A. CZUPRYÑSKI: PROPERTIES OF Al2O3/TiO2 AND ZrO2/CaO FLAME-SPRAYED COATINGS
205–212
PROPERTIES OF Al2O3/TiO2 AND ZrO2/CaO FLAME-SPRAYED
COATINGS
LASTNOSTI PLAMENSKO NANE[ENIH PREMAZOV Al2O3/TiO2
IN ZrO2/CaO
Artur Czupryñski
Silesian University of Technology, Faculty of Mechanical Engineering, The Welding Department,
Konarskiego 18A, 44-100 Gliwice, Poland
artur.czuprynski@polsl.pl
Prejem rokopisa – received: 2015-07-01; sprejem za objavo – accepted for publication: 2016-02-09
doi:10.17222/mit.2015.165
The article presents the results of a study on the exploitation properties of flame-sprayed ceramic coatings produced from an
oxide ceramic material in the form of powder based on an aluminum oxide (Al2O3) matrix with an addition of 3 % titanium
oxide (TiO2) and also on a zirconium oxide (ZrO2) matrix with 30 % of calcium oxide (CaO) on a substrate of unalloyed
structural steel of grade S235JR. The buffer layer was produced from a metallic powder on the basis of Ni-Al-Mo. Plates with
dimensions of (5 × 200 × 300) mm and also the front surfaces of 40 × 50 mm cylinders were flame-sprayed. The buffer
coatings were produced using a RotoTec 80 torch and external specific coatings were produced with a CastoDyn DS 8000 torch.
Investigations of the coating properties were based on metallography tests, a phase-composition research, a measurement of
microhardness, a research of the coating adhesion to the substrate, the abrasive-wear resistance (acc. to ASTM G65 standard),
the erosion-wear resistance (acc. to ASTM G76-95 standard) and a thermal-stroke study. The coatings were characterized by a
high adhesion to the substrate and also high erosion and abrasive-wear resistance and the resistance to cyclic thermal strokes.
Keywords: flame spray, coating, ceramic powder, abrasive-wear resistance, erosion-wear resistance, adhesion strength
^lanek predstavlja rezultate {tudija uporabnih lastnosti plamensko nane{enih kerami~nih premazov, izdelanih iz materiala
oksidne keramike v obliki prahov na osnovi aluminijevega oksida Al2O3 z dodatkom 3 % titanovega oksida TiO2 in tudi na
osnovi cirkonovega oksida (ZrO2) s 30 % kalcijevega oksida (CaO) na podlagi iz nelegiranega konstrukcijskega jekla S235JR.
Tamponska plast je bila izdelana s kovinskim prahom na osnovi Ni-Al-Mo. Plo{~a dimenzij 5 mm × 200 mm × 300 mm in tudi
~elna stran povr{ine valjev 40 mm × 50 mm sta bili plamensko nane{eni. Tamponski nanos je bil izdelan z gorilnikom
RotoTec 80, zunanji specifi~ni nanos z gorilnikom CastoDyn DS 8000. Preiskave lastnosti nanosov so bile izvr{ene z metalo-
grafijo, preiskavo sestave faz, meritvijo mikrotrdote, preiskavo prijemljivosti nanosa na podlago, z preizkusom odpornosti na
abrazijsko obrabo, (v skladu z ASTM G65 standardom), odpornost na erozijsko obrabo, (v skladu z ASTM G76-95 standardom)
in s preizkusom na termo{ok. Zna~ilnost nanosov je bila velika oprijemljivost na podlago, tudi odpornost na erozijsko in
abrazijsko obrabo ter odpornost na toplotne {oke.
Klju~ne besede: plamensko nana{anje, nanos, kerami~ni prah, odpornost na abrazijsko obrabo, odpornost na erozijsko obrabo,
adhezijska trdnost
1 INTRODUCTION
Thermal-spraying methods have developed signifi-
cantly in the recent years by applying more and more
technically advanced heat sources and new coating
materials.1–10 At present, this technology is used in about
70 % of industrial applications for manufacturing new
parts or devices, for which high-quality workmanship
and appropriate surface properties are required. An
improvement in the operating parameters of machine and
equipment parts associated with high loads and speeds,
causing accelerated wear and the necessity of an effec-
tive regeneration, also contributed to the rapid advance-
ment in the thermal-spraying technology.
