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ОРИГИНАЛНИ НАУЧНИ ЧЛАНЦИ ОРИГИНАЛЬНЫЕ НАУЧНЫЕ СТАТЬИ ORIGINAL SCIENTIFIC PAPERS
CHARACTERIZATION OF Cu10wt.%Al INTERMETALLIC COATINGS APPLIED BY THE ATMOSPHERIC PLASMA SPRAYING PROCESS
Mihailo R. Mrdak
Research and Development Center IMTEL Communications a.d.,
Belgrade, Republic of Serbia,
e-mail: drmrdakmihailo@gmail.com,
ORCID iD: http://orcid.org/0000-0003-3983-1605
DOI: 10.5937/vojtehg64-10688
FIELD: Chemical Technology ARTICLE TYPE: Original Scientific Paper ARTICLE LANGUAGE: English1
Summary:
The atmospheric plasma spray process is one of the procedures used for the deposition of coatings resistant to wear due to friction, erosion, cavitation and corrosion. In this paper, the APS process produced a Cu10wt.%Al intermetallic coating which is a reliable candidate for use in tribological environments because of a combination of low price and exceptional resistance to abrasion under different work conditions. The aim of this study was to investigate the mechanical properties and the structure of the Cu10wt.%Al intermetallic coating and develop an efficient method for repairing and improving light alloy resistance to wear. Many components of copper alloys tend to be degraded due to corrosive environment, friction, erosion and cavitation. Such components can be saved by surface engineering with the use of appropriate coatings on surface areas exposed to degradation. A typical microstructure of a coating for the APS process is lamellar, with micro pores, unmelted particles, inter-lamellar oxides and precipitates present in it. The mechanical properties of Cu10wt.% Al coatings were investigated by measuring the microhardness of coating layers using the HV03 method while the
ACKNOWLEDGEMENT: The author is thankful for the financial support from the Ministry of Education and Science of the Republic of Serbia (national project TR 34016).
bond strength was tested on a tensile machine. The morphologies of ¡powder particles and the coating surfaces were analyzed on a scanning electron microscope (SEM). The analysis of the coating microstructure was carried out with the use of an optical microscope, and a share of micro pores was determined by analyzing the micrographs through an optical microscope (OM).
Key words: wearing, intermetallics, erosion, corrosion, coatings, cavitation, Al, abrasives.
Introduction
APS - atmospheric plasma spraying is one of the technological processes used to manufacture coatings with a thickness between 0.1 and 0.5 mm. Plasma spray technology is one of possible solutions to produce copper-based coatings because of afordable production costs and possibilities to produce coatings on parts of complex shapes. The APS process includes the injection of powder particles into a plasma jet, its melting or semi-melting, and then accelerating and collision with the substrate where powder particles are deposited, forming a coating (Mrdak, 2015a, pp.137-159), (Mrdak, 2015b, pp.46-67). The microstructure of plasma spray coatings is characterized by a lamellar structure with limited inter-lamellar bonding due to the presence of micro pores. The coating microstructure and its mechanical properties are influenced by a large number of process parameters which directly affect the phase composition and porosity content for a specific powder and a range of powder particles (Mrdak, et al., 2015, pp.337-343), (Mrdak, 2016a, pp. 1-25), (Mrdak, 2016b, pp.411-430), (Vencl, et al., 2011, pp.1281-1288), (Vencl, et al., 2010, pp.591-604). Copper is a metal that is widely used in many applications because of its excellent thermal and electrical conductivity. The mechanical properties of copper can be improved by alloying. Some copper alloys such as Cu-Al, Cu-Si and Cu-Al-Fe are used for wider industrial applications, because they are quite resistant to wear and corrosion. Cu10wt.%Al alloys are widely used in the chemical industry thanks to their high corrosion resistance. In this alloy type, besides the a structure, there is the p structure as well. Wear resistant Cu10wt.%Al coatings are used on working parts to reduce damage due to friction, erosion, corrosion and cavitation (Bartuli, et al., 2007, pp.175-185). Cu-Al intermetallic coatings are good candidates for use in tribological environments because of a combination of low prices and exceptional resistance to abrasion under different work conditions. Optimum protection against wear of light metal substrates can be provided with effective application of thermal spray processes for coating
and powder depending on the working environment and working conditions (Sartale, Yoshitake, 2010, pp.353-360), (Wang, Seitz, 2001, pp.755-761). Intermetallic coatings or metal-ceramic composite coatings can be obtained by thermal spray powder spraying. Cu-Al intermetallic systems have been actively researched for use in aircraft, automotive, marine, construction, etc. The Cu-Al system have long been used for wheel bearings for planes and screws for ships because of its resistance to wear and corrosion (Sartale, Yoshitake, 2010, pp.353-360). Cu10wt.%Al powder marked Metco 445 is mechanically coated aluminum bronze which shows self-bonding for substrates during the thermal spray process as a result of the chemical reaction of the coated components which build intermetallic phases. The powder contains aluminum from 7.0 to 12.0 wt%Al (Material Product Data Sheet Aluminum Bronze Thermal Spray Powders Thermal Spray Powder Products Metco 445, 2012, DSMTS-0103.0, Sulzer Metco). Coatings have good resistance to friction and scuffing at low and moderate temperatures and excellent resistance to abrasion and cavitation. Testing of Cu10wt.