Multispecimen Fatigue Crack Propagation Testing

Chains of miniature center-cracked-tension specimens were tested on a conventional testing machine and on a prototypic in-reactor fatigue machine as part of the fusion reactor materials alloy development program. Annealed and 20 percent cold-worked 316 stainless steel specimens were cycled under various conditions of temperature, frequency, stress ratio and chain length. Crack growth rates determined from multispecimen visual measurements and from an electrical potential technique were consistent with those obtained by conventional test methods. Results demonstrate that multispecimen chain testing is a valid method of obtaining fatigue crack propagation information for alloy development.

High Resolution Sem Fractography of Te-Embrittled Hastelloy-N

Hastelloy-N (16%Mo-7%Cr-4%Fe-0.55%Mn-0.06%C-bal Ni) has long been a leading candidate material for a molten salt reactor. However, it was recently discovered that small amounts of Te, created by the fission process, caused grain boundary embrittlement in the structural material. Consequently, an alloy development program at this laboratory has directed considerable efforts towards modification of Hastelloy-N to improve its resistance to Te embrittlement and still retain excellent resistance to radiation damage. In this investigation, a JEOL 100C TEM with an energy dispersive x-ray spectrometer (EDX) and high resolution (50 Å) SEM attachments have been used to characterize the grain boundary surfaces of various Hastelloy-N alloys embrittled by Te.Samples of Hastelloy-N were exposed to the tellurium source, Cr3Te4, in a molten salt (LiF + BeF2 + ThF4) or to the vapor above Cr3Te4 in a closed quartz system. All corrosion tests were at 700°C. The samples were subsequently tensile tested to failure at room temperature.