Data pertaining to induction brazing of contact materials in a 3 layered sandwich structure consisting of a silver-tin oxide (Ag-SnO(II)) layer, a silver (Ag) inter-layer and a thin layer of phosphorous free braze-A4-TUD

Published: 05-07-2020| Version 2 | DOI: 10.17632/zg2pcm8r6w.2
Contributors:
Ali Zahid,
Umer Zahid

Description

Contact materials for electrical switch gears are widely used for connecting and disconnecting electric circuits. These contacts are two component systems, where the contact tips are brazed to the carriers prior to installation. The contacts used in the present work is a 3 layered sandwich structure consisting of a silver-tin oxide layer, a silver inter-layer and a thin layer of the braze. The carrier itself is copper-plated steel. The brazing process is accomplished by a high frequency inductive heating process. By varying the brazing parameters, namely, temperature and time, their influence on joint formation is investigated. The brazing joint of the contact tips were characterized by microscopy and physical analytical techniques. The mechanical characteristics were determined with Vickers micro-hardness. To investigate the dependence of temperature and/or time on joint formation, during induction brazing using high frequency inductive heating, experiments were carried out by setting up a proprietary brazing setup. Temperature monitoring was carried out using a pyrometer and thermocouple, placed deductively around the brazing sample to ascertain temperature variations in the brazing sample. Temperature disparities due to measurements with the pyrometer and thermocouple were also ascertained. To enable correct temperature determination using the pyrometer, the emissivity was investigated and compared with the thermocouple. Proper brazing data collection was ensured by investigating all relevant brazing parameters, namely, brazing temperature, sample heat up time, sample holding time under the specified brazing temperature and the time spent by the braze in the molten state. Scanning electron microscopy was carried out to investigate microstructural changes in the brazed joint at different brazing parameters. Optical light microscopy was used to acquire information about the layer thickness, microstructure evolution and porosity. Hardness of the individual brazed layers was assessed using Vickers Micro-hardness for different brazing parameters. EDX-SEM elemental mapping was carried out to ascertain the chemical compositional variations at the contact-carrier interface resulting from different brazing parameters. This data can be re-used for brazing experiments to ascertain the correct brazing parameters for effective brazing without the inclusion of porosity, determine the brazing parameters to monitor the increase in pore size and volume, ensure the formation of the Cu-Ag-P eutectic phase to encourage a decrease in the Phosphorus content in the joint zone, determine the temperature range for dissolution of the brittle Cu(III)P phase, and automate the brazing process by using a pyrometer to determine the brazing joint temperature.

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To investigate the influence of brazing temperature and brazing time on the formation of brazing zones, different experiments were carried out. The parameters for data collection are as follows: - Correct emissivity determination for pyrometer. - Braze joint temperature(s) monitoring and temperature generation - Variations in brazing temperature(s) and brazing time(s) to investigate chemical compositional gradients in the joint zone, pore distribution and morphology in the joint zones, layer micro-hardness, grain size and morphology. The brazing setup includes the following hardware: 1. Temperature of the inductive heating setup was generated, monitored, and controlled with EFD Induction HFP 12 with maximum power output 12kW, 100-450 kHz frequency, 17.5 kVA connected load, 12kW clamping frequency. 2. Infratherm Pyrometer IGA 140; measuring range: 300C-1300C; emissivity: 10%-100%; spectral range 1.45µm-1.8µm; measuring distance: 190mm-420mm; IR detector: Indium Gallium Arsenide (InGaAs) Photodiode. 3. Impac IGA 140 Series Cr Ni -Ni Thermocouple (DIN EN 60 584-1); length: 500 mm; measuring range: 200C to 1372C. 4. Pico-logger 6 (data logging software) for thermocouple and pyrometer. 5. Proprietary software, for controlling the application of brazing temperature and brazing time, from EFD Induction. The characterizations of the brazed samples (micro-hardness, microstructural investigations, scanning electron microscopy imaging, optical microscopy imaging, chemical compositional gradient determination) were carried out using the following hardware: - JOEL JFC-1200 Gold-Sputter-Coater for sample preparation for SEM investigations, - Compositional gradients at the brazed joints, for different brazing temperatures and brazing times, acquired through JOEL JSM6010LV SEM, - Layer micro-hardness, for different brazing temperatures and brazing times, acquired through Walter Uhl Technische Mikroskopie GmbH & Co. KG-VMH-002V Leica-Vickers micro-hardness tester, - Microstructural investigations, including pore distribution & morphology and layer thickness (at different brazing parameters) were acquired through using Zeiss Axioplan 2 Light Microscope; HAL 100; HBO 50 and Imagic MS software.