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Mechanical Characterization of Composite Coatings Formed by Reactive Detonation Spraying of Titanium
Received: 18 August 2017 / Accepted: 5 September 2017 / Published: 8 September 2017
The structure and mechanical properties of the coatings formed by reactive detonation spraying of titanium in a wide range of spraying conditions were studied. The variable deposition parameters were the nature of the carrier gas, the spraying distance, the O2/C2H2 ratio, and the volume of the explosive mixture. The phase composition of the coatings and the influence of the spraying parameters on the mechanical properties of the coatings were investigated. In addition, nanohardness of the individual phases contained in the coatings was evaluated. It was found that the composition of the strengthening phases in the coatings depends on the O2/C2H2 ratio and the nature of the carrier gas. Detonation spraying conditions ensuring the formation of composite coatings with a set of improved mechanical properties are discussed. The strength of the coatings was determined through the microhardness measurements and local characterization of the phases via nanoindentation. Three-point bending tests were employed in order to evaluate the crack resistance of the coatings. The strengthening mechanisms of the coatings by oxide or carbonitride phases were discussed.
detonation spraying; three-point bending; electron microscopy; micromechanics; composites; titanium alloys; powder methods; phase transformation
At present, several coating deposition methods are known and widely used in the industry. The choice of a particular method is dictated by a combination of factors, such as the level of loading and operating conditions, the shape, size and geometry of machine parts to be coated, the required thickness of the coating, the necessity for mechanical post-processing, the requirements for adhesive and cohesive strength and the cost of the final product.
Thermal spraying is widely used for surface strengthening and restoration. The variations of thermal spraying are plasma spraying, flame spraying, high-velocity oxy-fuel spraying (HVOF), cold gas-dynamic spraying and detonation spraying. Thermal spraying is used to deposit high-strength materials [1
] and multicomponent coatings reinforced with finely dispersed inclusions, which ensure high coating performance [2
]. In order to form coatings containing intermetallic phases with high adhesion strength and corrosion resistance, vacuum spraying [1
] is employed or deposition is carried out in an inert gas atmosphere [5
The sprayed metallic particles can chemically react with gases contained in the spraying atmosphere, which leads to the formation of finely dispersed ceramic phases in the coatings [4
A widespread technique for producing dispersion-strengthened coatings is the formation of oxide inclusions in metal matrices. This is achieved through oxidation of the molten particles when spraying is carried out in air. In this case, atmospheric plasma spraying can be efficiently employed [8
]. A substantial drawback of this method is the porosity of the coatings and the non-uniformity of their structure.
One of the efficient technologies for restoration, repair and strengthening of machine parts is cold gas-dynamic spraying [9
]. It is based on the layer-by-layer formation of coatings at supersonic flow velocities of the carrier gas and is associated with minimal heating of the sprayed material. The cohesive strength is, therefore, provided thanks to the high kinetic energy of the particles upon impact. This substantially reduces the probability of oxidation and eliminates the need for dynamic vacuum or an inert gas atmosphere. By selecting the optimal gas flow rate and the temperature of the gas, multicomponent coatings with a set of required physical and mechanical properties can be fabricated [10
]. In addition to spraying of the powder mixtures, a unique combination of coating properties can be achieved through the deposition of alternating layers of different compositions [11
In the framework of this classification, a technique of coating deposition from powder mixtures using concentrated pulsed energy flows has to be mentioned. This technique allows forming layers that possess low porosity, high adhesion to the substrate, and submicro- or nanocrystalline structures [12
]. The drawback of this method is poor control of the structure and geometry of the coatings.
Currently, detonation spraying and HVOF are the most efficient methods of depositing coatings that can protect machine parts from erosion, corrosion and different types of wear [13
]. Low porosity of the coatings is achieved due to high velocities of the particles [5
]. The method can also be applied for metallization of ceramics and periodic restoration of the worn machine parts [15
In Ref. [18
], the application of the HVOF technique to deposit WC-Co coatings is compared with the ecologically unfriendly chrome plating, which has been used in the industry for a long time. A comparative analysis of the structure and properties of Cu-Ni-In coatings formed by plasma and detonation sputtering onto Ti-4Al-6V substrate was performed in Ref. [19
]. It was shown that the detonation-sprayed coatings show a higher adhesion, a reduced porosity and a more uniform structure than the plasma sprayed ones. The improved structural characteristics increase the fatigue life and resistance to fretting corrosion of the coatings.
