Interfacial reactions in alumina/CuAgTi braze/CuNi system

Infiltrated Cu8Al–Ti alumina composites

“…This e↵ect parallels what happens when Ni is added to a Ti-containing CuAg-alloy, a system documented in Ref. [51]: the interface then shows a single roughly 100 nm thick titanium-enriched layer. This change in interface structure was explained the fact that strong Ni-Ti interactions within the melt (nickel has a strong chemical a nity for titanium) decrease the Ti chemical activity causing in turn a drastic decrease in the interfacial reactivity of titanium and a suppression of mixed oxide formation in that system [51].…”

“…[51]: the interface then shows a single roughly 100 nm thick titanium-enriched layer. This change in interface structure was explained the fact that strong Ni-Ti interactions within the melt (nickel has a strong chemical a nity for titanium) decrease the Ti chemical activity causing in turn a drastic decrease in the interfacial reactivity of titanium and a suppression of mixed oxide formation in that system [51]. Unlike nickel, however, the a nity between titanium and aluminum is apparently not su cient to suppress here the formation of a titanium-containing mixed oxide.…”

Wetting by Liquid Metals—Application in Materials Processing: The Contribution of the Grenoble Group

“…For instance, when one of the alumina pieces is replaced by a copper-nickel plate, the dissolution of Ni and Cu from the plate in the liquid braze leads to a dramatic change in joint microstructure and also a net change in reactivity at the alumina/braze interface ( Figure 20) consisting of a decrease in the thickness of the interfacial reaction layer by one order of magnitude (from ~2 μm to ~200 nm). Moreover, instead of the wettable Cu3Ti3O compound formed at the interfaces in the alumina to alumina joint, high oxidation-level Ti oxides are formed in the case of CuNi/alumina joint, resulting in a very significant increase in contact angle towards 90° and ultimately in the mechanical weakening of the interface and of the actual joint [42]. From these results, it appears that when ceramics are brazed to metallic parts, allowance must be made not just for the well-known problem of thermo-mechanical compatibility between these two types of solid but also for the interactions between the metallic part and the braze that can affect wetting as well as the joint composition and microstructure.…”

“…e denotes here the thickness of the interfacial reaction product. According to [42] Figure 20. Cross-sections of (a) alumina to alumina and (b) alumina to CuNi plates.…”

Ceramic-Metal Joining Using Active Filler Alloy-An In-Depth Electron Microscopic Study

“…The reactive Ti wets the ceramic/alumina and metal surfaces by reducing them, hence the reaction products are formed which facilitate the further bonding between the two substrates. [37] Wetting depends on the interfacial reactions and the thermodynamic activity of the Ti (a Ti ). The a Ti depends on the mole fraction of the Ti (χ Ti ) in the melt.…”