Molecular Dynamics Simulations Of Friction Behaviors Of Nanocrystalline Zirconium

Nuclear power,as an efficient and clean energy,is one of the important components in modern industry.The development of nuclear power is of practical significance for adjusting the energy structure,effectively coping with energy shortages,and promoting the green and sustainable development of the national economy.Zirconium alloy is widely used in nuclear reactor fuel assemblies.As a key component of nuclear fuel cladding tube material,it is the first safety barrier for nuclear power systems.During the operation of the reactor,significant fretting damage occurs between the zirconium alloy cladding tube and the positioning grid,which is one of the important factors affecting the safe operation.Therefore,carrying out basic theoretical research on fretting wear of zirconium and its alloy materials is of great significance for improving the service life of nuclear power equipment and the safe operation of nuclear power systems.In this paper,a series of rough body-plane contact models were established and molecular dynamics simulation methods were used to achieve sliding processes at different sliding velocities(0.1 ?/ps,0.2?/ps,0.3?/ps,0.4?/ps)at the nanoscale of Zirconium substrates with the total sliding distance of 150?.The effects of crystal orientation,average grain size of substrates and rough body size on the friction and wear behavior of nanocrystalline Zirconium were discussed.The frictional response and the wear amount of the substrate were calculated and analyzed.Besides,the atomic measurement of the contact area,the strain and dislocation analyses were also used to study the internal plastic deformation behavior mechanism.The main research contents of the paper are as follows:(1)The contact sliding processes between the single crystalline Zirconium substrates with three different orientations([0001],[10-10],[11-20])and the diamond hemisphere were simulated.The results showed the friction force responses increased with the increase of sliding velocities.Plowing effect is dominant at lower sliding velocities.At higher sliding velocities,atomic adhesion was the main factor which caused a significant increase in frictional responses.Furthermore,the friction and wear behaviors of single crystal Zr showed a strong crystal orientation dependence due to the changes of sliding systems in different orientations at the nanoscale.(2)The polycrystalline substrates with different average grain sizes(9.28 nm,6.28 nm,5.19 nm,4.33 nm,3.41nm)were established through voronoi diagram algorithm and they were also paired with diamond hemisphere tool and performed contact sliding processes.The results showed the friction responses and wear amounts increased significantly with the decrease of the average grain sizes of the substrates.The internal plastic deformation mechanisms of polycrystalline substrates experienced an evolution from dislocation interaction and motion to the grain rotation and sliding with the decrease of average grain sizes.(3)The diamond hemisphere tools with different radius(2.8nm,3.2nm,3.6nm,4.0nm)were paired with two typical single and poly crystalline substrates to performed contact sliding processes.The simulation results showed that the tool sizes had no significant effect on friction force responses.It was indicated that the increase in the number of atoms in the contact area increased the plouging effect,which was the main reason for the increase in the wear amounts.