Effects of CuO Content on the Wetting Behavior and Mechanical Properties of a Ag–CuO Braze for Ceramic Joining

Abstract

A silver-based joining technique referred to as reactive air brazing has been recently developed for joining high-temperature structural ceramic components of the type used in gas turbines, combustion engines, heat exchangers, and burners. It was found that additions of copper oxide to silver exhibit a tremendous effect on both the wettability and joint strength characteristics of the subsequent braze relative to polycrystalline alumina substrates. The effect is particularly significant at low copper oxide content, with substantial improvements in wetting observed in the 1-8 mol% range. The corresponding strength of the brazed polycrystalline alumina joints appears to be maximized at a copper oxide content of 8 mol%, with a maximum room temperature flexural strength approaching that of monolithic alumina. While further increases in oxide content lead to improved wetting on polycrystalline alumina, the effect on joint strength is deleterious. It appears that the formation of a continuous brittle copper-based oxide layer along the interface between the braze and alumina faying surface is responsible for the poor mechanical behavior observed in joints fabricated with higher copper oxide content brazes.

A review of wetting versus adsorption, complexions, and related phenomena: the rosetta stone of wetting

“…The equivalence of weighted mean curvature guarantees that there is no change in total energy if material from one facet is transported to another, which is a necessary condition for equilibrium. The interfacial energy can be determined by measuring two characteristic lengths in the Wulff shape of the crystal truncated by the substrate: the distances from the Wulff point of the crystal to the interface with the substrate (R 1 ), and from the Wulff point to the uppermost facet 4 of the crystal (R 2 ), as shown schematically in Fig. 10, which provides a basis for this method.…”

“…The degree by which a liquid wets a solid is an important technological parameter for processes such as joining [1][2][3][4][5][6], solidification [7][8][9], and composite processing [10][11][12][13][14]. While wetting is a measure of the ''energy'' of interfaces between bulk phases, and thus a parameter associated with equilibrium thermodynamics, the rate by which a liquid spreads in contact area with a solid is equally important for technological processes [15][16][17].…”

Synthesis and Characterization of New Ceramic Thermoelectrics Implemented in a Thermoelectric Oxide Module

“…Pure silver paste resulted in low wettability, and the contacts were droplet shaped with a contact angle of 114°. 21 By adding CuO, the contact angle decreased from 114°to 75°, showing an optimum at low CuO concentrations due to the formation of a homogeneous silver-copper oxide liquid. The test results revealed that the mechanical strength of the contacts was optimal when a mixture of Ag/0.…”

Brazing of ceramic-to-ceramic and ceramic-to-metal joints in air

“…Due to the metallic matrix of noble metals, good ductility, strength, and high corrosion resistance of the joints are expected. A solidus temperature commonly higher than 930°C permits high-temperature applications [1][2][3][6][7][8][9][10][11]. In this study, RAB was applied to produce ceramic-to-ceramic and (for SOFC applications) ceramic-to-metal joints.…”