Influence of the Brazing Paste Composition on the Wetting Behavior of Reactive Air Brazed Metal–Ceramic Joints

Abstract

Reactive air brazing (RAB) is a cost‐effective way to produce ceramic–ceramic or ceramic–metal brazed joints in air, without applying a protective gas atmosphere or a vacuum. In addition to conventional furnace technology, the brazing with induction heating can also be used effectively. Within the scope of this study the shrinkage and wetting behavior of self‐developed brazing pastes with different CuO contents and two qualities of silver powders with coarse and fine particle size are investigated by optical dilatometry on alumina (Al2O3, 99.7% purity). Thereby, the fine silver powder quality reveals a significant swelling effect at high temperatures, leading to an expansion of densified powder compacts caused by evolving gases. Joining tests are performed on ceramic–steel brazed joints using a muffle furnace and induction heating for short brazing cycles. The brazing seams and interfaces of the joints are investigated using scanning electron microscopy (SEM) and energy‐dispersive X‐ray spectroscopy (EDS). As a result, correlations between the brazing filler metal composition, the steel, and the brazing conditions are obtained.

Active Brazing for Energy Devices Sealing

“…This has minimized the deterioration of the brazed elements to a certain extent; at the same time, the gas tightness has been increased even under substantial pressure differentials. Enhancements have been implemented to address the unacceptable decline in strength and gas tightness during prolonged periods of stationary service as well as during start-stop cycles [8,60,107]. The RAB process has a significant drawback wherein it introduces an excessive amount of oxygen into the brazed joint.…”

“…It involves working at temperatures exceeding 450 • C but still below the melting point of the materials to be joined. This method allows the creation of ceramic-ceramic and ceramic-metal joints through two different approaches: indirect brazing, where ceramic surfaces are first metallized and then brazed using conventional filler metals, and direct (active) brazing, which utilizes filler alloys containing active elements like titanium [2][3][4][5][6] or metal oxides like CuO [7][8][9]. Brazing offers several significant advantages.…”

Reactive air wetting and brazing of Al 2O 3 ceramics using Ag–Nb 2O 5filler: Performance and interfacial behavior

“…RAB of Al 2 O 3 ceramics is an effective method to obtain complicated or large-sized Al 2 O 3 ceramic composite components, which can be applied in the electronic substrate and fuel cell [4,5]. Up to now, brazing fillers for RAB of Al 2 O 3 ceramics are mainly involved in Ag-CuO (or Ag-Cu) [4−8], Ag-Al [9], Ag-CuO-Pt [10], Ag-CuO-TiH 2 [11], and Ag-SiO 2 [12]. However, the Ag-CuO-based fillers cannot endure reducing atmosphere at higher temperatures for long time since CuO can be reduced into the elemental Cu, resulting in the generation of pores at the interface and a sharp decrease in joint strength [13−15].…”

Vacuum Brazing of Metallized YSZ and Crofer Alloy Using 72Ag-28Cu Filler Foil

“…As YSZ is a suitable solid-electrolyte material, many applications for YSZ-brazed joints require that the joints be gas-tight. Some such applications are oxygen transport membranes, gas sensors and fuel cells [ 26 , 27 , 28 ]. This investigation focused on brazing metallized YSZ and Crofer substrates using the BAg-8 braze alloy for gas-tight applications.…”