The creep properties of structural materials under extreme irradiation are crucial for the safety and stability of nuclear facilities. This work investigates the effect of irradiation on creep behavior of Ti3AlC2 MAX phase material, focusing on irradiation fluence (dose) and temperature. Interestingly, we discover for the first time that the relationship between the creep stress exponent (n) and irradiation fluence (phi) in Ti3AlC2 satisfies phi n=A center dot ln phi + B, enhancing the understanding of irradiation's impact on the Ti3AlC2 MAX phase. Additionally, the creep strain rate (epsilon) in Ti3AlC2 correlates with irradiation temperature (T) as epsilon=E center dot(e(-1/T))(F)+G. Results show that the creep stress exponent in irradiated Ti3AlC2 increases with fluence and decreases with temperature, surpassing unirradiated samples, while the strain rate follows the opposite trend. Compared to other candidate materials, Ti3AlC2 MAX phase demonstrates excellent creep resistance under irradiation. These findings provide valuable insights for developing advanced nuclear structural materials.

Ni-based alloys are promising materials for advanced nuclear reactors operating at high temperatures due to their exceptional resistance to high temperatures and corrosion. Understanding the synergy of phase stability and helium effects is crucial for assessing the long-term performance and reliability of these alloys in advanced nuclear reactors. This study has investigated the co-evolution behavior of M 23 C 6 precipitates and cavities in a boron-free solid solution strengthened Ni-based alloy GH3617 under high-temperature He ion irradiation, and its impact on alloy swelling and mechanical properties, by He ion irradiation experiments with the highest fluence of 1 x 1017 17 He/cm2 2 up to 800 degrees C. Transmission Electron Microscopy (TEM) and Nanoindentation are employed to investigate microstructural evolution and mechanical properties, respectively. The findings show that at room temperature and 500 degrees C, cavities and dislocation loops were the dominant irradiation defects, whereas at 800 degrees C, the density of cavities and dislocations reduced while the formation of M 23 C 6 precipitates increased. These precipitates act as effective trapping sites for He and point defect, leading to cavity formation at the interfaces or within the precipitates. Moreover, increased irradiation fluence accelerates the co-evolution process, resulting in an increase in the density and size of both precipitates and cavities, ultimately leading to enhanced swelling. The {111} planes are favored interfaces between intragranular M 23 C 6 precipitates and the matrix due to their minimal misfit, while the preferred interface planes between cavities with octahedral or cubo-octahedral shapes and the precipitate/matrix are also {111}, owing to their lower surface energy as well. The co-evolution of cavities and precipitates was found to influence mechanical properties, resulting in an irradiation hardening effect at lower fluences, while softening at higher fluences. This study provides novel insights into the degradation mechanisms of Ni-based alloys under coupling effect of He and high-temperature irradiation.

The presence of helium (He) bubbles, a typical irradiation defect, leads to swelling, hardening, and embrittlement in structural materials, resulting in a shortened service life. Nevertheless, certain high/medium-entropy alloys (HEAs/MEAs) are recognized for their significant potential in advanced nuclear systems due to their exceptional resistance to He ion irradiation. This work investigates the evolution behavior and mechanisms of He bubbles in BCC-phase HEAs/MEAs with irradiation tolerance from multiple perspectives (irradiation fluence, irradiation temperature and Ti addition) using FeCrVTix MEAs as model materials. We propose a new indicator to determine the He bubble evolution mechanism based on the ratio of the diffusion coefficients of He atoms to those of vacancies, which can more clearly and vividly represent the evolution characteristics of He bubbles with temperature in HEAs/MEAs. The excellent tolerance of FeCrVTix MEAs to He ion irradiation-induced swelling is consistent with the predictions obtained by He bubbles are near equilibrium pressures with slight under-pressurized and the percentage of He atoms inside bubbles does not exceed 10%. Furthermore, Ti addition can suppress the nucleation, growth and coarsening of He bubbles in the BCC-phase matrix by increasing local lattice distortion and chemical composition complexity as well as forming Laves-phase precipitation, thereby further enhancing the tolerance to swelling induced by He bubbles. These findings provide valuable theoretical insights for the development of HEAs/MEAs with outstanding irradiation resistance.

Accelerator-Driven System (ADS) represents an advanced nuclear energy system designed for the purpose of transmuting and eliminating nuclear waste. The irradiation tolerance of a material stands out as a critical factor in determining its availability for ADS beam/target windows. This study delves into the response of three promising candidates (T91, SIMP, and Ti-6Al-4V) for ADS beam/target windows to proton irradiation, as investigated by a 1.4 MeV H2+ irradiation experiment to dose of 1.5 peak dpa at 460 degrees C. Their cavity swelling and hardening behavior were estimated using Transmission Electron Microscope (TEM) and Nanoindentation, respectively. It was demonstrated that SIMP steel shows lower cavity swelling but slightly higher irradiation hardening compared to T91. Notably, no cavity swelling is observed in Ti-6Al-4V, but it experiences a higher level of irradiation hardening. The nucleation and evolution mechanisms of irradiation-induced defects (including cavities, dislocation loops, and precipitates) and their contributions to the proton irradiation response are discussed. Furthermore, a summary of the advantages and disadvantages of the three materials as candidates for proton beam/target windows is provided.

