Abstract
Pulsed electric current can be used for the fast sintering of powders as well as joining of macroobjects. In this work, we brazed copper plates using a silver layer that was formed in situ by the decomposition of a silver oxalate Ag2C2O4 powder placed between the plates. Joining was conducted in the chamber of a Spark Plasma Sintering (SPS) facility with and without a graphite die. In the die-assisted tooling configuration, indirect heating of the assembly from the graphite die carrying electric current occurred until the brazing layer transformed into metallic silver. The passage of electric current through a Cu/Ag2C2O4/Cu stack placed between the electrodes without a die was possible because of the formation of Cu/Cu contacts in the areas free from the Ag2C2O4 particles. Joints that were formed in the die-assisted experiments showed a slightly higher shear strength (45 MPa) in comparison with joints formed without a die (41 MPa). The shear strength of the reference sample (obtained without a die), a stack of copper plates joined without any brazing layer, was only 31 MPa, which indicates a key role of the silver in producing strong bonding between the plates. This study shows that both die-assisted tooling configurations and those without a die can be used for the SPS brazing of materials by the oxalate-derived silver interlayer.
Highlights
The Spark Plasma Sintering (SPS) method has attracted enormous interest from the materials science community thanks to its capabilities to consolidate different powder materials rapidly and efficiently [1]
In the die-assisted experiments, the passage of electric current through the punches and the die wall offered a means to indirectly heat the stack of copper plates
The use of silver oxalate Ag2 C2 O4 as a brazing material-generating precursor in an electric current-assisted joining process has been investigated for the first time
Summary
The Spark Plasma Sintering (SPS) method has attracted enormous interest from the materials science community thanks to its capabilities to consolidate different powder materials rapidly and efficiently [1]. In traditional tooling set-ups, die is a mandatory component, as the raw material is in the powder state [2]. Novel applications of the SPS method include surface engineering and materials joining, as recent studies have demonstrated [3]. Silver is a highly attractive material [4]. The process of joining by silver is essentially brazing, as silver (including nano-sized silver) has a higher melting temperature as compared with lead-based alloys used in the soldering processes. Metallic silver-based pastes are commonly used [5]. A lower melting temperature of nano-sized silver than that
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