To examine phonon transport during the friction process of commensurate–incommensurate transition, the vibrational density of states of contact surfaces is calculated based on molecular dynamics simulations. The results indicate that, compared with the static state, the relative sliding of the contact surfaces causes a blue shift in the interfacial phonon spectrum in or close to commensurate contact, whereas the contrast of the phonon spectrum in incommensurate contact is almost indiscernible. Further findings suggest that the cause of friction can be attributed to the excitation of new in-plane acoustic modes, which provide the most efficient energy dissipation channels in the friction process. In addition, when the tip and the substrate are subjected to a same biaxial compressive/tensile strain, fewer new acoustic modes are excited than in the no strain case. Thus, the friction can be controlled by applying in-plane strain even in commensurate contact. The contribution of the excited acoustic modes to friction at various frequency bands is also calculated, which provides theoretical guidance for controlling friction by adjusting excitation phonon modes.

γ-TiAl alloy is one of the most potentially lightweight and high-temperature structural materials, and its machined surface quality has a significant effect on member service performance. Despite the extensive research on plastic removal and defect evolution under different cutting parameters, the forming mechanism of surface topography is not perfect under different cutting parameters. It is necessary to study the variation law of surface topography under the influence of different cutting parameters from the atomic scale. To this end, the influence of cutting depths and cutting speeds on the machined surface topography is investigated during nano-cutting of polycrystalline γ-TiAl alloys based on molecular dynamics simulation methods, and the effect of defective grain boundaries on cutting force fluctuations is analyzed. The results show that the effect of grain boundary on material deformation and dislocation obstruction is the main reason for the peak cutting force; with the increase of cutting depth, the average cutting force and friction coefficient increase, and both Sa and Sq show an increasing trend, which is the result of the joint action of plowing effect and grain boundary distribution; Sa and Sq show a decreasing and then increasing trend with the increase of cutting speed, and the critical cutting speed is 200m/s. This indicates that a smaller cutting depth and an appropriately higher cutting speed can effectively improve the surface quality of the polycrystalline γ-TiAl alloy, and optimize its nano-cutting process.

γ-TiAl alloys are the most promising lightweight high-temperature structural materials, but the materials often fail from the surface, which is mainly attributed to the stress state of the material surface. In this paper, the orthogonal experiment method and molecular dynamics modeling are used to choose a set of the best process parameters for supersonic fine particle bombardment. Furthermore, by determining the optimal process parameters, this study examines the influence of residual stress distribution on the mechanical properties of the material under various process conditions. The simulation results reveal that the residual stress distribution is minimally impacted by particle radius, nonetheless, maintaining a moderate level of compressive residual stress within a specific range can substantially augment both the tensile strength and indentation hardness. An increase in the number of particles results in a more uniform distribution of surface residual stresses. Conversely, an increase in the number of impacts causes stress concentration to intensify at the particle's contact point, and thus a deeper distribution of residual stress is observed. This study illustrates how the mechanical properties of polycrystalline γ-TiAl alloy are affected by the process parameters of supersonic fine particle bombardment in terms of atomic size in order to develop and select the optimal supersonic fine particle bombardment parameters.

The effect of dissipation of dense plasmas on spontaneous radiation of ionized atom is investigated by Langevin equations and Weisskopf-Wigner approximation. Analytical expression for emission rate is obtained, the Einstein formula is corrected by a new added term caused by thermal photons and the Einstein A coefficient is also modified due to damping of the light. The life time of the excited ion will be modified correspondingly.