Study On Thermal Stability And Mechanical Properties Of Si-DLC Composite Coating

Diamond-like(DLC)coatings have excellent hardness,good wear resistance,good chemical stability,corrosion resistance and low friction coefficient.Which make it was widely used in various industries such as microelectronics,optics,manufacturing,transportation and biomedicine.In this paper,Si-DLC coatings were prepared on silicon carbide substrates by unbalanced magnetron sputtering technology,and the coating samples were annealed at different temperatures.The effects of annealing temperature on its thermal stability and mechanical properties were studied.At the same time,molecular dynamics simulation was used to explore from a microscopic point of view.Research indicates:1?The coating mainly contains carbon and silicon.Among them,carbon atoms mainly exist in two hybrid states:C-sp3 and C-sp2,and silicon atoms and carbon atoms exist in Si-C bonding state.Before the annealing temperature of 400?,the structural composition of the Si-DLC coating did not change significantly.When the annealing temperature reached 500?,significant graphitization occurred.It is found by molecular dynamics simulation that the C-sp3 bond is the dominant factor affecting the thermal stability of the coating,and the phase transition mechanism of C-sp3?C-sp2 exists a staged.The spa-sp3 with a longer bond length will start to transform first.Then,the spa-sp3 bond with a shorter bond length will begin to transform at higher temperature.Silicon can enhance the atomic structure of the coating and delay the graphitization rate.2?Before the annealing temperature of 400? the hardness and elastic modulus of the Si-DLC coating changed little,the decreased significantly at 500?.The nanoindentation simulation showed a similar trend.As the annealing temperature increased,the hardness of the coating gradually decreased,and the resistance of the coating to plastic deformation decreased.Low temperature annealing treatment is beneficial to reduce the residual compressive stress.The creep properties of Si-DLC coatings increase with the increase of loading rate,and the creep properties of coatings after low temperature annealing increase with the increase of annealing temperature,and the creep properties of coatings decrease after high temperature annealing.3?The critical load F1 and critical load F2 of the Si-DLC coating did not change significantly in the range of 25?300 ?,but there was a mutation in the range of 400?500?.Excessive thermal stress at 500? leads to weakening of film-based bonding properties and inhibition of crack propagation,and the film has greater plasticity.Molecular dynamics scratch simulation results show that as the annealing temperature increases,the surface resistance of the coating decreases,the shear resistance is reduced,and the tensile strength is enhanced.The positive pressure of the heading plays a leading role in the critical load F1,and the heading tangential force plays a leading role in the critical load F2.The degree of damage to the surface oxide layer and coating surface of the coating will result in an increase in the surface friction coefficient of the coating.