Microstructure and fracture morphology of thermally sprayed refractory metals and ceramics
The microstructural characteristics such as porosity, splat morphology and grain size of thermally sprayed coatings made of both ceramic and refractory metals are investigated. Al2O3 and Cr2O3 coatings represent ceramic materials while pure W and Mo coatings represent the refractory metals. The used...
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| Опубліковано в: : | Проблемы прочности |
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Інститут проблем міцності ім. Г.С. Писаренко НАН України
2008
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| Цитувати: | Microstructure and fracture morphology of thermally sprayed refractory metals and ceramics / O. Kovarik, J. Siegl // Проблемы прочности. — 2008. — № 1. — С. 89-92. — Бібліогр.: 8 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1859626878791319552 |
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| author | Kovarik, O. Siegl, J. |
| author_facet | Kovarik, O. Siegl, J. |
| citation_txt | Microstructure and fracture morphology of thermally sprayed refractory metals and ceramics / O. Kovarik, J. Siegl // Проблемы прочности. — 2008. — № 1. — С. 89-92. — Бібліогр.: 8 назв. — англ. |
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| description | The microstructural characteristics such as porosity, splat morphology and grain size of thermally sprayed coatings made of both ceramic and refractory metals are investigated. Al2O3 and Cr2O3 coatings represent ceramic materials while pure W and Mo coatings represent the refractory metals. The used deposition technology (RF-plasma, gas stabilized or water stabilized DC plasma) was found to influence the coatings microstructure to a great extent by providing different particle impact velocities and temperatures. At the same time the substrate temperature plays an important role as is shown fo r refractory metal coatings deposited at different substrate temperatures. Generally, all investigated coatings contained intrasplat cracks, intersplat pores and voids, individual splats of different degree of deformation and different degree of intersplat sintering, crystal grains formed inside individual splats or extending through many of them. It is shown that the size and abundance of the above-mentioned microstructural features predetermine the fracture morphology of the coating as well as mechanical properties.
Исследованы такие характеристики микроструктуры, как пористость, морфология частиц напыления и размер зерна газотермических покрытий из керамики ( Al2O3 и Cr2O3) и тугоплавких металлов ( W и Мо). Установлено, что технология напыления (высокочастотная плазма, газо- или водостабилизированная плазма постоянного тока) оказывает значительное влияние на микроструктуру покрытий при различных температурах и скоростях соударения частиц. В то же время отмечена важная роль температуры подложки для покрытий из тугоплавких металлов, нанесенных при различных температурах подложки. Все исследованные покрытия, как правило, содержали трещины внутри напыленных частиц, поры и полости между частицами, отдельные частицы с разными степенью деформации и межчастичного спекания, кристаллиты, образовавшиеся внутри отдельных частиц или проходящие через несколько таких частиц. Показано, что величина и распространенность указанных особенностей микроструктуры предопределяют морфологию поверхности излома покрытий, а также их механические свойства.
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UDC 539. 4
M ic r o s tr u c tu r e a n d F r a c tu r e M o r p h o lo g y o f T h e r m a lly S p r a y e d R e fr a c to r y
M e ta ls a n d C e r a m ic s
O. K o v a n k 1,a and J . S ieg l1
1 Czech Technical University in Prague, Faculty o f Nuclear Sciences and Physical Engineering,
Department of Materials, Prague, Czech Republic
a kovon@seznam.cz
The microstructural characteristics such as porosity, splat morphology and grain size o f thermally
sprayed coatings made o f both ceramic and refractory metals are investigated. Al2O3 and Cr2O3
coatings represent ceramic materials while pure W and Mo coatings represent the refractory
metals. The used deposition technology (RF-plasma, gas stabilized or water stabilized DC plasma)
was found to influence the coatings microstructure to a great extent by providing different particle
impact velocities and temperatures. A t the same time the substrate temperature plays an important
role as is shown fo r refractory metal coatings deposited at different substrate temperatures.
Generally, all investigated coatings contained intrasplat cracks, intersplat pores and voids, individual
splats o f different degree o f deformation and different degree o f intersplat sintering, crystal grains
form ed inside individual splats or extending through many o f them. It is shown that the size and
abundance o f the above-mentioned microstructural features predetermine the fracture morphology
o f the coating as well as mechanical properties.
K eyw o rd s : thermal spraying, refractory materials, microstructure, fractography, elastic
modulus.
In troduction . The increasing demands for sophisticated construction parts w ith
increased corrosion and heat resistance lead to the increased use o f protective coatings.
