Development of iron-base long-range ordered (LRO) alloys for fusion reactor first wall and blanket applications

Iron-base LRO alloys with base compositions (Fe,Ni)3V are being developed for fusion reactor applications. The base alloys are modified with <1% Ti for further improvement in metallurgical and mechanical properties. The phase relationships in the LRO alloys depend strongly on the nickel concentration in the range of 31 to 40%. The sigma phase field existing in the low nickel alloys at temperatures above their critical ordering temperature (T/sub c/), can be eliminated by increasing nickel content to 40%. Tensile tests as a function of temperature indicate that the LRO alloys have superior high-temperature strength. Unlike conventional alloys, the yield strength of the LRO alloys increases with temperature and reaches a maximum around T/sub c/. As a result, the LRO alloys are much stronger than commercial alloys such as type 316 stainless steel. Titanium additions improve the ductility of the LRO alloys at elevated temperatures. The alloys show excellent creep resistance and structural stability. Long term aging at 5500C does not cause any significant change in tensile properties. The alloys exhibit a sharp decrease in creep rate at T/sub c/. The formation of long-range order lowers the creep rate by more than two orders of magnitude