%Al coatings to abrasive wear and sliding wear using the ring-on-disk method and a load of 150 g over the sliding speed of 4.5 cm/s showed that the abrasive coating wear is 0.52mgm-1, and that sliding wear is 2.8x10"5mm3m'1. The main coating wear mechanism is plastic deformation (Limpichaipanit, et al., 2011, pp.123-126). Coatings machine easily and excellently. Typical components covered by Cu10wt.%Al coatings are: supports of bearings, sleeves of hydraulic presses, piston guides, air compressor seals, water pumps, turbine nozzles, etc. The presence of aluminum in bronze increases the resistance of the coating to corrosion because of the formation of a thin cohesive surface oxide which acts as a protective layer on the alloy rich in copper (Material Product Data Sheet Aluminum Bronze Thermal Spray Powders Thermal Spray Powder Products Metco 445, 2012, DSMTS-0103.0, Sulzer Metco). To understand better the reaction processes which occur between Cu and Al during the process of powder melting and the formation of intermetallic phases, it is necessary to know the Cu-Al equilibrium diagram. In the equilibrium phase diagram of Cu-Al, there are five stable intermetallic phases, i.e.: Cu9Al4, Cu3Al2, Cu4Al3, CuAl and CuAl2 with two solid solutions Cu(Al) which are often described as a-Cu and Al(Cu) (ASM Handbook, 1992, Volume 3, Alloy Phase Diagrams, ASM International, Metals Park). Studies have shown that in the process of powder melting in plasma, due to the reaction of Al and Cu, various intermetallic phases are formed, such as: CuAl2, Cu9Al4, Cu3Al2, Al4Cu9 (Altuncu, et al., 2012, pp.181-183). The main intermetallic phases which affect the wear resistance of the coating are Cu9Al4 and Cu3Al2. Plasma spray deposited Cu10wt.%Al coatings have a lamellar structure, with
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present unmelted particles, precipitates, and inter-lamellar pores. According to the authors (Hang, et al., 2008, pp.416-424), (Li, Sun, 2004, pp.92-101) in the microstructure there are present intermetallic phases of CuAl2 and Cu9Al4. The alloy base is a solid solution of a-Cu (90.6-100wt%Cu) and p-Cu (85.0- 91.5wt.%Cu). In the microstructure of the coating, there are not black oxide lamellae of Al2O3 oxide (Li, Sun, 2004, pp.92-101). Cu10wt.%Al coatings consist of a bright phase of copper and a dark phase of copper oxide Cu2O. Copper oxide is primarily formed when temperatures > 1000 °C and in the presence of oxygen, which occurs when using the plasma spray process (Hang, et al., 2008, pp.416-424), (Li, Sun, 2004, pp.92-101).
In this paper, plasma spraying at atmospheric pressure was used to deposit an aluminum bronze coating which contains 7.0 to 12.0 wt.%Al. The coating microstructure was analyzed with a light microscope and the coating surface was analysed with the SEM - scanning electron microscope. The aim of this study was to investigate the mechanical properties and the microstructure of the Cu10wt.%Al intermetallic coating and to develop an economically efficient method of depositing intermetallic coatings for improving resistance of worn aircraft parts made of Cu alloys exposed to a combination of corrosion and wear.
Materials and experimental details
The material on which layers of Cu10wt.%Al(7.0 to 12.0 wt%Al) intermetallic coatings were deposited was made of stainless steel X15Cr13 (EN 1.4024) in the thermally unprocessed state. Powder of the Sulzer Metco company labeled Metco 445 was used to produce the Cu10wt.%Al coating. The powder was manufactured using mechanical coating and spheroidization to a specific granulation density of 3.1-4.3 g/cm3. The powder melting point is 1040 °C. Powder with granules in a range of 45 -106 ^m was used for the experiment (Material Product Data Sheet Aluminum Bronze Thermal Spray Powders Thermal Spray Powder Products Metco 445, 2012, DSMTS-0103.0, Sulzer Metco). Figure 1 shows the (SEM) scanning electron photomicrographs of the Cu10wt.% Al powder particles morphology. The powder particles are approximately spherical in shape. The testing of the mechanical properties of the Cu10wt.% Al coating was done in accordance with the Pratt & Whitney standard (Turbojet Engine - Standard Practices Manual (PN 582005), 2002, Pratt & Whitney, East Hartford, USA). The bases on which were deposited layers of coatings for microhardness testing and evaluation of the microstructure in the deposited state are made of steel C.4171 (X15Cr13 EN 10027) in the thermally unprocessed state with the dimensions of 70x20x1.5 mm.
Figure 1 - (SEM) Scanning electron micrography of a Cu10wt.%Al powder particle Рис. 1 - (SEM) Электронная микрография частиц порошка Си10вес.%А1 Slika 1 - Skening elektronska mikrografija (SEM) cestice praha Cu10tez.%Al
The substrates for testing the bond strength are also made of steel C.4171 (X15Cr13EN10027) in the thermally unprocessed state with the dimensions of 025x50 mm.The microhardness of layers was tested using HV03 and bond strength tensile testing. The microhardness measurements were performed along the lamellae. Five readings of microhardness values of the layers were performed in the middle and at the ends of the samples while two extreme values were rejected. Out of three remaining values, the average value is shown. The bond strength was tested at room temperature with a tensile speed of 1cm/60s. Five specimens were tested, out of which two extreme values were rejected. Out of the three remaining values, the mean value of the bond strength is shown. The morphology of the powder particles and the surface of the deposited coating was examined using scanning electron microscopy (SEM). The microstructure of the deposited layers was examined on an optical microscope (OM). The share of micro pores in the coating was analysed by analysing 5 photos at 200x magnification. In this paper, the mean value of the share of micro pores in the coating is presented.
