Dihedral angles in Cu–1 wt.% Pb: Grain boundary energy and grain boundary triple line effects

The dihedral angle shown by intergranular lead inclusions in Cu–1 wt.% Pb alloys is measured varying the purity of the metal and the temperature. Several measurement methods are used and compared, namely classical two-dimensional (2D) methods based on metallurgical cross-section analysis and a recently developed 3D stereoscopic method that yields the true three-dimensional angle value for individual inclusions straddling a flat grain boundary. We confirm and extend earlier measurements using the new method. We show that a discrepancy found between the literature data and the stereoscopic 3D dihedral angle measurements is not caused by impurity effects. Rather, the data indicate that the discrepancy has its origin in a difference in average dihedral angle values measured between inclusions straddling two grains and values found at inclusions located where three or more grains meet.