Phase-field-crystal study on the evolution behavior of microcracks initiated on grain boundaries under constant strain

The initiation and propagation behavior of microcracks is closely associated with the cleavage of crystalline materials. We use phase-field-crystal method to explore the evolution process and mechanism of microcracks initiated on grain boundaries (GBs). Constant biaxial strain is applied to the (0001) crystal plane of hexagonal close-packed bicrystal. Under applied strain, cracks are initiated at the end of semi-boundaries between grains. Following this crack initiation (CIN) mechanism, grain boundary misorientation angle (GBMA) can greatly affect the process of crack initiation and propagation (CINPR) in normal GB system. Along with the increase in GBMA, CIN is promoted and the type of subsequent crack propagation changes from trans-granular propagation into inter-granular propagation. System temperature and applied strain also have influence on CINPR. Associated with fracture mechanics theory, the effects of GBMA, temperature and strain on the behavior of CINPR are investigated. Additionally, we give curves of change in free energy to illustrate these effects from energy perspective. Crack arrestment mechanism, especially the plastic relaxation mechanism, is also discussed. The simulation results acquired in this work are in good agreement with theoretical analyses and experimental results.