A study of intergranular fracture of molybdenum bicrystals

The effects of grain boundary structure of molybdenum bicrystals on the boundary cohesive strength, fracture mode transition, boundary segregation, and precipitation morphology were investigated to gain a better understanding of embrittlement and intergranular fracture in b.c.c. metals. Molybdenum bicrystals of simple tilt and simple twist boundaries with rotating axes along the (100) and the (110) directions were prepared in a vacuum zone melter. The misorientation angle of the bicrystals ranges from 0 deg to about 50 deg or more, with an interval of about 8 deg to 10 deg. Observations by Auger and scanning electron microscopy were used as the basis for a model which assumes that the weakening of molybdenum grain boundaries is caused by the segregation of interstitials such as carbon.