| Maintaining a low friction coefficient and high wear resistance in a wide temperature range have been the most urgent problems in the field of tribology,and it is also the bottleneck of key equipment development in many technical fields.Using the co-lubricating effect of multiple lubricating phases is one of the effective methods to realize the wide-temperature lubrication.When the added or generated content of lubrication phases is too small,the lubrication is not obvious,and the added or generated content is too high,the mechanical properties would be poor due to the low shear strength.In this paper,WCN,WSiN,TiN/W2N and TiAgN/W2N coatings were prepared by magnetron sputtering technology.The physico-chemical properties of the materials on the friction surface and oxidized surface are investigated,and the adaptive mechanism in the wide temperature range of tungsten nitride based coating is revealed.Firstly,WCN coating was prepared by adding C into W2N to improve its room-temperature lubrication.The mechanical properties,room-temperature tribological properties and oxidation behavior of the coatings were studied.The results show that the addition of C can form W-C-N solid solution by replacing atoms and refine the grains by increasing the number of nucleation,and then significantly improve the mechanical properties.The addition of C can also form amorphous phase and CNx,which can reduce the friction coefficient.As the C content is 14.8 at.%,the coating properties are optimal.Its hardness?36.7 GPa?increases by 31.0%,the friction coefficient decreases by 25.0%,and the wear resistance of the coating increases by 50.0%.The wear form is mainly adhesion wear.If the column structure of the coatings are not destroyed after adding some C,the antioxidant properties could be improved by increasing the bond energy,decreasing the pores among the columnar grain boundaries,squeezing the amorphous phase to withstand the expansion of oxidation and consuming some oxygen by oxidizing amorphous phase.Secondly,WSiN coating was prepared by adding Si into W2N to improve its high-temperature lubrication.The mechanical properties,room-temperature tribological properties and oxidation behavior of the coatings were studied.The results show that the addition of Si can significantly improve the mechanical properties and the room-temperature tribological properties.As the Si content is 13.4at.%,the coating properties are optimal.Its hardness?37.0 GPa?increases by 32.0%,the friction coefficient decreases by 25.0%,and the wear resistance of the coating increases by 66.7%.The wear form is mainly adhesion wear.The improvement of tribological properties is due to the increase of hardness.The improvement in antioxidant properties is due to the formation of solid solute?bond energy increasing?,network Si3N4?blocking oxygen diffusion?,and the formation of dense oxygen diffusion barriers?WO3 and SiO2?.Thirdly,based on the design concept of multilayer nanostructure,TiN/W2N multilayer coating?modulation ratio 1:1?was prepared to improve the wide-temperature wear resistance of W2N.The mechanical properties,wide-temperature tribological properties and oxidation behavior were studied.The results show that the hardness of TiN/W2N multilayer coatings?27.528.1 GPa?are between TiN?26.7 GPa?and W2N.The hardness of multilayer coating decreases with the increase of modulation period.At room temperature?25°C?,the friction coefficient of TiN/W2N coatings are 0.50,which are between TiN?0.55?and W2N?0.38?.The wear rate are 3.2×10-6mm3·N-1mm-1,which are 1/4 of TiN and 1/3 of W2N,respectively.At 300°C,the friction coefficient of TiN/W2N coatings are 0.46,which are between TiN?0.51?and W2N?0.35?.The wear rate are 4.5×10-66 mm3·N-1mm-1,which are about 1/3 of TiN and 1/2 of W2N,respectively.At 500°C,the friction coefficient of TiN/W2N coating are 0.43,which are between TiN?0.49?and W2N?0.32?.The wear rate are 5.2×10-66 mm3·N-1mm-1,which are about 2/5 of TiN and 1/2of W2N,respectively.The layer-layer interfaces in TiN/W2N multilayer coating can change the direction of the crack,limit the crack expansion,and then improve the wear resistance.With the increase of the modulation period,the grain sizes of TiN or W2N layer increase and the intergranular distances become larger,thus the surface oxidation become severe.Finally,on the basis of TiN/W2N multilayer coating,TiAgN/W2N multilayer coating?modulation ratio 1:1?was prepared by adding Ag into TiN to improve the wide-temperature lubrication of W2N.The mechanical properties,wide-temperature tribological properties and oxidation behavior were studied.The results show that the hardness of TiAgN/W2N multilayer coatings?24.227.6 GPa?are between TiAgN?4GPa?and W2N.The hardness of multilayer coating decreases with the increase of modulation period.At 25°C,the friction coefficient of TiAgN/W2N coatings are0.350.38,which are better than TiAgN?0.4?and W2N.The wear rate are?4.44.8?×10-6mm3·N-1mm-1,which are 1/5 of TiAgN and 1/2 of W2N,respectively.At 300°C,the friction coefficient of TiAgN/W2N coatings are 0.310.33,which are better than TiAgN?0.33?and W2N.The wear rate are?5.86.5?×10-66 mm3·N-1mm-1,which are 1/4 of TiAgN and 2/3 of W2N,respectively.At 500°C,the friction coefficient of TiAgN/W2N coating are 0.260.27,which are better than TiAgN?0.28?and W2N;The wear rate are?6.77.6?×10-66 mm3·N-1mm-1,which are 1/5 of TiAgN and 3/5 of W2N,respectively.The improvement of the friction properties are due to the formation of TiO2,WO3 and AgWO4 with a low shear strength.The layer-layer interfaces in TiAgN/W2N multilayer coating can change the direction of the crack,limit the crack expansion,and then improve the wear resistance.With the increase of the modulation period,the thickness of the loose modulation layer?TiAgN?increases,the grain size of the W2N layer increases and the intergranular distances become larger,thus the surface oxidation become severe.Based on the above results,this paper adopts multi-target magnetron co-sputtering technology,designs multi-layer nano-micro structure by modulating sputtering period,and uses the low-temperature lubrication of graphite or Ag,high temperature stability of Si-oxides,and high-temperature lubrication of friction oxidation phase to perform component compounding.This paper provides a technical scheme to effectively solve the problem of lubrication and wear resistance in wide temperature range. |
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