Article Formation of Metallic Glass Coatings by Detonation Spraying of a Fe66Cr10Nb5B19 Powder
Ivanna D. Kuchumova 1,2, Igor S. Batraev 1 , Vladimir Yu. Ulianitsky 1, Alexandr A. Shtertser 1 , Konstantin B. Gerasimov 3, Arina V. Ukhina 3, Natalia V. Bulina 3 , Ivan A. Bataev 2, Guilherme Yuuki Koga 4, Yaofeng Guo 4, Walter José Botta 4 , Hidemi Kato 5, Takeshi Wada 5, Boris B. Bokhonov 3, Dina V. Dudina 1,2,3,* and Alberto Moreira Jorge, Jr. 4,6
1 Lavrentyev Institute of Hydrodynamics (LIH) SB RAS, Lavrentyev Ave. 15, 630090 Novosibirsk, Russia 2 Department of Mechanical Engineering and Technologies, Novosibirsk State Technical University, K. Marx Ave. 20, 630073 Novosibirsk, Russia 3 Institute of Solid State Chemistry and Mechanochemistry SB RAS, Kutateladze str. 18, 630128 Novosibirsk, Russia 4 Department of Materials Science and Engineering, Federal University of São Carlos, Via Washington Luiz, km 235, SP 13565-905 São Carlos, Brazil 5 Institute for Materials Research, Tohoku University, Aoba Ku, 2-1-1 Katahira, Sendai, 980-8577 Miyagi, Japan 6 Grenoble Alpes University, CNRS, LEPMI and SIMAP, F-38000 Grenoble, France * Correspondence: [email protected]
Received: 11 July 2019; Accepted: 29 July 2019; Published: 31 July 2019
Abstract: The present work was aimed to demonstrate the possibility of forming Fe66Cr10Nb5B19 metallic glass coatings by detonation spraying and analyze the coating formation process. A partially amorphous Fe66Cr10Nb5B19 powder with particles ranging from 45 µm to 74 µm in diameter was used to deposit coatings on stainless steel substrates. The deposition process was studied for different explosive charges (fractions of the barrel volume filled with an explosive mixture (C2H2 + 1.1O2)). As the explosive charge was increased from 35% to 55%, the content of the crystalline phase in the coatings, as determined from the X-ray diffraction patterns, decreased. Coatings formed at explosive charges of 55–70% contained as little as 1 wt.% of the crystalline phase. In these coatings, nanocrystals in a metallic glass matrix were only rarely found; their presence was confined to some inter-splat boundaries. The particle velocities and temperatures at the exit of the barrel were calculated using a previously developed model. The particle temperatures increased as the explosive charge was increased from 35% to 70%; the particle velocities passed through maxima. The coatings acquire an amorphous structure as the molten particles rapidly solidify on the substrate; cooling rates of the splats were estimated. The Fe66Cr10Nb5B19 metallic glass coatings obtained at explosive changes of 55–60% showed low porosity (0.5–2.5%), high hardness (715–1025 HV), and high bonding strength to the substrate (150 MPa).
Keywords: detonation spraying; coating; metallic glass; microstructure; bonding strength; microhardness
1. Introduction In the past two decades, metallic glasses have received much attention from researchers and engineers due to their attractive mechanical properties, wear and corrosion resistance, and the ability to be thermoplastically processed in the super-cooled liquid region [1–3]. Metallic glasses are studied in the form of bulk materials [3], reinforcing phases in composites [4–7], and coatings [8]. Iron-based metallic glass coatings present viable solutions to protect surfaces from corrosion and increase their wear resistance [8–11]. Owing to reduced cost in comparison with other metallic
Metals 2019, 9, 846; doi:10.3390/met9080846 www.mdpi.com/journal/metals Metals 2019, 9, 846 2 of 12 glasses, Fe-based metallic glasses are of particular interest for practical applications. Several attempts to deposit Fe–based metallic glass coatings by the thermal spraying methods have been made [12–17]. The formation of metallic glass coatings by thermal spraying is a challenge, as, during the deposition, conditions should be created either to preserve an amorphous structure of the material (in the case of spraying of amorphous alloy powders) or to produce amorphous layers through melting of the particles and rapid solidification. The quality of coatings built by re-solidified particles is usually better compared with coatings formed by solid particles in terms of adhesion, cohesion, and porosity. During spraying, oxidation of the sprayed material should be prevented, as oxide particles formed in situ deteriorate the properties of the coatings and facilitate crystallization of the alloy acting as nucleation centers. In detonation spraying, coatings are formed as the powder particles are heated and accelerated towards a substrate by the detonation products of gaseous mixtures. The coatings can form upon collision of solid, partially molten or fully molten particles with the substrate. In the detonation coatings obtained from a Fe48Cr15Mo14C15B6Y2 fully amorphous alloy powder, the fraction of the amorphous phase was only 54% [16]. Despite partial crystallization, the ability of the coatings to resist localized corrosion allowed the authors to recommend them as surface protection for marine environments. Xie et al. [15] presented a comparative analysis of the microstructure and mechanical properties of Fe48Mo14Cr15Y2C15B6 coatings obtained by detonation, plasma, and high-velocity oxygen fuel spraying. It was found that the detonation coatings possess the highest content of the amorphous phase among the studied coatings. In the computer-controlled detonation spraying (CCDS) process developed at Lavrentyev Institute of Hydrodynamics, Siberian Branch of the Russian Academy of Sciences (LIH SB RAS) [18], the composition of the explosive gaseous mixture and its volume can be precisely controlled. As those parameters determine the thermal and chemical actions of the detonation products on the sprayed materials, the use of computer control of the process makes spraying results fully reproducible. It was shown that conditions of the splat formation during the deposition influence not only the microstructure of the coatings but also their phase composition, including the formation of metastable phases [19,20]. At present, in research laboratories, detonation spraying guns are still not as widespread as other thermal spray facilities. For this reason, studies of the deposition processes of amorphous alloy coatings by detonation spraying have been limited. The goal of the present work was to obtain Fe66Cr10Nb5B19 metallic glass coatings by detonation spraying and analyze the coating formation process.
