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CHARACTERIZATION OF ALUMINUM OXIDE - 40% TITANIUMDIOXIDE COATING WEAR RESISTANT
Mihailo R. Mrdak
Research and Develoopment Center IMTEL, Communications a.d., Belgrade
DOI: 10.5937/vojtehg62-3531
FIELD: Chemical Technology ARTICLE TYPE: Original Scientific Paper
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Summary:
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 Al2O3 40wt.%TiO2 coating resistant to dry friction slide, grain abrasion and erosion of particles at operating temperatures up to 5 540°C. In order to obtain the optimal characteristics of coating was perfor- § med optimization of deposition parameters. The powder Al20340wt.%Ti02 jl is deposited atmospheric plasma spraying (APS) process with a plasma ° current of 700, 800 and 900A. Evaluate the quality of the coating Al203-40wt.%Ti02 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 Al20340wt.%Ti02 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 HV03 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.
Key word: titanium dioxide; aluminum oxide; bond strength; microhard-ness; interface; atmospheric plasma spray-APS.
Introduction
Plasma spray coatings are commonly used for the abrasion resistance of materials in many applications. Tribological performance coatings are dependent on a number of properties such as the composition of the powder, the nature of phases and their distribution, microstructure, porosity and residual stresses. All of these properties determine the hardness of coatings, which are conventionally used as the primary parameter for wear resistance. Mechanical properties of the coatings depend not only on the nature and distribution of the phases present in the coating, but also a number of other characteristics such as microstructure, porosity, nature of residual stresses and their value within the coating and adhesion of the coating. Coatings based on Al2O3 ceramics are a good choice for protecting components subjected to excessive wear. Al2O3 ceramic is hard and its main deficit is the brittleness (Ananthapadmanabhan, et al., 2003), (Erickson, et al., 2001). Adding titanium dioxide TiO2 leads to a balanced properties, maintain sufficient strength, but also a significant increase in toughness coating. TiO2 has a lower melting point than Al2O3 and plays an important role in promoting the coatings with higher density (Pantelis, et al., 2000), (Gessasma, et al., 2006, pp.13-19), (Normand, et al., 2000, 278-287). Al2O340wt.%TiO2 coatings is one of the coatings which are largely deposited atmospheric plasma spray process APS. It is known for its resistance to abrasion, corrosion and erosion. Control of the plasma spray process is considered to be very important in improving the characteristics of the deposit and the melting of the powder particles, mechanical properties of coatings and coating properties in service. In addition, hardness and tribological properties of coatings are strongly influenced by the deposition process parameters which directly affect the distribution of porosity and phase content of a range of particle size and morphology. Porosity in the coating decreases with increasing plasma current. With the reduction of plasma currents and increasing the flow of powder is present in the microstructure inhomogeneity such as porosity, cracks unmelted particles, oxide inclusions, which reduce the microhardness. (Vencl, et al., 2006, pp.151-157), (Mrdak, 2010, pp.5-16), (Mrdak, 2012, pp.182-201), (Mrdak, 2013, pp.68-88). Al2O340%wt.TiO2 coatings deposited atmospheric plasma spray - APS has a porosity of 4 to 6% (Tomaszeka, et al., 2004, pp.137-149). The powder Al2O340%wt.TiO2 consisting of oxide Al2O3 and 40wt.%TiO2, which is used for the production of coatings for applications that require a moderate hardness and fracture strength greater than the strength of coatings produced from pure Al2O3, Al2O33wt.%TiO2 ili Al2O3-13wt.%TiO2 (Material Product Data Sheet, 2012, Amdry 6257 Aluminum Oxide 40% Titanium Dioxide Powders, DSMTS-0083.1, Sulzer Metco). The coatings Al2O340wt.%TiO2 in the deposited state contains two modi-
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fications a - Al2O3 and y - Al2O3,TiO2 and two spinel modification of rutile a <n - Al2TiO5 and p - Al2TiO5 (Tomaszeka, et al., 2004, pp.137-149), (Alford, ^
Materials and experimental details
For the experiment using powder company Sulzer Metco in terms Amdry 6257 (Material Product Data Sheet, 2012, Amdry 6257 Aluminum Oxide 40% Titanium Dioxide Powders, DSMTS-0083.1, Sulzer Metco). The powder Al2O3-40%wt.TiO2 was developed for the preparation of coatings used for surface protection of bearings and supports the protection of the base metal friction, abrasion and erosion of particles up to 540°C. The powder was produced by melting and casting into blocks that are sub-
2002), (Vlasova, et al., 2012, pp.17-24). Coatings are recommended for surfaces bearing supports, for grain abrasion, friction and erosion of particles at operating temperatures up to 540°C. Polished coatings have low wettability, which makes them resistant to weak acid environment and suitable for use in the chemical processing industry (Material Product Data Sheet, 2012, Amdry 6257 Aluminum Oxide 40% Titanium Dioxide Powders, DSMTS-0083.1, Sulzer Metco). The coatings Al2O3-TiO2 provide excellent protection to the exposed parts of dry sliding friction, abrasive wear and erosion at high temperatures. The coefficients of thermal expansion of the coating Al2O3-TiO2 were 8 and 7.5 (10"6K"1) (Normand, et al., 2000, pp.278-287). Such coatings are also desirable for electrical insulation, for protection axle sleeve and axle pumps. These coatings are generally resistant to abrasion, corrosion and thermal shock. With the addition of TiO2 coating increases wear resistance, tensile strength but the hardness decreases (Ramachandran, et al., 1998, pp.144-152). Titanium dioxide TiO2 has higher wear resistance with lower friction coefficient and lower hardness of Al2O3 coatings. Wear behavior of atmospheric plasma sprayed (APS) coatings Al2O3-TiO2 tested using the method described in (Pin-On- | Disk). The coefficient of friction decreases with an increasing sliding speed and applied load. In the initial period increases the coefficient of friction due to increased contact area and low surface roughness. Then the value of the coefficient of friction stabilizes (Krishnakumar, Swarnamani, 1996), ® (Guessasma, et al., 2006, pp.13-19). The coefficient of friction is determined by the method POD is 0.5-0.6 (Bounazef, et al., 2004, pp.2451-2455).
