Yaolin Guo

Unique visualization of multiply oriented lattice structures using a continuous wavelet transform

Abstract The application of continuous wavelet transformation in the phase field crystal model has yielded excellent results for the crystal lattice orientation and grain boundaries with different misorientation angles [H.M. Singer, I. Singer, Phys. Rev. E 74 (2006) 031103]. However, we show here that the orientation map from this simple method cannot distinguish symmetric orientations using a single convolution template. By introducing additional rotational templates, the grain orientation can be uniquely visualized in two and three dimensions.

Strain mapping in nanocrystalline grains simulated by phase field crystal model

In recent years, the phase field crystal (PFC) model has been confirmed as a good candidate to describe grain boundary (GB) structures and their nearby atomic arrangement. To further understand the mechanical behaviours of nanocrystalline materials, strain fields near GBs need to be quantitatively characterized. Using the strain mapping technique of geometric phase approach (GPA), we have conducted strain mapping across the GBs in nanocrystalline grains simulated by the PFC model. The results demonstrate that the application of GPA in strain mapping of low and high angles GBs as well as polycrystalline grains simulated by the PFC model is very successful. The results also show that the strain field around the dislocation in a very low angle GB is quantitatively consistent with the anisotropic elastic theory of dislocations. Moreover, the difference between low angle GBs and high angle GBs is revealed by the strain analysis in terms of the strain contour shape and the structural GB width.

Interactions between grain boundary and compositional domain boundary during spinodal decomposition in nanocrystalline alloys

Due to the large grain boundary (GB) volume fraction in nanocrystalline materials, interactions between GB and compositional domain boundary (CDB) play an important role in determining the nanoscale-modulated domain structures during spinodal decomposition. In the present paper, the phase field crystal model is employed to investigate the interactions between GB and CDB. Simulation results show that CDB coarsening can drive the GB migration and bring the impingement of particles with different orientations; the large volume fraction of GB can increase the dislocation volume fraction in CDBs but does not change its proportion in the whole defects number; the crossover point of the coarsening dynamic comes from the block effect of GB with large volume fraction.

Phase-field-crystal investigation of the morphology of a steady-state dendrite tip on the atomic scale

Through phase-field-crystal (PFC) simulations, we investigated, on the atomic scale, the crucial role played by interface energy anisotropy and growth driving force during the morphological evolution of a dendrite tip at low growth driving force. In the layer-by-layer growth manner, the interface energy anisotropy drives the forefront of the dendrite tip to evolve to be highly similar to the corner of the corresponding equilibrium crystal from the aspects of atom configuration and morphology, and thus affects greatly the formation and growth of a steady-state dendrite tip. Meanwhile, the driving force substantially influences the part behind the forefront of the dendrite tip, rather than the forefront itself. However, as the driving force increases enough to change the layer-by-layer growth to the multilayer growth, the morphology of the dendrite tips forefront is completely altered. Parabolic fitting of the dendrite tip reveals that an increase in the influence of interface energy anisotropy makes dendrite tips deviate increasingly from a parabolic shape. By quantifying the deviations under various interface energy anisotropies and growth driving forces, it is suggested that a perfect parabola is an asymptotic limit for the shape of the dendrite tips. Furthermore, the atomic scale description of the dendrite tip obtained in the PFC simulation is compatible with the mesoscopic results obtained in the phase-field simulation in terms of the dendrite tips morphology and the stability criterion constant.

Precisely detecting atomic position of atomic intensity images.

We proposed a quantitative method to detect atomic position in atomic intensity images from experiments such as high-resolution transmission electron microscopy, atomic force microscopy, and simulation such as phase field crystal modeling. The evaluation of detection accuracy proves the excellent performance of the method. This method provides a chance to precisely determine atomic interactions based on the detected atomic positions from the atomic intensity image, and hence to investigate the related physical, chemical and electrical properties.

Elastic strain response in the modified phase-field-crystal model*

To understand and develop new nanostructure materials with specific mechanical properties, a good knowledge of the elastic strain response is mandatory. Here we investigate the linear elasticity response in the modified phase-field-crystal (MPFC) model. The results show that two different propagation modes control the elastic interaction length and time, which determine whether the density waves can propagate or not. By quantitatively calculating the strain field, we find that the strain distribution is indeed extremely uniform in case of elasticity. Further, we present a detailed theoretical analysis for the orientation dependence and temperature dependence of shear modulus. The simulation results show that the shear modulus reveals strong anisotropy and the one-mode analysis provides a good guideline for determining elastic shear constants until the system temperature falls below a certain value.