2. Materials and Methods For making the master alloy, commercial purity metals and alloys were used as starting materials: Fe-B alloy (B content 16.54 wt.%, ACL Metais, Araçariguama, Brazil), Fe-Nb alloy (Nb content 66.4 wt.%, ACL Metais, Araçariguama, Brazil), metallic chromium (Cr content >99.3 wt.%, ACL Metais, Araçariguama, Brazil), and metallic iron (Fe content >99.5 wt.%, Höganäs, Mogi das Cruzes, Brazil). The Fe66Cr10Nb5B19 alloy powder was obtained by argon gas atomization using a HERMIGA 75/5VI gas atomizer (Phoenix Scientific Industries Ltd., Hailsham, East Sussex, UK). The 45–75 µm fraction was separated by sieving and used for the coating deposition. Detonation spraying was carried out using a CCDS2000 facility developed at LIH SB RAS, Novosibirsk, Russia. The barrel of the gun consisted of two sections: a combustion chamber (700 mm in length and 20 mm in diameter) and a muzzle section (300 mm in length and 16 mm in diameter). The design and advantages of barrel of this geometry are described in [21]. Spraying was conducted at an O2/C2H2 molar ratio of 1.1:1 and explosive charges (fractions of the barrel volume filled with the C2H2 + 1.1O2 mixture) of 35–70%. The powder injection point was located inside the barrel at a distance of 300 mm from the barrel open end. Nitrogen was used as a carrier gas to reduce the probability of oxidation of particles during the deposition process. Coatings were deposited at a rate of fire of the detonation gun of 2 shots per second. At this rate of fire, the consumption of the explosive mixture is about 200, 300, and 400 cm3 per second for the explosive charges of 35%, 55%, and Metals 2019, 9, 846 3 of 12
70%, respectively. Detonation of C2H2 + 1.1O2 explosive mixture is characterized by the following 1 parameters: a detonation front velocity of 2894 m s− , a pressure of 4.52 MPa, a temperature of the 1 detonation products of 4533 K, and a mass velocity behind the detonation front of 1300 m s− [18]. The coatings were deposited on stainless steel substrates at a stand-off distance of 200 mm. Before spraying, sandblasting of the substrates was carried out for better adhesion of the coatings. Sandblasting was carried out by abrasive particles 300–600 µm in size. The temperatures and velocities of the particles at the exit of the barrel were calculated using LIH software (LIH SB RAS, Novosibirsk. Russia) developed based on the analysis presented in [22]. The X-ray diffraction (XRD) phase analysis of the feedstock powder and detonation coatings was performed using a Bruker D8 ADVANCE diffractometer (Bruker AXS, Karlsruhe, Germany). The content of the amorphous phase in the coatings was determined by the Rietveld method using TOPAS 4.2 software (Bruker AXS, Karlsruhe, Germany). The feedstock powder was investigated by differential scanning calorimetry (DSC) using a STA 449 F1 JUPITER thermal analysis instrument (Netzsch, Selb, Germany) in a flow of argon at a heating 1 rate of 10◦ min− . The <45 µm fraction of the gas atomized powder was used for determining the glass transition Tg and crystallization temperatures Tx of the Fe66Cr10Nb5B19 metallic glass. The density of the alloy was measured using an argon pycnometer (Institute of Solid State Chemistry and Mechanochemistry SB RAS, Novosibirsk, Russia). The morphology and microstructure of the samples were studied by scanning electron microscopy using a TM-1000 Tabletop microscope (Hitachi, Tokyo, Japan), a Carl Zeiss EVO50 XVP (Oberkochen, Germany) microscope, and a Hitachi S-3400N (Tokyo, Japan) microscope. Energy-dispersive spectroscopy (EDS) was conducted using a NORAN Spectral System 7 (Thermo Fisher Scientific Inc., Waltham, MA, USA). The fine structure of the coatings was observed by transmission electron microscopy (TEM) using an EM–002B microscope (TOPCON, Tokyo, Japan) working at 200 kV. Dimpling and ion milling was used to prepare samples for TEM studies. The porosity of the coatings was measured using OLYMPUS Stream Image Analysis software Stream Essentials 