The application of flame-sprayed coatings has not
only been conducive to multifold enhancement in the
durability of the protection of steel structures against a
corrosive environment, but has also led to an extended
service life of textile machinery parts, cast moulds,
rollers for steel-industry conveyors, parts of pumps and
stirrers, plastic-injection moulders, and has also im-
proved the durability and reliability of power boilers.11
Sprayed-ceramic coatings providing excellent thermal
and electrical barriers have been manufactured more and
more often due to high corrosion, erosion and wear resis-
tance and hardness and high-temperature creep resis-
tance. Ceramic-oxide materials based on aluminium
oxide (Al2O3) and zirconium oxide (ZrO2) are especially
noteworthy. Thermal- and electric-barrier coatings
flame-sprayed with such materials are applied in multi-
ple cases, e.g., for electronic components, insulation
parts of ignition plugs and power turbines, and high-tem-
perature-resistant and heatstroke-resistant parts of com-
bustion chambers in modern car and airplane
engines.12–14
2 EXPERIMENTAL PROCEDURE AND RESULTS
The aim of the conducted investigations was to create
technological conditions of flame powder spraying and
Materiali in tehnologije / Materials and technology 51 (2017) 2, 205–212 205
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
UDK 66.017:621.793:620.193.19 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 51(2)205(2017)
to compare the operating properties of ceramic coatings
produced with Al2O3- and ZrO2-based powders on the
structural unalloyed S235JR steel acc. to EN 10025-
2:2004. A powder with a content of 97 % of Al2O3 and
3 % of TiO2, and a powder with a content of 70 % of
ZrO2 and 30 % of CaO were selected for spraying. The
binding powder (the buffer layer), i.e., a Ni-Al-Mo alloy,
was employed as the primer coating.
Plates with dimensions of (5 × 200 × 300) mm and
faces of 40 × 50 mm cylinders were subjected to a ma-
nual flame-spraying operation using the two aforemen-
tioned powders. Prior to the spraying process, the
surfaces of the plates and cylinders were cleaned with
shot blasting including an abrasive blasting treatment in
conformity with the EN 13507:2010 requirements. Sur-
face shot blasting was performed using angular particles
of cast iron. The spraying process consisted of the
following operations:
– a 50–100 μm primer coating (buffer layer) including
the Ni-Al-Mo powder sprayed with a RotoTec 80
torch (Table 1);
– an approx. 500 μm external specific coating in-
cluding the powder of 97 % Al2O3 + 3 % TiO2 and
the powder of 70 % ZrO2 + 30 % CaO using a
CastoDyn DS 8000 torch (Table 2).
Following the spraying process, the plates with cera-
mic coatings were cut into samples intended for further
examinations. Adhesion tests of the coatings sprayed
onto the substrates were performed on cylindrical sam-
ples. Metallographic macroscopic examinations of the
sprayed surfaces were undertaken with a stereomicro-
scope with a magnification of 4–25 times.
Table 1: Spraying parameters of the primer coating with Ni-Al-Mo
powder
Tabela 1: Parametri pri napr{evanju podlage s prahom iz Ni-Al-Mo
Torch type: RotoTec 80
Acetylene pressure: 0.7 (bar)
Oxygen pressure: 4.0 (bar)
Distance between the torch and the sprayed
surface: 200 (mm)
12744 Preheating temperature: 40 (°C)
Change in the torch advancement angle
relative to the next coating: 90°
Table 2: Spraying parameters of the external coating with aluminium
oxide and zirconium oxide matrices
Tabela 2: Parametri pri nana{anju zunanjega nanosa z osnovo iz
aluminijevega oksida in cirkonovega oksida
Torch type: CastoDyn DS8000
Torch tip: SSM 30
Powder flow rate:
for 97 % Al2O3 + 3 % TiO2 powder
for 70 % ZrO2 + 30 % CaO powder
2 (setting acc. to
the manual)
3 (setting acc. to
the manual)
Acetylene pressure: 0.7 (bar)
Oxygen pressure: 4.0 (bar)
Assist. gas (compressed air) pressure: 3.0 (bar)
*The required primer coating made with Ni-Al-Mo powder
A. CZUPRYÑSKI: PROPERTIES OF Al2O3/TiO2 AND ZrO2/CaO FLAME-SPRAYED COATINGS
