High-Temperature Properties of Heat Resisting Alloys in Impure Helium

A discussion has been made on the effect of HTGR*)-simulated He environment on high-temperature properties of heat resisting alloys. HTGR*)-He has low oxygen potential, and selective oxidation and internal oxidation along grain-boundaries of some alloying elements (such as Al and Ti) are observed during exposure to the environment depending on the partial pressure ratio of PH2/PH2O and temperature. Carburization or decarburization of the alloys also occurs according to the relation between carbon activity of gas and that of alloy. The decarburization results in the large decrease of creep rupture strength, and the carburization decreases the tensile elongation of the alloys. *)HTGR:High temperature gas cooled reactor.