Cu10wt.%Al powder is deposited with the atmospheric plasma spray system of the Plasmadyne company and the plasma gun SG-100, with controlled plasma spray parameters. The plasma gun SG-100 consists of a cathode type K1083-129, anode type A 2083-175 and the
gas injector type GI 1083-130. Ar in combination with He was used as an arc gas, and the power supply was 40kW. The plasma spray deposition parameters of Cu10wt.%Al powder are shown in Table 1. Before the deposition process, the substrate surfaces were roughened with white aluminum oxide particles of the size 0.7-1.5 mm. Coatings were deposited on the test samples with a thickness of 0.45-0.5 mm.
Table - 1 Plasma spray parameters Таблица 1 - Параметры плазменного напыления Tabela 1 - Plazma sprej parametri
Deposition parameters Values
Plasma current, I (A) 700
Plasma Voltage, U (V) 35
Primary plasma gas flow rate, Ar (l/min) 50
Secondary plasma gas flow rate, He (l/min) 12
Carrier gas flow rate, Ar (l/min) 5.6
Powder feed rate (g/min) 50
Stand-off distance (mm) 100
Results and discussion
The microhardness and the tensile bond strength of the coating had values characteristic for this type of coatings. The Cu10wt.%Al Intermetallic coating had an average microhardness of 176 HV03. The measured average value of microhardness was higher than the value specified by the powder manufacturer - 158 HV03 (Material Product Data Sheet Aluminum Bronze Thermal Spray Powders Thermal Spray Powder Products Metco 445, 2012, DSMTS-0103.0, Sulzer Metco), which indicates that a large share of micro pores was not present in the coating. This was confirmed by metallographic examinations of the coating layers. The mean value of the tensile bond strength measured on the samples with coated Cu10wt.%Al was 35 MPa. The coating was destroyed at the substrate / coating interface because of good bonding with the substrate. The measured values of the microhardness and the tensile bond strength of Cu10wt.%Al coatings were correlated with the microstructure of the deposited layers.
Figures 2 and 3 show the micrographs of a typical microstructure of the plasma spray coating.
Figure 2 - (OM) Cu10wt.%Al coating microstructure Рис. 2 - (ОМ) Микроструктура Си10вес.%А1 покрытия Slika 2 - (OM) Mikrostruktura Cu10tez.%Al prevlake
Figure 3 - (OM) Cu10wt.%Al coating microstructure Рис. 3 - (ОМ) Микроструктура Cu10Bec.%Al покрытия Slika 3 - Mikrostruktura (OM) Cu10tez.%Al prevlake
The photomicrographs clearly show the interfaces of coating layers and the substrate. The substrate/coating interface is very clean indicating a very good bonding of the coating with the substrate, which indicates a good substrate surface preparation. Because of good surface preparation, the interface does not show the presence of corundum particles left from roughening, which resulted in good adhesion of the coating with the substrate. At the interface between the substrate and the deposited coating layers, there are no defects such as discontinuities of deposited layers, microcracks, macrocracks, coating peeling and separation from the substrate. Generally, the layers are uniformly deposited on the substrate. The coatings have a lamellar structure, inter-lamellar oxides and inter-lamellar pores. The microstructure of the coating showed that powder particles are uniformly and homogeneously distributed. Through the coating layers, coarse micro pores, micro cracks and macro cracks cannot be seen. The average share of micro pores in the coating layers was 8%. At a higher magnification, in Figure 3, we can see the light gray lamellae of oxide Cu2O with a uniform distribution in the coating (Hang, et al., 2008, pp.416-424), (Li, Sun, 2004, pp.92-101) as well as micro pores in black. In the coating, unmelted powder particles were not detected, which indicates that powder particles had been deposited with the optimal deposition parameters. The Cu10wt.%Al coating base consists of solid solutions a-Cu and p-Cu rich in copper containing CuAl2 and Cu9Al4 intermetallic phases (Hang, et al. 2008, pp.416-424), (Lee, Sun, 2004, pp.92-101).
Figure 4 shows a SEM photomicrograph of the surface of the Cu10wt.%Al intermetallic coating.
Figure 4 - (SEM) Surface morphology of the Cu10wt.%Al coating Рис. 4 - (SEM) Морфология поверхности Си10вес.%А1 покрытия Slika 4 - (SEM) Morfologija povrsine Cu10tez.%Al prevlake
The analysis of the surface morphology of the Cu10wt.%Al intermetallic coating shows complete melting and regular melting of powder particles on the previously deposited layer. The red lines in SEM micrographs mark boundaries between the melted particles. The molten powder particles formed thin discs - splates in a collision with the substrate. Thus formed shapes of deposited particles have good cohesive bonding with the previously deposited particles, indicating that the powder particles were deposited with the optimum deposition parameters. Coarse micro pores cannot be seen on the coating surface. SEM micrographs clearly show black micro pores surrounded by yellow color of a size up to 10^m. The coating surface shows precipitates formed as a result of the collision of molten droplets with the substrate. At the moment of the collision of molten droplets with the substrate, the ends of molten particles chip and solidify as precipitates in the deposited coating layers.
