| The shearer occupies an important position in coal mining equipment.In the failure ratio of gearbox parts in the shearer arm system,the proportion of gear failure is relatively large,so gears are often used as fault diagnosis parts.The preparation of piezoelectric ceramic coatings on the side of gears using ceramic materials with piezoelectric effect is an important research idea to realize online monitoring of gears.In order to prepare a potassium sodium niobate ceramic coating with controllable thickness,this paper first prepared the sodium potassium niobate ceramic powder that conforms to the supersonic plasma spraying technology by atomization granulation method,and compensates for the volatilization of alkali metal by adding sodium potassium.At the same time,the particle size distribution and phase structure composition of the powder before and after granulation are studied.Then,the ceramic coating of potassium sodium niobate was prepared by supersonic plasma spraying.The microstructure of the coating was analyzed,and the mechanical and electrical properties of the coating were preliminarily characterized.Finally,Ni-based transition layer was sprayed and different thicknesses of sodium potassium niobate ceramic coatings were prepared on the transition layer surface to investigate the effect of ceramic coating thickness on its microstructure and properties.The main research of this paper is as follows.(1)Sodium potassium niobate ceramic powder with particle size conforming to supersonic plasma spraying was prepared by atomization granulation technique,and the particle size distribution and phase composition of sodium potassium niobate ceramic powder were analyzed.The results showed that the size and shape of the powder changed significantly after atomization granulation,and the particle size of the granulated powder was well controlled in the range of 30-80 μm,and showed good spherical characteristics.In addition,the granulation did not affect the phase structure of the powder significantly,which effectively ensured the subsequent spraying experiments.(2)A certain thickness of potassium potassium niobate ceramic coating was prepared by supersonic plasma spraying technology,and the micro structure and properties of the coating were systematically analyzed.The results show that the prepared coating structure is relatively complete,no obvious element diffusion between the coating and the substrate,and good interfacial mechanical bonding,while the prepared coating microhardness and residual compressive stress,respectively,are 329.6 HV and-29.17 MPa,and the coating dielectric constant is high at low frequency,reaching 506,and the coating dielectric constant is stable at about 300 at high frequency,and its dielectric loss is below 0.05 or less.In addition,the residual polarization of the coating reaches 17.09 μC·cm-2 and the maximum piezoelectric coefficient is 16 pC·N-1.The above indicates that the prepared coating has a complete structure,good mechanical properties,excellent electrical properties,can be more as a capacitor and conductor,and has a certain force-electric conversion capability.(3)By preparing the Ni-based transition layer to improve the persistence field value of the coating,four potassium sodium niobate ceramic coatings of different thicknesses were further prepared on the surface of the Ni-based transition layer,and the influence of ceramic coating thickness on its micro structure and properties was studied.It was found that the roughness values of the prepared transition layer were 10.236 μm and 19.382 μm for the line square root and surface square root roughness,respectively,which were large enough to ensure the effective bonding between the transition layer and the ceramic coating,and the average transition layer hardness was as high as 570 HV.Meanwhile,the surface of the prepared ceramic coating has unmelted spherical powder and particles with good melting state,and all thickness coatings show the inherent layered structure of thermal spraying,and the layered structure is more obvious as the thickness increases.It was also found that when the coating thickness was 300 μm,the porosity reached a minimum value of 4.32%and the hardness reached a maximum value of 438 HV,the residual compressive stress reached a maximum value of-129 MPa,the coating had the best dielectric and ferroelectric properties,and the piezoelectric coefficient also obtained a maximum value of 33 pC·N-1.The above study provides a basis for the preparation of controllable thickness and excellent electrical properties of sodium niobate piezoelectric coatings using supersonic plasma spraying technology.The above research has laid a solid foundation for the preparation of sodium niobate piezoelectric ceramic coatings with controllable thickness and excellent electrical properties by supersonic plasma spraying technology,and provides a theoretical basis for real-time monitoring of gear failure in shearers,which is of great theoretical value and practical significance. |
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