Microstructure and properties of Al2O3-13%TiO2 coatings sprayed using nanostructured powders (original) (raw)
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Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2006
Correlation of microstructure and wear resistance of Al2O3-TiO2 coatings plasma sprayed with nanopowders was investigated in this study. Four kinds of nanostructured Al2O3-13 wt pct TiO2 coatings were fabricated by varying plasma-spraying parameters and were compared with an Al2O3-13 wt pct TiO2 coating fabricated with conventional powders. The nanostructured coatings showed a bimodal microstructure composed of fully melted regions of γ-Al2O3 and partially melted regions, while the conventional coating mostly consisted of fully melted γ-Al2O3, together with some TiO2-rich regions and unmelted Al2O3 powders. The wear test results revealed that the wear resistance of the nanostructured coatings was 3 or 4 times better than that of the conventional coating, because the preferential delamination seriously occurred along TiO2-rich regions in the conventional coating. In the nanostructured coatings, TiO2 was homogeneously dispersed inside splats and around, thereby leading to higher splat bonding strength and to better wear resistance over the conventional coating.
Surface and Coatings Technology, 2008
The goal of this study is to compare two Atmospheric Plasma Spraying (APS) systems for elaborating alumina/titania coatings with good wear resistance. Both torches used were a common d.c. current Gas-Stabilized Plasma gun (GSP) with argon and hydrogen as plasma forming gases, and a Water-Stabilized high-throughput Plasma gun (WSP) working with water as plasma forming substance. The feedstock were either cladded alumina/titania powder or a mixture of conventional fused and crushed Al 2 O 3 powder with agglomerated TiO 2 nanometric particles, the resulting mean size in both cases being about 50 µm. Feedstock material phases were α-alumina and anatase titanium dioxide and the composition of both powders was 13 wt.% of TiO 2 in Al 2 O 3. Coatings obtained were analyzed by scanning electron microscopy (SEM). They presented lamellar structures with titania uniformly distributed in the alumina matrix, for both spray techniques. X-ray diffraction showed that anatase phase of titania was converted into rutile phase. The wear resistance tested by slurry abrasion (SAR) has shown that the best coating was that obtained with cladded powder sprayed by GSP process. This finding matched with the highest microhardness of this coating (Vickers indentation). It is worth noting that with these two relatively dissimilar torches similar results were obtained for the wear resistance of alumina-13 wt.% titania coating.
Acta Materialia, 2002
The development of constituent phases and microstructure in plasma sprayed Al 2 O 3 -13wt.%TiO 2 coatings and reconstituted nanocrystalline feed powder was investigated as a function of processing conditions. The microstructure of the coatings was found to consist of two distinct regions; one of the regions was completely melted and quenched as splats, and the other was incompletely melted with a particulate microstructure retained from the starting agglomerates. The melted region predominantly consisted of nanometer-sized γ-Al 2 O 3 with dissolved Ti 4+ , whereas the partially melted region was primarily submicrometer-sized α-Al 2 O 3 with small amounts of γ-Al 2 O 3 with dissolved Ti 4+ . The ratio of the splat microstructure to the particulate microstructure and thus the ratio of the γ-Al 2 O 3 to α-Al 2 O 3 can be controlled by a plasma spray parameter, defined as the critical plasma spray parameter (CPSP). This bimodal distribution of microstructure and grain size is expected to have favorable impact on mechanical properties of nanostructured coatings, as has been observed before.
Surface and Coatings Technology
Al 2 O 3 /xTiO 2 (where x = 0, 3, 13 and 20 wt%) composite coatings were deposited onto mild steel substrates by atmospheric plasma spraying of mixed micron-sized Al 2 O 3 and nano-sized TiO 2 powders. Phase transformation from mainly stable α-Al 2 O 3 and anatase-TiO 2 in the powders to predominant metastable γ-Al 2 O 3 and rutile-TiO 2 in the coatings was observed. Reaction between Al 2 O 3 and TiO 2 phase also occurred producing Al 2 TiO 5 phase. Microstructural investigation showed that well separated TiO 2 lamellas were homogeneously dispersed between Al 2 O 3 lamellas. Hardness was found to decrease with increasing TiO 2 content while fracture toughness increased. The average wear rates of composite coatings determined by sliding wear test were lower than that of monolithic Al 2 O 3 coating by approximately 40%. This was mainly attributed to an increase in fracture toughness and reduction of friction coefficient due to a presence of TiO 2 splats.
Microstructure of Al2O3-13TiO2 Coatings Deposited from Nanoparticles by Plasma Spraying
Archives of Metallurgy and Materials, 2013
The aim of the study was to characterize nanostructured Al2O3-13TiO2 coatings deposited by plasma spraying on a grit blasted steel substrate. The Al2O3-13TiO2 coatings were characterized using scanning and transmission electron microscopy and X-ray diffraction techniques. Obtained coatings possessed a unique microstructure consisting of fully melted regions with the microstructure similar to a typical plasma sprayed lamellar morphology as the conventional coatings and areas comprising unmelted or partially melted nanosized particles. The analysis showed that most of the α-Al2O3 phase from the nanostructured powders transformed into γ-Al2O3 phase after plasma spraying process. Moreover, the presence of amorphous phase was also observed.
