GRAIN BOUNDARY FRACTURE IN MOLYBDENUM BICRYSTALS.

Effects of grain-boundary structure and interstitial impurities on intergranular fracture in molybdenum were investigated quantitatively by using orientation-controlled bicrystals with various LT AN BR 110 RT AN BR symmetric tilt and twist boundaries. Bending stress-strain curves to fracture were measured at 77K and Auger electron spectroscopy (AES) analysis was made on grain-boundary surfaces. Main results obtained are as follows: (1) Both of grain-boundary fracture stress and strain to failure show peak at around SIGMA 1 low-angle and SIGMA 3 high-angle boundaries. (2) Carbon enrichment at grain boundaries strengthens the weak boundaries, whereas it weakens the strong boundaries. (3) For the weakest boundary, the carbon-concentration dependence of the strength is very different between LT AN BR 110 RT AN BR symmetric tilt and twist boundaries. The effect of oxygen is not conclusive because of large data scattering. However, there is a tendency that a small amount of oxygen strengthens the boundary but a large amount of oxygen weakens it.