The surface quality of the thermally sprayed coatings depends on the surface finish and can be improved by droplet elimination [20
]. Also, machining of the thermally sprayed coatings is needed to achieve dimensional tolerances [21
]. Therefore, the mechanical strength and integrity of the coatings are important not only for their functional performance, but also as guaranteeing the capability of the coatings to withstand the machining operations.
Chemical reactions involving the sprayed materials and phase transitions in the sprayed material can exert both positive and negative effects on the coating performance. TiO2
coatings formed by the HVOF technique were studied in Ref. [22
]. The powder was introduced by both internal and external injection. It was shown that by varying the composition of the sprayed powder and the way of its introduction into the gas flow, it is possible to control the amount of anatase that affects the structure and photocatalytic properties of the coating.
In this paper, the structure and mechanical properties of deposits formed on titanium substrates by reactive detonation spraying of a titanium powder were investigated. The aim of the present work was to determine the effect of the coating structure on the mechanical properties of the coatings.
2. Materials and Methods
The deposition of the coatings onto titanium substrates was carried out using a computer controlled detonation spraying (CCDS2000) facility (Lavrentyev Institute of Hydrodynamics SB RAS, Novosibirsk, Russia) [23
]. The substrates were sand-blasted before depositing the coating layers. Titanium (99% purity, average particle size 15 μm, “PTOM-2”, Russia) was used as a feedstock powder. The spraying distance was 10 mm or 100 mm. Air or nitrogen was used as a carrier gas. Spraying was performed using different compositions of acetylene-oxygen mixtures corresponding to O2
molar ratios of 0.7, 1.1 and 2.5 (Table 1
). The use of nitrogen as a carrier gas reduces the concentration of oxygen in the spraying atmosphere and the oxidation degree of the material. It should be kept in mind that air, when used as a carrier gas, is not the only source of oxidizing agents, as the detonation products themselves contain oxidizing species. The concentrations of oxidizing species in the detonation products depend on the O2
ratio. The spraying frequency was 4–5 shots per second. On average, in order to obtain a coating 300 μm thick on a spot 20 mm in diameter, 60–70 shots are needed. The volume fractions of the barrel filled with an explosive mixture (explosive charge) was 30–60% of the total barrel volume. Conditions of the enhanced nitride formation were created by introducing nitrogen into the explosive mixture.
Elemental microanalysis of the coatings was carried out by Energy Dispersive Spectroscopy (EDS) using an INCA unit (Oxford instruments, Abingdon, UK) attached to a LEO EVO 50 scanning electron microscope (Zeiss, Oberkochen, Germany). The X-ray diffraction (XRD) patterns of the coatings were recorded using a D8 ADVANCE powder diffractometer (Bruker AXS, Karlsruhe, Germany).
Three test samples of the coatings were obtained for each selected set of the detonation spraying parameters (spraying regime). The detonation spraying experiments showed good reproducibility in terms of the phase composition and structure of the deposited layers. The three samples obtained as a result of three runs under the constant conditions were used for the preparation of samples for mechanical testing. Accordingly, for a mechanical characteristic, an average of three measurements is reported for each spraying regime.
In order to study the correlation between the structure and the mechanical properties of the coatings, three-point bending tests were carried out using an electromechanical testing machine Instron 5582. This loading scheme was chosen as under applied external force, the surface layer (the detonation coating) plays a major role in providing resistance to deformation and fracture. The three-point bending tests in combination with photographing the specimen lateral surface allow gaining detailed information on the deformation behavior and estimating the cracking stress σcr
The stress under three-point bending was calculated with the help of Equation (1) [25
is the largest value of bending moment Equation (2) (P
is bending load; l
is the distance between the supports (span).
is the resistance momentum, which for rectangular-section specimens can be calculated by Equation (3) (b
is the width and h
is the gauge height of the specimens).
The shear stress was calculated by Equation (4) [26
is the coating thickness, σdelam
is the stress, at which the coating starts to delaminate (delamination stress) and Lc
is the distance between the cracks in the coating.
The interface fracture toughness (“coating shear resistance”) was determined by Equation (5) [26
For mechanical testing, rectangular specimens 20 × 10 × 2.5 mm3 in size were prepared using electroerosion cutting. The span (the distance between the supports) was 19 mm. Since the titanium substrates possess high ductility, it was nearly impossible to fracture the specimen using the selected loading scheme. For this reason, the evaluation of the mechanical properties was carried out at a bending deflection of 2.5 mm.
