Reactive wetting and spreading of Al–Si–Mg alloys on Si3N4/Si substrates

The wetting behavior of experimental Al–Si–Mg alloys on Si3N4/Si substrates was investigated using the sessile drop technique. The effects of the processing parameters on the contact angle (θ), surface tension (σLV), and the occurrence of chemical interactions were studied. In contrast with the behavior in nitrogen, in argon, optimized conditions lead to reactive wetting and almost full spreading, with θ = 9 ± 3° and σLV = 29 ± 9 × 10−5 kJ/m2. In nitrogen, the lack of wetting is attributed to the formation of MgO and MgAl2O4 on the droplet surface, through reactions involving Mg3N2(s) and impurity O2 in the flowing gas. Such reactions induce a decrease in σLV and θ transitions in the non-wetting regime. In argon, since the interactions at the liquid/vapor interface are limited, Mg participates mostly in liquid/solid interface reactions. In spite of the associated decrease in σLV, ΔGr results to be the predominant factor for wetting improvement.