Abstract
This study is aimed at identifying the change of residual stresses in suspension plasma sprayed (SPS) 8 mol% YSZ electrolytes on top of porous stainless steel substrate with varying processing parameters and temperatures. The residual stresses in the electrolyte layer are tensile with a value of approximately 90 MPa at room temperature. Porosity, microcracks and segmentation cracks are observed to form in the coating during post-deposition cooling. The decrease of residual stresses with increasing temperature is related to the changes in the Young’s modulus, thermal expansion mismatch, micro-defects and possible creeping of porous stainless steel substrate. The coating fabricated using a torch power of 133 kW and stand-off distance of 90 mm exhibits the highest residual stress due to the formation of a denser microstructure and less cracking. Furthermore, the fracture toughness and interface fracture toughness of the SPS YSZ coating at the optimized condition was determined and discussed.
Highlights
Thermal mismatch stress or secondary stress is caused by the difference in the thermal expansion coefficients between the coating and substrate, which leads to residual stresses induced by the mismatch of thermal shrinkage during cooling from the process temperature to room temperature, during the so-called secondary cooling
This work has addressed the need for understanding material microstructure, residual stress and properties in the development of metal-supported SOFCs
Much of the focus of this work was on characterizing the residual stresses of suspension plasma sprayed YSZ electrolyte for metalsupported SOFCs
Summary
Today fuel cells are frequently reported in the news since they appear to be one of the most efficient and effective solutions to environmental problems that we face. Total world energy demand is projected to increase by 50% [1]. With their ability to operate on a range of fuels [2,3], Solid Oxide Fuel Cells (SOFCs) present a unique opportunity to meet this demand in an environmentally responsible manner since they can increase the efficiency of the existing hydrocarbon-based infrastructure (with conversion efficiencies greater than 70% when utilized with co-generation) [3]. Extensive efforts to develop safe and reliable SOFCs for power generation and transportation applications are motivated by the pressing need for improved fuel efficiency, reduced anthropogenic greenhouse-gas emissions (GHG), and enhanced energy security [4-8]. The remainder of this chapter establishes the motivation and framework for metal-supported SOFCs and the need for enhanced understanding of stress and microstructure of YSZ electrolyte material, followed by an overview
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