Collaborating with the UK Atomic Energy Authority (UKAEA), the National Physical Laboratory, and TESCAN, the team deployed a high-resolution imaging technique to map residual stress within laser-welded joints made of P91 steel-a material known for its strength and heat resistance. Using plasma focused ion beam and digital image correlation (PFIB-DIC), they were able to detect mechanical stress zones previously too small to analyze.
This advanced mapping revealed how internal stress influences material strength. While some stress patterns increased hardness, others created zones of weakness. At reactor-relevant temperatures of 550oC, the welded P91 steel lost more than 30% of its strength and exhibited greater brittleness.
"Fusion energy has huge potential as a source of clean, reliable energy that could help us to reduce carbon emissions, improve energy security and lower energy costs in the face of rising bills," said Dr Tan Sui, Associate Professor in Materials Engineering at Surrey. "Previous studies have looked at material performance at lower temperatures, but we've found a way to test how welded joints behave under real fusion reactor conditions, particularly high heat."
The findings offer a more accurate representation of how reactor components will perform under harsh conditions, providing engineers with critical data for future safety assessments and design choices.
Beyond laboratory applications, the technique developed by the team supports the validation of finite element models and machine learning tools that simulate material behavior. These technologies can guide the design of future fusion systems such as the UK's STEP and the EU's DEMO projects, while also lowering the cost of experimental development.
Dr Bin Zhu, Research Fellow at Surrey's Centre for Engineering Materials, emphasized the broader relevance: "Our work offers a blueprint for assessing the structural integrity of welded joints in fusion reactors and across a wide range of extreme environments. The methodology we developed transforms how we evaluate residual stress and can be applied to many types of metallic joints."
Jiri Dluhos, FIB-SEM Product Manager at TESCAN, added: "We are proud that our FIB-SEM instruments can be part of such a crucial topic in materials research for the energy industry. Our long-standing collaboration with the University of Surrey to automate microscopic residual stress measurements proves that the plasma FIB-SEM can be successfully used for high-precision machining at the microscale."
The research strengthens the pathway to commercial fusion energy by providing tools and insights needed to extend the operational lifespan of reactor components.
Research Report:Assessing residual stress and high-temperature mechanical performance of laser-welded P91 steel for fusion power plant components
Related Links
UK Atomic Energy Authority
Powering The World in the 21st Century at Energy-Daily.com
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