Conclusion
In this paper, the APS - atmospheric plasma spray process produced a Cu10wt.%Al intermetallic coating based on copper with a content of aluminum from 7.0 to 12.0wt.%Al. The coating deposited on the test samples had a thickness of 0.45-0.5 mm. We analyzed the mechanical properties and the microstructure of the coatings in the deposited state, which led to the following conclusions.
The Cu10wt.%Al intermetallic coating had good mechanical properties, with a microhardness value of 176 HV03 which was above the value of 158 HV03 prescribed by the powder manufacturer. The bond strength was 35 MPa. The microstructure is lamellar, consisting of lamellas of oxide Cu2O formed by Cu oxidation in the process of deposition of the powder and inter lamellar pores with an average proportion of 8%.
The base of the Cu10wt.%Al coating consisted of solid solutions a-Cu and p-Cu rich in copper with CuAl2 and Cu9Al4 intermetallic phases as a result of the thermal reaction between Cu and Al in plasma during melting and deposition.
Applying Cu10wt.%Al coatings on aircraft parts made of light alloys and exposed to a combination of corrosion and wear has significantly improved the efficiency and reliability of the parts in exploitation and also significantly reduced the costs of repair.
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References
Alloy Phase Diagrams 1992. ASM International, Metals Park. Volume 3.
Altuncu, E., Irig, S., & Ustel, F. 2012. Wear - resistant intermetallic arc spray coatings. Materiali in tehnologije / Materials and technology, 46(2), pp.181-183.
Aluminum Bronze Thermal Spray Powders Thermal Spray Powder Products Metco 445, DSMTS-0103.0 2012. Sulzer Metco. Material Product Data Sheet.
Bartuli, C., Valent, T., Casadei, F., & Tului, M. 2007. Advanced thermal spray coatings for tribological applications, Proceedings of the Institution of Mechanical Engineers, Part L. Journal of Materials: Design and Applications, 221, pp.175-185.
Hang, C.J., Wang, C.Q., Mayer, M., Tian, Y.H., Zhou, Y., & Wang, H.H. 2008. Growth Behavior of Cu/Al Intermetallic Compounds and Cracks in Copper Ball Bonds during Isothermal Aging. Microelectronics Reliability, 48, pp.416-424.
Li, C., & Sun, B. 2004. Microstructure and Property of micro-plasma-sprayed Cu coating. Materials Science and Engineering A, 379, pp.92-101.
Limpichaipanit, A., Watcharapasorn, A., Wirojanupatump, S., & Jiansirisomboon, S. 2011. Fabrication and Mechanical Properties of Thermal Sprayed Copper-based Coatings. Journal of the Microscopy Society of Thailand, 4(2), pp.123-126.
Mrdak, M., Rakin, M., Medjo, B., & Bajic, N. 2015. Experimental Study of Insulating Properties and Behaviour of Thermal Barrier Coating Systems in Thermo Cyclic Conditions Materials and Design. Materials and Design, 67, pp.337-343.
Mrdak, M. 2015a. Characteristics of APS and VPS plasma spray processes. Vojnotehnicki glasnik / Military Technical Courier, 63(3), pp.137-159.
Mrdak, M. 2015b. Morphology of powder particles produced by spray atomization and other processes. Vojnotehnicki glasnik/ Military Technical Courier, 63(4), pp.46-67.
Mrdak, M. 2016a. Study of the application of plasma sprayed coatings on the sections of the Astazou III B turbo - jet engine. Vojnotehnicki glasnik / Military Technical Courier, 64(1), pp.1-25.
Mrdak, M. 2016b. Properties of the ZrC^MgO/MgZrOaNiCr/NiCr triple-layer thermal barrier coating deposited by the atmospheric plasma spray process. Vojnotehnicki glasnik / Military Technical Courier, 64(2), pp.411-430.
Sartale, S.D., & Yoshitake, M. 2010. Investigation of Cu-Al surface alloy formation on Cu substrate. Journal of Vacuum Science & Technology B, 28, pp.353-360.
Standard Practices Manual (PN 582005) 2002. East Hartford, USA: Pratt & Whitney.
Vencl, A., Arostegui, S., Favaro, G., Zivic, F., Mrdak, M., Mitrovic, S., & Popovic, V. 2011. Evaluation of adhesion/cohesion bond strength of the thick plasma spray coatings by scratch testing on coatings cross-sections. Tribology International, 44(11), pp.1281-1288.
Vencl, A., Manic, N., Popovic, V., & Mrdak, M. 2010. Possibility of the abrasive wear resistance determination with scratch tester. Tribology Letters, 37(3), pp.591-604.
Wang, B.Q., & Seitz, M.W. 2001. Comparison in erosion behavior of ironbase coatings sprayed by three different arc-spray processes. Wear, 250, pp.755-761.
Zhang, Z., Li, D., & Wang, S. 2006. High Temperature Performance of Arc-sprayed Aluminium Bronze Coatings for Steel. Transactions of Nonferrous Metals Society of China, 16, pp.868-872.
