Using the phase field crystal approach, the crystallization process within the liquid-solid coexistence region is inves- tigated for a square lattice on an atomic scale. Two competing growth modes, i.e., the diffusion-controlled growth through long-range atomic migration in liquid and the diffusionless growth through local atom rearrangement, which give rise to two completely different crystallization behaviors, are compared. In the diffusion-controlled regime, the interface migrates in a layerwise manner, leading to a gradual change of crystal morphology from truncated square to four-fold symmetric dendrite with the increase of driving force. For the diffusionless growth mode, a single crystal with no significant density change occupies the whole system at a faster rate while exhibiting a small growth anisotropy. The competition between these two modes is also discussed from the key input of the phase field crystal model： the correlation function.
The second phase particle effect on texture evolution of polycrystalline material is studied through phase-field method. A unique field variable is introduced into the phase-field model to represent the second phase particles. Elastic interaction between particles and grains is also considered. Results indicate that in the presence of second phase particles the average particle diameter turns smaller than in the absence of these particles and retards texture formation by pinning effect. The second phase particles change the strain energy profile, which tremendously influences the pinning effect.
The formation and evolution of deformation texture in polycrystalline materials are studied by phase-field dynamic model. In addition, the driving force of texture evolution is also discussed. In this model, grains with different orientation are defined by a set of continuous non-conserved order parameter fields. Simulation results show that grains with preferred orientation grow at the expense of those with unfavorable orientations. It is more important that, elastic potentia evolution of texture whether the polycrystalline system rather than elastic energy plays a crucial role in the s subjected to uniaxial stress or shear stress.
The influence of temperature on the inverse Hall-Petch effect in nanocrystalline （NC） materials is investigated using phase field crystal simulation method. Simulated results indicate that the inverse Hall-Petch effect in NC materials becomes weakened at low temperature. The results also show that the change in microscopic deformation mechanism with temperature variation is the main reason for the weakening of the inverse Hall-Petch effect. At elevated temperature, grain rotation and grain boundary （GB） migration seriously reduce the yield stress so that the NC materials exhibit the inverse Hall-Petch effect. However, at low temperature, both grain rotation and GB migration occur with great difficulty, instead, the dislocations nucleated from the cusp of serrated GBs become active. The lack of grain rotation and GB migration during deformation is mainly responsible for the weakening of the inverse Hall-Petch effect. Furthermore, it is found that since small grain size is favorable for GB migration, the degree of weakening decreases with decreasing average grain size at low temperature.
