Grain Boundary Strength of Molybdenum Bicrystals with a 〈110〉 Twist Boundary

Grain boundary fracture in molybdenum was investigated by the four-point bending test at 77 K as a function of misorientation angle, by using bicrystals with a 〈110〉 twist boundary. Main results obtained are as follows: (1) Fracture always occurs at the grain boundary. (2) The fracture strength and strain to fracture markedly depend on the misorientation angle, i.e., the bicrystals of misorientation up to 20° and those of around 70° (Σ3) have much higher fracture strength than the others, and some appreciable plastic strain is only observed for these strong bicrystals. (3) Misorientation width of the peak in strength agrees with the predicted value from the Brandon’s equation. (4) There are no peaks in strength around Σ9 and Σ11 coincidence boundaries.