206 Materiali in tehnologije / Materials and technology 51 (2017) 2, 205–212
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 2: View after flame spraying with 70 % ZrO2 + 30 % CaO
powder: a) structure of specific external coating (C), primer Ni-Al-Mo
coating (B) and base material (A), magn. of 100×; b) structure of
external coating with microhollows and image of binding zone of
external coating with primer coating, magn. of 400×; c) structure of
primer coating over the area of deformed steel with a developed
surface line, magn. of 400×; d) structure of external coating, magn. of
400×
Slika 2: Izgled plamensko nane{enega prahu s 70 % ZrO2 + 30 %
CaO: a) struktura posebnega zunanjega nanosa (C), nanos podlage iz
Ni-Al-Mo (B) in osnovno jeklo (A), pove~ava 100×, b) struktura
zunanjega nanosa z mikro prazninami in posnetek vezivnega podro~ja
zunanjega nanosa z nanosom podlage, pove~ava 400×, c) struktura
nanosa podlage na deformiranem jeklu, z jasno linijo povr{ine,
pove~ava 400×, d) struktura zunanjega nanosa, pove~ava 400 ×
Figure 1: View after flame spraying with 97 % Al2O3 + 3 % TiO2
powder: a) structure of specific external coating (C), primer Ni-Al-Mo
coating (B) and base material (A), magn. of 100×; b) structure of
external coating and image of binding zone of external coating with
primer coating, magn. of 400×; c) structure of primer coating over the
area of deformed steel with a developed surface line, magn. of 400×;
d) structure of external coating, magn. of 400×
Slika 1: Izgled plamensko nane{enega prahu s 97 % Al2O3 + 3 %
TiO2: a) struktura posebnega zunanjega nanosa (C), nanos podlage iz
Ni-Al-Mo (B) in osnovno jeklo (A), pove~ava 100×, b) struktura
zunanjega nanosa in slika vezivnega podro~ja zunanjega nanosa na
vmesni nanos, pove~ava 400×, c) struktura vmesnega nanosa na
deformiranem jeklu z razvito linijo povr{ine, pove~ava 400×; d)
struktura zunanjega nanosa, pove~ava 400×
Metallographic microscopic examinations were
carried out on metallographic microsections perpendi-
cular to the coating, cut from the plates after flame
spraying with the powder matrix of aluminium oxide and
zirconium oxide. The structure of the examined coatings
was revealed on the microsections etched in a 4 % nitric
acid solution (HNO3) and ethyl alcohol solution
(C2H5OH). Metallographic microscopic examinations
were performed with a magnification of 100–1000×. The
grain size in the plate structure was determined with the
comparative method. The thickness of the coatings was
determined with the metallographic method in com-
pliance with ISO 1463 1997.
Table 3: Results of the hardness measurement on the cross-section of
the sample after spraying it with 97 % Al2O3 + 3 % TiO2 powder
Tabela 3: Rezultati meritve trdote na preseku vzorca po napr{enem
nanosu prahu s 97 % Al2O3 + 3 % TiO2
Test area Test point Load (N) HV hardness
External coating
(C)
(97 % Al2O3 +
3 % TiO2)
1 5.0 747
2 5.0 823
3 5.0 910
4 5.0 672
5 5.0 762
6 5.0 747
Primer coating
(B)
(Ni-Al-Mo)
7 0.1 469
8 0.1 353
9 0.1 458
Substrate
material (A)
(S235JR)
10 0.5 226
11 0.5 189
12 0.5 145
13 0.5 131
14 0.5 128
15 0.5 110
Every result was represented by the average value of
ten measurements. The results of the metallographic
microscopic examinations allowed us to evaluate the
structure of the base material, the primer coating and the
specific external coating and their thickness after the
flame-spraying operation (Figures 1 and 2).
The coating-hardness measurement was made with
the Vickers method. The examinations were carried out
in conformity with ISO 6507-1:2007. The load applied
during the hardness measurement was between 0.1 and
5 N. The hardness measurement was made at the cross-
sections of the samples with the ceramic coatings
including the powders of 97 % Al2O3 + 3 % TiO2 and
70 % ZrO2 + 30 % CaO. Fifteen hardness measurements
were made on the cross-sections of the samples, six
measurements were made on the specific external
coating (C), three on the primer coating (B) and six on
the base material (A), in the micro-areas marked in Fig-
ure 3. The results of the measurements are presented in
Tables 3 and 4.
