SEDL / STP / STP1049-EB / STP24072S

Effects of Stress and Stress History on the Magnitude of the Environmental Attack in Renè 80

Balsone, SJ
Structural materials engineer and senior scientist, Air Force Wright Aeronautical Laboratories, Materials Laboratory, Wright-Patterson Air Force Base, OH

Nicholas, T
Structural materials engineer and senior scientist, Air Force Wright Aeronautical Laboratories, Materials Laboratory, Wright-Patterson Air Force Base, OH

Khobaib, M
Research engineer, University of Dayton Research Institute, Dayton, OH

Pages: 16    Published: Jan 1990

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Abstract

Sustained-load creep tests using smooth, round bar specimens of Renè 80 were conducted at 900°C (1652°F) in two environments, namely, laboratory air and a 90% Na²SO⁴/10% NaCl molten salt film. Results show approximately a factor-of-two reduction in the rupture life of specimens tested in the molten salt environment. Metallographic examination of the failed specimens showed greater depths of environmental attack in the cross section as stress level increased from 207 to 310 MPa (30 to 45 ksi). Below a “critical” stress level, the depth of environmental attack remains nearly constant. Failure initiated by cracking along oxide-metal interfaces resulting from oxygen penetration and the formation of internal oxide fingers in the substrate material. A periodic unloading/reloading fatigue cycle superimposed on sustained-load creep tests had no effect on rupture lives for specimens tested in laboratory air,and the depth of environmental attack remained constant. However, rupture lives obtained in the molten salt environment were significantly reduced by the periodic fatigue cycle where spallation of the surface oxide layer during cycling was extensive and the depths of hot corrosion attack were greater.