CREEP RUPTURE PROPERTIES OF NICKEL-BASE HEAT RESISTANT ALLOYS IN TWO IMPURE HELIUM ENVIRONMENTS OF HTGR.

To investigate the effect of impure helium environments on creep rupture properties of alloys for intermediate heat exchanger tubes, a test was carried out on four nickel-base superalloys in He-2 and PNP-He at 1 000 degree C. All alloys were decarburized in PNP-He, while some of them were carburized in He-2 during testing. The alloy hardened by gamma prime (Ni//3(Al,Ti)) precipitation, R4286, suffered from environmental effects resulting in the formation of gamma prime depleted zones, Al internal oxides and grain boundary carbide depleted zones beneath the surface. Creep rupture life in PNP-He was one-third of that in He-2. The alloys hardened by alpha -W precipitation, KSN and 113MA, suffered from environmental effects resulting in the formation of alpha -W and grain boundary carbide depleted zones. The creep rupture life of KSN containing the highest concentration of tungsten, 26% W, almost the same in the two environments. Alloy SZ was only slightly decarburized in PNP-He.