Table 4: Results of the hardness measurement on the cross-section of
the sample after spraying it with 70 % ZrO2 + 30 % CaO powder
Tabela 4: Rezultati meritve trdote na preseku vzorca po napr{enem
nanosu prahu iz 70 % ZrO2 + 30 % CaO
Test area Test point Load (N) HV hardness
External
coating (C)
(70 % ZrO2 +
30 % CaO)
1 5.0 705
2 5.0 479
3 5.0 549
4*) 5.0 1176
5 5.0 961
6 5.0 449
Primer coating
(B)
(Ni-Al-Mo)
7 0.1 446
8 0.1 397
9 0.1 380
Substrate
material (A)
(S235JR)
10 0.5 231
11 0.5 209
12 0.5 245
13 0.5 140
14 0.5 126
15 0.5 127
* The hardness measured on oxide precipitates with a larger area
A. CZUPRYÑSKI: PROPERTIES OF Al2O3/TiO2 AND ZrO2/CaO FLAME-SPRAYED COATINGS
Materiali in tehnologije / Materials and technology 51 (2017) 2, 205–212 207
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 4: Diffraction pattern of the coating flame-sprayed with 97 %
Al2O3 + 3 % TiO2 powder
Slika 4: Rentgenogram plamensko nane{enega nanosa iz prahu s 97 %
Al2O3 + 3 % TiO2
Figure 3: Diagram of hardness measurements at the cross-section of a
sample after flame spraying: C – external specific coating, B – primer
coating, A – substrate material
Slika 3: Prikaz meritve trdote na preseku vzorca po nanosu s
plamenom: C – zunanji specifi~ni premaz, B – nanos podlage, A –
material osnove
X-ray structure tests of the surfaces of the samples
after flame spraying made with an X-ray diffractometer
enabled us to determine the phase compositions of the
external specific surfaces including the powders of alu-
minium oxide and zirconium oxide on the substrate of
the primer coating created using the Ni-Al-Mo powder
and the base material of the S235JR low-carbon steel.
The results of the X-ray qualitative analysis are shown
with diffraction patterns (Figures 4 and 5). Exact exa-
minations of the structures of the coatings were carried
out with an electronic scanning microscope. Metallo-
graphic microsections were viewed with a magnification
of 250–5000×. The results of the examinations with the
scanning microscope allowed us to determine the
influence of the type of the powder used in the spraying
process on the structure of an external specific coating
and the concentration of the elements in the selected
micro-areas. The examples of observing the microstruc-
tures of the external coating and the primer coating are
shown in Figures 6 and 7.
An abrasive-wear-resistance test of the mineral-mine-
ral type of coatings involving the selected powders was
performed on samples with dimensions of 5 mm ×
25 mm × 75 mm in line with ASTM G65. The weight
wear of a sample was determined as a result of the test,
found after (100, 125, 250, 500 and 1500) revolutions of
an abrasive pressure plate. The tests results allowed us to
determine the abrasive-wear resistance of the deposited
coatings. The measurement results of the abrasive-wear-
resistance tests are presented in Table 5.
An erosion-resistance test was carried out in accord-
ance with ASTM G76-95 on the samples with dimen-
sions of 5 × 25 × 75 mm with the coatings involving the
powders of 97 % Al2O3 + 3 % TiO2 and 70 % ZrO2 +
30 % CaO. Aluminium oxide (Al2O3) powder with a
particle diameter of 45–70 μm was used as the erosion
material. The test was undertaken at a molecular velocity
of 70 ± 2 m/s, an erodent flow rate of approx. 2 g/min, a
nozzle outlet-to-sample distance of 10 mm and incidence
angles of the abrasive stream of (90, 60, 30 and 15)°.
The test lasted for 10 min. The results are presented in
Table 6.
