Plasma Spraying Carbon Fiber And Alumina Composite Coating Structure And Performance Study

Having the general characteristics of carbon materials, such as hightemperature performance, friction resistance, conductivity, thermal conductivity,low expansion coefficient, the outstanding advantages of carbon fiber are itshigh strength and stiffness, light weight, thereafter, it is considered the mostpromising reinforcing materials. In recent years, many researches on thepreparation of carbon nanotubes reinforced composite coating fabricated byplasma spraying system were systematically conducted, and the technology hasbecome matured. Meanwhile, preparation of short carbon fiber compositeceramic coating via plasma spraying process is rarely reported. The structureand properties of plasma sprayed carbon fiber and aluminum oxide compositecoatings were studied in this research, providing reference for futureoptimization of processing.Carbon fiber was mechanically ball-milled to particles pretty short in length.Alumina-1wt.%,2wt.%and4wt.%carbon fiber composite coatings were plasmasprayed after homogeneously blended. Field emission scanning electronmicroscopy (FESEM), transmitted electron microscopy (TEM) and X-raydiffraction (XRD) were utilized to characterize the microstructure of rawmaterial and composite coating. XRD method was also used to evaluate residualstress of composite coatings. Thermal stability of composite coating wasachieved by TG/DTA and thermal diffusitivity coefficient was evaluated throughlaser thermal conductivity tester. Observations of surface and cross-section ofcoatings by SEM show that carbon fiber particles were randomly distributedamong splats and the coarse surfaces were full of heat etched grooves, filledwith tiny alumina droplets. The infiltration of alumina splat was furtherconfirmed through TEM observation. Validation of carbon fiber structure wasconducted via Laser-Raman spectroscopy. ID/IGratio of carbon fiber particles incomposite coating was comparatively decreased to that of original carbon fiber and with increase of carbon fiber content, it was likely for original carbonstructure retaining in composite coating. Mechanical properties were testedutilizing Instron multifunction tester, micro hardness indenter andmultifunctional wear tester. Vickers`hardness, tensile strength test andball-on-disk test were designed to characterize the micro hardness,adhesion/cohesion strength and abrasive wear of composite coating and theanti-corrosion property was observed via neutral salt spray test. It was observedin Vickers`indentation that difference introduced by carbon fiber was notobvious, a slightly increase. According to ASTM-C633-79, the adhesion strengthwas tested via tensile method and25%，32%，28%increase was achievedrespectively for carbon fiber composite coating compared to original aluminacoating. Ball-on-disk test was performed under the load of5N、10N、30Nrespectively. Effect of carbon fiber incorporation was analyzed. Wear scars werecharacterized under SEM and carbon fiber structure was validated through laserRaman spectrum. It turns out that effective carbon fiber structure still existedafter wear and the degree of graphitization and defects were enhanced due towear. It was elucidated that friction coefficient has been through a trend ofdecrease under the load of5N and10N, but as to the low content of carbon fiber,the fluctuation was small except for the coating with4wt.%. When suffered30N,significantly decrease of friction coefficient was observed even in low contentcarbon fiber coatings. Apart from alumina-1wt%composite coating, the wearresistance of2wt%and4wt.%composite coating was close to that of purealumina.