The main objective of this study was to atmospheric plasma spraying - APS deposited coatings Al2O3-40wt.%TiO2 with the best structural and mechanical properties to be applied to aerospace parts bearing supports. Made three groups of samples with the current values g of 700, 800 and 900 A. Analyzed and studied the microstructure and mechanical properties of layers of coatings. The best performance showed layers deposited with 900A.
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sequently milled to a specific granularity. This technological process to produce powders with angular grains. For the experiment using the powder granules had a range of 15-45pm. Figure 1 shows the (SEM) scanning electron micrographs of the morphology of the powder particles.
Figure 1 - (SEM) Scanning electron micrography of Al2O3-40%wt.TiC>2 powder particles Slika 1 - (SEM) Skening elektronska mikrografija cestica praha Al2O3-40%tez.TiO2
On micrography seen angular grains of powder consisting of oxide Al2O3 dark gray color and titanium dioxide TiO2 light gray. The bases on which the deposited coatings for testing microhardness and evaluation of microstructure in deposited state are made of steel C.4171 (X15Cr13 EN10027) in thermally unprocessed dimensions of 70x20x1, 5mm (Turbojet Engine-Standard Practices Manual, 2002). Basis for testing the bond strength are also made of steel C.4171 (X15Cr13EN 10027) in thermally unprocessed dimension 025x50 mm (Turbojet Engine-Standard Practices Manual, 2002).
Microhardness testing, bond strength and microstructure
Examination of microhardness coating was performed by HV03. The measurement was carried out in the direction along the fins in the middle and at the ends of the sample. Done five readings in three places, and the paper shows the minimum and maximum values.
Tests for tensile bond strength were performed at room temperature on hydraulic equipment with a speed of 10 mm / min, for all tests. For each group of samples were done three test specimen, and the paper presents the mean. Mechanical and microstructural characterization of the coating were carried out according to standard Pratt & Whitney (Turbojet Engine-Standard Practices Manual, 2002).
Microstructural analysis of the coating and image analysis of the share of micro pores in the coating was performed under a light microscope. The morphology of the powder particles was performed on the SEM (Scanning Electron Microscope).
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Plasma spray deposition parameters are shown in Table 1 Powder deposition Al2O3-40%wt.TiO2 was performed with an atmospheric plasma spray system company Plasmadyne and plasma gun SG - 100, with appropriate control robotic spray conditions. Plasma Gun SG -100 consisted of a cathode type K 1083-129, anode type A 2084-145 and gas injectors type GI 2083 - 113. As the arc gas was used Ar in combination with He and power supply up to 40 kW. Before the process of depositing steel substrate are roughed corundum particles with sizes of 0.7-1.5 mm. The coatings were formed with thicknesses from 0,25 to 0,30 mm.
Table 1 - Plasma spray parameters Tabela 1 - Plazma sprej parametri
Deposition parameters Values
Plasma current, I (A) 700 800 900
Plasma Voltage, U (V) 36 38 40
Primary plasma gas flow rate, Ar (l/min) 47 47 47
Secondary plasma gas flow rate, He (l/min) 15 15 15
Carrier gas flow rate, Ar (l/min) 6 6 6
Powder feed rate (g/min) 50 50 50
Stand-off distance (mm) 110 110 110
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Results and discussion
The microhardness and microhardness ranges Al203-40%wt.Ti02 coatings were directly related to the values of the plasma current. The layers Al203-40%wt.Ti02 coatings were measured different values of microhardness with ones of various ranges. At least values of microhardness of min. 676 to max.734HV03 with the largest range of 58HV03 microhard-ness were observed in the deposited layers with values plasma current of 700A. The highest values of microhardness min. 950 to max 994HV0.3 to
the lowest range of 44HV0. 3 microhardness were observed in the deposited layers with values plasma current of 900A. Ranges microhardness of the coatings are the result of the different distribution of pores in the deposited layers. These values were confirmed by image analysis to determine the total content of pores in the layers. Figure 2 shown min. and max. values of the microhardness ceramic coatings Al203-40% wt.TiO2.
