The effect of relative crystal orientation on the liquid metal induced grain boundary fracture of aluminum bicrystals

Abstract

The effects of relative crystal orientation on liquid metal induced intergranular fracture were studied to: 1) verify the existence of the theoretically and experimentally predicted orientation dependence of this process; and 2) determine which crystallographically related property produced such dependence. A base metal of 99.993 pct pure aluminum and a liquid metal of Hg-3 at. pct Ga were chosen as the embrittlement couple. Bicrystals of aluminum were grown with symmetric tilt boundaries so that: 1) individual boundaries could be tested; and 2) the resulting embrittlement susceptibility of each boundary could be correlated with a controlled crystallographic variable, the tilt angle. A fracture mechanics testing method was developed which enabled the crack propagation resistance of each grain boundary in the Hg-3 at. pct Ga atmosphere to be determined by yielding the crack extension force of a propagating crack. The variation in crack extension force with symmetric tilt angle was analyzed to determine what crystallographically related property produced the observed variations. Consideration of the crystallographically related properties of: 1) slip compatibility between adjacent grains; 2) grain boundary atomic density; and 3) grain boundary energy led to the conclusion that the observed variations were caused by variations in grain boundary energy, and a mathematical relationship was developed that expressed the dependency.