Damage tolerance of nuclear graphite at elevated temperatures.
Damage tolerance of nuclear graphite at elevated temperatures.
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DOI：
10.1038/ncomms15942
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发表时间：
2017-06-30
影响因子：
16.6
通讯作者：
Ritchie RO
中科院分区：
文献类型：
--
作者：
Liu D;Gludovatz B;Barnard HS;Kuball M;Ritchie RO
核级石墨是世界范围内当前和潜在的下一代裂变反应堆的一种至关重要的高温结构材料。必须了解其损伤容限行为，并弄清其在服役条件下的损伤演化机制。在这里，我们使用同步辐射X射线计算机显微断层扫描技术，在环境温度到1,000 °C之间的环境温度下，对核级的Gilocarbon石墨进行现场力学测试。我们发现，这种石墨的强度和断裂韧性在高温下都得到了提高。虽然这一行为与观察到的在较高温度下平行于共价sp2键合的石墨烯层形成的微裂纹闭合，从而容纳了垂直于这些层的十倍以上的较大热膨胀，但我们将强度和韧性的提高主要归因于800-1,000 °C下残余应力状态的变化，特别是由于处理后冻结在石墨中的残余拉应力水平的显著降低。核级石墨是裂变反应堆重要的高温结构材料。在这里，作者对核级石墨进行了同时的X射线断层扫描和机械测试，发现在高温下强度和韧性同时提高，这主要归因于减少了制成材料中的残余拉应力。
Nuclear-grade graphite is a critically important high-temperature structural material for current and potentially next generation of fission reactors worldwide. It is imperative to understand its damage-tolerant behaviour and to discern the mechanisms of damage evolution under in-service conditions. Here we perform in situ mechanical testing with synchrotron X-ray computed micro-tomography at temperatures between ambient and 1,000 °C on a nuclear-grade Gilsocarbon graphite. We find that both the strength and fracture toughness of this graphite are improved at elevated temperature. Whereas this behaviour is consistent with observations of the closure of microcracks formed parallel to the covalent-sp2-bonded graphene layers at higher temperatures, which accommodate the more than tenfold larger thermal expansion perpendicular to these layers, we attribute the elevation in strength and toughness primarily to changes in the residual stress state at 800–1,000 °C, specifically to the reduction in significant levels of residual tensile stresses in the graphite that are ‘frozen-in’ following processing. Nuclear-grade graphite is an important high-temperature structural material for fission reactors. Here, the authors perform simultaneous X-ray tomography and mechanical testing on a nuclear-grade graphite, finding simultaneous improvement of strength and toughness at elevated temperatures which they attribute primarily to reduction of residual tensile stresses in the as-made material.