1.9.1 (Tokyo, Japan). The optical images of the samples were obtained using an OLYMPUS GX-51 Optical Microscope (Tokyo, Japan). Vickers microhardness of the coatings was measured on the polished cross-sections using a DuraScan 50 hardness tester (EMCO-TEST, Kuchl, Austria) at a load of 100 g. The average values of microhardness were determined from 10 measurements. The bonding strength of the coating was determined following ASTM C633–13 standard. The coating/substrate samples were fixed with Permabond® ES558 adhesive and subjected to tensile loading using a Zwick/Roell Z100 mechanical testing machine (Ulm, Germany). The bonding strength of the coatings was also determined by the pin test method, as described in [20]. The reported values of the bonding strength are averaged from five measurements. Standard deviation is also reported.
3. Results and Discussion
The morphology and microstructure of the Fe66Cr10Nb5B19 feedstock powder are shown in Figure1. The particles have a spherical or near-spherical shape. It can be seen that the majority of particles have satellites—particles of smaller sizes attached to their surface (Figure1a), which is typical for the gas-atomized powders. As is seen in Figure1b, the powder is partially crystalline. The dendritic structure is visible near the particle surface, indicating crystallization of the melt upon cooling. Figure2 shows results of the EDS analysis of the powder confirming its elemental composition. MetalsMetals2019 2019, 9,, 8469, x FOR PEER REVIEW 4 of4 13 of 12
(a) (b)
Figure 1. Scanning electron micrographs of the feedstock Fe66Cr10Nb5B19 powder: (a) particle FigureFigure 1. 1.Scanning Scanning electron electron micrographs micrographs ofof thethe feedstockfeedstock FeFe6666CrCr1010NbNb55BB1919 powder:powder: (a) ( aparticle) particle morphology;morphology; (b ()b particle) particle microstructure. microstructure.
FigureFigure 2. Energy-dispersive2. Energy-dispersive spectroscopy spectroscopy (EDS) (EDS) ofof thethe FeFe66Cr10NbNb5B19B feedstockfeedstock powder. powder. Figure 2. Energy-dispersive spectroscopy (EDS) of the Fe6666Cr1010Nb5B519 19feedstock powder. The DSC profile of the feedstock powder indicates the presence of an amorphous phase: glass The DSC profile of the feedstock powder indicates the presence of an amorphous phase: glass transition and crystallization take place upon heating (Figure3). The solidus and liquidus temperature of transition and crystallization take place upon heating (Figure 3). The solidus and liquidus thetemperature alloy were determined of the alloy towere be 1169determined and 1287 to◦ beC, 1169 respectively. and 1287 The °C, XRDrespectively. pattern ofThe the XRD Fe66 patternCr10Nb of5B 19 feedstock66 powder10 5 19 is presented in Figure4. The pattern exhibits a broad halo between 40 and 50 the Fe66Cr10Nb5B19 feedstock powder is presented in Figure 4. The pattern exhibits a broad◦ halo ◦ θ (2 between), indicating 40° and the presence50° (2θ), indicating of an amorphous the presence phase. of The an crystallineamorphous phasesphase. containedThe crystalline in the phases powder 2 arecontainedα-Fe and in Fe the2B. powder In the present are α-Fe work, and Fe the2B. gas-atomized In the present powder work, the particles gas-atomized<45 µm powder in size particles were fully amorphous<45 µm in (accordingsize were fully to the amorphous XRD analysis), (according while to thosethe XRD 45–75 analysis),µm in while size were those partially 45–75 µm crystalline. in size Metals 2019, 9, x FOR PEER REVIEW 5 of 13 were partially crystalline. The Tg and Tx of the Fe66Cr10Nb5B19 metallic glass were determined by the Thewere Tg andpartially Tx of crystalline. the Fe66Cr The10Nb Tg 5andB19 Tmetallicx of the Fe glass66Cr10 wereNb5B19 determined metallic glass by were the DSCdetermined analysis by ofthe the DSC analysis of the particles <45 µm in size: Tg = 521 °C; Tx = 573 °C. particlesDSC analysis<45 µm of in the size: particles Tg = 521<45 ◦µmC; Tinx size:= 573 Tg◦ =C. 521 °C; Tx = 573 °C.
