Friction-Induced Deposition of a Functional Titanium Coating on Oxide Ceramics for Subsequent Brazing with Metallic Filler Alloys

Abstract

The brazing of dissimilar materials, despite significant progress in the field, still requires fundamental physical, chemical, and technological research and necessitates improvements to existing brazing processes and filler alloys and the development of new multicomponent alloys, metallization coatings, and methods for their application. An option for improving the wetting of nonmetallic materials by filler melts that do not wet ceramic surfaces includes their metallization with adhesion promoters deposited by friction-induced rubbing. Three new types of titanium tools for rubbing nonmetallic surfaces, using a porous sponge-like structure or foil of VT1-0 titanium with a thickness of 0.07–0.10 mm, were proposed and fabricated. This approach is intended to reduce both the force separating the metallizing particles from the tool and the rigidity of the contact interaction. A device was developed for argon purging of the ceramic surface during air metallization. The purging operation in the metallization process significantly improves brazing by lowering the wetting onset temperature and reducing the amount of titanium oxides in the brazed joint. Samples of high-alumina A995 and VK94-1 ceramics were metallized by the proposed method. The wetting of these ceramics with PSr72 filler alloy (copper–silver eutectic) was studied, brazed joints were produced, and the microstructure of the metal–oxide interface was analyzed. Microstructural analysis revealed that the PSr72 melt permeated the titanium coating, became saturated with titanium, and wetted the ceramic surface. This indicates that this metallization method does not require a dense coating and accelerates the saturation of the melt with titanium. The surface roughness of nonmetals was found to influence the composition and microstructure of the coating deposited in air. As surface roughness decreased, both the coating density and oxidation increased. The primary role of friction-induced metallization is to deliver titanium into the filler melt. The advantages of rubbing nonmetallic materials with a porous titanium sponge or foil, compared to tools made from compact titanium, were indicated. The best results were showed by the porous titanium tool.