FeCrVTix medium-entropy alloys (MEAs) with BCC matrix and Laves precipitation have high yield strength (1097-1493 MPa), good fracture strain (27.1-47.7%) and excellent thermal conductivity (42.2-69.7 W/(m center dot K) at 673-1273 K), it is expected to be widely applied in the fields of advanced nuclear energy and aerospace. However, what is this kind of MEAs strengthening and high thermal conductivity mechanisms? According to the experimental results and theoretical calculations, a mixed-strengthening-mechanism model dominated by precipitation and fine-grain strengthening is proposed, it can well explain the increase in yield strength of FeCrV-based MEAs due to Ti-added. Meanwhile, the Laves-phase precipitation formed by adding Ti improves the compressive plastic deformation through grain refinement, crack bridging and crack deflection. Moreover, the high thermal conductivity of FeCrVTix MEAs is primarily due to the inelastic scattering of phonons and electrons in the medium/high-temperature regions. Based on the above mechanisms, the mechanical and thermal properties of MEAs/HEAs can be regulated in the pre-design and post-treatment stages, which provide new ideas and methods for the design and performance-optimization of high-performance structural materials.

The phase transitions and He bubble evolution in Ti3AlC2 with the sequential He ions implantation and Fe ions irradiation at room temperature were investigated with grazing incidence X-ray diffraction and transmission electron microscopy. The pre-implanted He makes an obviously effect of suppressing the phase transitions caused by the following Fe ions irradiation. The following Fe ions irradiation was also found to create a competitive effect on the evolution of the pre-formed He bubbles. It can cause not only the growth of He bubbles, but the shrinkage (or re-solution of He bubbles). This will improve the resistance to He bubbles induced damage for Ti3AlC2. Both He ions implantation and Fe ions irradiation actually inhibit each other's irradiation damage to the material. This may play a positive role in reducing irradiation damage to the Ti3AlC2 material, and also provides new insight into irradiation resistance of this material.

The materials' issue is one of the main bottlenecks restricting the development of nuclear energy systems. Based on the requirements of low activation, high-temperature thermal stability, high strength, high ductility, high thermal conductivity, irradiation resistance, corrosion resistance and other characteristics, the FeCrVTix medium-entropy alloys (MEAs) were designed for the working under extreme environments of the advanced nuclear energy systems. Here, thermodynamic calculation and coupling with the selection of low activation and functional elements and phase composition estimation, to MEAs are shown in the effort to design this kind of modern advanced alloy materials. Meanwhile, a kind of FeCrVTix (x=0, 0.05, 0.1, 0.2, 0.3) MEAs, as a model material, was prepared by arc melting and its above-mentioned properties were investigated. The results show that FeCrVTix MEAs have excellent properties and quite match the previous expected design, which have great potential for nuclear applications as structural materials. Most importantly, this novelty and proven method of alloy design based on the target requirements and configuration entropy has been proven to be correct and feasible, providing a new way for the design and rapid screening of new materials. (C) 2021 Elsevier B.V. All rights reserved.

For the structure materials applied in the innovative nuclear energy system, the strongly environment radiation source is always a big concern which will severely degrade the materials performance especially at high temperature. To explore the mechanisms of the anti-irradiation properties in Ti3AlC2 , a typical MAX phase material showing excellent irradiation damage tolerance and resistance to amorphization, we conducted a series of 1 MeV C4(+) ions irradiation experiments on them at different temperatures (RT, 300 degrees C, 500 degrees C and 800 degrees C). Through Grazing Incidence X-ray Diffraction (GIXRD), Raman spectra (Raman), slow positron annihilation Doppler Broadening Spectroscopy (DBS) and high resolution Transmission Electron Microscopy (HRTEM), the anti-irradiation properties were systematically investigated. For the first time, an entire microstructure phase transformation process of Ti3AlC2 from alpha to beta to gamma and to perfect fee structure phase induced by irradiation at RT and it is inverse (recovery) process of phase transformation under high temperature (>= 300 degrees C) irradiation conditions are found and confirmed. And lots of simple vacancies are induced by irradiation and the density of them gets saturated above 5 x 10(15) ions/cm(2) fluences. These processes of phase transformation and recovery and vacancy saturation phenomenon are the primary reasons for why Ti3AlC2 has excellent irradiation damage tolerance and resistance to amorphization. In addition, the micro strain and lattice parameters are also affected by microstructure transformation and have been discussed. In a word, Ti3AlC2 materials show good anti-irradiation properties especially at high temperature, and now it is a primary candidate as the coating of the cladding material and the spallation target beam windows material in Chinese ADS project. And studies on this kind of materials provide a promising new concept and way for designing the structural materials for innovative nuclear energy system. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

MAX phase materials have shown a series of interesting, even sometimes unusual, properties and exhibited combined attributes of both metals and ceramics, which are due to their “layered ternary transition metal carbides” structures. In the process of studying the multistage phase transformation of 312-MAX phase materials, we found that there were some confusions and mistakes when describing the crystal structures of the β-phase in the existing literature. In order to clarify their structural and physical properties, the β-phase Ti3SiC2 materials have been prepared by using 500 keV He2+-ion irradiation-induced phase transformation and examined by first-principles calculations and Rietveld analysis of grazing incidence x-ray diffraction patterns. Two accurate descriptions of the β-Ti3SiC2 structure are given here. In order to avoid confusion again, it is recommended to use one of the two descriptions uniformly. In addition, some physical properties parameters of β-Ti3SiC2 have been calculated and compared, which also confirmed the correctness of the structure description. Finally, the vacancy formation energies of β-Ti3SiC2 have been predicted and discussed in detail from the points of phase stability and transformation for the first time.

Currently, classic methods and some machine learning algorithms are popular with researchers in nuclear pulse shape discrimination (PSD). Although decision tree (DT) is widely used as a classification algorithm, it is rarely found in PSD studies. In this paper, compared with the support vector machine (SVM), the effect and efficiency of the combined application of principal component analysis (PCA) and DT in PSD are reported. The results show that the DT is an efficient, effective method when combined with PCA because the accuracies are all above 90.7%, even though the difference among the pulse shapes cannot be discriminated with the naked eye. The testing speeds of the DT with PCA are over 36 times those of SVM, and the processing speeds are sufficiently high for most situations.