Using first-principles electronic structure methods, the effects of B impurities in bulk Cu and at surfaces and grain boundaries were calculated. It was found that B segregation to the Σ = 5 (310)[001] grain boundary should strengthen the boundary up to 1.5ML coverage (15.24at/nm2). The maximal effect was observed at 0.5ML and corresponds to B atoms filling exclusively grain boundary interstices. In Cu bulk, B causes significant distortion in both interstitial and regular lattice sites, for which B atoms were either too big or too small. The distortion was compensated to a large extent when the interstitial and substitutional B combined together to form a strongly bound dumb-bell. The prediction was that bound boron impurities should appear in a sizable proportion if not dominate under most experimental conditions. A large discrepancy between calculated heats of solution and experimental terminal solubility of B in Cu was found, indicating either a significant failure of the density functional approach or, more likely, strongly overestimated solubility limits in the existing B-Cu phase diagram.

Boron in Copper - a Perfect Misfit in the Bulk and Cohesion Enhancer at a Grain Boundary. A.Y.Lozovoi, A.T.Paxton: Physical Review B, 2008, 77[16], 165413 (14pp)