The MD Simulation Study Of Lattice Thermal Properties On Polycrystalline Tungsten

The materials in the fusion device inevitably come into contact with the plasma.Plasma-facing materials(PFMs)cause radiation damage to the materials,and the sputtered atoms contaminate the plasma and affect the operation of the fusion reaction.Due to the advantages of high melting point,low retention rate,and high thermal conductivity,poly crystal line materials are prioritized as PFMs.But these materials also have many problems which need to be further studied.Aiming at the problems of polycrystalline tungsten,an improvement trend is to refine the grains.However,the grain refinement brings about the problem of the decrease of thermal conductivity,so the research on the thermal conductivity of polycrystalline tungsten materials has important engineering significance.This thesis mainly studies the thermal conductivity of the lattice in polycrystalline tungsten,and analyzes the influence of physical factors such as grain boundaries and grain size on thermal conductivity,the results indicate that:(1)The grain size will affect the lattice thermal conductivity.As the grain size decreases,the lattice thermal conductivity also decreases.The reason is that when the grain size decreases,the influence of the grain boundary on the heat conduction begins Increase.Calculations show that as the grain size increases,the lattice thermal conductivity also gradually increases.When the crystal grain size is on the order of micrometers,the grain boundary has almost no effect on the thermal conductivity of the lattice.(2)This thesis also studies the thermal resistance at the symmetrical tilted grain boundary at different grain boundary angles.By analyzing the relationship between the grain boundary energy and the thermal resistance,it is concluded that the thermal resistance is proportional to the grain boundary energy.(3)Since helium irradiation easily forms helium bubbles at the grain boundary position,this work also studied the total thermal resistance performance after inserting helium bubbles at the grain boundary position.The results of the study show that overall,the thermal conductivity of the grain boundary deteriorates further after being irradiated.Compared with the helium bubble,the grain boundary has a major influence on the heat conduction;when the pressure of the helium bubble is large enough,the influence of the helium bubble begins to become significant.