Influence of mercury environment on the fatigue behavior of spallation neutron source (SNS) target container materials

The high-cycle fatigue behavior of 316 LN stainless steel (SS), the prime candidate target-container material for the spallation neutron source (SNS), was investigated in air and mercury at frequencies from 10 to 700 Hz with a R ratio of 0.1. A decrease in the fatigue life of 316 LN SS in air was observed with increasing frequency. However, little influence of frequency on fatigue life was found in mercury. An increase in the specimen temperature at 700 Hz seems to be the main factor that contributed to the decrease of the fatigue life in air, relative to that at 10 Hz. However, because of the cooling effect of mercury, only a small temperature increase was found at 700 Hz, and, therefore, there was little frequency influence in mercury. At 10 Hz, a shorter fatigue life of 316 LN SS was measured in mercury than in air at stresses greater than yield strength, which may have resulted from liquid metal embrittlement (LME). At lower stresses, no difference in fatigue lives between mercury and air was detected at 10 Hz. At 700 Hz, the fatigue life in mercury was longer than in air. The fatigue endurance limit measured at both frequencies in mercury and in air was approx. 350 MPa.