A method of using the electric charge in a capacitor was applied for the manufacture of thermocouple micro-joints. The motivation for the study was the need to produce a stable welded connection without affecting the geometry of the substrate, which was a thin sheet of Inconel 625 alloy (UNS designation N06625). Within the framework of the research work, a suitable workstation for micro-joints elaboration was built and welding experiments were performed using different electric charges. Studies carried out within the framework of the present work have shown that joints based on Inconel 625 alloy and platinum have the best application properties in the range of small-scale temperature measurements. They can be used, e.g., for monitoring the temperature distribution on the inner surfaces of electric motor casings. An undeniable advantage is in this case the high thermal resistance of both materials used to produce the joint, i.e. the Inconel 625 alloy and platinum. This allows them to be used at high temperatures under atmospheric conditions.
The presented work describes issue of magnetic mixing and segregation of metals during the formation of micro-joints using the capacitor welding method. The key aspect is the very short weld time, which is below 2 ms. The Pt/Inconel 625 micro-joints have been tested in the work. The 100-μm platinum wire was welded to Inconel 625 with the same thickness. During the welding process, the capacitor discharge characteristics were recorded with the oscilloscope. This allowed for a mathematical description of phenomena occurring during the creation of the micro-joint. Observations of the micro-structures from the scanning electron microscope in BSE mode confirmed the strong micro-segregation of the joint components. In addition, the effect of magnetic mixing of the joint components was observed. Weld geometry results obtained from the calculations showed good compliance with the real joint micro-structure observation data.
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