ХАРАКТЕРИЗАЦИЯ ИНТЕРМЕТАЛЛИЧЕСКОГО ПОКРЫТИЯ Си10вес.%А1 НАНЕСЕННОГО ПЛАЗМЕННЫМ НАПЫЛЕНИЕМ
Михаило Р. Мрдак
Центр исследований и развития А. О. «ИМТЕЛ коммуникации», Белград, Республика Сербия
ОБЛАСТЬ: химические технологии
ВИД СТАТЬИ: оригинальная научная статья
ЯЗЫК СТАТЬИ: английский
Резюме:
Плазменное напыление является одним из методов нанесения износостойких покрытий, устойчивых в т.ч. к истеранию, эрозии, кавитации и коррозии. В данной работе описан процесс создания интерметаллического покрытия Си10вес.%А1, являющегося надежным кандидатом для применения в трибологических условиях эксплуатации. Преимуществом покрытия данного вида является сочетание низкой стоимости и повышенной стойкости к абразии в различных режимах эксплуатации. Цель данного исследования заключается в изучении механических свойств и структур интерметаллических покрытий Си10вес.%А1 и развитии эффективной методологии нанесения покрытия, а также в повышении износостойкости легких сплавов. Многие компоненты сплава меди в коррозийных условиях подвергаются кавитационному и эрозийному разрушению, но своевременная инженерия поверхности соответсвующим покрытием деградирующих слоев, поможет сохранить их. Типичная микроструктура покрытия напылением -ламеллярная, с микропорами, несплавленными частицами, межламеллярными оксидами и преципитатами. Испытания механических характеристик покрытия Си10вес.%А1 проводились методом HV03 а испытания прочности соединений - методом растяжения. Морфология частиц порошка и поверхности покрытия испытаны методом электронной микрографии (SEM). Испытания микроструктуры покрытия проведены методом оптической микроскопии, а микропоры исследованы методом оптической микрографии (ОМ).
Ключевые слова: износ, интерметаллиды, эрозия, коррозия, покрытие, кавитация, Al, абразия.
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KARAKTERIZACIJA INTERMETALNE PREVLAKE Cu10tez.%Al NAPRSKANE ATMOSFERSKIM PLAZMA SPREJ POSTUPKOM
Mihailo R. Mrdak
Istrazivacki i razvojni centar IMTEL Komunikacije a.d., Beograd, Republika Srbija
OBLAST: hemijske tehnologije VRSTA C LANKA: originalni naucni clanak JEZIK CLANKA: engleski
Sazetak:
Atmosferski plazma sprej je jedan od postupaka koji se koristi za depoziciju prevlaka otpornih na habanje usled trenja, erozije, kavitacije i korozije. U ovom radu, APS postupkom proizvedena je intermetalna prevlaka Cu10tez.%Al, koja je pouzdana za primenu u triboloskim okruze-njima zbog kombinacije niske cene i izuzetne otpornosti na abraziju pri razlicitim uslovima rada. Cilj ovoga rada bio je da se izuce mehanicka svojstva i struktura intermetalne prevlake Cu10tez.%Al i razvije efikasan metod za reparaciju i poboljsanje otpornosti lakih legura na habanje. Mnoge komponente od legure bakra imaju tendenciju da se degradiraju zbog korozivne sredine, trenja, erozije i kavitacije. Takve komponente mogu se spasti inzenjerstvom povrsina sa primenom odgovarajucih prevlaka na povrsinama izlozenim degradaciji. Tipicna mikrostruktura prevlake za APS postupak je lamelarna u kojoj su prisutne mikropore, neis-topljene cestice, medulamelarni oksidi i precipitati. Mehanicke karakteri-stike prevlake Cu10tez.%Al ispitane su merenjem mikrotvrdoce slojeva prevlake metodom HV03 i cvrstoce spoja metodom ispitivanja na zateza-nje. Morfologija cestica praha i povrsina prevlake analizirana je na ske-ning elektronskom mikroskopu (SEM). Analiza mikrostrukture prevlake uradena je uz koriscenje optickog mikroskopa, a udeo mikropora odre-den je analizom mikrofotografija sa optickog mikroskopa (OM).