Scratch tests were carried out to evaluate the adhesion strength. A Revetest-RST scratcher (CSM-Instruments, Peseux, Switzerland) was used for these measurements. The velocity of the indenter was 2 mm/min. The load was increased from 0.6 N to 200 N. The friction coefficient was calculated as an average over the entire scratch length. The depth of the scratch tracks was estimated by a white light optical interferometer NewView 6200 (Zygo, Berwyn, PA, USA).
Microhardness of the coatings Hμ was measured on the polished surface parallel to the coating/substrate interface using a PMT-3 testing machine (LOMO, St. Petersburg, Russia). The load onto the Vickers pyramid was 100 g. Local characterization of the mechanical properties of the coating phases through nanohardness measurement was carried out by nanoindentation with the help of a Nano Indenter G200 (MTS Systems Corporation, Eden Prairie, MN, USA). Nanohardness was measured on the polished cross-sections of the coatings.
The work was partially supported by Cheung Kong Scholar of Jilin University, and performed with a partial support by Grant No. 11.2 of the Russian Academy of Sciences (Department of Power Engineering, Mechanical Engineering, Mechanics, and Control Processes). The authors are grateful to “Nanotech” Shared Use Center of ISPMS SB RAS for the assistance in running fractographic investigations. The nanoindentation tests were carried out at Tomsk Polytechnic University within the framework of Tomsk Polytechnic University Competitiveness Enhancement Program grant.
Igor Batraev performed detonation spraying, Ilya Vlasov, Roman Stankevich and Dina Dudina carried out experimental studies of the coatings, Sergei Panin, Ilya Vlasov, Dina Dudina and Vladimir Ulianitsky analyzed the data; Sergei Panin, Ilya Vlasov, Dina Dudina, Vladimir Ulianitsky, Filippo Berto wrote the paper.
Conflicts of Interest
The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.
- Deevi, S.C.; Sikka, V.K.; Swindeman, C.J.; Seals, R.D. Application of reaction synthesis principles to thermal spray coatings. J. Mater. Sci. 1997, 32, 3315–3325. [Google Scholar] [CrossRef]
- Fauchais, P.; Montavon, G.; Lima, R.S.; Marple, B.R. Engineering a new class of thermal spray nano-based microstructures from agglomerated nanostructured particles, suspensions and solutions: An invited review. J. Phys. D Appl. Phys. 2011, 44, 093001. [Google Scholar] [CrossRef]
- Kovaleva, M.; Tyurin, Y.; Kolisnichenko, O.; Prozorova, M.; Arseenko, M. Properties of detonation nanostructured titanium-based coatings. J. Therm. Spray Technol. 2013, 22, 518–524. [Google Scholar] [CrossRef]
- Zhao, L.; Lugscheider, E. Reactive plasma spraying of TiAl6V4 alloy. Wear 2002, 253, 1214–1218. [Google Scholar] [CrossRef]
- Fauchais, P.; Montavon, G.; Bertrand, G. From powders to thermally sprayed coatings. J. Therm. Spray Technol. 2010, 19, 56–80. [Google Scholar] [CrossRef]
- Valente, T.; Galliano, F.P. Corrosion resistance properties of reactive plasma-sprayed titanium composite coatings. Surf. Coat. Technol. 2000, 127, 86–92. [Google Scholar] [CrossRef]
- Ulianitsky, V.Y.; Dudina, D.V.; Batraev, I.S.; Kovalenko, A.I.; Bulina, N.V.; Bokhonov, B.B. Detonation spraying of titanium and formation of coatings with spraying atmosphere-dependent phase composition. Surf. Coat. Technol. 2015, 261, 174–180. [Google Scholar] [CrossRef]
- Yao, Y.; Wang, Z.; Zhou, Z.; Jiang, S.; Shao, J. Study on reactive atmospheric plasma-sprayed in situ titanium compound composite coating. J. Therm. Spray Technol. 2013, 22, 509–517. [Google Scholar] [CrossRef]
- Peat, T.; Galloway, A.; Toumpis, A.; McNutt, P.; Iqbal, N. The erosion performance of cold spray deposited metal matrix composite coatings with subsequent friction stir processing. Appl. Surf. Sci. 2017, 396, 1635–1648. [Google Scholar] [CrossRef]