Refractory materials fulfill the demands for corrosion, thermal, wear and fatigue resistance
and, w hen applied as coatings, help to preserve the low w eight and m echanical properties
o f the substrate material. A great advantage o f protective coatings is the p ossib ility to
renew the part by replacing any worn coating.
We discuss deposit properties o f several therm ally sprayed coatings o f engineering
importance sprayed b y three different techniques. The spray technology and process
parameters used are selected for each feedstock in order to provide favorable particle state
for the deposition based on previous experim ents [1 -3 ].
E xp erim en ta l. Refractory ceram ics A l2O3 and Cr2O3 were deposited on flat 4 mm
thick m ild steel substrates by WSP® PAL 160 water stabilized plasm a torch at IPP, CAS,
C zech R epublic. Tungsten deposits were prepared on thick stainless steel substrates by
Tekna PL-50 RF-ICP torch in an inert atmosphere at CREPE Sherbrooke, Quebec,
Canada. M olybdenum coatings were prepared on flat 4 m m thick m ild steel substrates by
A PS DC plasm a torch M etco 3M B at CTSR, Stony Brooke, NY, U SA . Spray conditions
are listed in Table 1. A ll substrates w ere grit-blasted before spraying.
The in-flight particle properties w ere measured using D P V -2000 instrument. The
elastic m odulus o f the M o coatings w as m easured by four-point bending tests as described
in [4]. M oduli o f other deposits were estim ated from resonance frequency o f the coating
beam. The total deposit porosity (open and closed) w as estim ated by w eighting a sample
o f the know n volum e using a precision scale.
M etallographic specim ens for structure observations were prepared by electrolytic
polishing and etching. The splat thickness w as m easured by im age analysis on a
polished/etched cross-section and the value is an average o f approxim ately 200
m easurements.
© O. KOVARIK , J. SIEGL, 2008
ISSN 0556-171X. Проблемы прочности, 2008, № 1 89
mailto:kovon@seznam.cz
O. Kovârik and J. Siegl
T a b l e 1
The Most Important Deposition Process Parameters
Feedstock Spray
techno-
i°gy
TTs-
0C
qc,
slpm*
qp ,
slpm
qs,
slpm
feed
rate,
g/mm
̂
1 T ,Tp
0C
vp ,
0C
dmean,
fim
W RF/ICP 560 6.3 (He) 30 (Ar) 100 (Ar) +
15 (H2)
40 80 4120** 40** 61**
W RF/ICP 430 6.3 (He) 30 (Ar) 100 (Ar) +
15 (H2)
40 80 4120** 40** 61**
W RF/ICP 285 6.3 (He) 30 (Ar) 100 (Ar) +
15 (H2)
40 80 4120** 40** 61**
Mo GSP 250 6 (Ar) 40 (Ar) 10 (H2) 60 33 3100 132 65
Mo GSP 120 6 (Ar) 40 (Ar) 10 (H2) 60 33 3100 132 65
AI2O3 WSP 120 n 2 - - 433 160 - - 50
Cr2Ü3 WSP 90 N2 - - 530 160 - - 50
Notes: * standard liters per minute; ** volumetric median; GSP = gas stabilized plasma; WSP =
water stabilized plasma; Ts is substrate temperature; qc is carrier gas flowrate; qp is primary
(plasma) gas flowrate; qs is secondary (sheath) gas flowrate; P is torch power; Tp is mean particle
temperature; vp is mean particle velocity; dmean is mean particle diameter.
R esu lts and D iscu ssion . The m easured in-flight temperature data ensure proper
m elting o f the feedstock pow ders and lim ited feedstock evaporation (see Table 1). The
im pact velocity o f the M o particles w as m uch higher than that o f the W particles (see
Table 1) resulting in thinner splats (Table 2). E lastic m oduli (Table 2) o f the coating
ranges from 4 to 44% o f bulk material m odulus, both extreme cases were obtained for the
W deposits sprayed under the sam e conditions, but different Ts . The deposit porosity ^
(see Table 2) ranges from 2% to 33% w ith the low est porosity achieved for W and highest
for A l2O 3.
