Simulation Study of Helium Effect on the Microstructure of Nanocrystalline Body-Centered Cubic Iron

Abstract

Helium (He) effect on the microstructure of nanocrystalline body-centered cubic iron (BCC-Fe) was studied through Molecular Dynamics (MD) simulation and simulated X-ray Diffraction (XRD). The crack generation and the change of lattice constant were investigated under a uniaxial tensile strain at room temperature to explore the roles of He concentration and distribution played in the degradation of mechanical properties. The simulation results show that the expansion of the lattice constant decreases and the swelling rate increases while the He in the BCC region diffuses into the grain boundary (GB) region. The mechanical property of nanocrystalline BCC-Fe shows He concentration and distribution dependence, and the existence of He in GB is found to benefit the generation and growth of cracks and to affect the strength of GB during loading. It is observed that the reduction of tensile stress contributed by GB He is more obvious than that contributed by grain interior He.

Helium Effects on the Mechanical Properties of Nanocrystalline Fe: Based on Molecular Dynamics

“…The initial model was relaxed using conjugate gradient minimization at 0 K. Then the intergranular distribution of He was introduced into the models, since the He atom at GB was a key factor affecting the mechanical properties of nanocrystalline Fe [17]. For simplicity, the "GB He" represents He atoms located at the GB region of nanocrystalline Fe hereinafter.…”

“…GIXRD was also used to detect the microstructure of Heirradiated nanochannel W films [16], and it was observed that the lattice swelling is lower Crystals 2021, 11, 532 2 of 9 in nanochannel W films than that in bulk W due to the He atoms that are released in the former. He effects on the microstructure of nanocrystalline BCC Fe was studied by simulated X-ray diffraction (XRD) [17], showing that the crack generation has a close relationship with the change in the lattice constant during loading. These studies show that the XRD method is reliable to study He effect on the microstructure of nuclear structural material.…”

“…In our previous research [17], the relationship between the crack generation and structural distortion was described in the framework of the average lattice constant. However, the change in the average lattice constant is not sensitive enough to the generation of cracks.…”

Plasma Facing Material by Self-Interstitial Solid Solution Strengthening – Problem, Proposition, and a Solution

“…To this end, various materials (such as W [47][48][49][50], addition of Rh in W [51], use of bcc Fe [52,53], Ta [54], W-Ta [55], Ta/Fe [56], Pd [57], nanocrystalline Cu [58], SiOC/Crystalline Fe nanocomposite [59], W-K [60], reduced activation steel [61], ferritic [62], ferritic/martensitic steels [63], Be pebbles [64][65][66][67], Be and beryllides [68], graphite, carbon fiber composite [69]) and high Z atoms (Zr, No, Mo, Hf, Ta) [70] have been tested but none proved satisfactory [71][72][73][74]. All show rapid surface degradation exhibiting surface blisters [75][76][77][78] and formation of fuzz [51,[79][80][81][82] or under dense nanostructure [40] after bubble.…”

Special Issue: Radiation Damage in Materials—Helium Effects

“…This is followed up by a detailed MD simulation by Xu et al, that explores the role of He generation on both grain boundary stability and crack growth in BCC-Fe. This modeling effort also takes advantage of recent advancements in computational code to produce simulated X-Ray Diffraction (XRD) patterns that permit rapid experimental validation [11].…”