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Figure 2 - Microhardness of Al2O3-40%wt.TiO2 layers Slika 2 - Mikrotvrdoca Al2O340%tez.TiO2 slojeva
Figure 3 shows the values of tensile strength of Al2O3-40%wt.TiO2 coating. For the deposited coatings were measured for different values of tensile bond strength.
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Figure 3 - Al203-40%wt.Ti02 bond strength layers Slika 3 - Cvrstoca spoja Al203-40%tez.Ti02 slojeva
Bond strength coatings is significantly influenced by the value of the plasma current. The lowest tensile bond strength of 17MPa, coatings deposited with the lowest values of plasma current of 700A resulted in a lower degree of melting of the powder particles in comparison to the other two coatings deposited. The highest value of the bond strength of the 30MPa had layers that were deposited with the highest values of plasma current of 900A. The high value of the plasma current is allowed to deposit coatings with good inter - lamellar bonding and good bonding lamella for coating a substrate. A higher value of plasma current is increased the adhesion of coatings, mechanical properties and improvement of microstructure, as confirmed by metallographic examination. When the proportion of pores is directly related to the values of the bond strength of coatings, to the measured values of the coating deposited with the highest values of plasma current indicates that their rate of the lowest compared to the other two films. These values were confirmed by analyzing the microstructure of coatings under a light microscope. For all the deposited layer coating failure mechanism was adhesion at the interface between the substrate and the coating.
Microstructure and properties of coatings Al203-40%wt.Ti02 were under the influence of the plasma current. A higher value of plasma current is because of an improved microstructure. Plasma currents of 900A provide better and more even melting of the powder particles Al203-40%wt.Ti02. Evenly melted powder particles are more properly formed in the collision with the substrate and the deposited layers with a lower content of pores with higher cohesive strength and tensile strength. The minimum value of plasma current of 700A is influenced on less and limited bonding layers deposited in lamellae which increased the proportion of pores and reduce the coating hardness and adhesion of coating. 0n Figures 4 and 5 shows the microstructure of the deposited layers Al203-40%wt.Ti02 coatings with values of plasma current 900A, which had the best microstructure and mechanical properties.
Coating - Al203 + 4Qwt.%Ti02
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Figure 4 - Al2C>3-40%wt.Ti02 coating microstructure deposited with 900A Slika 4 - Mikrostruktura Al20340%tez.Ti02 slojeva prevlake deponovane sa 900A
Figure 5 - Al2O3-40%wt.TiO2 coating microstructure deposited with 900A Slika 5 - Mikrostruktura Al2O3-40%tez.TiO2 slojeva prevlake deponovane sa 900A
Figure 4 shows the macro coatings Al2O3-40%wt.TiO2 which confirms that uniform coating layers deposited on the substrate. Qualitative analysis of the deposited layers Al2O3-40%wt.TiO2 (Figure 4 and Figure 5) showed that the interface between the substrate and the coating bond good with negligible content of particles Al2O3 of roughening. Along the interface between the substrate and the coating are not present micro cracks and macro cracks. Bond coating with the substrate is uniform, without removing layers of coating with substrate. The structure of the coating is lamellar, with visible dark lamellae oxide Al2O3 and light lamellae titanium dioxide TiO2. Coating layers were deposited with a small rate of pores and microcracks in the absence of macro cracks in coating. The layers are not present unmelted powder particles.
Figure 6 shows the microstructure of the coatings deposited with the lowest values of plasma current 700A, which had the highest rate of pores and the worst mechanical properties.
Coating - А1г03 + 40wt.%Ti02
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Figure 6 - Al203-40%wt.Ti02 coating microstructure deposited with 900A Slika 6 - Mikrostruktura Al203-40%tez.Ti02 slojeva prevlake deponovane sa 900A
Through the layers of coating are observed spherical pores black. In layers deposited with 900A micro pores are present up to 5 |jm. In layers deposited with 700A micro pores are present above 5 ^m. Image analysis showed that the overall rate of pores in the coating layers deposited with the 900A was 2%, In layers deposited with the 700A rate micro pores was 3.5%, and the deposited layers 800A rate of pores was 6%.
In Figure 7 shows the phases in the microstructure of coating with the best mechanical and structural characteristics.
