| Components of high-end equipment require materials with low friction coefficient and high wear resistance from room temperature to high temperature.In recent years,for materials,keeping low friction coefficient and high wear resistance at wide-range temperatures to satisfy the extreme environments such as high temperature,high load and high speed has been a hot research problem.One of the effective methods for the application at wide-range temperatures is to utilize the synergistic effect of various lubricants.However,the mismatch between lubricants and matrix materials and excessive addition of lubricants will lead to the decrease of mechanical properties and wear resistance.In order to improve the wear resistance of materials,the carbides,oxides and nitrides have been developed on the basis of the tribological theory of improving the hardness and toughness.And the friction coefficient has been reduced by adding organic and inorganic lubricants with low friction coefficient.In this paper,the bimodal WC-12Co coatings were prepared to improve the toughness.The in-situ lubricant,soft metal addition and changing surface morphology were used to improve the tribological properties at wide-range temperatures.This paper provides a new kind of self-lubricating material with wide temperature range.The main results are as follows:Firstly,bimodal WC-Co coatings were prepared using nano/micron WC particles.The strength and toughness,friction and wear properties in wide temperature range and oxidation properties were studied.The results show that the bimodal WC-Co coating exhibits denser microstructure,higher hardness(1164.32±96.13 HV0.1)and fracture toughness(11.53±1.42 MPa?m1/2)than the traditional coating.With the increase of the temperature the friction coefficient decreases and the wear rate first increase and then decrease.The minimum wear rate is obtained at 450?,which is3.16±0.22×10-6mm3?N-1?m-1,and the friction coefficient is 0.49±0.04.The oxidation activation energy of coatings is Q=92.26 k J?mol-1.In the initial stage of oxidation,the O reacts preferentially with W element,in?-phase,to form WO3,and the oxidation rate is 2.84×10-4mg2·cm-4·h-1.The nano/micron structure can improve strength and toughness of WC-Co coating,synchronously.The continuous WO3 friction film can form at high temperature due to the nano-WC,which enable the coating have good wear resistance at high temperature.Secondly,the In-situ formation of WO3 by heat treatment is to improve the wide Temperature tribological properties.The results show that after heat treated at 450?for 4h,the hardness increase,the value is 1261±34 HV0.1.The phases content of WC:WO3:Co WO4 in the coating is 84.2:13.3:2.5.The tribological properties of heat-treated(450?-4h)coating are excellent,the friction coefficient and wear rate are0.47±0.023 and 3.95±0.42×10-6mm3?N-1?mm-1,respectively.For the high temperature testing,the heat-treated coating shows better tribological properties than that of the as-sprayed coating.The friction coefficient of the heat-treated coatings remains 0.47at each temperature,and the wear rate decreases first and then increases with the increase of temperature.The minimum value is 2.41±0.27×10-6 mm3?N-1?m-1 which is obtained at 450?.The microstructure and mechanical properties of the coatings were improved by heat treatment.The existence of prefabricated oxide film during friction made the coatings in the initial stage of lubrication and improved the friction and wear properties.Thirdly,the soft metal Cu addition in the coating to improve the tribological properties at wide temperature range has been investigated.The results show that the hardness first increases and then decreases with the increase of the Cu addition,and the maximum hardness is obtained at 4.0wt.%addition,which is 1254.78±66.17HV0.1.At room temperature,the friction coefficient and wear rate first decreases and then increases with the increase of the Cu addition,the minimum values are 0.47±0.02and 3.38±0.25×10-6mm3?N-1?mm-1,respectively,when the Cu addition is 4.0wt.%.At elevated temperatures,the coating with 4.0wt.%Cu addition shows stable and low friction coefficient(?0.5)and wear rate(?3×10-6 mm3?N-1?m-1).The lubricating Cu film can protect the coating and improve the wear resistance at wide temperature range.Finally,the WC/Cu self-lubricating coating with textured surface structure was designed to improve the tribological properties at wide temperature range.The results show that at room temperature,WC/Cu self-lubricating coating shows low friction coefficient and wear rate,which are 0.47±0.06 and 3.52±0.25×10-6mm3?N-1?mm-1,respectively,reduced by 30.88%and 25.74%respectively compared with traditional WC-Co coatings.At high temperature,the WC/Cu self-lubricating coating keeps stable and low friction coefficient(?0.45)and wear rate(?3×10-6mm3?N-1?m-1).During friction,the Cu can form a film on the WC-Co surface and the wear debris can form hard friction film with Cu phase.The WC/Cu self-lubricating textured coating can keep load-bearing capacity at high temperature due to soft Cu film,and the continuous lubrication film can form on the worn surface with,which can improve the friction coefficient and wear resistance in a wide temperature range. |
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