Roles of structure-dependent hardening at grain boundaries and triple junctions in deformation and fracture of molybdenum polycrystals

Structure-dependent grain boundary hardening and triple junction hardening were investigated in connection with plastic deformation and fracture in polycrystalline molybdenum with different carbon contents by the microindentation test. Low-angle and Σ coincidence boundaries showed a lower degree of grain boundary hardening than random boundaries. The triple junctions composed of low-angle and Σ boundaries showed a lower degree of triple junction hardening than the junctions composed of random boundaries. The roles of grain boundaries and triple junctions in deformation and the fracture of polycrystalline molybdenum were discussed on the basis of the results of observations on structure-dependent grain boundary hardening and triple junction hardening. It is found that the triple junctions composed of low-angle and Σ boundaries can arrest the crack propagation.