The coating-adhesion test Rh (the stripping strength)
was determined with the stripping method involving a
static tensile test, in accordance with EN 582:1996, on
cylindrical samples with a diameter of 40 mm, flame-
sprayed with the powders containing 97 % Al2O3 + 3 %
TiO2 and 70 % ZrO2 + 30 % CaO. The face of a
cylindrical sample with a coating deposited was bonded
to the counter specimen with the Henkel Loctite Hysol
3478 A&B Superior Metal bonding agent with a tensile
A. CZUPRYÑSKI: PROPERTIES OF Al2O3/TiO2 AND ZrO2/CaO FLAME-SPRAYED COATINGS
208 Materiali in tehnologije / Materials and technology 51 (2017) 2, 205–212
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 6: View of the coating after flame spraying 97 % Al2O3 + 3 %
TiO2 powder: a) structure of external coating with primer coating and
base material with visible hollows of a varied size in the external
coating of the sample; b) small amount of hollows in the external
coating in the border area with primer coating; c) structure of external
coating; d) area of base material and primer coating
Slika 6: Izgled nanosa po plamenskem nana{anju prahu s 97 % Al2O3
+ 3 % TiO2: a) struktura zunanjega nanosa z nanosom podlage in
osnovnim jeklom, z razli~nimi vidnimi prazninami razli~ne velikosti v
zunanjem nanosu vzorca, b) malo praznin v zunanjem nanosu na mej-
nem podro~ju z osnovnim nanosom, c) struktura zunanjega nanosa, d)
podro~je osnovnega jekla in osnovnega nanosa
Figure 5: Diffraction pattern of the coating flame-sprayed with 70 %
ZrO2 + 30 % CaO powder
Slika 5: Rentgenogram plamensko nane{enega nanosa iz prahu s 70 %
ZrO2 + 30 % CaO
Figure 7: View of the coating after flame spraying 70 % ZrO2 + 30 %
CaO powder: a) external coating with a small amount of hollows, b)
primer coating, c) structure of external coating, d) area of primer
coating
Slika 7: Izgled nanosa po plamenskem nana{anju prahu s 70 % ZrO2
+ 30 % CaO: a) zunanji nanos z majhnim dele`em praznin, b) osnovni
nanos, c) struktura zunanjega nanosa, d) podro~je osnovnega nanosa
A. CZUPRYÑSKI: PROPERTIES OF Al2O3/TiO2 AND ZrO2/CaO FLAME-SPRAYED COATINGS
Materiali in tehnologije / Materials and technology 51 (2017) 2, 205–212 209
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Table 5: Results of the wear tests for the coatings made of 97 % Al2O3 + 3 % TiO2 powder and 70 % ZrO2 + 30 % CaO powder
Tabela 5: Rezultati preizkusov obrabe napr{enih nanosov s prahom s 97 % Al2O3 + 3 % TiO2 in 70 % ZrO2 + 30 % CaO
Powder
composition Sample No.
Revolutions
(n) Test No.
Sample weight
prior to the test
(g)
Sample weight
after the test
(g)
Mass loss
(g)
Average
mass loss
(g)
Volume loss
(mm3)
97%Al2O3+
3%TiO2
S 1.1 1500
1 75.8406 75.0086 0.8320
0.8314 207.852 75.8396 75.0086 0.8310
3 75.8395 75.0084 0.8311
S 1.2 500
1 75.0825 74.6428 0.4397
0.4387 109.662 75.0821 74.6431 0.4390
3 75.0802 74.6427 0.4375
S 1.3 250
1 75.4531 75.2617 0.1914
0.1840 92.002 75.4524 75.2618 0.1906
3 75.4517 75.2816 0.1701
S 1.4 125
1 75.8165 75.6092 0.2073
0.2074 51.852 75.8164 75.6091 0.2073
3 75.8167 75.6094 0.2073
S 1.5 100
1 73.8637 73.7352 0.1285
0.1283 32.072 73.8635 73.7351 0.1284
3 73.8634 73.7355 0.1279
70%ZrO2+
30%CaO
S 2.1 250
1 74.7266 74.0916 0.6350
0.6347 112.342 74.7263 74.092 0.6343
3 74.7262 74.0915 0.6347
S 2.2 500
1 77.6013 76.638 0.9633
0.9633 170.492 77.6014 76.6378 0.9636
3 77.6012 76.6381 0.9631
S 2.3 1500
1 76.9207 75.458 1.4627
1.4626 258.872 76.9205 75.4578 1.4627
3 76.9206 75.4581 1.4625
S 2.4 125
1 76.8146 76.1956 0.6190
0.6190 109.562 76.8148 76.1954 0.6194
3 76.8143 76.1958 0.6185
S 2.5 100
1 78.5391 77.8907 0.6484
0.6485 114.782 78.5394 77.8905 0.6489
3 78.5391 77.891 0.6481
Table 6: Mass-loss values in erosion tests for the coatings made of 97%Al2O3+3%TiO2 and 70%ZrO2+30%CaO powders
Tabela 6: Vrednosti masne izgube pri erozijskem preizkusu napr{enega nanosa iz prahov s 97 % Al2O3 + 3 % TiO2 in 70 % ZrO2 + 30 % CaO
Erodent
incidence angle
(°)
Type of powder sprayed
97 % Al2O3 + 3 % TiO2 70 % ZrO2 + 30 % CaO
Sample mass
prior to the test
(g)
Sample mass
after the test
(g)
Mass loss
(g)
Sample mass
prior to the test
(g)
Sample mass
after the test
(g)
Mass loss
(g)
90o 73.8752 73.8703 0.0049 75.9886 75.9560 0.0026
45o 73.8703 73.8485 0.0218 75.9560 75.9118 0.0442
30o 73.8485 73.8206 0.0279 75.9118 75.8640 0.0378
15o 73.8206 73.8027 0.0179 75.8640 75.8020 0.0620
Table 7: Results of the adhesion tests for the coatings made of 97 % Al2O3 + 3 % TiO2 and 70 % ZrO2 + 30 % CaO powders
Tabela 7: Rezultati adhezijskih preizkusov nanosov napr{enih s prahovi s 97 % Al2O3 + 3 % TiO2 in 70 % ZrO2 + 30 % CaO
Material of the
external coating Sample No.
