ON CRYSTALLOGRAPHIC CRACK TRANSFER ACROSS INTERFACES IN 4 TYPES OF ALUMINUM BICRYSTAL

Crack growth behavior across grain boundaries (GBS) in four types of a luminum bicrystal, including [121BAR] tilt symmetric, [121BAR] tilt ps eudosymmetric, [012]-[111], and [121BAR] 180-degrees tilt bicrystals, was studied. Cracks generally decelerate at GBs in these bicrystals un der a constant cyclic load. It was also found that the variation in gr owth rate at a GB depends on the relative orientation of the two grain s on opposite sides of the GB, the GB microstructure, and the applied stress. Two modes of crack transfer across GBs were identified: at a G B with a pair of nearly parallel slip systems, located respectively, o n its two sides, the crack transfers smoothly by following the pair of slip bands; at other GBs the crack splits, branches into up to three secondary slip bands, and decelerates dramatically at a constant cycli c stress. Interface-resistance to fatigue crack transfer across a GB w as rationalized according to dislocation movement across it.