Materials technology assessment for a 1050 K Stirling Space Engine design

MATERIALS TECHNOLOGY ASSESSMENT FOR A 1050 K STIRLING SPACE ENGINE DESIGNCoulson M. Scheuermann, Robert L. Oreshfield, Darrell J. Gaydosh,James D. Kiser, Rebecca A. MacKay, David L. McDanels,Donald N. Petrasek, Raym_)nd D. Vannucci,Kenneth J. Bowles, and Cordon K. NatsonNational Aeronautics and SF:ace AdministrationLewis Research CenterCleveland, Ohio 44135SUMMARYAn assessment of materials technology _nd proposed materials selectionwas made for the 1050 K (superalloy) Stirli_Ig Space Engine design. The objec-tives of this assessment were to evaluate p-'eviously proposed materials selec-tions, evaluate the current state-of-the-art materials, propose potentialalternate materials selections and identify research and development effortsneeded to provide materials that can meet the stringent system requirements.This assessment generally reaffirmed the choices made by the contractor_ how-ever, in many cases alternative choices were described and suggestions forneeded materials and fabrication research and development were made.INTRODUCTIONThe Stirling engine is under development for a feasibility demonstrationof its potential use as a space auxiliary F_ower source (ref. I). This engineoffers several potential advantages: high system efficiency, low specificweight, low vibration amplitude, and long life (ref. 2).Sunpower, Inc., of Athens, Ohio, was _warded a contract in May 1984 todesign a Stirling engine for space applicaiions. The contract was modified inJanuary 1986 to include an engine design u_ing superalloys and having a designoperating temperature of 1050 K over a system life of 60 000 hr. The materi-als selections for this superalloy design (i_re the subject of this assessment.Materials selections for various portions of the engine were recommended bythe contractor (ref. 3). A team of materi,_Is specialists from the NASA LewisResearch Center Materials Division was assembled to assess the proposed materi-a}s selections and the state-of-the art materials technology, to propose poten-tial alternate selections and to identify J-esearch and development effortsneeded to provide materials that could meet the stringent system requirements.This report documents the findings of that team of specialists.THE PROPOSED IOEO K DESIGNA cutaway drawing of the Stirling Space Engine (SSE) 1050 K superalloydesign is shown in figure I. The engine receives energy through an assembly ofsodium (Na) heat pipes from a nuclear heat source. A similar engine designcould be coupled with a solar receiver and concentrator, if desired. The heatfrom the condensing Na passes through the heat pipe walls and heats the helium(He) working fluid. The regenerator is used to store most of the heat from theHe working fluid as it passes from the hot side to the cold side. It returns