Zirconium is used inside nuclear reactors as fuel cladding. The in-reactor performance of zirconium alloys is strongly influenced by the properties that develop during thermo-mechanical processing, such as the microstructure and crystallographic texture. Optimising the combination of properties would enable improved reactor efficiency, longer component lifetimes and reductions in nuclear waste. Achieving the desired texture and microstructure requires a mechanistic understanding of the processes that govern them: deformation and recrystallisation. These mechanisms are influenced by numerous variables including temperature, strain-rate, and the initial state of the material. This work aims to clarify how texture develops as a result of the active deformation mechanisms of slip and twinning and how these mechanisms are influenced by temperature. The alloy chosen for this is Zircaloy-4.This work has shown that texture evolution varies with deformation temperature. The activation of {10-12}<10-11> tensile twinning dramatically alters the texture up to at least 300°C. In the absence of much twinning at 500°C prismatic slip appears to govern the texture evolution up to moderately high strain. Prismatic slip is generally considered the easiest slip system in zirconium. This work highlights its distinct effect upon both texture and microstructure evolution. In particular the extent of grain fragmentation by prismatic slip is shown to depend upon the initial grain orientation. As a result the break-up of the microstructure takes place heterogeneously. This then has implications for the microstructure and texture development during subsequent recrystallisation treatments. Experimental data indicates that the slip anisotropy between <c+a> and prismatic <a> slip increases with temperature. Crystal Plasticity simulations suggest that the variation of both the twin variant selection and the grain fragmentation with temperature are consistent with increasing slip anisotropy, in contrast to previous experimental and modelling studies on high purity zirconium alloys. The character of {10-12}<10-11> tensile twins and the texture change they induce is influenced by temperature, strain path and weakly influenced by the neighbouring orientations. Increasing temperature causes twin fraction variation, thicker twins and an increased frequency of less favourable twin variants. Plane strain compression also causes less favourable variants to activate more often. Looking at the twinned orientations highlights the importance of grain orientation. Poorly orientated grains do still twin. This work shows that in these instances neighbouring interactions can play a role. In summary, this work contributes to the current understanding of deformation in hexagonal close packed metals. It is hoped that this aids the development of improved physically based crystal plasticity models.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:626893 |
| Date | January 2014 |
| Creators | Honniball, Peter Daniel |
| Contributors | Quinta Da fonseca, Joao |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/the-influence-of-temperature-upon-the-deformation-of-alpha-zirconium(ea5d6180-0730-492f-89ab-04c6938398f1).html |
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