Atmosferski plazma sprej (APS) jedan je od tehnoloskih postupaka koji se koristi za proizvodnju prevlaka debljine izmedu 0,1 i 0,5 mm. Pla-zma sprej tehnologija je jedna od mogucih resenja proizvodnje prevlaka na bazi bakra zbog povoljnih troskova proizvodnje i sposobnosti da se proizvedu prevlake na delovima slozenih oblika. APS proces ukljucuje ubacivanje cestica praha u mlaz plazme, njegovo topljenje ili polutopljenje, a zatim ubrzavanje i sudaranje sa podlogom, gde se cestice praha depo-nuju i formiraju prevlaku (Mrdak, 2015a, pp.137-159), (Mrdak, 2015b, pp. 46-67). Mehanicke karakteristike i mikrostruktura prevlaka pod utica-jem je velikog broja parametara procesa koji direktno uticu na fazni sastav i sadrzaj poroznosti za odredeni prah i raspon cestica praha (Mrdak, et al., 2015, pp.337-343), (Mrdak, 2016a, pp.1-25), (Mrdak, 2016b, pp.411-430),
Uvod
(Vencí, et aí, 2011, pp.1281-1288), (Vencí, et ai, 2010, pp.591-604). Ba-kar je metal koji ima siroku primenu u mnogim apíikacijama zbog svoje od-íicne topíotne i eíektricne provodíjivosti. Mehanicke osobine bakra mogu se poboíjsati íegiranjem, sto karakterise íegure bakra. Neke íegure bakra, kao sto su Cu-Aí, Cu-Si i Cu-Aí-Fe, koriste se za siru industrijsku primenu, jer su priíicno dobri materijaíi kada je u pitanju otpornost na visoko habanje i koroziju. Legura Cu10tez.%Aí mnogo se upotrebíjava u hemijskoj indu-striji radi veíike otpornosti na koroziju. U íeguri Cu10tez.%Aí, pored a strukture pojavíjuje se iß struktura. Prevíaka Cu10tez.%Aí otporna na ha-banje koristi se na radnim deíovima da smanji stetu usíed trenja, erozije, kavitacije i korozije (Bartuíi, et aí., 2007, pp.175-185). Prah Cu10tez.%Aí, oznake Metco 445, jeste mehanicki obíozena aíuminijumska bronza koja pokazuje samovezivanje za substrate za vreme termo-sprej procesa kao rezuítat hemijske reakcije obíozenih komponenti koji grade intermetaíne faze. Prah sadrzi aíuminijum od 7,0 do 12,0tez.%Aí (Materiaí Product Data Sheet Aíuminum Bronze Thermaí Spray Powders Thermaí Spray Powder Products Metco 445, 2012, DSMTS-0103.0, Suízer Metco). Prevíake ima-ju dobru otpornost na trenje i zaribavanje na niskim i umerenim tempera-turama i odíicnu otpornost na abraziju i kavitaciju. Ispitivanje prevíake Cu10wt.%Aí na abraziono habanje i habanje kíizanjem, gde se koristiía metoda prsten - na - disku i opterecenje od 150 g pri brzini kíizanja od 4,5 cm/s pokazaío je da je abraziono habanje prevíake 0,52 mgm-1, a habanje kíizanjem 2,8x105mm3m1. Gíavni mehanizam habanja prevíake je píastic-na deformacija (Limpichaipanit, et aí., 2011, pp.123-126). Prevíake se íako i odíicno obraduju masinski. Tipicne komponente na kojima se koristi Cu10tez.%Aí prevíaka su: osíonci íezajeva, rukavci hidrauíicnih presa, vo-dice kíipova, zaptivaci kompresora vazduha, pumpe za vodu, turbinske míaznice i dr. Prisustvo aíuminijuma u bronzi uvecava otpornost prevíake na koroziju usíed formiranja tankog kohezivnog povrsinskog oksida koji deíuje kao zastitni síoj na íeguri bogatoj bakrom (Materiaí Product Data Sheet Aíuminum Bronze Thermaí Spray Powders Thermaí Spray Powder Products Metco 445, 2012, DSMTS-0103.0, Suízer Metco). Da bi se boíje razumeíi procesi reakcije koji se desavaju izmedu Cu i Aí za vreme procesa topíjenja praha i formiranja intermetaínih faza, neophodno je znati rav-notezni dijagram Cu-Aí. U ravnoteznom dijagramu faza Cu-Aí postoji pet stabiínih intermetaínih faza, kao sto su: Cu9Aí4, Cu3Aí2, Cu4Aí3, CuAí i CuAí2, sa dva cvrsta rastvora Cu(Aí), koji se cesto opisuju kao a-Cu i Aí(Cu) (ASM Handbook, 1992, Voíume 3, Aííoy Phase Diagrams, ASM In-ternationaí, Metaís Park). Istrazivanja su pokazaía da se u procesu topíje-nja praha u píazmi, usíed reakcije Cu i Aí, formiraju razíicite intermetaíne faze kao sto su: CuAí2, Cu9Aí4, Cu3Aí2, Aí4Cu9 (Aítuncu, et aí., 2012, pp.181-183). Gíavne intermetaíne faze koje uticu na otpornost na habanje prevíake su Cu9Aí4 i Cu3Aí2. Píazma sprej deponovana Cu10tez.%Aí pre-víaka ima íameíarnu strukturu, sa prisutnim neistopíjenim cesticama, preci-pitatima i interíameíarnim porama. Po autorima (Hang, et aí., 2008, pp.416-424), (Li, Sun, 2004, pp.92-101) u mikrostrukturi su prisutne intermetaíne faze tipa CuAí2 i Cu9Aí4. Osnovu íegure cini cvrsti rastvor a-Cu(90,6-100tez.%Cu) i ß-Cu(85,0-91,5tez.%Cu). U mikrostrukturi pre-
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vlake nisu prisutne crne oksidne lamerle oksida Al2O3 (Li, Sun, 2004, pp.92-101). Prevlake Cu10tez.%Al sastoje se od svetle faze bakra i tamne faze oksida bakra Cu2O. Oksid bakra se, pre svega, formira kada je temperatura >1000 °C i prisutan kiseonik, sto se desava pri primeni plazma sprej postupka (Hang, et al., 2008, pp.416-424), (Li, Sun, 2004, pp.92-101).
U ovom radu plazma sprej postupkom na atmosferskom pritisku deponovana je prevlaka aluminijumske bronze koja sadrzi 7,0-12,0 tez.%Al. Mikrostruktura prevlake je analizirana na svetlosnom mikrosko-pu i povrsina prevlake na skening elektronskom mikroskopu. Cilj ovoga rada bio je da se izuce mehanicka svojstva i mikrostruktura intermetalne prvlake Cu10tez.%Al i razvije ekonomski efikasan metod deponovanja intermetalne prevlake za poboljsanje otpornosti pohabanih vazduhoplov-nih delova od legura Cu izlozenih kombinaciji korozije i habanja.
