| 摘要: | 研究期間：10108~10207;Various types of fuel cells are now being intensely developed around the world because they give higher energy conversion efficiencies, generate less pollutant emissions, and can serve as distributed electricity sources. The solid oxide fuel cell (SOFC) operates at a high-temperature range of 650 to 1000oC in a direct conversion process such that they have the highest efficiencies of all fuel cells. As planar SOFC systems have several advantages over tubular ones such as simple structural geometry, lower fabrication cost, higher energy efficiency, and lower operating temperature (below 800oC), most of the current research on SOFC is being focused on the planar type. A typical unit cell in a planar SOFC stack is composed of a ceramic anode-electrolyte-cathode assembly, a porous nickel mesh, two end bipolar interconnect plates, and gas seals. In practical applications of SOFC, multiple cells are assembled to form a stack and make a serial connection in the electric loop to generate a high voltage and power. The high-temperature operation, however, gives rise to significant thermal stresses due to mismatch of coefficient of thermal expansion between components and temperature gradients in the SOFC stack. Such thermal stresses can cause significant deformation and damages in the components and degrade the structural integrity and electrochemical performance of SOFC stacks under long-term operation. In particular, creep and thermo-mechanical fatigue could take place in the metallic interconnect plates leading to unpredictable, considerable deformation and rupture. Therefore, a comprehensive analysis of creep and thermo-mechanical fatigue properties for the SOFC interconnects is necessary for a success in design and operation of an SOFC system. The aim of this proposed three-year study is to systematically characterize the high-temperature tensile strength, creep, stress relaxation, and thermo-mechanical fatigue properties of Crofer 22 ferritic stainless steels for use in SOFC applications and to develop applicable life assessment models. In the first year, it is proposed to investigate the effects of environmental temperature on the tensile and creep properties of Crofer 22 APU and Crofer 22 H ferritic stainless steels. In the second year, stress relaxation tests will be conducted to investigate the effects of environmental temperature on the high-temperature viscous behavior of the given two stainless steels. It is also intended to develop suitable creep life assessment models for the given steels used in SOFC interconnects. In the third year, out-of-phase thermo-mechanical fatigue tests as well as thermo-mechanical fatigue-creep interaction tests will be conducted to study the long-term structural durability of the given two Crofer 22 stainless steels under SOFC operating conditions. In addition, based on the creep and thermo-mechanical fatigue testing results, it is intended to develop a mechanical life assessment model suitable for metallic interconnects used in planar SOFC stacks. Comprehensive comparisons between the given two Crofer 22 stainless steels will be made on the tensile strength, creep resistance, stress relaxation phenomenon, and thermo-mechanical fatigue damage so as to characterize the influence of addition of refractory elements and associated microstructure. |
