Using molecular dynamics (MD) simulation, we study the thermal shock behavior of tungsten (W), which has been used for the plasma facing material (PFM) of tokamaks. The thermo-elastic stress wave, corresponding to the collective displacement of atoms, is analyzed with the Lagrangian atomic stress method, of which the reliability is also analyzed. The stress wave velocity corresponds to the speed of sound in the material, which is not dependent on the thermal shock energy. The peak pressure of a normal stress wave increases with the increase of thermal shock energy. We analyze the temperature evolution of the thermal shock region according to the Fourier transformation. It can be seen that the "obvious" velocity of heat propagation is less than the velocity of the stress wave; further, that the thermo-elastic stress wave may contribute little to the transport of kinetic energy. The heat propagation can be described properly by the heat conduction equation. These results may be useful for understanding the process of the thermal shock of tungsten.

Molecular dynamics simulations are used to study cascades near the surface in hcp Zr. The influences of several factors, namely the primary knock-on atom (PKA) in different layers, angle of incidence, temperature and stress, on the number and type of defects are considered. Compared to bulk cascades, near-surface cascades show different characteristics in defect type and quantity when the PKA is in different layers. Low angle incidences create surface sputtering while the effects of high angle incidences are similar to those of bulk cascades. The effect of temperature is mainly focused on the number of sputtered atoms, with little influence on the total number of surviving defects. Stress helps to create more defects and the influence of compressive stress is more prominent than tensile stress.

The relative stability of 𝑓 𝑐𝑐 and 𝑏𝑐𝑐 solid solutions and amorphous phase with different compositions in the Cu-Al system is studied by molecular dynamics simulations with 𝑛-body potentials. For Cu1−𝑥Al𝑥 alloys, the calculations show that the 𝑓 𝑐𝑐 solid solution has the lowest energies in the composition region with 𝑥 < 0.32 or 𝑥 > 0.72, while the 𝑏𝑐𝑐 solid solution has the lowest energies in the central composition range, in agreement with the ball-milling experiments that a single 𝑏𝑐𝑐 solid solution with 0.30 < 𝑥 < 0.70 is obtained. The evolution of structures in solid solutions and amorphous phase is studied by the coordination number (CN) and bond-length analysis so as to unveil the underlying physics. It is found that the energy sequence among three phases is determined by the competition in energy change originating from the bond length and CNs (or the number of bonds).