T a b l e 2
Deposit Properties
Feedstock Spray
technology
TTs
0C
E,
GPa
Ebulk ,
GPa
E <P hcoating '
mm
h ,hsplat
mmEbulk
W RF/ICP 560 182 411 0.44 0.09 0.60 6.30
W RF/ICP 430 179 411 0.44 0.02 0.42 6.30
W RF/ICP 285 17 411 0.04 0.06 0.46 7.00
Mo GSP 120 45 329 0.14 0.15 0.28 4.60
Mo GSP 250 43 329 0.13 0.27 0.31 4.50
Al2O3 WSP 120 48 345 0.14 0.33 0.35 7.00
Cr2O3 WSP 90 43 350 0.12 0.30 0.44 7.50
The results obtained clearly show the importance o f the substrate temperature on the
deposit properties. The micrographs in Fig. 1 reveal tw o types o f the deposit structure. For
the M o deposits and the tungsten deposit at 29 0 oC, the intersplat porosity contributes
significantly to the total porosity. O n the other hand, the W deposits at 4 3 0 oC (Fig. 1) and
560oC (not included on Fig. 1) show intersplat boundaries but on ly a lim ited number o f
intersplat pores. In the case o f W, the steep increase o f elastic m odulus betw een 290 and
430oC w as detected (Fig. 2), suggesting the transition temperature (change from splash-
90 ISSN 0556-171X. npoôëeubi npounocmu, 2008, N 1
Microstructure and Fracture Morphology
splats to disc-splats, [5]) o f W on W system is situated in that range. N o similar change
w as detected for M o, probably due to a lo w substrate temperature. The transition
temperature o f M o on steel is reported in the range o f 3 0 0 -4 0 0 oC in [6 ] and around 300oC
in [7].
Fig. 1. The influence o f substrate temperature on coating microstructure for W and Mo coatings.
0.50
0.45
0.40
0.35
a 0.30
t l 0.25
0.20
0.15
0.10
0.05
0.00
; ; . - o -
_ _ - U
O ! " ' P- - - - •
□ -
\ r
— #
t \
— j-------------------
; ; # ; ;
* - » - E/Ebulk(W)
1 f
- ■ - E/Ebu,k(Mo)
P/Pbulk(W) -
p/Pbulk(MO) -
■ - ■ : - ■
O -
•
: » , : :
100 200 300 400
T,(C)
500
1.00
0.90
O.SO
0.70
0.60
0.50 ,
0.40 '
0.30
0.20
0.10
0.00
600
Fig. 2. The elastic modulus and relative density o f Mo and W deposits vs. the substrate temperature.
The m etallographic sam ples o f ceramic deposits prepared by ion m illing show ed an
extensive porosity network formed by intersplat pores and intrasplat cracks. In order to
visualize the crystal structure, the specim ens w ere ruptured on a tensile m achine and the
coating fracture w as observed (Fig. 3). The micrographs show columnar grain structure o f
the splats and dendritic structure o f spherical particles (that im pacted in solid state). The
transition temperature for ceramic materials is supposed to be low er than that for metals
(in the range betw een 100 and 200°C, [8 ]). Thus, it is possible that ceramic coatings were
deposited above the transition temperature, as suggested by the splat morphology.
ISSN 0556-171X. npoôëeubi npounocmu, 2008, № 1 91
O. Kovarik and J. Siegl
Fig. 3. The fracture surfaces o f ceramics deposits showing lamellar structure o f the deposit and
spherical particles.
C onclusions. The coating structure o f the deposits investigated consists o f
individual splats and a porosity network form ed by intersplat pores and intrasplat cracks.
More intrasplat cracks occurred in ceramic deposits due to its brittle nature. D ense W
deposits w ith a h igh m odulus were obtained at an elevated substrate temperature.
Acknowledgment. This research has been supported by the Czech Science Foundation through
Grant No. 106/05/0483 “Influence o f Microstructure on Mechanical Properties o f Thermally
Sprayed Materials.”
1. O. Kovarik, S. Xue, X. Fan, and M. Boulos, “RF plasma deposition of refractory metals: Case
study for tungsten,” in: B. R. Marple, M. M. Hyland, Y. C. Lau, et al. (Eds.), Building on 100
Years o f Success, Proc. o f the 2006 International Thermal Spray Conference (Seattle, USA),
ASM International (2006), pp. 215-218.
2. J. Matejicek, S. Sampath, D. Gilmore, and R. Neiser, Acta Mater., 51, No. 3, 873-885 (2002).
3. J. Dubsky, B. Kolman, and M. Vysohlid, in: E. Lugscheider and P. A. Kammer (Eds.), Proc.
o f the United Thermal Spray Conference (UTSC 99), Verlag fer Schweien und Verwande
Veflahren, D.V.S-Verlag (1999), pp. 659-663.
4. O. Kovarik, J. Nohava, J. Siegl, and P. Chraska, J. Therm. Spray Technol., 14, No. 2, 231-238
(2005).
5. P. Fauchais, M. Fukumoto, A. Vardelle, and M. Vardelle, J. Therm. Spray Technol., 13, No. 3,
337-360 (2004).
