NSUF 16-859: In-situ Observation of Defect Clustering in High Entropy Alloys
The emerging applications of high-entropy alloys (HEAs) have received great attentions from the field of nuclear materials because of its potentially superior radiation resistance. HEAs contain multicomponent (usually five or more) of roughly equimolar ratios. HEAs exhibit excellent strength, corrosion and wear resistance, and softening resistance at high temperatures. For nuclear applications, the severe lattice distortion and the high configuration entropy have been hypothesized to be the mechanisms that could make HEAs more radiation-resistant compared to conventional structural materials.
To evaluate the suitability of HEAs for nuclear applications, a microstructural understanding of irradiation process is necessary. Previous studies with ex-situ ion irradiation showed that HEAs had a great phase stability, a low void swelling, and a slower growth rate of dislocation loops. However, the dynamic information such as defect clustering, coalescence or cluster migration in HEAs under irradiation has not been well studied. In-situ TEM experiments in IVEM can provide this important information to fundamentally understand the difference between HEAs and traditional alloys about the irradiation process on the microstructure. In addition, previous works have been mostly for FCC HEAs, while little is known for the irradiation effects on BCC and duplex (BCC and FCC two phase) HEAs. An effort is apparently needed for these two categories.
This work will perform in-situ ion irradiation experiments in IVEM on three HEAs, CuCoNiCr(Al0.5)Fe, CuCoNiCr(Al1.5)Fe and CuCoNiCr(Al3.0)Fe, which are respectively FCC, FCC+BCC and BCC. 1 MeV Kr ions will be used to introduce irradiation damage at a few relevant irradiation temperatures while the microstructure evolution is observed in-situ with electron microscopy. Dislocation loops will be imaged with weak-beam dark field in order to reveal the small loops with sharp and confined contrast for accurate size measurement. Voids will be imaged with under and over focus. Diffraction pattern will be monitored at each step of irradiation dose to monitor the phase stability under irradiation. This study will generate quantitative data of the defect clusters as a function of irradiation dose and irradiation temperature for these three types of HEAs. The data will be compared with previous irradiation studies on conventional alloys (e.g. 316, G91) to show the potential of HEAs in nuclear applications.
In addition, this study will take advantage of the newly-installed Gatan OneView digital camera to capture high-resolution videos of loop formation process with high frame rate. The technique has successfully shown the involvement of local point-defect diffusion in the loop production after cascade. By performing this technique, the effect of sluggish diffusion of HEAs on the formation of dislocation loops can be investigated.
This work proposes to perform 3 irradiation conditions for each HEAs. A total of 9 days are required to complete 9 experimental conditions. Specimens will be ready for experiments in IVEM in early 2017.
Additional Info
| Field | Value |
|---|---|
| Abstract | The emerging applications of high-entropy alloys (HEAs) have received great attentions from the field of nuclear materials because of its potentially superior radiation resistance. HEAs contain multicomponent (usually five or more) of roughly equimolar ratios. HEAs exhibit excellent strength, corrosion and wear resistance, and softening resistance at high temperatures. For nuclear applications, the severe lattice distortion and the high configuration entropy have been hypothesized to be the mechanisms that could make HEAs more radiation-resistant compared to conventional structural materials. To evaluate the suitability of HEAs for nuclear applications, a microstructural understanding of irradiation process is necessary. Previous studies with ex-situ ion irradiation showed that HEAs had a great phase stability, a low void swelling, and a slower growth rate of dislocation loops. However, the dynamic information such as defect clustering, coalescence or cluster migration in HEAs under irradiation has not been well studied. In-situ TEM experiments in IVEM can provide this important information to fundamentally understand the difference between HEAs and traditional alloys about the irradiation process on the microstructure. In addition, previous works have been mostly for FCC HEAs, while little is known for the irradiation effects on BCC and duplex (BCC and FCC two phase) HEAs. An effort is apparently needed for these two categories. This work will perform in-situ ion irradiation experiments in IVEM on three HEAs, CuCoNiCr(Al0.5)Fe, CuCoNiCr(Al1.5)Fe and CuCoNiCr(Al3.0)Fe, which are respectively FCC, FCC+BCC and BCC. 1 MeV Kr ions will be used to introduce irradiation damage at a few relevant irradiation temperatures while the microstructure evolution is observed in-situ with electron microscopy. Dislocation loops will be imaged with weak-beam dark field in order to reveal the small loops with sharp and confined contrast for accurate size measurement. Voids will be imaged with under and over focus. Diffraction pattern will be monitored at each step of irradiation dose to monitor the phase stability under irradiation. This study will generate quantitative data of the defect clusters as a function of irradiation dose and irradiation temperature for these three types of HEAs. The data will be compared with previous irradiation studies on conventional alloys (e.g. 316, G91) to show the potential of HEAs in nuclear applications. In addition, this study will take advantage of the newly-installed Gatan OneView digital camera to capture high-resolution videos of loop formation process with high frame rate. The technique has successfully shown the involvement of local point-defect diffusion in the loop production after cascade. By performing this technique, the effect of sluggish diffusion of HEAs on the formation of dislocation loops can be investigated. This work proposes to perform 3 irradiation conditions for each HEAs. A total of 9 days are required to complete 9 experimental conditions. Specimens will be ready for experiments in IVEM in early 2017. |
| Award Announced Date | 2016-12-16T07:48:37.293 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Wei-Ying Chen |
| Irradiation Facility | None |
| PI | WEIYING CHEN |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 859 |