Rapid solidification processing of iron-base alloys for structural applications

The response of iron-base alloys to rapid solidification is reviewed with an emphasis on the effects of processing on the microstructure and mechanical property behavior. The processing topics addressed are powder atomization, powder consolidation, joining, and thermal-mechanical exposure. The value of rapid solidification processing (RSP) lies in the ability to promote compositional homogeneity and retention of fine and stable (to high temperatures) microstructures. Achieving the maximum benefit from RSP requires proper application of the basic principles of composition control and rapid crystallization. This investigation has disclosed two very important facets of the RSP approach that can be applied using current technologies. Dissociated oxygen appears to play a significant role in stabilizing microstructural features. In conjunction with oxygen, vacancies trapped during crystallization provide a very stable matrix dispersion for enhanced strengthening. With a fundamental understanding of the response of iron-base alloys to RSP, alloys can be designed that will have substantially better properties and performance than their conventionally processed counterparts. 77 refs., 94 figs., 14 tabs

Evaluation of ex-reactor loading event on high-fluence EBR-II control-rod thimble 5E3

A Type 304 stainless steel EBR-II control-rod thimble (CRT 5E3) with high fluence was damaged while undergoing dimensional evaluation. The damage, which occurred when the thimble was inadvertently loaded in a bending mode, consisted of rather localized but extensive fracture. An elastic stress analysis of the bending mode was done on the thimble, using semimembrane shell theory. The analysis disclosed several important aspects that the simpler and more commonly employed techniques do not disclose. The hoop stress was found to be the most probable to initiate failure in that crack initiation would most likely result from localized yielding from the hoop stress. Structural assessment of the failure with the aid of scanning electron, transmission electron, and optical microscopy qualitatively supported the stress analysis in that the failure was associated with localized yielding and was accompanied by some, but limited, ductility. There was no evidence that a premature failure occurred (e.g., a failure at stresses below the yield stress of the material and which might be associated with grain-boundary embrittlement). (auth