The effect of carbon nanolayers on wetting of alumina by NiSi alloys

Ionocovalent oxides such as alumina, silica or magnesia are not wetted by Si and Si-rich alloys, the contact angles being close to 90A degrees. The aim of this work is to study the effect of submicron carbon layers on wetting in this type of system. In principle, silicon reacts with carbon to form silicon carbide, a compound wettable by Si alloys. However, the formation of silicon carbide at the interface can be affected by the dissolution of this compound into the molten alloy occurring in order to saturate the melt in carbon. These phenomena are studied using a model system consisting of Ni-63 at.%Si alloy and monocrystalline alumina substrate coated with carbon layers. Wetting experiments are performed by the dispensed drop technique in high vacuum varying the parameters: thickness of coating (from 0 to 100 nm), temperature and degree of carbon saturation of the alloy. The surfaces and reactive interfaces are characterised by SEM, X-ray microanalysis and XPS.