Newly developed active braze powders based on commercial nickel brazes using zirconium as active element for joining ceramic to metal

Abstract

Schlüsselwörter: Aktivlöten / mechanisches Legieren / Nickelbasislote / Zirkon / Aluminiumoxidkeramik / The increased requirements of highly stressed components, concerning the resistance to thermal-induced stresses, oxidation, corrosion, hardness as well as wear resistance make high-performance technical ceramics ideally suited for such applications. On the other hand they exhibit properties like high brittleness, partly low thermal shock resistance, low workability and consequential limitations in the engineering design. Hybrid material concepts, as combination of highperformance technical ceramics and metallic engineering materials, can offer interesting technological solutions, if suitable and joining technologies are available. Active brazing, which is a very flexible joining technology in respect of the material selection, arises for the development of new and innovative applications, such as high-temperature fuel cells. Currently silver/copper, copper and silver active brazing filler metals are already used in the industry and are characterised by a decrease of their mechanical strength at approx. 500 8C. Referring to this, gold and palladium ac- tive brazing filler metals show better features, but because of their high price, they are seldom used. The aim of the reported investigations is the development of active brazing filler metals with reasonable raw materials costs for working temperatures above 500 8C and moreover to be used in hydrocarbonated environments with better corrosion-resistance than silver/copper, copper and silver active brazing filler metals. Experimental brazing filler metals with zirconium as surface-active element has been manufactured on the basis of nickel brazing filler metals NI 102, NI 105 and NI 107. The modification of each nickel brazing filler metal was carried out on the one hand by powder metallurgy, whereby zirconium hydride has been mixed or mechanically alloyed. On the other hand the nickel brazing filler metals have been alloyed with zirconium by melting metallurgy. The content of active metal varied between 2 weight-% and 10 weight-%. For the characterisation, the melting range of all experimental brazing filler metals has been determined by thermoanalytical methods and the ones, which have been manufactured by powder metallurgy, have been investigated by means of an x-ray diffraction analysis and a morphological analysis of the powder particles. The suitability of the experimental brazing filler metals for the active brazing has been probed in wetting tests on alumina in high-vacuum brazing trials and examined metallographically.Keywords: active brazing / mechanical alloying / nickel brazing filler metals / zirconium / alumina ceramic / 1 Einleitung

In situ observation of the pore formation during laser based reactive air brazing of alumina

“…This contradicts the ndings of Bobzin et. al [12], who observed a continuous CuO phase band at the interface of alumina and ller metal. In contrast to the set up used in this work, the brazing process of Bobzin was carried out with horizontally placed samples, so that the in uence of gravity on the distribution of the CuO in the molten ller metal is much smaller.…”

“…Adding Al, on the other hand, enhanced the wetting and strength [10], [11]. The addition of Ni or Mn led to an improvement in wetting only above temperatures of 1350 and 1050°C, respectively [12].…”