Figure 7 - Al2O3-40%wt.TiC>2 coating microstructure deposited with 900A Slika 7 - Mikrostruktura Al2O3-40%tez.TiO2 slojeva prevlake deponovane sa 900A
On photomicrograph shows that the molten powder particles regularly deposited. In microstructure not present unmelted particles and micro cracks. The structure of the inner layers of the coating is lamellar. The base coating is made of dark phase of basic oxide Al2O3. The structure of the present two modifications of a - Al2O3 and y - Al2O3 (Tomaszeka, et al., 2004, pp.137-149), (Alford, 2002), (Vlasova, et al., 2012, pp.17-24). Through ceramic layers of Al2O3 phase is clearly observed light lamellae not degradable titanium dioxide TiO2 and two spinel modifications rutile of a -Al2TiO5 and p - Al2TiO5 which are formed by reaction of oxides Al2O3 and TiO2 powder melting process in the plasma (Tomaszeka, et al., 2004, pp.137-149), (Alford, 2002), (Vlasova, et al., 2012, pp.17-24).
Conclusion
Plasma spraying coatings Al203-40%wt.Ti02were deposited with three different values of the plasma current 700, 800 and 900A. Examined and analyzed the microstructure and mechanical properties of the deposited coatings on the basis of which came to the following conclusions.
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Mechanical properties and microstructure of coatings Al2O3-40% wt.TiO2 were under the influence of the plasma current. A higher value of plasma current is increased mechanical properties and improved adhesion of the coating microstructure.
With increasing plasma current were deposited the coatings by a higher values of microhardness and a smaller range of microhardness through layers coatings.
Coatings deposited with a plasma current of 900 A also had the highest values of microhardness and tensile bond strength. For all of coating failure was at the interface between the coating and the substrate. The microhard-ness and tensile bond strength were correlated with their microstructures.
The structure of the deposited coatings Al2O3-40%wt.TiO2 is lamellar. The coatings are present spherical pores black color. The smallest rate of micro pores than 2% had layers deposited with a plasma current of 900A, and the largest rate of micro pores of 6% had layers deposited with a plasma current of 700A. The structure of ceramic coatings Al2O3-40%wt.TiO2 present two modifications of aluminum oxide a - Al2O3 and y - Al2O3, titanium dioxide TiO2 and two spinel modifications of rutile a -Al2TiO5 and p - Al2TiO5 which are formed by reaction of oxides Al2O3 and TiO2 powder melting process in the plasma.
Literature
Ananthapadmanabhan, P.V., Thiyagarajan, T.K., Satpute, R.U., Venkatra-mani, N., Ramachandran, K., 2003, Surf Coat Technol., 168:231-40.
Alford, N.McN., EPSRC Final Report, No. GR/K70649, August 2002, available on
http://www.eeie.ac.uk/research/pem/reports%5cFINAL%20REPORT%20GRM33 686.html.
Bounazef, M., Guessasma, S., Ghislain, M., Christian, C., 2004, Effect of APS process parameters on wear behaviour of alumina - titania coatings, Materials Letters, Vol. 58, pp. 2451-2455.
Erickson, L.C., Hawthorne, H.M., Troczynski, T., 2001, Wear; 250:569-75.
Guessasma, S., Bounazef, M., Nardin, P., Sahraoui, T., 2006b, Note on POD test parameters to study wear behaviour of alumina - titania coatings, ceramics International, Vol.52, pp.13-19.
Krishnakumar, V. and Swarnamani, S., 1996, Tribological Behaiour of plasma sprayed Al2O3 and TiO2 ceramic hard coating under dry contact., IIT Madras, department of applied Mechanics.
Material Product Data Sheet, 2012, Amdry 6257 Aluminum Oxide 40% Titanium Dioxide Powders, DSMTS-0083.1, Sulzer Metco.
Mrdak, M., 2010, Uticaj brzine depozicije praha na mehanicke karakteristi-ke i strukturu APS - NiCr/Al prevlake, Vojnotehnicki glasnik/Military Technical Courier, Vol.58, No.4, pp. 5-16.
Mrdak, M., 2012, Plasma deposited layers of nickel-chrome-aluminum-yttrium coatings resistant to oxidation and hot corrosion, Vojnotehnicki gla-snik/Military Technical Courier, Vol. 60, No.2, pp.182-201.
Mrdak, M., 2013, Characterization of sealing nickel-graphite coating in the system with bonding of nickel-aluminum coating, Vojnotehnicki glasnik/Military Technical Courier, Vol. 61, No.1, pp.68-88.
Normand, B., Fervel, V., Coddet, C., Nikitine, V., 2000a, Tribological properties of plasma sprayed alumina-titania coatings:role and control of the microstructure, surface and coatings technology, Vol.123, pp.278-287.
Pantelis, DI., Psyllaki, P., Alexopoulos, N., 2000, Wear; 237:197-204.
Ramachandran, K., Selvarajan V., Ananthapadmanabhan P. V., Sreekumar K.P., 1998, Microstructure, adhesion, microhardness, abrasive wear resistance of the plasma sprayed alumina and alumina - titania coatings, Thin solid film, Vol. 315, pp.144-152.