Tl Ts
0.0
T -1 g Tx - 0.5 DSC, mWmg DSC, - 1.0
- 1.5 0 200 400 600 800 1000 1200 1400 Temperature, °C
Figure 3. Differential scanning calorimetry (DSC) curve of the Fe66Cr10Nb5B19 feedstock powder
(45–75Figureµm). 3. Differential scanning calorimetry (DSC) curve of the Fe66Cr10Nb5B19 feedstock powder (45–75 µm).
- α-Fe
- Fe2B Intensity, a.u. Intensity,
20 30 40 50 60 70 80 90 100 2θ, deg.
Figure 4. X-ray diffraction (XRD) pattern of the Fe66Cr10Nb5B19 feedstock powder (45–75 µm).
The XRD patterns of the detonation coatings are shown in Figure 5. A common feature of the patterns is the presence of a broad diffraction halo between 40° and 50° (2θ) indicating the presence of an amorphous phase. The content of the crystalline phase in the coatings estimated from the XRD patterns is given in Table 1. Coatings formed at explosive charges of 55–70% contain as little as 1 wt.% of the crystalline phase. At an O2/C2H2 molar ratio of 1.1:1, the detonation products have a reducing character containing 58% of carbon monoxide CO and 22% of atomic hydrogen [23]. Under these conditions, no oxidation of the sprayed particles can take place [23]. The absence of extensive oxidation of the sprayed material is believed to be crucial for the formation of metallic glass coatings.
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Tl Ts
0.0
T -1 g Tx - 0.5 DSC, mWmg DSC, - 1.0
- 1.5 0 200 400 600 800 1000 1200 1400 Temperature, °C
Figure 3. Differential scanning calorimetry (DSC) curve of the Fe66Cr10Nb5B19 feedstock powder (45–75 µm). Metals 2019, 9, 846 5 of 12
- α-Fe
- Fe2B Intensity, a.u. Intensity,
20 30 40 50 60 70 80 90 100 2θ, deg.
Figure 4. X-ray diffraction (XRD) pattern of the Fe66Cr10Nb5B19 feedstock powder (45–75 µm).
TheFigure XRD 4. patterns X-ray diffraction of the detonation (XRD) pattern coatings of the areFe66Cr shown10Nb5B in19 feedstock Figure5. powder A common (45–75 feature µm). of the patterns is the presence of a broad diffraction halo between 40◦ and 50◦ (2θ) indicating the presence of The XRD patterns of the detonation coatings are shown in Figure 5. A common feature of the an amorphous phase. The content of the crystalline phase in the coatings estimated from the XRD patterns is the presence of a broad diffraction halo between 40° and 50° (2θ) indicating the presence patterns is given in Table1. Coatings formed at explosive charges of 55–70% contain as little as 1 wt.% of an amorphous phase. The content of the crystalline phase in the coatings estimated from the XRD of the crystalline phase. At an O /C H molar ratio of 1.1:1, the detonation products have a reducing patterns is given in Table 1. Coatings2 2 2formed at explosive charges of 55–70% contain as little as 1 character containing 58% of carbon monoxide CO and 22% of atomic hydrogen [23]. Under these wt.% of the crystalline phase. At an O2/C2H2 molar ratio of 1.1:1, the detonation products have a Metalsconditions, 2019, 9, x no FOR oxidation PEER REVIEW of the sprayed particles can take place [23]. The absence of extensive oxidation6 of 13 reducing character containing 58% of carbon monoxide CO and 22% of atomic hydrogen [23]. Under of the sprayed material is believed to be crucial for the formation of metallic glass coatings. these conditions, no oxidation of the sprayed particles can take place [23]. The absence of extensive oxidation of the sprayed material isα-Fe believed to be crucial for the formation of metallic glass coatings.
50 % 70 %
45 % 65 %
40 % Intensity, a.u. Intensity, a.u. Intensity, 60 %
55 % 35 %
20 30 40 50 60 70 80 90 100 20 30 40 50 60 70 80 90 100 2θ, deg. 2θ, deg.
