Design of wrought nickel-base alloys for advanced high-temperature gas-cooled reactor applications

The utilization of the high-temperature gas-cooled reactor (HTGR) for advanced or process heat applications will require the use of wrought components operating at temperatures up to 10000C (18320F) for times approaching 30 yr. Alloys for such components must withstand the corrosive effects (carburization and oxidation) of the impure helium primary coolant environment and maintain adequate elevated temperature strength. Commercially available wrought alloys have been found to be seriously limited for such applications because of their inherently poor resistance to corrosion in impure helium. As one approach to the solution of this problem, a program has been initiated to develop wrought alloys having a better combination of corrosion resistance and high-temperature strength, under advanced HTGR conditions, than commercial alloys currently available. This program culminated in 1980 with the design, melting, and fabrication of ten experimental Ni-Cr-Mo-W-Al-Ti-Zr-C alloys and with the initiation of efforts to evaluate their corrosion and mechanical behavior. Results of tests showed that all the experimental alloys exhibited superior carburization resistance in advanced reactor helium. In addition, several of the alloys exhibited excellent mechanical properties, including, in the case of one alloy, creep rupture strength at 9000C (16520F), significantly better than that of the commercial alloy Inconel-617