Tomaszeka, R., Pawlowskia, L., Zdanowskib, J., Grimblotc, J., Laureynsd, J., 2004, Microstructural transformations of Ti02, Al203+13Ti02 and Al203+40Ti02 at plasma spraying and laser engraving, Surface & Coatings Technology 185, pp. 137-149.
Turbojet Engine - Standard Practices Manual (PN 582005), 2002, Pratt & Whitney, East Hartford, USA.
Vencl, A., Mrdak, M., Cvijovic, I., 2006, Microstructures and tribological properties of ferrous coatings deposited by APS (Atmospheric Plasma Spraying) on Al-alloy substrate, FME Transactions, Vol.34, No.3, pp.151-157.
Vlasova, M., Kakazey, M., Sosa, B., Coeto, Marquez Aguilar, P. A., Rosales, I., Escobar Martinez, A., Stetsenko, V., Bykov, A., Ragulya, A., 2012, Laser Synthesis of Al2Ti05 and Y3Al5012 Ceramics from Powder Mixtures Al203- Ti02 and Al203-Y203, Science of Sintering, Vol.44, pp.17-24.
KARAKTERIZACIJA ALUMINIJUM OKSID 40% TITANIJUM DIOKSID PREVLAKE OTPORNE NA HABANJE
OBLAST: hemijske tehnologije VRSTA CLANKA: originalni naucni clanak
Sazetak:
Plazma sprej prevlake predstavljaju vaznu ulogu u projektovanju povrsinskih osobina inzenjerskih komponenti u cilju povecanja njihove izdrzljivosti i performansi pod razlicitim uslovima rada. Prevlake se naj-cersce koriste za otpornost na habanje. U radu su prikazane mikrostrukture i mehanicke karakteristike prevlake Al2O3-40tez.%TiO2 otpor-ne na suvo trenje klizanjem, abraziju zrna i eroziju cestica na radne temperature do 540°C. U cilju dobijanja optimalnih karakteristika prevlake izvrsena je optimizacija parametara depozicije. Prah Al2O— 40tez.%TiO2 je deponovan atmosferskim plazma sprej (APS) postup-
kom sa plazma strujom od 700, 800 i 900A. Procene kvaliteta prevlake Al203-40tez. %TiO2 su uradene na osnovu njihovih mikrotvrdoca, zate-zne cvrstoce spoja i mikrostrukture. Najbolje perfomanse su pokazali slojevi deponovani sa 900A. Morfologija cestica praha Al20— > 40tez.%Ti02je ispitana na SEM-u (skening elektronskom mikroskopu).
Mikrostruktura prevlaka ispitana je na svetlosnom mikroskopu. Analiza deponovanih slojevima je uradena u skladu sa standardom Pratt & Whitney. Procena mehanickih karakteristika slojeva je uradena ispitiva-njem mikrotvrdoce metodom HV03 i zatezne cvrstoce spoja ispitiva-E njem na zatezanje. Istrazivanja su pokazala da plazma struja bitno uti-
o ce na mehanicke osobine i mikrostrukture prevlaka koje su od presud-
o nog uticaja za zastitu delova izlozenih habanju.
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0 Plazma sprej prevlake se najcesce koriste za otpornost na habanje materijala u mnogim aplikacijama. Triboloske performanse prevlaka za> vise od niza osobina kao sto su: sastav praha, priroda faza i njihova ras-
< podela, mikrostruktura, poroznost i zaostali naponi. Sve ove osobine od-reduju tvrdocu prevlaka, koja se konvencionalno koristi kao primarni pa-rametar za procenu otpornost na habanje. Mehanicke osobine prevlake ne zavise samo od prirode i distribucije faza prisutnih u prevlaci, vec i od
^ niza drugih osobina kao sto su mikrostruktura, poroznost, priroda zao-
< stalih napona i njihova vrednost u okviru prevlake i adhezija prevlake. u Prevlake na bazi Al2O3 keramike su dobar izbor za zastitu delova izloze-g nih prekomernom habanju. Al2O3 keramika je tvrda i njen glavni nedo-
statak je krtost (Ananthapadmanabhan, et al., 2003), (Erickson, et al.,
1 2001). Dodavanjem titanijum dioksida TiO2 dovodi do uravnotezenih j— svojstava, odrzavanja dovoljne tvrdoce, ali i znacajnog povecanja zilavo-§ sti prevlake. TiO2 ima manju tacku topljenja od Al2O3 i ima vaznu ulogu u o promovisanju prevlake sa vecom gustinom (Pantelis, et al., 2000), (Ges> sasma, et al., 2006), (Normand, et al., 2000). Prevlaka Al2O—
