Interaction Mechanisms Between Dislocation And Interface:Phase Field Modeling

Most strengthening phenomena in nanocrystalline metals are related to the fact that interfaces block the motion of dislocations, understanding the interface strengthening mechanisms is important to material design. The interaction between dislocation and interface depends on many multi-scale factors, evaluating the effects of these factors require multi-scale computational and modeling approaches. In this thesis, by using the phase field microelasticity (PFM) model of dislocation, we study the dislocation interacting with coherent sliding interface and dislocation networks in grain boundary (GB) at continuum scales.We explore the interaction mechanisms between dislocation and sliding interface. Weak interface can be siding by the shear of the glide dislocation, and this interface slid-ing can attract the glide dislocation and then trap the dislocation at the interface, thus can lead large interface barrier strength to dislocation transmission. The results indicate that such interface barrier strength might be rate dependent, because the interface slid-ing zone shrinks in the case of high applied stress and low mobility for the interfacial dislocation.The effects of interface strength and stacking fault (SF) energy on the slip trans-mission of an extended dislocation across a coherent interface are investigated. There is a partial transmission mode where the trailing partial dislocation remains after the leading partial crosses the interface. A long SF forms behind the leading partial dis-location and thus increases twinnability. A deformation map for the glide dislocation from partial to full transmission with respect to the interface strength and the SF energy for the glide plane, is constructed in good agreement with a scaling analysis.We develop a new expression of the crystalline energy in PFM model depending on the total Burgers vector of all the dislocations. Compared with the original expression, the developed one can accurately describe the structure, energy, unzipping stress and unzipping mechanism of the collinear dislocation junction formed in the intersecting line of two slip planes.By using the developed PFM model, we study the transmission of a lattice screw across the dislocation networks in low angle twist GB. There are two typical grain boundary structures:hexagonal networks consisting of full dislocations in high SF energy materials and triangle networks consisting of partial dislocations and stacking faults in low SF energy materials. The transmission position has effects on the trans-mission barrier of the hexagonal dislocation networks, the barriers are related to the collinear reactions between the lattice dislocation and collinear GB dislocations, but not the formation of different dislocation junctions in traditional assumptions. The bar-rier of the triangle dislocation networks does not depend on the transmission position, existing of the multi-SFs distributes the dislocations evenly in the GB. Additionally, for some transmission positions in triangle dislocation networks, there are partial transmis-sion modes.