Abstract
The automotive Stirling engine, being developed by the United States Department of Energy and NASA, uses highpressure hydrogen as the working fluid. The longterm effects of hydrogen at high temperature on the properties of alloys are relatively unknown. The most critical component in the engine is the heater head, which consists of the cylinders, tubings, and regenerator housing. Candidate alloys for these parts must meet the property requirements and be of low cost for automotive application. Wrought alloys for tubing and cast alloys for cylinders and regenerator housings were tested in air and 15 MPa hydrogen at 650° to 925 °C. This paper evaluates the results for wrought alloy 19-9DL and cast alloy CRM-6D. Six specimens were evaluated in creeprupture simultaneously at 15 MPa H2 under constant initial stress conditions, and creep extensions were monitored with transducers placed internally. Air and H2 data were analyzed using the Orowan-Sherby-Dorn relationship. In both 19-9DL and CRM-6D, H2 did not significantly affect the stress level of 3500- hour rupture life, and the design limits of 28 MPa at 870 °C for 19-9DL tube alloy and 119 MPa at 775 °C for CRM-6D cast housing alloys were met. However, H2 had a deleterious effect on ductility in both alloys, and alloy development is under way.
Published Version
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