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ABSTRACT: Nanostructured and conventional Al2O3-3 wt% TiO2 coatings were deposited by atmospheric plasma spraying. The wear and friction properties of both coatings against a steel ball under dry friction conditions were examined. It was found that the wear resistance of the nanostructured Al2O3-3 wt% TiO2 coating was superior to that of the corresponding conventional counterpart. The improvement in wear resistance of the nanostructured coating was attributed to its higher toughness and cohesion strength between splats. As for the nanostructured coating, the wear mechanism was mainly adhesion with micro-abrasion at low loads (20 N). At high loads (80 N), the wear of the nanostructured coating was controlled by plastic deformation and associated delamination along the splat boundaries, which was similar to that of the conventional coating at low loads. However, the failure of the conventional coating was predominantly brittle fracture within the splats and delamination between splats at high loads.
Tribology Letters 01/2004; 17(1):19-26. · 1.58 Impact Factor
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ABSTRACT: Nanostructured and conventional alumina–3 wt.% titania coatings were deposited by air plasma spraying (APS). The microstructure and phase composition of the coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Mechanical properties including hardness, adhesion strength, crack extension force (GC) and sliding wear rate were measured. Equiaxed α-Al2O3 grains were observed in the nanostructured Al2O3–3 wt.% TiO2 coating and the diameter of α-Al2O3 grains were about 150 to 700 nm in size. The microhardness of both kinds of coating was similar and about 820 HV0.2. However, the adhesion strength and crack extension force of the nanostructured coating increased by 33 and 80%, respectively, as compared with those of the conventional coating. The wear rate of the nanostructured coating was lower than that of the conventional coating. The results were explained in terms of characteristics of the powders and microstructure of the coatings.
Journal of the European Ceramic Society.
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ABSTRACT: Nanostructured and conventional Al2O3–3 wt.% TiO2 coatings were deposited by atmosphere plasma spraying. The tribological properties of both coatings against a silicon nitride ball were examined in the temperature range from room temperature to 600 °C. The friction coefficients of both coatings were similar and ranged from 0.85 to 0.10. The wear rates of both coatings increased with the increase in temperature. At room temperature, a protective layer consisting of silicon oxide existed on the worn surface of both coatings and led to the lower wear rate. At high temperature, brittle fracture occurred on the worn surfaces of both coatings, which was enhanced with the increase of temperature. But, the wear resistance of the nanostructured coating was superior to that of the conventional coating except at room temperature. The improvement in wear resistance of the nanostructured Al2O3–3 wt.% TiO2 coating was discussed in the terms of its microstructural characteristics.
Wear.
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ABSTRACT: The microstructure of plasma-sprayed alumina–3wt.% titania coatings with the nanostructured powders was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the nanostructured coating exhibited a bimodal microstructure: splat lamellae similar to the conventional coating and equiaxed grains originating from the starting feedstock. The splat lamellae consisted of γ-Al2O3 grains and most of them were less than 200 nm in diameter. Equiaxed grains took the modification of α-Al2O3 and ranged from 150 to 800 nm in size. In addition, the modifications of TiO2 disappeared and Ti element was dissolved in γ-Al2O3 grains. The bimodal microstructure contributed to the improvement in mechanical properties of the nanostructured coating.
Materials Science and Engineering: A.
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ABSTRACT: Nanostructured and conventional alumina–3 wt.% titania monolithic coatings were deposited by air plasma spraying (APS). The thermal diffusivity was measured by the laser flash technique. The thermal diffusivity of the nanostructured Al2O3–3 wt.% TiO2 coating was higher compared with that of the corresponding conventional coating at temperature ranging from 200 to 1000 °C. For the nanostructured coating, there was no difference in the thermal diffusivity between during heating and cooling. However, the thermal diffusivities of the conventional coating were higher during cooling than those during heating. SEM and TEM examination showed that the nanostructured coating contained equiaxed grains with sizes from 150 to 800 nm besides splat lamellae. In the nanostructured coating, most of columnar grains in splat lamellae were less than 200 nm. Splat lamellae of the nanostructured coating bonded well each other and their thickness ranged from 0.4 to 1 μm. The decrease of thermal diffusivity of the nanostructured coating was attributed to the increase of grain boundaries and defective crystal structure. The stability of thermal diffusivity of the nanostructured coating was considered to relate to the absence of narrow long micro-cracks between splat lamellae. Nanostructured and conventional alumina–3 wt.% titania monolithic coatings were deposited by air plasma spraying (APS). The thermal diffusivity was measured by the laser flash technique. The thermal diffusivity of the nanostructured Al2O3–3 wt.% TiO2 coating was higher compared with that of the corresponding conventional coating at temperature ranging from 200 to 1000 °C. For the nanostructured coating, there was no difference in the thermal diffusivity between during heating and cooling. However, the thermal diffusivities of the conventional coating were higher during cooling than those during heating. SEM and TEM examination showed that the nanostructured coating contained equiaxed grains with sizes from 150 to 800 nm besides splat lamellae. In the nanostructured coating, most of columnar grains in splat lamellae were less than 200 nm. Splat lamellae of the nanostructured coating bonded well each other and their thickness ranged from 0.4 to 1 μm. The decrease of thermal diffusivity of the nanostructured coating was attributed to the increase of grain boundaries and defective crystal structure. The stability of thermal diffusivity of the nanostructured coating was considered to relate to the absence of narrow long micro-cracks between splat lamellae.
Surface and Coatings Technology.
