Study Of Alumina Coatings Onto Carbon Fiber Reinforced Polymer Matrix Compoite

Carbon fiber reinforced polymer matrix composite materials （PMCs） havehigh strength-to-weight ratios in comparison to metals, therefore are verycompetitive in many application aspects. Because of their outstanding properties,PMCs attracts special attentions in the design of next generation aircraft andnavy ships.However, as a competitive alternative material, PMCs are not aswidely used in many applications due to their low heat and wear resistanceproperties in comparison to metals. This study is focused on the deposition ofprotective coatings onto PMCs by plasma spray, arc spray and microarcoxidation technology to improve the wear and thermal resistance of PMCs.Considering the huge difference between the thermal expansion coefficientof polymer composites and ceramic coatings, which resulting departure of thecoatings, thermal spraying and microarc oxidation porous coatings were chosenas protective coatings. By controlling the parameters of the processes, theprotective coatings with high surface hardness and adhesion strength weresuccessfully deposited on the polymer composites. The properties of the coatingswere analyzed, and the mechanism of the coatings’ growth were studied, finallythe characteristics of the coatings fabricated by different methods werecompared.First, Al bond coatings were deposited on PMCs by plasma spray and arcspray technology. The best parameters （180A spray current,190mm spraydistance） were determined by detection of temperature of substrates duringspraying, XRD analysis and SEM observation. However, sufficient cool downtime is required during spraying.The Al₂O₃ceramic coatings were deposited on the as-sprayed Al bondcoatings. XRD analysis found that the coatings were composed by α-Al₂O₃andγ-Al₂O₃. The SEM observation revealed that there were two kinds ofmicrostructures distributing irregularly over the surface of coatings:1. coarseand coral-like splats with pores and2. smooth and relatively flat splats. Thereare lesscoral-like splats in the coating sprayed by higher current. The nano-hardness test proved that high hardness protective ceramic coatings can beproduced by plasma spray on PMCs. However the adhesion strength of ceramic coatings dropped below1.2MPa, implying the thermal damage took by plasmaspray.Microarc oxidation was applied on plasma sprayed Al bond coatings toform Al₂O₃coatings. XRD analysis and SEM observation with EDS analysiswere carried out on the coatings were treated by different treatment time anddifferent voltage. It was found that there were α-Al₂O₃, γ-Al₂O₃and amorphousin coatings. Furthermore, the amount of α-Al₂O₃andγ-Al₂O₃increases with theincrease of treatment time/voltage. The adhesion strength test proved that thecoatings with relatively high adhesion strength （4.67MPa） can be obtained bymicroarc oxidation technology.Finally, the wear resistance test were carried out on the ceramic coatingsproduced by different method. It proves that all the ceramic coatings canimprove the wear resistance of PMCs, however the coatings formed by microarcoxidation have better properties. Also, thermal resistance abilities of the coatingswere tested, it was found that both coatings can improve the thermal resistanceof PMCs significantly. Coatings deposited by plasma spraying technology havebetter thermal protective ability due to their high porosity.