| Studies on reinforcement of plasma sprayed Al2O3 coatings have been popular with researchers all the time. It will bring incalculable social and economic benefits, if a way of low cost and effective to solve this problem is found. Carbon fiber(CF) was regarded as the king of reinforcers. Advanced composites mainly reinforced by carbon fiber were widely applied in aerospace, national defense, sports leisure products, industrial and other fields. And applications of carbon fiber reinforced composites played an important role in high-tech and economic development. However, there are few studies on applying short carbon fiber into thermal spraying field, especially for thermal-sprayed ceramic coatings manufacturing. Plasma-sprayed composite coatings fabricated by combination of short carbon and Al2O3 might be of great potential application value.In this paper, the agglomeration of nano-Al2O3-carbon fiber(NAC) and nanoAl2O3(NA) powders were produced by spray drying method. In additon, micro-Al2O3-13%TiO2-carbon fiber(MATC) composite podwers were prepared by mechanical mixing. The powders above were used to deposite coatings by plasma sprayed, respectively. And the coatings made up of commercial micro-Al2O3(MA) and microAl2O3-13%Ti O2(MAT) set as reference objects were produced, too. The mechanical and tribolorical performance of the prepared coatings above were tested. The morphology of all five feedstocks, coatings and wear traces were represented by transmission electron microscope(TEM), scanning electron microscope(SEM) and energy dispersive spectrometer(EDS) primarily. The results are as follows:1. Feedstocks of nano-Al2O3 and nano-Al2O3-5%CF produced by spray-drying showed regular sphere, and fluidity of them satisfied the demand of plasma spraying pcocess. Besides, CF in nano-Al2O3-5%CF composite powders distributed uniformly owing to spray-drying method.2. Plasma sprayed coatings of micro-coatings(MA, MAT and MATC) showed typical layered structure, wherein occupied by more porosity and micro cracks. While nano-coatings(NA and NAC) consisted of fully molten zone(FM) and partial molten zone(PM) showed improvement in microdefects. Compared with conventional Al2O3 coatings, coatings made of nano-materials and composite coatings reinforced by TiO2 or CF showed lower porosity, which contributed to densification of coatings.3. Coatings reinforced by Ti O2 showed lower microhardness than coatings without Ti O2. While, Coatings made up of nano-materials or with CF addition showed higher microhardness. In view of the analysis of standard deviation on microhardness, the CF adding method of spray drying was more helpful to uniformity of coatings than mechanical mixing method. Compared with MA coatings, tensile strength of NA and MAT coatings increased by 20.1% and 23.9%, respectively. Meanwhile, due to the addtion of CF, tensile strength of MATC and NAC coatings increased by 18.9% and 45.9%, respectively. Moreover, coatings made of nano-materials and composite coatings reinforced by TiO2 or CF showed higher fracture toughness than conventional Al2O3 coatings.4. Compared with MA coatings, the friction coefficient of MAT and NA coatings was reduced effectively and presented more stable at the same experimental conditions, which would contribute in decreasing wear rate. Friction and wear properties of coatings within CF were superior to coatings without CF, and different addition methods of CF had different effect on tribological behaviors of coatings.5. The main wear form of the coatings was fatigue spalling and groove ploughing in all five kinds of coatings. MA, MAT and MATC coatings showed worse wear resistance because of much more serious atigue spalling generated by crack growth compared with NA and NAC coatings. |
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