After Fukushima nuclear accident in 2011, the event of supplies for accident-tolerant gasoline (ATF) has turn into a significant concern analysis and improvement path for worldwide nuclear organizations and nuclear industries [1], [2], [3], [4]. Cr-coated zirconium alloy supplies have glorious oxidation resistance in excessive temperature steam and successfully make the most of lots of the benefits inherent in conventional zirconium alloys [5], [6]. Subsequently, they’re thought-about as essentially the most promising candidate supplies for the ATF cladding. Nevertheless, because of the brittle traits of chromium, the Cr coatings nonetheless must be improved by way of mechanical properties to keep away from gasoline cladding failure on account of put on throughout operation [7], [8]. Alloying idea provides a possible technique for bettering the general efficiency of Cr-coated zirconium cladding. The strengthening of coatings will be achieved by including steel parts, introducing stable answer strengthening, grain refinement or increased residual stresses [9], [10], [11]. Amongst them, the addition of niobium (Nb) can enhance the power and ductility of the coating, and in addition has a optimistic impact on the oxidation resistance at excessive temperatures [12]. As Nb content material within the CrNb coatings will increase, the floor wetting properties change from hydrophilic to hydrophobic, and the wear and tear properties and hardness are improved [8], [13]. Nevertheless, along with the problems on which present analysis has centered, similar to materials preparation and the mechanical, oxidative or frictional properties of the fabric, irradiation resistance can also be a vital criterion for evaluating the great efficiency of coating purposes.
The irradiation resistance of pure Cr and Cr-based coatings and their response to irradiation have been tentatively explored. Wu et al. [14] have reported adhesion of Zr/Cr interface after irradiation, which nonetheless has good chemical and microstructural stability when irradiated with 20 MeV Kr8+ at 673 Okay as much as 10 dpa. In-situ research [15], [16] have probed the evolution of irradiation-induced dislocation loops in Cr coatings, together with nucleation, migration, coalescence and disappearance, that are just like many of the typical body-centered cubic (BCC) supplies [17], [18]. Our earlier work [19] has revealed that the scale and density of helium bubbles enhance with helium focus in Cr coatings, and helium bubbles will preferentially precipitate alongside the Cr grain boundaries, which then additional mixture to kind quick bubble microcracks. And these irradiation-induced defects not solely result in irradiation hardening and embrittlement, but in addition have an apparent impact on the corrosion conduct of the coating. Beneath high-temperature steam atmosphere, defects within the coating will act as oxygen diffusion channels, accelerating the inward diffusion of oxygen and thus decreasing the oxidation resistance of the coating [20]. Nevertheless, it’s nonetheless unclear whether or not irradiation-induced displacement cascades throughout irradiation immediately have an effect on the oxidation conduct of the coating. As well as, CrNb coatings with totally different Nb contents will current totally different crystalline buildings, the upper Nb content material coating will result in smaller grain measurement, and when the Nb content material exceeds a sure essential worth, the coating will even current a nanocrystalline construction or amorphous part. [8]. The crystalline construction and grain measurement will clearly have an effect on the efficiency of plastic deformation [21], [22], corrosion [23], and irradiation resistance [24]. Subsequently, it’s pressing to know the response variations of those CrNb coatings with totally different Nb contents beneath irradiation, and to disclose the impact of grain variations on the irradiation resistance of the coatings, in order to information additional coating design and software.
The transmission electron microscope (TEM) coupled with high-energy accelerators will considerably improve the flexibility to check irradiation harm in nuclear supplies. It has been confirmed that ion irradiation carried out inside an in-situ TEM not solely offers higher management of irradiation parameters [25], [26], [27], together with irradiation dose, dose charge, and temperature, in comparison with the extraordinarily harsh atmosphere of nuclear reactors, but in addition permits figuring out dynamic processes inside the areas of curiosity [28], [29], permits for the continual monitoring of the real-time response of microstructures to exterior stimuli (irradiation, thermal, stress, and so forth.) [30], [31], [32], [33], and eliminates or quantifies the consequences of analysis variables similar to microstructural variations.
Right here, we report the response of pure Cr coatings and CrNb coatings with totally different Nb contents beneath ion irradiation through the use of superior in-situ TEM. Particle accelerators are used to generate Cr+, He+, and H2+ beams, after which they’re concurrently launched into TEM to irradiate the coatings. Beneath high-temperature (633 Okay) irradiation, the oxidation conduct of the coatings in addition to the dynamic means of amorphous to crystalline part transition of CrNb coatings have been efficiently tracked with the assistance of in-situ TEM bright-filed photos and in-situ chosen space electron diffraction (SAED) patterns. And the bodily mechanisms of irradiation-accelerated oxidation and irradiation-induced crystallization are additionally mentioned.
