| Tungsten fibers are ideal reinforcing material of high temperature alloys and composite materials due to high density, high melting point, high strength, good tensile strength and specifice strength,. In this paper, the CeO2and A12O3coatings on pretreated tungsten fibers were fabricated by sol-gel method.The characterisitc functional groups of sol and gel were analyzed by FT-IR. The thermal reaction, oxidation weight gain behavior and phase composition of gel were investigated by TG-DSC and XRD. The morphology and microstructure of the coatings were investigated by SEM. The main results are as followings:(1) Sol-gel technology was applied to fabricate intact, compact and uniform CeO2coatings growing on coarsened grooves on tungsten fibers by following steps. First,0.1mol of Ce (NO3)3·6H2O,0.3mol of citric acid and0.075mol of DMAC were galated for12h; Second the coating was calcined for2h under600℃with a heating rate of1-2℃/min after step-drying. However the coatings were not combined tightly enough with tungsten fibers. It has been shown that pretreatment with mixed acid can enhance the surface roughness of the fiber and improve the binding force of coatings.(2) The integrated, compact and smooth A12O3coatings can be obtained via sol-gel method under the conditions of0.33mol/L in Al-collosol,0.3g in PVA, glue dissolvation and aging of8h, and then calcination for2h at950℃with a heating rate of3-5℃/min after step-drying, which exhibits better bonding in fibers interface.(3) The oxidation resistance of the coated fibers was tested through TG. The results indicated that the initial and rapid oxidation temperatures of tungsten fibers coated by CeO2and A12O3were about50℃and120℃higher than the original tungsten fibers, and the oxidation weight gain was reduced by3%and8%, respectively. |
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