1992 Volume 41 Issue 1 Pages 31-38
The effect of grain boundary inclination on hydrogen embrittlement was investigated on Alloy 600 with coarse columnar crystals. As the deviation of the growing direction from ‹100› orientation was within 10°, the grain boundaries were treated approximately as simple tilt boundaries with ‹100› rotation axis. Brittle cracking occured at grain boundaries in tensile test after hydrogen charge. The mean crack depth (h) increased with the increases in charging time (t) and temperature. There was a relation, h∝t1/2, between h and t. The activation energy for the diffusion of hydrogen atoms obtained from the temperature dependence of h·t-1/2 was estimated to be 13.6kcal·mol-1. On the other hand, that for grain boundaries with relative tilt angle (ω) of less than 10° was estimated to be 16.9kcal·mol-1. The crack depth (h) varied considerably even at the same ω and no clear relation was found between h and ω. It suggests that h depends on other factors such as grain boundary inclination as well as ω. At the symmetrical tilt boundaries, h decreased at coincidence boundaries such as ∑5 and ∑13 against the normal relation of h with ω. It was found that the grain boundaries which have the planes close to (110) of both component crystals have lower susceptibility to cracking.
