Direct Observation of Wetting and Spreading of Molten Aluminum on TiB₂ in the Presence of a Molten Flux from the Aluminum Melting Point up to 1033 K (760 °C)

The wetting and spreading of molten aluminum on TiB₂ substrates between the aluminum melting point and 1033 K (760 °C) was investigated in the presence of different types of fluxes. The wetting and spreading behavior is observed to depend on the flux, its melting point, its chemistry, and its ability to dissolve alumina. When the flux melting point is higher than the melting point of aluminum, the molten aluminum takes on an initial spherical shape as a result of the thin alumina layer on its surface. After the flux is melted, it dissolves the alumina layer on the liquid aluminum surface causing the aluminum to wet and spread on the substrate. When the flux melts before the aluminum, the alumina layer on the solid aluminum surface is dissolved into the flux. In this case, the aluminum surface in contact with the molten flux is alumina layer free. Thus, the aluminum does not take a spherical shape after melting; it rapidly melts, wets, and spreads on the substrate. The use of a flux allows the wetting behavior of aluminum on TiB₂ to be observed at lower temperatures than previously reported.