(a) (b)
FigureFigure 5. 5. XRDXRD patternspatterns of of the the Fe FeCr66CrNb10NbB5B19detonation detonation coatings coatings obtained obtained at different at different explosive explosive charges. 66 10 5 19 charges. Table 1. Content of the crystalline phase, porosity, and Vickers microhardness of the Fe66Cr10Nb5B19
Tabledetonation 1. Content coatings. of the For crystalline the content phase, of the porosi crystallinety, and phase Vickers and microhardness porosity, the standard of the Fe deviations66Cr10Nb5B are19 detonationgiven. For coatings. Vickers microhardness, For the content theof the confidence crystallin intervalse phase and are givenporosity, (for the a confidence standard deviations level of 0.95). are
given. For Vickers microhardness,Content the confidence of the intervals are given (for a confidenceVickers Microhardness, level of 0.95). Explosive Charge, % Porosity, % Crystalline Phase, wt.% HV Vickers100 Explosive35 Content 5of the0.2 Crystalline 4.0 1.0 540 210 ± Porosity,± % Microhardness,± Charge,40 % Phase, 4 0.2 wt.% 3.0 0.8 750 55 ± ± ± 45 3 0.2 2.5 1.0 780HV100145 ± ± ± 3550 2 5 ±0.2 0.2 2.5 4.00.5 ± 1.0 540 875 ± 130210 ± ± ± 55 1 0.2 1.0 0.5 920 95 40 ± 4 ± 0.2 ± 3.0 ± 0.8 750 ±± 55 60 1 0.2 2.0 0.5 870 155 45 ± 3 ± 0.2 ± 2.5 ± 1.0 780 ±± 145 65 1 0.2 1.2 0.5 770 100 ± ± ± 5070 1 2 ±0.2 0.2 2.5 2.50.5 ± 0.5 875 770 ± 13075 55 ± 1 ± 0.2 ± 1.0 ± 0.5 920 ±± 95 60 1 ± 0.2 2.0 ± 0.5 870 ± 155 Figure6 shows cross-sections of the detonation coatings. It can be seen that the coatings possess a 65 1 ± 0.2 1.2 ± 0.5 770 ± 100 lamellar structure typical of thermally sprayed coatings formed from molten or semi-molten particles. 70 1 ± 0.2 2.5 ± 0.5 770 ± 75
Figure 6 shows cross-sections of the detonation coatings. It can be seen that the coatings possess a lamellar structure typical of thermally sprayed coatings formed from molten or semi-molten particles. As the explosive charge is increased from 35% to 60%, fewer defects (pores, non-melted particles, and cracks) are observed in the microstructure of the coatings.
(a) (b)
Metals 2019, 9, x FOR PEER REVIEW 6 of 13
α-Fe
50 % 70 %
45 % 65 %
40 % Intensity, a.u. Intensity, a.u. Intensity, 60 %
55 % 35 %
20 30 40 50 60 70 80 90 100 20 30 40 50 60 70 80 90 100 2θ, deg. 2θ, deg.
(a) (b)
Figure 5. XRD patterns of the Fe66Cr10Nb5B19 detonation coatings obtained at different explosive charges.
Table 1. Content of the crystalline phase, porosity, and Vickers microhardness of the Fe66Cr10Nb5B19 detonation coatings. For the content of the crystalline phase and porosity, the standard deviations are given. For Vickers microhardness, the confidence intervals are given (for a confidence level of 0.95).
Vickers Explosive Content of the Crystalline Porosity, % Microhardness, Charge, % Phase, wt.% HV100 35 5 ± 0.2 4.0 ± 1.0 540 ± 210 40 4 ± 0.2 3.0 ± 0.8 750 ± 55 45 3 ± 0.2 2.5 ± 1.0 780 ± 145 50 2 ± 0.2 2.5 ± 0.5 875 ± 130 55 1 ± 0.2 1.0 ± 0.5 920 ± 95 60 1 ± 0.2 2.0 ± 0.5 870 ± 155 65 1 ± 0.2 1.2 ± 0.5 770 ± 100 70 1 ± 0.2 2.5 ± 0.5 770 ± 75
Metals 2019Figure, 9, 846 6 shows cross-sections of the detonation coatings. It can be seen that the coatings possess6 of 12 a lamellar structure typical of thermally sprayed coatings formed from molten or semi-molten particles. As the explosive charge is increased from 35% to 60%, fewer defects (pores, non-melted As theparticles, explosive and cracks) charge are is observed increased in fromthe microstructure 35% to 60%, of fewer the coatings. defects (pores, non-melted particles, and cracks) are observed in the microstructure of the coatings.
Metals 2019, 9, x FOR PEER REVIEW 7 of 13 (a) (b)
(с) (d)
(e) (f)
(g) (h)
FigureFigure 6. Cross-sections 6. Cross-sections of of the the Fe Fe66Cr66Cr1010NbNb55B1919 detonationdetonation coatings coatings obtained obtained at different at different explosive explosive charges:charges: (a) 35%;(a) 35%; (b )(b 40%;) 40%; (c )(с 45%;) 45%; (d (d)) 50%, 50%, ((ee)) 55%;55%; (f) 60%; 60%; ( (gg) )65%; 65%; (h ()h 70%.) 70%.
