Grain boundary wetting and premelting in the Cu–Co alloys

Abstract

The complete and incomplete wetting of Cu/Cu grain boundaries (GBs) by the Co-containing melt has been observed. The GB wetting in a peritectic system, where the GB wetting layer is depleted by a second component and not enriched like in the conventional cases, has been observed for the first time. The submicrograined structure in Cu–2.2wt.% Co and Cu–4.9wt.% Co alloys has been produced by the high pressure torsion. The melting process of both HPT-treated alloys was studied by the differential scanning calorimetry (DSC). The DSC melting curves were very asymmetric and have been deconvoluted into 2 and 4 different components, respectively. The positions of onsets and minima of high-temperature component peaks for both alloys correspond well with respective liquidus and solidus temperatures in the Cu–Co bulk phase diagram. The low-temperature component peaks were interpreted as GB premelting. The respective GB solidus line was constructed. The step-wise viscosity change of Cu–Co solid solutions was previously observed below the bulk solidus line. The viscosity changes 40–50°C below the GB solidus line observed in this work. This difference can be explained by the difference in the GB character distribution or (alternatively) by the premelting in dislocations cores.