40%tez.TiO2 deponovana atmosferskim plazma sprejom - APS ima poroznost od 4 do 6% (Tomaszeka, et al., 2004, pp. 137-149). Prah Al2O— 40%tez.TiO2 se sastoji od oksida Al2O3 i 40tez.%TiO2 koji se koristi za proizvodnju prevlaka za aplikacije koje zahtevaju umerenu tvrdocu i vecu cvrstocu preloma u odnosu na cvrstocu prevlaka proizvedenih od ci-stog Al2O3, Al2O—3tez.%TiO2 ili Al2O3-13tez.%TiO2 (Material Product Data Sheet, 2012, Amdry 6257 Aluminum Oxide 40% Titanium Dioxide Powders, DSMTS-0083.1, Sulzer Metco). Prevlaka Al2O340tez.%TiO2 u deponovanom stanju sadrzi dve modifikacije a - Al2O3 i y - Al2O3 ,TiO2 i dve spinel modifikacije rutila a - Al2TiO5 i £> - Al2TiO5 (Tomaszeka, et al., 2004, pp.137-149), (Alford, 2002), (Vlasova, et al., 2012, pp.17-24). Prevlake se preporucuju za povrsine oslonaca lezajeva, za otpornost na abraziju zrna, trenje i eroziju cestica na radne temperature do 540°C. Ove prevlake su generalno otporne na habanje, koroziju i toplotne uda-re. Sa dodatkom TiO2 povecava se otpornost prevlake na habanje, zate-zna cvrdtoca spoja ali se tvrdoca smanjuje (Ramachandran, et al., 1998,
pp. 144-152). Titanijum dioksid TiO2 ima vecu otpornost na habanje, sa manjim koeficijentom trenja i manjom tvrdocom od Al2O3 prevlake. Po-nasanje na habanje atmosferski plazma naprskane (APS) prevlake Al2O3TiO2 se ispituje pomocu metode POD (Pin-On-Disk). Koeficijent trenja se smanjuje sa povecanjem brzine klizanja i primenjenog optere-cenja. U periodu uhodavanja se povecava koeficijent trenja zbog pove-canja kontaktne povrsine i nize hrapavosti. Zatim se vrednost koeficijen-ta trenja stabilizuje (Krishnakumar, Swarnamani, 1996), (Guessasma, et al., 2006, pp. 13 -19). Koeficijent trenja odreden metodom POD je 0.50.6 (Bounazef, et al., 2004, pp. 2451-2455).
Glavni cilj rada je bio da se atmosferskim plazma sprej postup-kom - APS deponuju prevlake Al2O3-40tez.%TiO2 sa najboljim struk-turnim i mehanickim karakteristikama koje ce se primeniti na vazduho-plovnim delovima oslonaca lezajeva. Uradene su tri grupe uzoraka sa vrednostima struje od 700, 800 i 900 A. Analizirane su i proucavane mikrostrukture i mehanicke karakteristika slojeva prevlaka. Najbolje perfomanse su pokazali slojevi deponovani sa 900A.
Materijali i eksperimentalni detalji
Za eksperiment se koristio prah firme Sulcer Metko (Sulzer Met-co) sa oznakom Amdry 6257(Material Product Data Sheet, 2012, Am-dry 6257 Aluminum Oxide 40% Titanium Dioxide Powders, DSMTS-0083.1, Sulzer Metco). Prah Al2O3-40%tez.TiO2 je razvijen za izradu prevlaka koje se koriste za zastitu povrsine oslonaca lezajeva i zastitu metalnih osnova od trenja, abrazije i erozije cestica do 540°C. Prah je proizveden metodom topljenja i livenja u blokove koji se naknadno me-lju na odredenu granulaciju. Ovim tehnoloskim postupkom se proizvo-de prahovi sa uglastim zrnima. Za eksperiment se koristio prah koji je imao raspon granulata od 15 - 45pm.
Osnove na koje su deponovane prevlake za ispitivanje mikrotvr-doce i za procenu mikrostrukture u deponovanom stanju su napravlje-ne od celika C.4171 (X15Cr13 EN10027) u termicki neobradenom stanju dimenzija 70x20x1,5mm (Turbojet Engine - Standard Practices Manual (PN 582005), 2002, Pratt & Whitney, East Hartford, USA). Osnove za ispitivanje cvrstoce spoja su takode napravljene od celika C.4171(X15Cr13EN10027) u termicki neobradenom stanju dimenzija 025x50 mm (Turbojet Engine - Standard Practices Manual (PN 582005), 2002, Pratt & Whitney, East Hartford, USA).
Ispitivanje mikrotvrdoce,cvrstoce spoja i mikrostrukture
Ispitivanje mikrotvrdoce slojeva prevlaka uradeno je metodom HV03. Merenje je obavljeno u pravcu duz lamela, u sredini i na krajevi-ma uzorka. Uradeno je pet ocitavanja na tri mesta, a u radu su prikaza-ne minimalne i maksimalne vrednosti.
