Search

Simulating collision cascades and radiation damage poses a long-standing challenge for existing interatomic potentials, both in terms of accuracy and efficiency. Machine-learning based interatomic potentials have shown sufficiently high accuracy for radiation damage simulations, but most existing ones are still not efficient enough to model high energy collision cascades with sufficiently large space and time scales. To this end, we here extend the highly efficient neuroevolution potential (NEP) framework by combining it with the Ziegler-Biersack-Littmark (ZBL) screened nuclear repulsion potential, obtaining a NEP-ZBL framework. We train a NEP-ZBL model for tungsten and demonstrate its accuracy in terms of the elastic properties, melting point, and various energetics of defects that are relevant for radiation damage. We then perform large-scale molecular dynamics simulations with the NEP-ZBL model with up to 8.1 million atoms and 240 ps (using a single 40-GB A100 GPU) to study primary radiation damage of tungsten in both bulk and thin-foil forms. In bulk tungsten, the interstitial dislocation loops formed by cascades are dominated by 1/2 loops, but we also observe interstitial dislocation loops forming directly in the first few picoseconds of a cascade simulation. The damage resulting from the cascades differs significantly in foil and shows that larger and more vacancy clusters as well as smaller and fewer interstitial clusters are produced due to the presence of a free surface.

With scientific research in materials science becoming more data intensive and collaborative after the announcement of the Materials Genome Initiative, the need for modern data infrastructures that facilitate the sharing of materials data and analysis tools is compelling in the materials community. In this paper, we describe the challenges of developing such infrastructure and introduce an emerging architecture with high usability. We call this architecture the Materials Genome Engineering Databases (MGED). MGED provides cloud-hosted services with features to simplify the process of collecting datasets from diverse data providers, unify data representation forms with user-centered presentation data model, and accelerate data discovery with advanced search capabilities. MGED also provides a standard service management framework to enable finding and sharing of tools for analyzing and processing data. We describe MGED’s design, current status, and how MGED supports integrated management of shared data and services.

The formation condition of hydrogen blister in 18Ni maraging steel without any inner or external stress was investigated. The results show that the critical diffusible hydrogen concentration of a blister forming is about 1.4 × 10–5, which is corresponding to the current density of 30 mA/cm2 during cathodic charging in a sodium hydroxide solution. For a 0.1 cm thick sample, no matter the current density is equal to or much larger than the critical value, it spends at least about 132 h to form a hydrogen blister when hydrogen charging in single direction. It is approximately equal to the time for hydrogen atom to diffuse throughout the sample, which exactly depends on the hydrogen diffusion coefficient and the penetration depth. The very first clear suggestion was reported that the incubation period for hydrogen blister nucleation was necessary. According to the Fick’s laws, calculations show that the normalized hydrogen concentration in the escaping surface almost reaches 0.96 times of the charging surface, which means that the diffusion almost reaches a dynamic balance. A model was illustrated to describe the competitive relationship between hydrogen diffusion and blister formation.

Studies of high-pressure synthesized Hg-Ba-Ca-Cu-O superconductor by electron diffraction and high-resolution electron microscopy are reported. The results of electron diffraction indicate that two superconducting phases 1212 and 1223 exist in the sample and their cell parameters are a=b=3.8 Angstrom, c=12.7 Angstrom and a=b=3.8 Angstrom, c=15.8 Angstrom, respectively. High-resolution electron micrographs were taken from the two phases Hg-1212 and Hg-1223 and from the region of the intergrowth of the two phases. The relation between the structure and superconducting transitional temperature T-c is discussed.

High critical temperature superconductors of mercury-based system were synthesized under high pressure and high temperature. The resistance and ac magnetic susceptibility measurements for sample prepared at 25 kbar and 850°C for 1.5 h show that the sample without any added treatment was a mixture of Hg-1201 and Hg-1223. The Tc values of Hg-1223 phase and Hg-1201 phase are 132 and 98 K, respectively.

The growing process of a hydrogen blister in a wheel steel was observed in situ with an optical microscope, and the fracture surfaces formed from broken blisters on a wheel steel and bulk metallic glass were investigated. The initiating, growing, cracking and breaking of hydrogen blisters are as follows. Supersaturated vacancies can increase greatly during charging and gather together into a vacancy cluster (small cavity). Hydrogen atoms become hydrogen molecules in the vacancy cluster and hydrogen molecules can stabilize the vacancy cluster. The small cavity becomes the nucleus of hydrogen blister. The blister will grow with entering of vacancies and hydrogen atoms. With increasing hydrogen pressure, plastic deformation occurs first, the hydrogen blister near the surface extrudes, and then cracks initiate along the wall of the blister with further increasing hydrogen pressure. A cracked blister can grow further through propagating of cracks until it breaks.

The role of atomic hydrogen and hydrogen-induced martensites in hydrogen embrittlement in slow strain rate tensile tests and hydrogen-induced delayed cracking (HIC) in sustained load tests for type 304 L stainless steel was quantitatively studied. The results indicated that hydrogen-induced martensites formed when hydrogen concentration C 0 exceeded 30 ppm, and increased with an increase in C 0, i.e. M(vol%)=62–82.5 exp (−C 0/102). The relative plasticity loss caused by the martensites increased linearly with increasing amount of the martensites, i.e. l δ(M), %=0.45 M (vol %)=27.9−37.1 exp(−C0/102). The plasticity loss caused by atomic hydrogen l δ(H) increased with an increase in C 0 and reached a saturation value l δ(H)max=40% when C 0>100 ppm. l δ(H) decreased with an increase in strain rate $$\dot \varepsilon $$ , i.e. l δ(H), $$\% = - 21.9 - 9.9\dot \varepsilon $$ , and was zero when $$\dot \varepsilon \geqslant \dot \varepsilon _c = 0.032/s$$ . HIC under sustained load was due to atomic hydrogen, and the threshold stress intensity for HIC decreased linearly with in C 0, i.e. K IH (Mpam1/2)=91.7−10.1 In C 0 (ppm). The fracture surface of HIC was dimple if K 1 was high or/and C 0 was low, otherwise it was quasi-cleavage. The boundary line between ductile and brittle fracture surface was K 1-54+25exp(−C 0/153)=0.