- Klinkov, S.V.; Kosarev, V.F.; Sova, A.A.; Smurov, I. Deposition of multicomponent coatings by Cold Spray. Surf. Coat. Technol. 2008, 202, 5858–5862. [Google Scholar] [CrossRef]
- Sova, A.; Pervushin, D.; Smurov, I. Development of multimaterial coatings by cold spray and gas detonation spraying. Surf. Coat. Technol. 2010, 205, 1108–1114. [Google Scholar] [CrossRef]
- Panin, V.; Gromov, V.; Romanov, D.; Budovskikh, E.; Panin, S. The Physical Basics of Structure Formation in Electroexplosive Coatings. Dokl. Phys. 2017, 472, 650–653. [Google Scholar] [CrossRef]
- Dongmo, E.; Wenzelburger, M.; Gadow, R. Analysis and optimization of the HVOF process by combined experimental and numerical approaches. Surf. Coat. Technol. 2008, 202, 4470–4478. [Google Scholar] [CrossRef]
- Smurov, I.; Ulianitsky, V. Technology vision. Surf. Eng. 2011, 27, 557–559. [Google Scholar] [CrossRef]
- Senderowski, C.; Chodala, M.; Bojar, Z. Corrosion behavior of detonation gun sprayed Fe-Al type intermetallic coating. Materials 2015, 8, 1108–1123. [Google Scholar] [CrossRef] [PubMed]
- Saladi, S.; Menghani, J.; Prakash, S. Effect of CeO2 on cyclic hot-corrosion behavior of detonation-gun sprayed Cr3C2-NiCr coatings on Ni-based superalloy. J. Mater. Eng. Perform. 2015, 24, 1379–1389. [Google Scholar] [CrossRef]
- Senderowski, C. Nanocomposite Fe-Al Intermetallic coating obtained by gas detonation spraying of milled self-decomposing powder. J. Therm. Spray Technol. 2014, 23, 1124–1134. [Google Scholar] [CrossRef]
- Ibrahim, A.; Berndt, C.C. Fatigue and deformation of HVOF sprayed WC-Co coatings and hard chrome plating. Mater. Sci. Eng. A 2007, 456, 114–119. [Google Scholar] [CrossRef]
- Rajasekaran, B.; Raman, S.G.S.; Joshi, S.V.; Sundararajan, G. Performance of plasma sprayed and detonation gun sprayed Cu-Ni-In coatings on Ti-6Al-4V under plain fatigue and fretting fatigue loading. Mater. Sci. Eng. A 2008, 479, 83–92. [Google Scholar] [CrossRef]
- Rodríguez-Barrero, S.; Fernández-Larrinoa, J.; Azkona, I.; de Lacalle, L.N.L.; Polvorosa, R. Enhanced performance of nanostructured coatings for drilling by droplet elimination. Mater. Manuf. Proc. 2016, 31, 593–602. [Google Scholar] [CrossRef]
- de Lacalle, L.N.L.; Lamikiz, A.; Fernandes, M.H.; Gutiérrez, A.; Sánchez, J.A. Turning of thick thermal spray coatings. J. Therm. Spray Technol. 2001, 10, 249–254. [Google Scholar] [CrossRef]
- Toma, F.L.; Bertrand, G.; Chwa, S.O.; Klein, D.; Liao, H.; Meunier, C.; Coddet, C. Microstructure and photocatalytic properties of nanostructured TiO2 and TiO2-Al coatings elaborated by HVOF spraying for the nitrogen oxides removal. Mater. Sci. Eng. A. 2006, 417, 56–62. [Google Scholar] [CrossRef]
- Ulianitsky, V.; Shtertser, A.; Zlobin, S.; Smurov, I. Computer-controlled detonation spraying: From process fundamentals toward advanced applications. J. Therm. Spray. Technol. 2011, 20, 791–801. [Google Scholar] [CrossRef]
- Isakov, M.; Matikainen, V.; Koivuluoto, H.; May, M. Systematic analysis of coating-substrate interactions in the presence of flow localization. Surf. Coat. Technol. 2017, 324, 264–280. [Google Scholar] [CrossRef]
- Gere, J.; Goodno, B. Mechanics of Materials, 7th ed.; Cengage Learning: Toronto, ON, Canada, 2008; pp. 352–454. [Google Scholar]
- Zhou, Y.C.; Tonomori, T.; Yoshida, A.; Liu, L.; Bignall, G.; Hashida, T. Fracture characteristics of thermal barrier coatings after tensile and bending tests. Surf. Coat. Technol. 2002, 157, 118–127. [Google Scholar] [CrossRef]
(a) three-point bending diagram for coated titanium specimens; (b,c) scratching diagrams of the coatings.
Scanning electron microscope (SEM)-micrographs of the cross section of specimens produced in regime No. 1 (a,b) and No. 2 (c,d).