A TEM bright-field image of the substrate/coating sample obtained at an explosive charge of 60% (Figure 7a) shows that an amorphous layer has a well-developed interface with the substrate. Selected-area electron diffraction patterns (SAEDP) confirm the crystalline nature of the substrate and the amorphous nature of the coating. A high-resolution image of the coating (Figure 7b) and a corresponding fast Fourier transform (inset in Figure 7b) provides convincing evidence of the amorphous structure. Only rarely were nanocrystals found in an amorphous matrix (at some inter-splat boundaries, Figure 8a). The chemical composition of the nanocrystals corresponds to the as-sprayed alloy, as is seen in Figure 8b.
Metals 2019, 9, 846 7 of 12
A TEM bright-field image of the substrate/coating sample obtained at an explosive charge of 60% (Figure7a) shows that an amorphous layer has a well-developed interface with the substrate. Selected-area electron diffraction patterns (SAEDP) confirm the crystalline nature of the substrate and the amorphous nature of the coating. A high-resolution image of the coating (Figure7b) and a corresponding fast Fourier transform (inset in Figure7b) provides convincing evidence of the amorphous structure. Only rarely were nanocrystals found in an amorphous matrix (at some inter-splat Metalsboundaries, 2019, 9, xFigure FOR PEER8a). REVIEW The chemical composition of the nanocrystals corresponds to the as-sprayed8 of 13 alloy, as is seen in Figure8b.
(a)
(b)
Figure 7. Transmission electron microscopymicroscopy (TEM)(TEM)bright-field bright-field image image of of the the substrate substrate/Fe/Fe6666CrCr1010NbNb55BB1919 coating samplesample andand selected-area selected-area electron electron di ffdiffractionraction patterns patterns (SAEDP) (SAEDP) (a), high-resolution (a), high-resolution TEM imageTEM imageof the coatingof the coating structure structure and fast and Fourier fast Fourier transform transform (inset) ((inset)b). Explosive (b). Explosive charge charge 60%. 60%.
Metals 2019, 9, x FOR PEER REVIEW 9 of 13 Metals 2019, 9, 846 8 of 12
(a)
(b)
FigureFigure 8.8. TEMTEM imageimage ofof the detonation coating structure showing showing nanocrystals nanocrystals found found occasionally occasionally at at thethe inter-splat inter-splat boundaries boundaries and and a corresponding a corresponding SAEDP SAEDP (a), elemental (a), elemental analysis resultsanalysis of theresults nanocrystals of the (bnanocrystals). Explosive ( chargeb). Explosive 60%. charge 60%.
TheThe temperaturestemperatures andand velocitiesvelocities of the particlesparticles leaving leaving the the gun gun barrel barrel calculated calculated for for different different explosiveexplosive chargescharges andand threethree particleparticle sizessizes are presentedpresented in Figure 99.. SimplificationSimplification has been made made duringduring the the calculations: calculations: it it was was assumed assumed that that the the material material melts melts at 1442 at 1442 K (horizontal K (horizontal sections sections of curves of incurves Figure in9 a).Figure For obtaining9a). For obtaining a lower bounda lower of bound the temperature of the temperature of the particles of the reachingparticles thereaching substrate the andsubstrate assessing and theassessing coating the formation coating conditions,formation conditions, this simplification this simplification is acceptable. is acceptable. After exiting After the barrel,exiting the the particles barrel, the experience particles additionalexperience heating addition asal they heating continue as they to continue be surrounded to be surrounded by the cloud by of thethe detonation cloud of the products. detonation Calculations products. Calculations show that, show at an that, explosive at an explosive charge of charge 45%, particles of 45%, particles 45 µm in diameter45 µm in experiencediameter experience melting upon melting leaving upon the leavin barrelg the (Figure barrel9a). (Figure When 9a). an When explosive an explosive charge of charge 60% is used,of 60% even is used, particles even 75 particlesµm in diameter 75 µm in are diameter heated upare to heated 1442 K. up The to calculated1442 K. The particle calculated temperatures particle aretemperatures consistent withare consistent results of with the structuralresults of the investigations structural investigations of the coatings of the (Figure coatings6e,f): (Figure at explosive 6e,f): chargesat explosive of 55–60%, charges the of coatings55–60%, arethe formedcoatings mainly are formed by solidification mainly by solidification of the molten of splats.the molten splats.
