EMIR&A – Damian Kalita

Title: Understanding the Influence of Chemical Complexity on Irradiation-Induced Defect Accumulation in Novel Low-Activation W-Ta-Cr-V Concentrated Solid Solution Alloy (CSA)

Abstract: The rapidly increasing global demand for energy consumption requires the development of new advanced nuclear reactor technologies characterized by higher safety, better fuel efficiency, and lower long-term environmental effects. The upcoming fusion systems could meet this needs, but their efficiency will greatly rely on the performance of the structural materials used in their construction. Concentrated solid-solution alloys (CSAs) are recently gaining significant attention in this field. In contrast to the traditional approach, those alloys contain multiple elements (typically 2 – 5) in the equimolar or near-equimolar ratios. The random distribution of different-size atoms in the crystal structure of CSAs creates severe lattice distortions, which macroscopically results in their superior mechanical properties. Interestingly, recent studies have shown that the CSAs exhibit also superior radiation resistance to pure elements or their conventional counterparts. Although underlying mechanisms remain unclear, presumably, it is connected with the high chemical complexity of those materials leading to local structural distortions. At the atomic level, site-to-site chemical disorder, leads to the non-uniform formation and migration energies of defects, rougher local traps, and anisotropic diffusion channels. These affect defects’ evolution by reducing their mobility and increasing their recombination rate. Taking this into consideration, the enhanced irradiation-resistance of the CSAs is most likely related to the increased vacancy-interstitial recombination rate compared to pure metals and conventional alloys. Among the broad family of CSAs, the BCC-structured CSAs containing mainly the refractory metals, exhibit sufficient high-temperature phase stability and creep resistance, making them suitable as structural materials for critical components of fusion reactors, such as divertor or plasma-facing components (PFCs).

With the frame of this proposal, we aim to investigate the formation and accumulation of irradiation defects in three various alloys from the W-Ta-Cr-V system, differing in the number of constituent elements. Pure W will be used as a reference material. To achieve this goal, we propose to conduct in-situ TEM irradiation experiments at the JANNuS-Orsay facility. This will allow for the direct observation of the mechanism of the nucleation and further evolution of the irradiation defects such as dislocation loops and voids, with the increasing damage level. Considering the potential applications of BCC-CSAs which is the PFCs/divertor the ion-irradiation will be performed with the application of the heating holder at the elevated temperature, of about 1000°C. We believe this approach will test the hypothesis that, in the case of CSAs, irradiation behavior is closely related to the material's chemical complexity. It is anticipated that the obtained results will contribute to the fundamental understanding of the performance of these materials and the elementary phenomena occurring in their structure during irradiation.