Preliminary results of the Inconel 617 Optimization Program. Advanced Gas Cooled Reactor Materials Program

This report describes the progress in the Advanced Gas Cooled Reactor Materials program to improve the thermal stability of Inconel 617, a top candidate alloy for a Nuclear Process Heat (NPH) steam reformer. The effect of exposures at the temperatures expected for the NPH steam reformer on the room temperature toughness (impact energy and tensile ductility) and tensile strength are presented. Changes in the microstructures of the exposed specimens and the relationship between microstructural and mechanical property changes are discussed. In addition, details of the microstructural changes that are necessary for understanding the mechanisms of the thermal instability for this alloy also are included. Methods of improving the thermal stability of Inconel 617 are suggested based on the detailed microstructural changes that occur due to elevated temperature exposures. A heat treatment method for improvement of thermal stability, which has given some very encouraging preliminary results, is presented