Materijali i eksperimentalni detalji
Materijal na kojem su deponovani slojevi intermetalne prevlake Cu10tez. %Al (7,0-12,0tez.%Al) bio je od nerdajuceg celika X15Cr13(EN1.4024) u termicki neobradenom stanju. Za proizvodnju Cu10tez.%Al prevlake upotrebljen je prah firme „Sulzer Metco" sa oznakom Metco 445. Prah je proizveden metodom mehanickog oblaganja i sferoidizacije na odredenu granulaciju gustine 3,1 - 4,3 g/cm3. Temperatura topljenja praha je 1040°C. Za eksperiment se koristio prah koji je imao raspon granulata od 45 do 106 pm (Material Product Data Sheet Aluminum Bronze Thermal Spray Powders Thermal Spray Powder Products Metco 445, 2012, DSMTS-0103.0, Sulzer Metco).
Ispitivanje mehanickih karakteristika prevlake Cu10tez.%Al rade-no je prema standardu Pratt&Whitney (Turbojet Engine-Standard Practices Manual (PN 582005), 2002, Pratt & Whitney, East Hartford, USA). Osnove na kojima su deponovani slojevi prevlake za ispitivanje mikrotvrdoce i za procenu mikrostrukture u deponovanom stanju izra-dene su od celika C.4171 (X15Cr13 EN10027) u termicki neobradenom stanju, dimenzija 70x20x1,5 mm. Osnove za ispitivanje cvrstoce spoja takode su izradene od celika C.4171(X15Cr13EN10027) u termicki neobradenom stanju, dimenzija 025x50 mm. Mikrotvrdoca sloje-va ispitivana je metodom HV03} a cvrstoca spoja ispitivanjem na zate-zanje. Merenje mikrotvrdoce izvrseno je u pravcu duz lamela. Uradeno je pet ocitavanja vrednosti mikrotvrdoce slojeva u sredini i na krajevima uzoraka od kojih su odbacene dve krajnje vrednosti. Od tri preostale vrednosti prikazana je srednja vrednost. Ispitivanje cvrstoce spoja ra-deno je na sobnoj temperaturi sa brzinom zatezanja 1 cm/60 s. Ispita-no je pet epruveta od kojih su odbacene dve krajnje vrednosti. Od tri preostale vrednosti prikazana je srednja vrednost cvrstoce spoja. Mor-fologija cestica praha i povrsina deponovane prevlake uradena je ske-ning elektronskom mikroskopijom, a mikrostruktura deponovanih sloje-va ispitana je na optickom mikroskopu. Analiza udela mikropora u pre-vlaci uradena je obradom 5 fotografija na uvelicanju 200x. U radu je prikazana srednja vrednost udela mikropora u prevlaci.
Depozicija Cu10tez.%Al praha uradena je sa atmosferski plazma sprej sistemom firme „Plasmadyne" i plazma pistoljem SG-100, sa kontro-lisanim plazma sprej parametrima. Plazma pistolj SG-100 sastojao se od katode tipa K 1083A-129, anode tipa A 2083-175 i gas injektora tipa GI 1083A-130. Kao lucni gas koristio se Ar u kombinaciji sa He i snaga napa-janja do 40kW. Plazma sprej parametri depozicije Cu10wt.%Al praha pri-kazani su u tabeli 1. Pre procesa deponovanja povrsine substrata su hra-pavljene cesticama belog korunda velicine od 0,7 do 1,5mm. Prevlake su deponovane na ispitnim uzorcima sa debljinama od 0,45 do 0,5mm.
Rezultati i diskusija
Mikrotvrdoca i zatezna cvrstoca spoja prevlake imale su vrednosti koje su karakteristicne za ovaj tip prevlake. Intermetalna prevlaka Cu10tez.%Al imala je prosecnu vrednost mikrotvrdoce 176 HV03. Iz-merena prosecna vrednost mikrotvrdoce bila je veca od vrednosti koju propisuje proizvodac praha 158 HV03 (Material Product Data Sheet Aluminum Bronze Thermal Spray Powders Thermal Spray Powder Products Metco 445, 2012, DSMTS-0103.0, Sulzer Metco), sto ukazuje na to da u prevlaci nije prisutan veliki udeo mikropora. To su potvrdila metalografska ispitivanja slojeva prevlake. Srednja vrednost zatezne cvrstoce spoja izmerena na uzorcima sa prevlakom Cu10tez.%Al bila je 35 MPa. Prevlaka je razorena na interfejsu supstrat/prevlaka zbog dobrog spoja sa substratom. Izmerene vrednosti mikrotvrdoce i zatezne cvrstoce spoja Cu10tez.%Al prevlake bile su u korelaciji sa mikro-strukturom deponovanih slojeva. Na mikrofotografijama se jasno uoca-vaju medugranice spoja slojeva prevlake i substrata. Medugranica iz-medu substrata i slojeva prevlake je izuzetno Cista, ukazujuci na izu-zetno dobru vezu slojeva prevlake sa substratom, sto govori o dobroj pripremi povrsine substrata. Zbog dobre pripreme povrsine substrata na interfejsu nisu prisutni ostaci Cestica korunda od hrapavljenja, sto se odrazilo na dobru adheziju prevlake sa substratom. Na interfejsu iz-medu substrata i deponovanih slojeva prevlake nisu prisutni defekti kao sto je diskontinuitet deponovanih slojeva, mikropukotine, makropu-kotine, ljustenje i odvajanje prevlaka sa substrata. Generalno, slojevi su ravnomerno deponovani na podlogu. Prevlake imaju lamelarnu strukturu, interlamelarne okside i interlamelarne pore. Mikrostruktura prevlake pokazuje da su Cestice praha ravnomerno i homogeno distri-buirane. Kroz slojeve prevlake ne uocavaju se grube mikropore, mikropukotine i makropukotine. Prosecan udeo mikropora u slojevima prevlake bio je 8%. Pri vecem uvelicanju (slika 3) jasno se vide svetlo- si-ve lamele oksida Cu2O sa ravnomernom raspodelom u prevlaci (Hang, et al., 2008, pp.416-424), (Li, Sun, 2004, pp.92-101) i mikropore crne boje. U prevlakama nisu uocene neistopljene cestice praha, ukazujuci da su cestice praha deponovane sa optimalnim parametrima depozicije. Osnova prevlake Cu10tez.%Al sastoji se od cvrstih rastvora a-Cu i fi-Cu bogatih bakrom u kojima se nalaze intermetalne faze CuAl2 i Cu9A4 (Hang, et al., 2008, pp.416-424), (Li, Sun, 2004, pp.92-101).
