MICROSTRUCTURAL INVESTIGATION OF THE EFFECTS OF OXYGEN EXPOSURE ON NARLOY-Z

NARloy-Z is a Cu-base alloy used to fabricate the liner of the main co mbustion chamber (MCC) for the space shuttle main engine (SSME). This study was undertaken to assess the effects of unusual or transient con ditions (i.e., high temperature and exposure to high levels of oxygen) on the robustness of the MCC design, providing a data base to better quantify environmental conditions. The results indicated that, upon ex posure to severe environmental conditions, wrought NARloy-Z develops e xtensive microstructural variations which will reduce the service life of an MCC. Oxygen diffusion into the material closely followed predic tions based on theoretical considerations. Above 760 degrees C, the pr esence of oxygen dissociates Cu/AgZr) intermetallics, forms ZrO2, and embrittles the alloy. Above 593 degrees C, Ag precipitates coarsen in the matrix, becoming incoherent and degrading material strength.