Characterizing Quenched Microstructures in Relation to Processing

摘要

Quenching from the β phase occurs at several steps during the processing of zirconium alloy cladding or flat products, from the ingot melting to the final quench on some channel material, along with quenching after log forging. The quenched microstructure is constituted of needles or platelets arranged in parallel plates or basket-weave microstructures, in Burgers relationships with the former β phase. Thanks to polarized micrographs or orientation imaging microscopy, a quantification of the platelet or basket-weave character is derived, based on the boundary length, normalized by the mean needle size. The number and fraction of variant orientations in a former β grain is also measured. A thermal model has been derived to compute the quenching rate in Zircaloy, taking into account not only the fact that there is an exothermic phase transformation, but also its dependence on temperature versus the quenching rate itself.