Jianhua Ding

Interaction between helium and intrinsic point defects in 3C-SiC single crystal

Silicon carbide (SiC) is a candidate structural material for fission and fusion reactors as well as an important wide band-gap semiconductor for electronic devices. Using first-principles calculations, we systemically investigate the energetics and stability of helium (He) atoms and intrinsic point defects inside single-crystalline 3C-SiC. We find that the formation energy of interstitial He is lower than those of point defects. Inside 3C-SiC, the He-C interaction is stronger than He-Si. Hence, the interstitial He atom in the Si tetrahedral site has a stronger interaction with the six C atoms in the second nearest neighbor than the four nearest neighboring Si atoms. For interstitial He atoms, the equilibrium He-He distance is about 1.81 A with a weak attraction of 0.09 eV. According to the binding energies of Hen (n = 2–4) clusters, He interstitials can form He bubbles without involving other types of structural defects. Moreover, a Si (C) monovacancy can accommodate up to 11 (9) He atoms. The Hen cluster...

Irradiation-induced void evolution in iron: A phase-field approach with atomistic derived parameters*

A series of material parameters are derived from atomistic simulations and implemented into a phase field (PF) model to simulate void evolution in body-centered cubic (bcc) iron subjected to different irradiation doses at different temperatures. The simulation results show good agreement with experimental observations — the porosity as a function of temperature varies in a bell-shaped manner and the void density monotonically decreases with increasing temperatures; both porosity and void density increase with increasing irradiation dose at the same temperature. Analysis reveals that the evolution of void number and size is determined by the interplay among the production, diffusion and recombination of vacancy and interstitial.

Three-dimensional phase field simulation of intragranular void formation and thermal conductivity in irradiated α-Fe

Nucleation and growth of the irradiation-induced void, which is a fatal concern for the thermal conductivity of a structural material, is highly sensitive to the extreme irradiation conditions. A three-dimensional phase field model in conjunction with an explicit nucleation algorithm has been developed and utilized to investigate this issue. The temperature-dependent material parameters of α-Fe are derived from ab initio calculations. Phase field simulations reveal the effects of temperature and damage rate on the void formation behavior. At the same temperature, lower damage rate leads to longer incubation time, smaller void radius and less void number, while at the same damage rate, higher temperature causes shorter incubation time, larger void radius but less void number. The effective thermal conductivity of irradiated α-Fe is examined and analyzed by taking into account of void volume fraction, which agrees well with the calculated results using the Maxwell and Bauer models. The void formation behavior revealed by the phase field simulations and the effect of void volume fraction on thermal conductivity could be helpful in understanding the irradiation damage of structural materials.