Micrographs of the coating cross-section and Energy Dispersive Spectroscopy (EDS) results: specimen produced in regime No. 1 (a–d) and No. 2 (e–h). A circle within red rectangle shows the location where EDS analysis was carried out.
SEM-micrographs of the coating cross-section of specimens produced in regime No. 3 (a,b) and No. 4 (c,d).
Micrographs of the coating cross-section and EDS results: specimen produced in regime No. 3 (a–d) and No. 4 (e–h). A circle within red rectangle shows the location where EDS analysis was carried out.
SEM-micrographs taken at the cross section of the specimens produced in regime No. 5 (a,b) and No. 6 (c,d).
SEM-micrographs of the coating cross-section and EDS results: specimen produced in regime No. 5 (a–d) and No. 6 (e–h). A circle within red rectangle shows the location where EDS analysis was carried out
SEM micrographs of the cross sections of specimens produced in regime No. 7 (a,b) and No. 8 (c,d).
Micrographs of the coating cross-section and EDS results: specimen produced in regime No. 7 (a–d) and No. 8 (e–h). A circle within red rectangle shows the location where EDS analysis was carried out.
Parameters of detonation spraying and the coating thickness.
|Spraying Regime||O2/C2H2||Spraying Distance, mm||Explosive Charge, %||Carrier Gas||Coating Thickness (hcoat), μm|
|7||1.1 + added 33 vol % N2||10||60||nitrogen||235|
|8||1.1 + added 33 vol % N2||100||60||nitrogen||285|
Mechanical properties of the coatings and coated specimens measured by scratch tests and 3-point bending.
|No.||σ2.5, MPa||σcr, MPa||σdelam, MPa||Kc, MPa·m1/2||τ, MPa||Hμ, GPa||Friction Coefficient, μ0||Maximum Depth of the Scratch, μm|
|1||955||98.4||540||10.4||237.3||3.70 ± 0.03||0.406||66.6|
|2||850||140.5||630||12.7||295.3||3.84 ± 0.07||0.412||63.4|
|3||825||87.9||620||4.8||73.1||2.68 ± 0.07||0.637||83.3|
|4||1055||44.9||70||0.9||10.9||2.45 ± 0.11||0.661||140.5|
|5||945||94.2||730||7.6||132.9||2.72 ± 0.09||0.580||50.7|
|6||870||10||650||-||-||2.02 ± 0.01||0.594||102.2|
|7||945||372.1||800||11.6||228.7||2.74 ± 0.09||0.675||103.5|
|8||875||33.5||560||6.8||93.1||2.29 ± 0.02||0.585||80.9|
Microstructure characteristics and nanohardness of the coatings detonation sprayed under various regimes.
|Regime No.||Characteristic Regions on the Cross-Section||Chemical Composition Determined by EDS, at. %||Phases Detected by the XRD||Crystallite Size, nm||Nanohard-Ness, GPa|
|1||Bright areas||Ti ~99%, O ~1%||-||-||2.7 ± 1|
|Dark areas||Ti ~65%, O ~35%||TiNxOy||20||16.3 ± 3|
|2||Bright areas||Ti ~92%, O ~8%||-||-||7.8 ± 2|
|Dark areas||Ti ~55%, O ~45%||TiO||-||9.7 ± 2|
|3||Bright areas||Ti ~94%, O ~6%||-||-||3.9 ± 0.6|
|Dark areas||Ti ~50%, O ~15%, C ~35%||TiN||20||7.7 ± 1.4|
|4||Bright areas||Ti ~94%, O ~6%||-||-||1.8 ± 0.8|
|Dark areas||Ti ~70%, O ~5%, C ~25%||TiNvCw||20||3.6 ± 1.5|
|5||Bright areas||Ti ~93%, O ~7%||-||-||4.6 ± 0.8|
|Dark areas||Ti ~70%, O ~10%, C ~20%||TiNvCw||20||7.6 ± 1.7|
|6||Bright areas||Ti ~97%, O ~3%||-||-||1.8 ± 0.6|
|Dark areas||Ti ~60%, O ~15%, C ~25%||TiNvCw||30||6.8 ± 1.6|
|7||Bright areas||Ti ~95%, O ~5%||-||-||2.5 ± 0.4|
|Dark areas||Ti ~64%, O ~30%, C ~6%||TiN||35||4.5 ± 1|
|8||Bright areas||Ti ~95%, O ~5%||-||-||4.6 ± 0.5|
|Dark areas||Ti ~77%, O ~15%, C ~8%||TiN||-||6.8 ± 1.8|
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