Nanostructured and conventional alumina–13 wt.% titania powders were thermally sprayed using air plasma spray (APS) process. Scanning electron microscopy (SEM) was used to examine the morphology of the agglomerated powders and the cross-section of the alumina–titania coatings. The microstructure and phase composition of the coatings were characterized by X-ray diffraction (XRD), and scanning electron microscopy (SEM). The fatigue and mechanical properties of the coatings were investigated. SEM analysis was also carried out on the worn surfaces of conventional and nanostructured coatings following the wear test. The experimental data indicated that the nanostructured coated samples exhibited higher hardness, wear resistance and fatigue strength compared to the conventional coated samples.
The nanostructured and two conventional alumina–titania coatings were deposited by atmospheric plasma spray. The presented studies show that nanoparticles are the predominant component of nanostructured Al2O3–13TiO2 powder grains. The microstructure of coating consisted of two distinct regions: fully melted and unmelted or partially melted nanostructured areas, which were comprised of components of a starting powder. Microhardness and modulus of these coatings were significantly lower than the values obtained for nanostructured coating. It was found that the plasma-sprayed nanostructured Al2O3–13TiO2 coating possessed better tribological properties than those of conventional alumina–titania coatings. The lower coefficient of friction and wear of the nanostructured Al2O3–13TiO2 coating is attributed to the bimodal microstructure and the enhanced mechanical properties in comparison to conventional alumina–titania coatings.
Deposition of Al2O3-TiO2 Nanostructured Powders by Atmospheric Plasma Spraying
Journal of Thermal Spray Technology, 2008
Al 2 O 3-13%TiO 2 coatings were deposited on stainless steel substrates from conventional and nanostructured powders using atmospheric plasma spraying (APS). A complete characterization of the feedstock confirmed its nanostructured nature. Coating microstructures and phase compositions were characterized using SEM, TEM, and XRD techniques. The microstructure comprised two clearly differentiated regions. One region, completely fused, consisted mainly of nanometer-sized grains of c-Al 2 O 3 with dissolved Ti +4. The other region, partly fused, retained the microstructure of the starting powder and was principally made up of submicrometer-sized grains of a-Al 2 O 3 , as confirmed by TEM. Coating microhardness as well as tribological behavior were determined. Vickers microhardness values of conventional coatings were in average slightly lower than the values for nanostructured coating. The wear resistance of conventional coatings was shown to be lower than that of nanostructured coatings as a consequence of Ti segregation. A correlation between the final properties, the coating microstructure, and the feedstock characteristics is given.
Microstructure and mechanical properties of plasma sprayed Al2O3 - 13%TiO2 Ceramic Coating
2017
This paper focused on the effect of deposition conditions on the microstructural and mechanical properties of the ceramic coating. In this study, Al 2 O 3 – 13%TiO 2 coated mild steel were prepared by using atmospheric plasma spray technology with different plasma power ranging from 25 kW to 40 kW. The as-sprayed coatings consist of γ-Al 2 O 3 phase as the major phase and small amount of the titania phase existed in the coating structure. High degree of fully melted region was observed in the surface morphology for the coating sprayed with high plasma power, which lead to the high hardness and low percentage of porosity. In this study, nanoindentation test was carried out to investigate mechanical properties of the coating and the results showed that the coatings possess high elastic behaviour, which beneficial in engineering practice.
Characterization of aluminum oxide - 40% titanium dioxide coating wear resistant
Vojnotehnicki glasnik, 2014
Plasma spray coatings play an important role in the design of surface properties of engineering components in order to increase their durability and performance under different operating conditions. Coatings are the most often used for wear resistance. This paper presents the microstructure and mechanical properties Al 2 O 3 40wt.%TiO 2 coating resistant to dry friction slide, grain abrasion and erosion of particles at operating temperatures up to 540°C. In order to obtain the optimal characteristics of coating was performed optimization of deposition parameters. The powder Al 2 O 3 40wt.%TiO 2 is deposited atmospheric plasma spraying (APS) process with a plasma current of 700, 800 and 900A. Evaluate the quality of the coating Al 2 O 3-40wt.%TiO 2 were made on the basis of their hardness, tensile bond strength and microstructure. The best performance showed the deposited layers with 900A. The morphology of the powder particles Al 2 O 3 40wt.%TiO 2 was examined with SEM (Scanning Electron Microscope). Microstructure of the coatings was examined by light microscopy. Analysis of the deposited layers was performed in accordance with standard Pratt & Whitney. Evaluation of mechanical properties of the layers was done by examining HV 0.3 microhardness and tensile strength of the tensile testing. Studies have shown that plasma currents significantly affects the mechanical properties and microstructure of coatings which are of crucial importance for the protection for components subjected to wear.