Brazing filler metals

Abstract

Brazing is a 5000-year-old joining process which still meets advanced joining challenges today. In brazing, components are joined by heating above the melting point of a filler metal placed between them; on solidification a joint is formed. It provides unique advantages over other joining methods, including the ability to join dissimilar material combinations (including metal-ceramic joints), with limited microstructural evolution; producing joints of relatively high strength which are often electrically and thermally conductive. Current interest in brazing is widespread with filler metal development key to enabling a range of future technologies including; fusion energy, Solid Oxide Fuel Cells and nanoelectronics, whilst also assisting the advancement of established fields, such as automotive lightweighting, by tackling the challenges associated with joining aluminium to steels. This review discusses the theory and practice of brazing, with particular reference to filler metals, and covers progress in, and opportunities for, advanced filler metal development.

High Entropy Alloys as Filler Metals for Joining

“…To achieve its optimum power production, the temperature needs to be 550 • C or above [77,78], but temperatures that exceed 620 • C may lead to sublimation of Sb from the material and thus degrade it [82]. To survive operation, but not damage these skutterudite thermoelectrics on processing, the optimal melting temperature range for the filler metal would be T = 550-620 • C. Initially, examination of the standard fillers ( Figure 9) suggests 2 silverbased and 10 aluminum-based fillers will meet this requirement, but they either contain the banned element cadmium [2], react with the thermoelectric to form detrimental compounds [83], or otherwise see excessive diffusion of filler elements into the thermoelectric, compromising performance [84].…”

“…Joining technology, applied in industries as diverse as electronics, aerospace, automotive, and energy, offers a wide range of different techniques, each with particular characteristics, which will determine their suitability for a certain application. Among these, brazing and soldering offer the principal advantage that they are capable of forming a metallurgical joint between widely dissimilar substrate materials (the parts being joined) with minimal modification of those materials [ 1 , 2 , 3 ]. In both brazing and soldering processes, a molten filler metal is used to form a metallurgical bond between two (or more) components (the convention is for the two methods to be distinguished by a watershed of 450 °C).…”

“…Brazing covers a very wide range of temperatures, and the joining of many different materials. As a result, there is a wide range of filler metals available (for a full account see [ 2 ]). These include Al-based alloys, which are the lowest melting point common brazing filler metals.…”

Wide-Gap Brazing of K417G Alloy Assisted by In Situ Precipitation of M3B2 Boride Particles

“…As a result, relatively large cracks or worn areas (>1.5 mm) are discovered in aerospace components, where the narrow gap TLP bonding technique would be inadequate [ 13 ]. For wide-gap brazing, the selection and design of the filler metal composition is the key factor to improve the brazing performance [ 14 , 15 , 16 , 17 , 18 , 19 ]. Considerable effort has been devoted to adding a second gap-filler powder, (hereafter termed additive powder) of similar composition to that of the base metal (BM), to the joint gap, for use with braze powder during the high-temperature brazing process [ 14 , 20 , 21 ].…”

Evaluation of Biomedical Ti/ZrO2 Joint Brazed with Pure Au Filler: Microstructure and Mechanical Properties

“…constructed via these bonding methods display a low strength and are easy to loosen in practice, which can shorten the life of implants and lead to potential dangers in applications. Brazing, a bonding technology with the advantages of convenience, cost-effectiveness and high quality, has been widely employed for joining metals and ceramics [21][22][23]. Sharma et al [24,25] realized the brazing of Ti-6Al-4V to ZrO 2 successfully using Ag-Cu-In-Ti active filler and Ag-Cu-Ti composite fillers.…”