Part II. Effects of grain-boundary structure on the path of cracking in polycrystals

Four triple junctions along an intergranular crack caused by oxygen-induced dynamic embrittlement of the nickel-base superalloy IN718 have been modeled with bicrystals having the same kinds of boundaries as the boundaries at the triple junctions that did and did not crack. It was found that in all cases the cracking susceptibilities of the bicrystals matched those found at the triple junctions. A low-angle boundary and a Σ3 boundary were found to be much more resistant to cracking than four random boundaries and a Σ19 and a Σ31 boundary. This supports the position that thermo-mechanical processes that increase cracking resistance do so mainly because they increase the content of Σ3 boundaries.