Ispitivanja zatezne cvrstoce spoja su radena na sobnoj tempera-turi na hidraulicnoj opremi sa brzinom od 10 mm/min, za sva ispitiva-
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nja. Za svaki grupu uzoraka uraúene su tri epruvete, a u radu su prika-zane srednje vrednosti. Mehanicke i mikrostrukturne karakterizacije dobijenih prevlaka su izvrsene prema standardu Pratt & Whitney (Turbojet Engine - Standard Practices Manual (PN 582005), 2002, Pratt & Whitney, East Hartford, USA).
Mikrostrukturna analiza prevlaka i image analiza udela mikro pora u prevlakama uradena je na svetlosnom mikroskopu. Morfologija cesti-ca praha uradena je na SEM-u (skening elektronskom mikroskopu).
Depozicija praha
Depozicija praha Al203-40%tez.Ti02 je uradena sa atmosferski plazma sprej sistemom firme Plasmadyne i plazma pistoljem SG - 100, sa odgovarajucim robotizovanim kontrolnim sprej uslovima. Plazma pi-stolj SG -100 se sastojao od katode tipa K 1083 - 129, anode tipa A 2084 - 145 i gas injektora tipa GI 2083 - 113. Kao lucni gas koristio se Ar u kombinaciji sa He i snaga napajanja do 40 KW. Pre procesa de-ponovanja povrsine celicnih substrata su hrapavljene sa cesticama ko-runda velicine od 0,7 - 1,5 mm. Prevlake su formirane sa debljinama od 0.25-0.30 mm.
Rezultati i diskusija
Vrednosti mikrotvrdoce i rasponi mikrotvrdoce Al203-40%tez.Ti02 prevlaka su bile u direktnoj vezi sa vrednostima plazma struje. U sloje-vima Al203-40%tez.Ti02 prevlaka izmerene su razlicite vrednosti mikrotvrdoce sa razlicitim rasponima mikrotvrdoca. Najmanje vrednosti mikrotvrdoce od min.676 do max.734HV03 sa najvecim rasponom mikrotvrdoce od 58HV03 su izmerene u deponovanim slojevima sa vre-dostima plazma struje od 700A. Najvece vrednosti mikrotvrdoce od min.950 do max.994HV03 sa najmanjim rasponom mikrotvrdoce od 44HV03 su izmerene u deponovanim slojevima sa vredostima plazma struje od 900A. Rasponi mikrotvrdoce u prevlakama su posledica razlicite raspodele mikro pora u deponovanim slojevima. 0ve vrednosti su potvrdene image analizom pri odredivanju ukupnog sadrzaja mikro pora u slojevima.
Za deponovane prevlaka su izmerene razlicite vrednosti zatezne cvrstoce spoja. Cvrstoca spoja prevlaka je bitno zavisila od vrednosti plazma struje. Najniza vrednost zatezne cvrstoce spoja od 17MPa, prevlake deponovane sa najmanjom vrednosti plazma struje od 700A utica-la je na manji stepen stapanja cestica praha u odnosu na druge dve deponovane prevlake. Najvecu vrednost cvrstoce spoja od 30MPa su imali slojevi, koji su deponovani sa najvecom vrednosti plazma struje od 900A. Visoka vrednost plazma struje je omogucila da se deponuju pre-vlake sa dobrim medu - lamelarnim vezivanjem i dobrim vezivanjem lamela prevlake za substrat. Veca vrednost plazma struje je uticala na po-vecanje adhezije prevlaka, mehanickih svojstava i poboljsanje mikrostrukture, sto su potvrdila metalografska ispitivanja. Posto je udeo mikro
pora u direktnoj vezi sa vrednostima cvrstoce spoja prevlaka, to izmere-ne vrednosti za prevlaku deponovanu sa najvecom vrednosti plazma struje ukazuje da je njihov udeo najmanji u odnosu na druge dve prevla-ke. Ove vrednosti su potvrdene analizom mikrostrukture prevlaka na svetlosnom mikroskopu. Za sve deponovane slojeve prevlaka mehani-zam razaranja je bio athezioni na interfejsu izmedu substrata i prevlaka.
