of γ' phase particles growing and coarsening is further modeled by performing 3D simulation. The results show that the average particle size is linearly related to the evolution time and satisfies the Lifshitz-Slyozov-Wagner (LSW) classical coarsening theory when the external stress is not applied. Particles exhibit a strong special orientation under tensile stress, and the orientation is in excellent agreement with previous studies. In the nucleation stage, the collision and coalescence between particles promote rafting significantly, and the number of soft particles is obviously larger than that of hard particles. In the coarsening stage, the growth rate of soft particles is higher than that of hard particles. Three-dimensional simulation results show that the effect of final characteristic size of precipitated particles is not significant by external loads. The morphology evolution and coarsening mechanism of the precipitated particles are of great significance for studying the strengthening mechanism of super-alloy.
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