THE INFLUENCE OF METALLIC NANOCOATINGS DEPOSITED ON SILICON OXIDE ON ITS WETTING BY SOLDERING MELTS
II. EFFECT FROM THE ANNEALING OF NANOCOATINGS DEPOSITED ON SiO₂ ON THEIR STRUCTURE AND INTERACTION WITH THE OXIDE

Abstract

The sessile drop method using the capillary melt cleaning in the experiment was employed to study the effect of metallic nanocoatings (single Ti, Nb, and Mo coatings and binary Ti–Cu, Nb–Cu, and Mo–Cu coatings at a constant thickness of the copper layer) on the wetting of silicon oxide by Pb–15 wt.% In melt in a vacuum of 1 ∙ 10^–3 Pa at 500 °C after annealing of the coatings at 900 °C. Metallic coatings were applied by electron beam evaporation in vacuum. The binary coatings were produced by sequential sputtering of layers. The dependences of contact angle on the coating thickness show that the “threshold” thickness is determined by the annealing temperature of the coating, that is, its structure. The “threshold” coating thickness for different metals depends on the chemical affinity of the coating metal to oxygen. When a freshly applied coating and annealed single Mo, Nb, and Ti coatings are wetted, their “threshold” thickness increases from 70 to 80 nm for titanium, from 63 to 70 nm for niobium, and from 50 to 60 nm for molybdenum. The structure of Cu, Ni, Mo, Cr, Nb, and Ti coatings annealed at 600, 900, and 1200 °C was studied. The initial (freshly deposited) metallic coatings have high integrity. The coatings are dispersed after annealing and their integrity decreases with increasing temperature. The dispersed metallic coating forms “islands” of various shapes, round shape being predominant, depending on the chemical affinity of the coating metal to oxygen. The so-called “solid” wetting is observed. The shape of the “islands” is determined by the equilibrium between the attraction forces (interaction, adhesion) of the metal to the substrate and the very strong surface tension of the metal (with such small coating thickness). When metallic coatings are used for brazing quartz with aluminum alloys, coatings of adhesive active metals (Mo, Cr, Nb, Ti) should be annealed at temperatures of 900–1000 °С and a holding time of 10 min. The thickness of the coatings should be within the “threshold” value.