Metals 2019, 9, x FOR PEER REVIEW 10 of 13
Metals 2019, 9, 846 9 of 12
2400 45 μm 2200
2000 60 μm 1800
1600 melting
Temperature, K Temperature, 75 μm 1400
1200
1000 35 40 45 50 55 60 65 70 Explosive charge, %
(a)
480
460
440 45 μm
-1 420
400
380 60 μm Velocity, m s m Velocity,
360
340 75 μm
320 35 40 45 50 55 60 65 70 Explosive charge, %
(b)
FigureFigure 9.9. CalculatedCalculated temperaturestemperatures (a(a)) and and velocities velocities ( b()b of) of Fe Fe66Cr66Cr1010NbNb55BB1919 particles as functionsfunctions ofof explosiveexplosive charge.charge. Calculations were conducted for particles 45, 60, and 7575 µµmm inin diameter.diameter. ItIt waswas assumedassumed thatthat thethe materialmaterial meltsmelts atat 14421442 KK (horizontal(horizontal sectionssections ofof thethe curvescurves inin( (a)).a)).
TheThe velocitiesvelocities of of the the particles particles pass pass through through maxima maxima as theas the explosive explosive charge charge is increased is increased from from 35% to35% 70% to (Figure70% (Figure9b). The 9b). location The location of the powder of the injectionpowder injection point on thepoint barrel on the determines barrel determines the explosive the charge,explosive at whichcharge, the at which maximum the maximum velocity is velocity reached is [24 reached]. Low particle[24]. Low velocities particle atvelocities large explosive at large chargesexplosive may charges cause may deterioration cause deterioration of the coating of the quality coating (uniformity quality (uniformity and contiguity). and contiguity). AccordingAccording toto [25[25],], during during argon argon gas gas atomization, atomization, Fe Fe alloy alloy particles particles 50 50µm µm in sizein size cool cool down down at an at 5 1 averagean average rate rate of 10of 10K5 sK− s.−1 As. As mentioned mentioned above, above, the the gas-atomized gas-atomized powder powder particles particles< <4545 µµmm inin sizesize obtainedobtained inin thethe presentpresent workwork areare fullyfully amorphous.amorphous. Consequently,Consequently, forfor thethe metallicmetallic glassglass coatingscoatings toto bebe 5 1 formed,formed, coolingcooling ratesrates higherhigher than than 10 105K K ss−−1 shouldshould be provided for the detonationdetonation splats.splats. TheThe coolingcooling = h2 rate of the splats can be estimated using the characteristic cooling time defined as t a , where h is Metals 2019, 9, x FOR PEER REVIEW 11 of 13 Metals 2019, 9, 846 10 of 12 rate of the splats can be estimated using the characteristic cooling time defined as 𝑡= , where ℎ is the thickness of the splat (can be taken equal to 15 µm for particles 45 µm in diameter) and 𝑎 is the thickness of the splat (can be taken equal to 15 µm for particles 45 µm in diameter) and a is the the thermal diffusivity of the material, k𝑎= (𝑘 is the thermal conductivity, 𝜌 is the density; 𝑐 thermal diffusivity of the material, a = (k is the thermal conductivity, ρ is the density; c is the heat ρcp p −1 −1 −1 −1 is the heat capacity) [26]. For calculations, 𝑘1 = 101 W m K and 𝑐1 = 11 kJ kg K were used. The capacity) [26]. For calculations, k = 10 W m− K− and cp = 1 kJ kg− K− were used. The measured measured density of the alloy is 37580 kg m−3. If, within the characteristic cooling time, a temperature density of the alloy is 7580 kg m− . If, within the characteristic cooling time, a temperature drop from drop from the liquidus temperature of 1560 K to 760 K is assumed, a cooling rate of the order6 of 101 6 the liquidus temperature of 1560 K to 760 K is assumed, a cooling rate of the order of 10 K s− is K s−1 is obtained. This cooling rate is high enough to ensure the formation of metallic glass coatings. obtained. This cooling rate is high enough to ensure the formation of metallic glass coatings. Thinner Thinner splats cool at even higher rates. splats cool at even higher rates. The porosity and microhardness of the detonation coatings are given in Table 1. Coatings The porosity and microhardness of the detonation coatings are given in Table1. Coatings obtained obtained at explosive charges of 55% and 60% show low porosity (0.5–2.5%). The microhardness of at explosive charges of 55% and 60% show low porosity (0.5–2.5%). The microhardness of these these coatings is in the 715–1025 HV range. These values of microhardness are encountered in some coatings is in the 715–1025 HV range. These values of microhardness are encountered in some Fe-based Fe-based bulk metallic glasses [27]. As the explosive charge is increased from 35% to 55%, the bulk metallic glasses [27]. As the explosive charge is increased from 35% to 55%, the porosity of porosity of the coatings decreases, while their microhardness increases. This can be explained by the the coatings decreases, while their microhardness increases. This can be explained by the increase increase in the temperature of the particles and the fraction of the material experiencing melting in the temperature of the particles and the