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Analiza morfologije povrsine intermetalne prevlake Cu10tez.%Al pokazuje potpuno topljenje i pravilno razlivanje cestica praha na pret-hodno deponovani sloj. Na SEM mikrofotografiji crvenom linijom su oznacene granice izmedu razlivenih cestica. Istopljene cestice praha formirale su tanke diskove - splates u sudaru sa podlogom. Tako for-mirani oblici deponovanih cestica ostvaruju dobru kohezivnu vezu sa prethodno deponovanim cesticama, ukazujuci da su cestice praha de-ponovane sa optimalnim parametrima depozicije. Na povrsini prevlake se ne uocavaju grube mikropore. Na SEM mikrofotografiji jasno se vide crne mikropore, zaokruzene zutom bojom velicine do 10 pm. Na povrsini prevlake uocavaju se precipitati koji su nastati kao posledica sudara istopljenih kapi sa substratom. U trenutku sudara istopljenih kapi sa podlogom dolazi do odlamanja krajeva istopljenih cestica, koji ocvrsca-vaju kao talog u deponovanim slojevima prevlake.
Zakljucak
U radu je atmosferskim plazma sprej procesom (APS) proizvede-na intermetalna prevlaka Cu10tez.%Alna bazi bakra sa sadrzajem alu-minijuma od 7,0 do 12,0tez.%Al. Prevlake deponovane na ispitnim uzorcima bile su debljine od 0,45 do 0,5 mm. Analizirane su mehanic-ke karakteristike i mikrostrukture prevlaka u deponovanom stanju, na osnovu cega se doslo do odredenih zakljucaka.
Intermetalna prevlaka Cu10tez.%Al imala je dobre mehanicke osobine, cija je mikrotvrdoca od 176 HV0.3 bila iznad vrednosti 158 HV0.3 koju propisuje proizvodac praha, i cvrstocu spoja od 35 MPa. Mi-krostruktura prevlake je lamelarna, a sastoji se od oksidnih lamela Cu2O formiranih oksidacijom Cu u procesu depozicije praha i interla-melarnih pora sa prosecnim udelom od 8%. Osnova Cu10tez.%Alprevlake sastoji se od cvrstih rastvora a-Cu i fi-Cu bogatih bakrom u koji-ma se nalaze intermetalne faze CuAl2 i Cu9Al4 nastale kao rezultat ter-micke reakcije izmedu Cu i Al u plazmi u toku procesa topljenja i depo-novanja.
Primenom Cu10tez.%Al prevlake u remontu na vazduhoplovnim delovima od lakih legura izlozenih kombinaciji korozije i habanja znat-no se poboljsala efikasnost i pouzdanost rada delova u eksploataciji i smanjili se troskovi remonta.
Kljucne reci: habanje, intermetali, erozija, korozija, prevlaka, kavitacija, Al, abrazija.
Paper received on / Дата получения работы / Datum prijema clanka: 09. 04. 2016. Manuscript corrections submitted on / Дата получения исправленной версии работы / Datum dostavljanja ispravki rukopisa: 20. 04. 20l6. Paper accepted for publishing on / Дата окончательного согласования работы / Datum konacnog prihvatanja clanka za objavljivanje: 22. 04. 2016.
© 2016 The Author. Published by Vojnotehnicki glasnik / Military Technical Courier (www.vtg.mod.gov.rs, втг.мо.упр.срб). This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/3.0/rs/).
© 2016 Автор. Опубликовано в "Военно-технический вестник / Vojnotehnicki glasnik / Military Technical Courier" (www.vtg.mod.gov.rs, втг.мо.упр.срб). Данная статья в открытом доступе и распространяется в соответствии с лицензией "Creative Commons" (http://creativecommons.org/licenses/by/3.0/rs/).
© 2016 Autor. Objavio Vojnotehnicki glasnik / Military Technical Courier (www.vtg.mod.gov.rs, втг.мо.упр.срб). Ovo je clanak otvorenog pristupa i distribuira se u skladu sa Creative Commons licencom (http://creativecommons.org/licenses/by/3.0/rs/).
