Misorientation dependence of fracture stress and grain boundary energy in molybdenum with 〈110〉 symmetric tilt-boundaries

The fracture strength in molybdenum depends markedly on the grain boundary character. In order to clarify the relationship between the grain boundary fracture strength and the grain boundary energy, purified bicrystals with 〈110〉 symmetric tilt boundaries were prepared and grain boundary energies were measured by the thermal grooving technique. Further, the misorientation angle, φ, dependence of the fracture strength was investigated in a range of φ from 90° to 180° over which the data are scarcely available. The main results obtained are summarized as follows. (1) The fracture strength depends on the misorientation angle: the (111) Σ3 boundary is as strong as the single crystal, whereas the (122) Σ9 boundary is weak. The (334) Σ17b boundary is stronger than near the Σ9 and Σ11 boundaries in spite of its low coincidence density. (2) There is a correlation between the fracture strength and the grain boundary energy though the data scattering is large. The energy cusps are observed for the (112) and (111) Σ3 boundaries which are high in fracture strength, while the energy is high for the near-Σ9 and Σ11 boundaries which are low in fracture strength. (3) No peak in fracture strength is found around the (233) Σ11 boundary, though the boundary is regarded as a stable one in the bcc structure.