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W foil: Toughness - Identification of the mechanisms of the evolution of the activation energy of the brittle-to-ductile transition caused by cold rolling

W箔：韧性——冷轧引起的脆塑转变活化能演化机制的识别

基本信息

批准号：
274714564
负责人：
Dr.-Ing. Jens Reiser
金额：
--
依托单位：
Institut für Angewandte Materialien - Angewandte Werkstoffphysik (IAM-AWP)
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2015
资助国家：
德国
起止时间：
2014-12-31 至 2017-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/274714564?language=en
关键词：
foil Toughness Identification mechanisms evolution

项目摘要

Up to now, tungsten (W) has only been used as a functional material, as its low fracture toughness at room temperature and its high brittle-to-ductile transition temperature (BDTT) exclude W from being used as a structural material. So here the question of how to make W ductile arises. The approach assessed by the author of this proposal is the synthesis of a W laminate made of W foil. Cold-rolled W foil has extraordinary properties in terms of ductility and toughness. Through the synthesis of a W laminate the author succeeded in transferring the properties of the foil to the bulk. Furthermore, the author produced W laminate pipes that are convincing due to their thermo-mechanical properties and are discussed with a view to being used as structural parts for innovative high-temperature energy conversion systems.Based on the work of the author on W laminate materials, several scientific questions arise. Within the framework of this proposal, the mechanism of the evolution of the activation energy of the brittle-to-ductile transition, HBDT, caused by cold rolling will be identified.Results on the BDT of W single crystals from ROBERTS and GUMBSCH are inconsistent and show no clear scientific model. This discrepancy continues for polycrystalline W materials. Here ROBERTS says that grain boundaries have no influence on the BDT, while simulation results from HARTMAIER show that very fine-grained W materials have a reduced rate dependence and thus an increased HBDT. The reason for this behaviour is the confinement of the plastic zone by grain boundaries. This confinement leads to dislocation pile-ups at the grain boundaries and thus reduced mobility. HARTMAIER now assumes that the HBDT might be a kind of dislocation-grain-boundary interaction energy (activation of slip systems in the neighbouring grains). However, according to this model, the fracture toughness would decrease through grain refinement and the BDTT would increase through grain refinement. But this is in conflict with the experimental results of PIPPAN and the author of this proposal.The aim of the project is to identify the mechanisms of the evolution of the activation energy of the brittle-to-ductile transition through cold rolling and to support the understanding and knowledge of the brittle-to-ductile transition of polycrystalline W. In doing this, the mechanisms are identified both in a direct manner through electron microscopy analyses (EBSD, HR-EBSD, KAM, ECCI, TEM) and in an indirect manner through the determination of the activation energy of the brittle-to-ductile transition. Finally, by comparing the results of the electron microscopy analyses with the evolution of the activation energy of the brittle-to-ductile transition, the conflicts in the models of HARTMAIER, ROBERTS, PIPPAN, as well as the author of this proposal, will be solved and a modified and mechanism-based model of the brittle-to-ductile transition of W will be presented.

迄今为止，钨（W）仅被用作功能材料，因为其室温下的低断裂韧性和高的脆塑转变温度（BDTT）使W无法用作结构材料。那么这里就出现了如何使W具有延展性的问题。该提案的作者评估的方法是合成由钨箔制成的钨层压板。冷轧W箔在延展性和韧性方面具有非凡的性能。通过合成 W 层压板，作者成功地将箔的特性转移到本体上。此外，作者还生产了 W 层压管，其热机械性能令人信服，并对其作为创新高温能量转换系统的结构部件进行了讨论。基于作者在 W 层压材料方面的工作，出现了几个科学问题。在该提案的框架内，将确定冷轧引起的脆性转变HBDT活化能的演化机制。ROBERTS和GUMBSCH关于钨单晶BDT的结果不一致，并且没有显示出明确的科学模型。对于多晶钨材料来说，这种差异仍然存在。 ROBERTS 在此表示，晶界对 BDT 没有影响，而 HARTMAIER 的模拟结果表明，非常细晶粒的 W 材料的速率依赖性降低，因此 HBDT 增加。造成这种现象的原因是晶界对塑性区的限制。这种限制导致位错在晶界处堆积，从而降低了迁移率。 HARTMAIER 现在假设 HBDT 可能是一种位错-晶界相互作用能（相邻晶粒中滑移系统的激活）。然而，根据该模型，断裂韧性会通过晶粒细化而降低，而BDTT会通过晶粒细化而增加。但这与PIPPAN和该提案的作者的实验结果相冲突。该项目的目的是确定冷轧脆性到韧性转变的活化能演化机制，并支持对多晶W脆性到韧性转变的理解和认识。在此过程中，通过电子显微镜分析（EBSD， HR-EBSD、KAM、ECCI、TEM）并通过测定脆性转变的活化能以间接方式进行。最后，通过将电子显微镜分析的结果与脆韧转变活化能的演化进行比较，将解决HARTMAIER、ROBERTS、PIPPAN以及该提案的作者模型中的冲突，并提出一个改进的、基于机制的W脆韧转变模型。