Environmental effects on properties of structural alloys

Several constant-stress compatibility tests and continuous-cycle fatigue tests have been conducted on HT-9 alloy and Type 304 stainless steel at 755 K in a flowing lithium environment. The results indicate that for applied stresses below the yield stress of the material, the corrosion behavior of HT-9 alloy and Type 304 stainless steel is independent of stress. The fatigue properties of these materials are strongly influenced by the concentration of nitrogen in lithium. For HT-9 alloy, the fatigue life in lithium containing 100 to 200 wppM nitrogen is a factor of 2 to 5 greater than that in lithium with 1000 to 5000 wppM nitrogen. In low-nitrogen lithium, fatigue life is also independent of strain rate. The lower fatigue lives observed in high-nitrogen lithium may be attributed to corrosion. Fatigue tests on lithium-exposed specimens are in progress to investigate the long-term environmental effects