Misorientation dependence of grain boundary fracture strength and grain boundary energy for molybdenum < 001 > symmetric tilt boundaries

It has been well known that the boundary fracture strength of molybdenum de pends strongly on factors such as grain boundary character and impurity seg regation (C and O). In order to clarify the influence of grain boundary geo metrical and chemical factors on the boundary fracture strength of molybden um, bicrystals with a [001] symmetric tilt boundary were prepared in a rang e of misorientation angles phi from 0 degrees to 90 degrees, and the bounda ry fracture strength was measured for not-purified and purified specimens b y a four-point bending test. In addition, misorientation dependence of the grain boundary energy was measured by a thermal grooving method, and the co rrelation between the grain-boundary energy and the boundary fracture stren gth for purified specimens was also investigated. The main results obtained here are as follows. (1) The grain-boundary energy depends remarkably on the misorientation angl e. Large energy cusps were observed at the near 36.9 degrees/(1 (3) over ba r 0) and 53.1 degrees/(1 (2) over bar 0)Sigma 5 coincidence tilt boundaries , and small energy cusp was observed at the near 22.6 degrees/(1 (5) over b ar 0)Sigma 13 coincidence tilt boundary. (2) For the purified specimens, the boundary fracture strength depends on i ts misorientation angles rp. However, for the not-purified specimen, the mi sorientation dependence was not observed at large angle boundaries in the r ange of phi from 16 degrees to 54 degrees. (3) The conspicuous difference in the boundary fracture strength between th e not-purified and purified specimens was not recognized. It is concluded t hat the influence of impurity atoms (C and O) on the boundary fracture stre ngth was relatively small for the [001] symmetric tilt boundaries. (4) A relatively good correlation was obtained between the grain boundary e nergy and the boundary fracture strength in the [001] symmetric tilt bounda ry.