CREEP-RUPTURE PERFORMANCE OF SUPERALLOYS IN HIGH-PRESSURE HYDROGEN ENVIRONMENT

Abstract

Significant progress has been achieved in the development of an automotive engine that is over 50% more efficient than the current internal combustion engine. The automotive Stirling engine uses high-pressure hydrogen as the working fluid and is being developed jointly by the United States Department of Energy and NASA, Its advantages include the potential for high fuel efficiency, multiple fuel capability, low pollution, and low noise. To achieve these operating characteristics, the Stirling engine will operate near 870°C and use 15 MPa hydrogen as the working fluid. The severe service conditions require that the critical components of the engine–namely, the heater head consisting of cylinders, tubings, and regenerator housing–be made of superalloys, preferably the economical iron-base type. Ten such alloys were evaluated in air and 15 MPa hydrogen: six tube alloys (A-286, 800H, N-155, 19–9DL, CG-27, and 12RN72) and four cast alloys (CRM-6D, XF-818, SA-F11, and HS-31). Several alloys were found suitable for application. Stress-rupture life and minimum creep rates were not affected in hydrogen; however, rupture ductility was adversely affected in both cast and tube alloys.