The capture efficiency of coated voids
Abstract
Segregation of impurities and alloying elements to voids produces a shell of different composition which significantly affects the mechanical interaction with point defects. This interaction determines the capture efficiency for interstitials and vacancies, and contains several contributions. Two contributions, namely the change of the relaxation energy of the point defect, and the interaction with coherency strains, have not previously been considered. The former arises when composition affects the local shear modulus, and the latter, when it causes a change in lattice parameter. Both contributions are added to two considered in previous works, the image interaction and the stress-induced interaction. The total mechanical interaction is evaluated for voids coated with a shell of material with properties different from those of the matrix, and an expression is derived for the capture efficiency. It is found that shells with a shear modulus only a few per cent larger than in the matrix make voids strongly biased against interstitials. This strong effect is due mainly to the change in relaxation energy rather than to the image interaction. Therefore, shells with diffuse or sharp interfaces are equally effective. However, shells with lower shear modulus are ineffective unless they possess a larger lattice parameter.
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From suppressed void growth to significant void swelling in NiCoFeCr complex concentrated solid-solution alloy
2020, MaterialiaCitation Excerpt :But segregation around voids may also lead to additional effects in point defects-void interactions. For example, the capture efficiency of voids changes due to changed mechanical interaction between point defects and voids [46,47]. So while tuning the chemical complexity to suppress swelling, various mechanisms should be considered.
Void swelling can result in dimensional instability and undermine the safe operation of nuclear reactors. Current strategies to inhibit void swelling mainly focus on enhancing defect absorption and recombination by introducing high-density defect sinks. Complex concentrated solid-solution alloys (CSAs), including high-entropy alloys, can withstand severe radiation damage due to their inherent chemical complexity without interfaces. However, the underlying mechanisms for void suppression in CSAs are far from clear. In this research, we studied the void evolution with respect to irradiation depths, doses, and temperatures in equiatomic NiCoFeCr under 3 MeV Ni ion irradiations. At relatively low doses (16 and 54 displacements per atom, dpa), voids form mainly outside of the ion-damaged region, and void formation in the peak damage region is suppressed, leading to negligible swelling. However, with further increase of dose (86 up to 250 dpa), significant void growth occurs in the peak damage region and extended dislocation lines dominate instead of short dislocation lines and loops formed at lower doses. From 500 to 700 °C, the dislocation density decreases while dislocations grow. Although the overall void swelling increases dramatically from 500 to 580 °C at 54 dpa, void growth in the peak damage region is still suppressed. The transition from suppressed void growth to significant void swelling is attributed to dislocation evolution and local chemical inhomogeneity (enrichment of Fe/Cr in the matrix) at higher doses. Our study shows that controlling element diffusion and defect evolution through tuning chemical complexity can further enhance the swelling resistance of CSAs.
Chemically-biased diffusion and segregation impede void growth in irradiated Ni-Fe alloys
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