Abstract
In order to investigate the grain boundary fracture in molybdenum with ⟨110⟩ symmetric tilt boundaries, the four-point bending test was conducted at 77 K by using bicrystals with various misorientations from 0° to 90°. A stress-strain curve to fracture was measured as a function of misorientation angle φ. Two classes of specimens were used to clarify the impurity effect on the grain boundary fracture: One was as-grown specimens which contained carbide precipitates at grain boundaries and the other was purified specimens in which no precipitates were observed. A marked misorientation dependence of fracture stress and plastic strain to fracture, was observed for the purified specimen; the stress and strain were both much higher for φ=0°–10° (Σ1), around 70° (Σ3, (112) twin boundary) and around 87°(Σ17, (223) twin boundary) than for the other boundaries. The dependence observed for the as-grown specimen was qualitatively similar to, but quantitatively much less than, that for the purified specimen. The misorientation dependence of grain boundary energy (cohesion) and the effect of carbon impurity on this cohesion were discussed.