fraction of the material experiencing melting (Figure9a). (Figure 9a). The degree of consolidation of particles (cohesion) also increases. Explosive charges of The degree of consolidation of particles (cohesion) also increases. Explosive charges of 55–60% can 55–60% can be recommended for producing Fe66Cr10Nb5B19 metallic glass coatings with low porosity be recommended for producing Fe Cr Nb B metallic glass coatings with low porosity and high and high hardness by detonation spraying.66 10 5 19 hardnessThe bybonding detonation strength spraying. of the coatings was determined using samples obtained at an explosive chargeThe of bonding 55%. The strength bonding of the strength coatings of wasthe determinedcoatings determined using samples according obtained to ASTM at an explosiveC633–13 chargestandard of 55%. was found The bonding to be higher strength than of 76 the MPa, coatings whic determinedh is the tensile according strength to of ASTM Permabond C633–13 ES standard558; the wasspecimen found torupture be higher occurred than 76through MPa, whichthe polymer is the tensile layer. strengthThe bonding of Permabond strength measured ES 558; the by specimen the pin rupturetest method occurred was through150 ± 10 theMPa. polymer The fracture layer. surface The bonding (the surface strength of the measured pin) is shown by the pinin Figure test method 10. It was 150 10 MPa. The fracture surface (the surface of the pin) is shown in Figure 10. It can be seen can be ±seen that rupture occurred along the coating/substrate interface. The obtained bonding thatstrength rupture values occurred are higher along thethan coating those /substratetypically found interface. in metallic The obtained coatings bonding obtained strength by detonation values are higherspraying than [20]. those typically found in metallic coatings obtained by detonation spraying [20].
(a) (b)
FigureFigure 10. 10.General General view view of of the the flat flat end end of of the the pin pin after after the the bonding bonding strength strength test test (a); (a morphology); morphology of theof pinthe surface pin surface indicating indicating rupture rupture along al theong coatingthe coating/substrate/substrate interface interface (b). (b).
4.4. Conclusions Conclusions A possibility of forming Fe Cr Nb B metallic glass coatings by detonation spraying of a A possibility of forming Fe6666Cr1010Nb5B1919 metallic glass coatings by detonation spraying of a gas-atomizedgas-atomized powderpowder waswas demonstrated.demonstrated. Thanks Thanks to to the the pulse pulse nature nature of of the the detonation detonation spraying spraying process,process, thethe temperaturetemperature of the the particles particles depositing depositing on on the the substrate substrate can can be adjusted be adjusted by changing by changing the thetime time between between the the shots. shots. Conditions Conditions of ofrapid rapid coolin coolingg of ofthe the splats splats can can thus thus be be met. met. Although Although the the FeFe6666CrCr1010Nb5BB1919 feedstockfeedstock powder powder was was partially partially crystalline, crystalline, coatings coatings with with an an amorphous amorphous structure structure formed,formed, which which was was due due to melting to melting of the of particles the particles and rapid and solidification rapid solidification of the splats. of the The splats. amorphous The structureamorphous of the structure coatings of wasthe coatings confirmed was by confirmed XRD and by TEM. XRD Nanocrystals and TEM. Nanocrystals in the metallic in the glass metallic matrix wereglass only matrix rarely were found only (at rarely inter-splat found boundaries). (at inter-splat The boundaries). glassy Fe66Cr The10Nb glassy5B19 coatings Fe66Cr10Nb exhibit5B19 coatings hardness comparable to that of some bulk Fe-based metallic glasses and extremely high bonding strength to a stainless steel substrate. Metals 2019, 9, 846 11 of 12
Author Contributions: Conceptualization, D.V.D., I.A.B. and A.M.J.J.; methodology, I.S.B., W.J.B., A.A.S. and V.Y.U.; investigation, I.D.K., B.B.B., N.V.B., A.V.U., K.B.G., Y.G. and G.Y.K.; writing—original draft preparation, I.D.K. and I.S.B.; writing—review and editing, D.V.D., B.B.B., H.K., T.W. and A.M.J.J.; supervision, D.V.D.; project administration, V.Y.U. and A.M.J.J.; funding acquisition, D.V.D., I.D.K., I.S.B., A.A.S. and V.Y.U. Funding: I.D.K. and I.S.B. acknowledge partial support by the Russian Foundation for Basic Research and the Novosibirsk region, project 19-43-543034 r_mol_a. Acknowledgments: TEM studies were conducted within the Global Institute for Materials Research Tohoku program (proposal 18GK0003), IMR Tohoku University, Japan. The authors are grateful to Shun Ito (Tohoku University) for his help in conducting TEM investigations and Konstantin A. Tsarakhov (LIH SB RAS) for technical assistance. Conflicts of Interest: The authors declare no conflicts of interest.
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