INTERGRANULAR CORROSION OF COPPER AND ALPHA-CU-AL ALLOY BICRYSTALS

Intergranular corrosion in copper bicrystals with symmetrical [110] tilt boundaries and in Cu-9 at.% Al alloy bicrystals with symmetrical [110] and [100] tilt boundaries was investigated by examining the depths of corrosion grooves developed at the boundaries after an immersion test in acid solutions (modified Livingston's etchants) usually used to reveal lattice dislocations. On the plot of depth of penetration against misorientation, cusps (sharp minima) were observed at misorientations of 38.9-degrees, SIGMA = 9 (221), 70.5-degrees, SIGMA = 3 (111) and 129.5-degrees, SIGMA = 11 (113) in the [110] tilt boundaries of copper and Cu-9 at.% Al alloy, and at those of 22.6-degrees, SIGMA = 13a (015), 36.9-degrees, SIGMA = 5 (013), 43.6-degrees, SIGMA = 29a (025), 53.1-degrees, SIGMA = 5 (012) and 67.4-degrees, SIGMA = 13a (023) in the [100] tilt boundary of Cu-9 at.% Al alloy. The misorientation dependences of the penetration depth were compared with those of grain-boundary energies in copper and aluminium reported in the literature.