| In order to meet the demand of lubricating and wear-resistant materials in wide temperature range in modern aerospace,nuclear industry and other high-tech fields.The composition design,material preparation,lubrication and wear mechanism of lubricating wear-resistant materials in wide temperature range are carried out,and lubricating and wear-resistant materials with excellent tribological properties in wide temperature range(RT-800℃)are developed.Compared with traditional materials,the high entropy materials show excellent mechanical and tribological properties in wide temperature range because of their high mixing entropy effect.The high entropy oxide MgCoNiCuZnO5(HEO)ceramics show a great application prospects in the field of tribology because of their natural oxidation resistance and layered rock salt phase structure.In this paper,the HEO bulk ceramics,ceramics powders and ceramics coatings were prepared by vacuum hot pressing sintering,high temperature solid state reaction and atmospheric plasma spraying,respectively,and the phase formation temperature of HEO ceramics was investigated.Secondly,the effect of sintering temperature on the microstructure and mechanical properties of the HEO ceramics was investigated,and its mechanical and tribological properties in wide temperature range were investigated.In addition,based on the ion potential theory,the MgCoNiCuZnO5-MoO3(HEOM)composite ceramics coatings were prepared by atmospheric plasma spraying,and the effect of MoO3 addition mass ratio on the mechanical and tribological properties of the HEOM composite ceramics coatings were studied systematically.Finally,the wear morphology and surface phase composition of the HEO and HEOM at different temperatures were analyzed by SEM,EDS,XRD and Raman,and the lubrication and wear mechanism were described.The main research contents and conclusions were as followed:(1)The phase formation temperature of single rock salt phase of the HEO bulk ceramics was investigated.The effect of sintering temperature on microstructure and mechanical properties was studied,and mechanical and tribological properties in wide temperature range were investigated.The results showed that the phase formation temperature of single rock salt phase was 800℃when preparing bulk ceramics.When the sintering temperature increased from 800℃ to 1000℃,the density increased continuously,which leaded to the increase of Vickers hardness.In the balance between densification and grain growth,the fracture toughness and bending strength increased greatly at first and then decreased slightly.With the increase of test temperature,the Vickers hardness decreased at first and then increased,and the wear rate increased at first and then decreased.The phase separation of HEO bulk ceramics occured again at 400℃,which leaded to a sharp decrease in Vickers hardness and a sharp increase in wear rate.At 600℃ and 800℃,a lubricating film with easy shearing was formed on the worn surface,so it had lower friction coefficient(0.3-0.33)and wear rate(the level of 10-6 mm3 N-1 m-1).(2)The phase formation temperature of single rock salt phase of the HEO ceramics powders was investigated.The effect of powder sintering temperature on the mechanical properties of HEO ceramics coatings was studied,and tribological properties in wide temperature range were investigated.The results showed that the phase formation temperature of single rock salt phase was 900℃ when preparing the HEO ceramics powders.Compared with HEO900 ceramics coatings,the Vickers hardness of HEO 1000 ceramics coatings increased by 9.6%,and the bonding strength increased by 6.2%.The ceramics coatings had lower friction coefficient(0.44-0.61)and wear rate(0.28-1.41 ×10-4 mm3 N-1 m-1)at and below 400℃.Under the drive of configuration entropy,the single rock salt phase separated part of CuO at 600℃ and 800℃.The change of phase structure caused serious abrasive wear of the ceramics coatings,and the wear rate increased sharply.(3)The effect of MoO3 addition mass ratio on the mechanical and tribological properties of HEOM composite ceramics coatings was studied systematically.The results showed that the HEOM composite ceramics coatings had excellent mechanical properties.The Vickers hardness of the HEOM was 4.92-5.45GPa and the bonding strength was 46.2-50.2MPa.With the increase of test temperature,the friction coefficient decreased continuously,and the wear rate increased at first and then decreased.Compared with single HEO ceramics coatings,the high temperature tribological properties of HEOM composite ceramic coating had been effectively improved.Among the three kinds of HEOM coatings,the tribological properties of the composite ceramics coatings with 20%MoO3(HEOM2)were relatively stable in wide temperature range,which was a better ratio.The wear rate of the HEOM2 composite ceramics coating was as low as 3.63×10-5 mm3 N-1 m-1,and the friction coefficient was as low as 0.26.The substantial reductions in friction coefficient and wear rate were mainly due to the formation of hightemperature lubricating film on the worn surface. |
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