Mikrostrukture i svojstava Al2O3-40%tez.TiO2 prevlaka su bila pod uticajem plazma struje. Veca vrednost plazma struje je poboljsala mikrostrukturu. Plazma struja od 900A omogucila je bolje i ravnomer-nije topljenje cestica praha Al2O3-40%tez.TiO2. Ravnomerno istoplje-ne cestice praha su se pravilnije oblikovale u sudaru sa substratom i deponovale slojeve sa manjim sadrzajem mikro pora, koji imaju vecu kohezionu cvrstocu i zateznu cvrstocu spoja. Najmanja vrednost plazma struje od 700A je uticala na slabije i ograniceno vezivanje lamela u deponovanim slojevima sto je povecalo udeo mikro pora i smanjilo vrednosti tvrdoce prevlake i cvrstocu spoja prevlake. Kvalitativna analiza deponovanih Al2O340%tez.TiO2 slojeva je pokazala da je na interfejsu izmedu substrata i prevlake spoj dobar sa zanemarljivim sadrzajem cestica Al2O3 od hrapavljenja. Duz interfejsa izmedu substrata i prevlake nisu prisutne mikropukotine i makropukotine. Veza prevlake sa substratom je uniformna bez odvajanja slojeva prevlake sa substrata. Struktura prevlake je lamelarna, sa vidljivim tamnim lamelama oksi-da Al2O3 i svetlim lamelama titanijum dioksida TiO2. Slojevi prevlake su deponovani sa malim udelom mikro pora bez prisustva mikropukotina i makropukotina u uprevlaci. U slojevima nisu prisutne neistopljene cestice praha. Kroz slojeve prevlaka se uocavaju sferne pore crne boje. U slojevima deponovanim sa 900A su prisutne mikro pore velicine do 5 pm. U slojevima deponovanim sa 700A su prisutne mikro pore iznad 5 pm. Image analiza je pokazala da je ukupan udeo mikro pora u slojevima prevlake deponovane sa 900A bio 2%, u slojevima deponovanim sa 700A udeo mikro pora je bio 3.5%, a u slojevima deponovanim sa 700A udeo mikro pora je bio 6%. U mikrostruktri nisu prisutne neistopljene cestrice i mikroprskotine. Struktura unutrasnjih slojeva prevlake je lamelarna. Osnova prevlake se sastoji od tamne faze osnovnog ok-sida Al2O3. U strukturi su prisutne dve modifikacije a - Al2O3 i y - Al2O3 (Tomaszeka, et al., 2004, pp.137-149), (Alford, 2002), (Vlasova, et al., 2012, pp.17-24). Kroz keramicke slojeve Al2O3 faza jasno se uocavaju svetle lamele nerazgradenog titanijum dioksida TiO2 i dve spinel modifikacije rutila a - Al2TiO5 i ß - Al2TiO5 koje se formiraju reakcijom oksi-da Al2O3 i TiO2 u procesu topljenja praha u plazmi (Tomaszeka, et al., 2004, pp.137-149), (Alford, 2002), (Vlasova, et al., 2012, pp.17-24).
Zakljucak
Plazma sprej postupkom su deponovane prevlake Al2O— 40%tez.TiO2 sa tri razlicite vrednosti plazma struje 700, 800 i 900A. Is-pitane su i analizirane mehanicke osobine i mikrostrukture deponovanih prevlaka na osnovu cega se doslo do sledecih zakljucaka.
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Mehanicka svojstava i mikrostrukture Al203-40%tez. Ti02 prevla-ka su bila pod uticajem plazma struje. Veca vrednost plazma struje je povecala mehanicka svojstava poboljsala mikrostrukturu i adheziju prevlake.
> Sa povecanjem plazma struje doponovale su se prevlake sa ve-cim vrednostima mikrotvrdoce i manjim rasponom mikrotvrdoce kroz slojeve prevlaka. Prevlake deponovane sa plazma strujom od 900 A je imala najvece vrednosti mikrotvrdoce i zatezne cvrstoce spoja. Za sve
2Í prevlake lom je bio na interfejsu izmedu prevlake i substrata. Vrednosti
E mikrotvrdoce i zatezne cvrstoce spoja su bile u korelaciji sa njihovim
o mikrostrukturama.
o Struktura deponovanih prevlake Al203-40%tez.Ti02 je lamelarna.
< U prevlakama su prisutne sferne pore crne boje. Najmanji udeo mikro
- pora od 2% su imali slojevi deponovani sa plazma strujom od 900A, a
x najveci udeo mikro pora od 6% su imali slojevi deponovani sa plazma
ft strujom od 700A. U strukturi keramickih prevlaka Al203-40%tez. Ti02
su prisutne dve modifikacije aluminijum oksida a - Al203 i y - Al203 , ti-o£ tanijum dioksid Ti02 i dve spinel modifikacije rutila a - Al2Ti05 i ß -
¡í l2Ti05 koje su nastale reakcijom oksida Al203 i Ti02 u procesu topljenja
praha u plazmi.
Prevlake deponovane sa plazma strujom 900A su pokazale naj-_ bolje mikrostrukture i mehanicka svojstva. Primenom prevlake na va-
ot zduhoplovnim delovima oslonaca lezajeva poboljsala se efikasnost de-
lova i pouzdanost rada.
2 Kljucne reci: titanijum dioksid; aluminijum oksid; cvrstoca spoja; mikro-
's tvrdoca; interfejs; atmosferski plazma-sprej (APS).
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O Datum dostavljanja ispravki rukopisa/Manuscript corrections submitted on: 19. 11. 2013.
> Datum konacnog prihvatanja clanka za objavljivanje/ Paper accepted for publishing on: 21. 11. 2013.
Datum prijema clanka/Paper received on: 10. 05. 2013.
