NSUF 17-1065: Fundamental Study of Alloying Complexity Effects on the Irradiation Process in High Entropy Alloys
High entropy alloys (HEAs) have attracted wide attention for its potential applications in nuclear energy. Containing multicomponents in roughly equimolar ratios, HEAs exhibit unique properties such as high configurational entropy, lattice distortion and sluggish diffusion. These properties have been suggested to make HEAs radiation resistant. Especially, the sluggish diffusion in HEAs was considered as the main mechanism that leads to their lower void swelling as compared with conventional austenitic stainless steels (SS).
In addition, the sluggish diffusion and lattice distortion of HEAs were suggested to suppress the evolution of irradiation-induced dislocation loops by retarding the growth of dislocation loops and by providing abundant recombination sites. Recent work on CrMnFeNi irradiated with Ni ions at 400-700°C to 10 dpa observed significantly smaller dislocation loops (5 nm), as compared with 30-100 nm in 316 SS under equivalent irradiation conditions, which is in support of the above postulate.
However, our ion irradiation experiment showed an opposite result as is described as follows. CoCrMnFeNi, Al0.3CoCrFeNi and 316 SS were irradiated with 1 MeV Kr at 500°C to 1 dpa. Both HEAs had larger dislocation loops (17-25 nm) than 316 SS (10 nm). The contradicting results indicate that the irradiation process in HEAs is still not well understood, and further investigation is needed.
This proposal aims to solve the puzzle of the contradicting observations on the loop size in HEAs and in 316 SS as mentioned above. Ni, NiCo and NiCoCr will be irradiated with 1 MeV Kr at 300°C, 500°C, and 700°C. The density and size of the irradiation-induced dislocation loops will be analyzed, and their dependence on the alloying elements will be studied. In hypothesis, with increasing numbers of alloying elements, the diffusivity decreases, and the size of irradiation-induced dislocation loops should decrease as well. If the above statement is successfully observed in the proposed IVEM experiments, the current conception about the correlation between alloying complexity with the diffusivity and the defect clustering in HEAs is still correct. However, meanwhile, the general belief that the diffusion is more sluggish in HEAs than in 316 SS needs to be re-evaluated.
On the other hand, if opposite trend was observed (i.e. increasing loop size with increasing number of alloying elements), it indicates either that the conception of the sluggish diffusion and the formation of dislocation loops in HEAs should be re-examined, or that there were other factors (e.g. sink density) dominating the process. For the latter, the in-situ observation of IVEM provides useful information about how defect clusters interact with defect sinks such as pre-existing dislocations and grain boundaries in real time.
This proposed work needs nine days to finish the proposed experimental conditions. The materials will be ready for IVEM experiments as soon as the schedule permits after August. This work will enhance the understanding fundamentally on the effect of alloying complexity on the formation of dislocation loops in HEAs, and will provide information for evaluating the potential of HEAs for nuclear applications.
Additional Info
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|---|---|
| Abstract | High entropy alloys (HEAs) have attracted wide attention for its potential applications in nuclear energy. Containing multicomponents in roughly equimolar ratios, HEAs exhibit unique properties such as high configurational entropy, lattice distortion and sluggish diffusion. These properties have been suggested to make HEAs radiation resistant. Especially, the sluggish diffusion in HEAs was considered as the main mechanism that leads to their lower void swelling as compared with conventional austenitic stainless steels (SS). In addition, the sluggish diffusion and lattice distortion of HEAs were suggested to suppress the evolution of irradiation-induced dislocation loops by retarding the growth of dislocation loops and by providing abundant recombination sites. Recent work on CrMnFeNi irradiated with Ni ions at 400-700°C to 10 dpa observed significantly smaller dislocation loops (5 nm), as compared with 30-100 nm in 316 SS under equivalent irradiation conditions, which is in support of the above postulate. However, our ion irradiation experiment showed an opposite result as is described as follows. CoCrMnFeNi, Al0.3CoCrFeNi and 316 SS were irradiated with 1 MeV Kr at 500°C to 1 dpa. Both HEAs had larger dislocation loops (17-25 nm) than 316 SS (10 nm). The contradicting results indicate that the irradiation process in HEAs is still not well understood, and further investigation is needed. This proposal aims to solve the puzzle of the contradicting observations on the loop size in HEAs and in 316 SS as mentioned above. Ni, NiCo and NiCoCr will be irradiated with 1 MeV Kr at 300°C, 500°C, and 700°C. The density and size of the irradiation-induced dislocation loops will be analyzed, and their dependence on the alloying elements will be studied. In hypothesis, with increasing numbers of alloying elements, the diffusivity decreases, and the size of irradiation-induced dislocation loops should decrease as well. If the above statement is successfully observed in the proposed IVEM experiments, the current conception about the correlation between alloying complexity with the diffusivity and the defect clustering in HEAs is still correct. However, meanwhile, the general belief that the diffusion is more sluggish in HEAs than in 316 SS needs to be re-evaluated. On the other hand, if opposite trend was observed (i.e. increasing loop size with increasing number of alloying elements), it indicates either that the conception of the sluggish diffusion and the formation of dislocation loops in HEAs should be re-examined, or that there were other factors (e.g. sink density) dominating the process. For the latter, the in-situ observation of IVEM provides useful information about how defect clusters interact with defect sinks such as pre-existing dislocations and grain boundaries in real time. This proposed work needs nine days to finish the proposed experimental conditions. The materials will be ready for IVEM experiments as soon as the schedule permits after August. This work will enhance the understanding fundamentally on the effect of alloying complexity on the formation of dislocation loops in HEAs, and will provide information for evaluating the potential of HEAs for nuclear applications. |
| Award Announced Date | 2017-09-20T12:37:23.117 |
| Awarded Institution | University of Michigan |
| Facility | Michigan Ion Beam Laboratory |
| Facility Tech Lead | Kevin Field, Wei-Ying Chen |
| Irradiation Facility | None |
| PI | WEIYING CHEN |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 1065 |