Intercrystalline Precipitation in Al-Cu bicrystals of Definite Orientation.

Experimental data show that after quenching and tempering, the density of intercrystalline precipitates in Al-Cu bicrystals bent around the 001 and 011 direction axes increases as the coincidence of the crystal lattices at the boundary increases. The highest densities correspond to the smallest dimensions of the precipitates. Interpretation of the results on the basis of a model of grain boundary structures, leads to the conclusion that the sites of nucleation of precipitates are the intercrystalline sites of atoms of maximum energy.