6. X. Jiang, J. Matejicek, and S. Sampath, Mat. Sci. Eng. A, 272, No. 1, 189-198 (1999).
7. X. Jiang and S. Sampath, Mat. Sci. Eng. A, 304-306, 144-150 (2001).
8. L. Bianchi, F. Blein, P. Lucchese, et al., in: C. Berndt and S. Sampath (Eds.), Thermal Spray
Industrial Applications, ASM International, Metals Park, Ohio (1994), p. 569.
Received 28. 06. 2007
92 ISSN 0556-171X. npo6neMbi npouuocmu, 2008, № 1
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| id | nasplib_isofts_kiev_ua-123456789-48452 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 0556-171X |
| language | English |
| last_indexed | 2025-11-29T12:43:51Z |
| publishDate | 2008 |
| publisher | Інститут проблем міцності ім. Г.С. Писаренко НАН України |
| record_format | dspace |
| spelling | Kovarik, O. Siegl, J. 2013-08-19T17:08:37Z 2013-08-19T17:08:37Z 2008 Microstructure and fracture morphology of thermally sprayed refractory metals and ceramics / O. Kovarik, J. Siegl // Проблемы прочности. — 2008. — № 1. — С. 89-92. — Бібліогр.: 8 назв. — англ. 0556-171X https://nasplib.isofts.kiev.ua/handle/123456789/48452 539. 4 The microstructural characteristics such as porosity, splat morphology and grain size of thermally sprayed coatings made of both ceramic and refractory metals are investigated. Al2O3 and Cr2O3 coatings represent ceramic materials while pure W and Mo coatings represent the refractory metals. The used deposition technology (RF-plasma, gas stabilized or water stabilized DC plasma) was found to influence the coatings microstructure to a great extent by providing different particle impact velocities and temperatures. At the same time the substrate temperature plays an important role as is shown fo r refractory metal coatings deposited at different substrate temperatures. Generally, all investigated coatings contained intrasplat cracks, intersplat pores and voids, individual splats of different degree of deformation and different degree of intersplat sintering, crystal grains formed inside individual splats or extending through many of them. It is shown that the size and abundance of the above-mentioned microstructural features predetermine the fracture morphology of the coating as well as mechanical properties. Исследованы такие характеристики микроструктуры, как пористость, морфология частиц напыления и размер зерна газотермических покрытий из керамики ( Al2O3 и Cr2O3) и тугоплавких металлов ( W и Мо). Установлено, что технология напыления (высокочастотная плазма, газо- или водостабилизированная плазма постоянного тока) оказывает значительное влияние на микроструктуру покрытий при различных температурах и скоростях соударения частиц. В то же время отмечена важная роль температуры подложки для покрытий из тугоплавких металлов, нанесенных при различных температурах подложки. Все исследованные покрытия, как правило, содержали трещины внутри напыленных частиц, поры и полости между частицами, отдельные частицы с разными степенью деформации и межчастичного спекания, кристаллиты, образовавшиеся внутри отдельных частиц или проходящие через несколько таких частиц. Показано, что величина и распространенность указанных особенностей микроструктуры предопределяют морфологию поверхности излома покрытий, а также их механические свойства. This research has been supported by the Czech Science Foundation through Grant No. 106/05/0483 “Influence of Microstructure on Mechanical Properties of Thermally Sprayed Materials.” en Інститут проблем міцності ім. Г.С. Писаренко НАН України Проблемы прочности Научно-технический раздел Microstructure and fracture morphology of thermally sprayed refractory metals and ceramics Микроструктура и морфология поверхности излома газотермических покрытий из тугоплавких металлов и керамики Article published earlier |
| spellingShingle | Microstructure and fracture morphology of thermally sprayed refractory metals and ceramics Kovarik, O. Siegl, J. Научно-технический раздел |
| title | Microstructure and fracture morphology of thermally sprayed refractory metals and ceramics |
| title_alt | Микроструктура и морфология поверхности излома газотермических покрытий из тугоплавких металлов и керамики |
| title_full | Microstructure and fracture morphology of thermally sprayed refractory metals and ceramics |
| title_fullStr | Microstructure and fracture morphology of thermally sprayed refractory metals and ceramics |
| title_full_unstemmed | Microstructure and fracture morphology of thermally sprayed refractory metals and ceramics |
| title_short | Microstructure and fracture morphology of thermally sprayed refractory metals and ceramics |
| title_sort | microstructure and fracture morphology of thermally sprayed refractory metals and ceramics |
| topic | Научно-технический раздел |
| topic_facet | Научно-технический раздел |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/48452 |
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