Sample size Maximum
breaking load
(N)
Adhesion of sprayed coating
(N/mm2)
Sample diameter
(mm)
Cross-section
field (mm2) Rh Rh Av.
*
97 % Al2O3 +
3 % TiO2
1/1 39.4 1218.6 7614.0 6.0
6.51/2 39.0 1193.9 6418.0 5.4
1/3 39.8 1243.5 10095.0 8.1
70 % ZrO2 +
30 % CaO
2/1 39.8 1243.5 4104.0 3.3
3.32/2 39.8 1243.5 4376.0 3.5
2/3 39.5 1224.8 3735.0 3.1
*average value
strength of 17 MPa. The samples, together with the
fixing device, were placed in a tensile-testing machine
and subjected to static stretching until rupture. Tensile
test results allowed us to determine the values of the
force detaching the coatings from the substrate and cal-
culate the adhesion coefficient (Table 7).
A thermal-resistance test was carried out, in line with
ISO 14923:2003, on the samples with the dimensions of
5 × 25 × 75 mm with an external coating including 97 %
Al2O3 + 3% TiO2 and an external flame-sprayed coating
including 70 % ZrO2 + 30 % CaO. Three stages of the
test were determined as no detailed guidance concerning
this type of test was available:
– the first stage – heating to 1050 °C and slow cooling,
together with the oven, at a rate of 40 °C/h;
– the second stage – heating to 1050 °C and cooling
the samples in a stream of compressed air at a rate of
25 °C/s, the cycle was repeated ten times;
– the third stage – heating to 1050 °C and a rapid cool-
ing of the samples in water at a rate of 100 °C/s. The
test result identified the number of the cycle, after
which discontinuities and delamination were visible
on the coating surface (Figure 8).
3 DISCUSSION
After carrying out the spraying process, the visual
examinations did not reveal any sample-surface imper-
fections after flame spraying the 97 % Al2O3 + 3 % TiO2
and 70 % ZrO2 + 30 % CaO powdes. The metallographic
examinations of the microsections perpendicular to the
surface of the sample sprayed with the 97 % Al2O3 + 3 %
TiO2 powder showed that two coatings existed on the
surface of the steel, with a developed surface line: the
primer coating (B) and the external specific coating (C)
(Figure 1a). The 30–110 μm primer coating (B) con-
sisted of bright areas made of the Ni-Al-Mo alloy and
dark oxide inclusions (Figure 1c); it was observed
immediately above the base-material surface (A). A
banded structure of the base material, distinctive for the
strengthening of the steel surface during the shot blasting
of the examined material, existed in the boundary area,
along the primer coating. The external coating, sprayed
on the first buffer coatings, had a thickness varying bet-
ween 450 μm to 510 μm. The coating exhibited nume-
rous voids with different sizes and a waved line of its
external surface (Figure 1d).
After the flame spraying of the steel surface with the
70 % ZrO2 + 30 % CaO powder, the following individual
layers were identified: the primer coating (B) and the ex-
ternal specific coating (C) (Figure 2a). A banded struc-
ture with a considerable plastic deformation, existing on
the thickness of approx. 50 μm, was observed underneath
the primer coating, in the steel. The primer coating
consisted of bright areas of the elements forming the
Ni-Al-Mo powder used for spraying and also of dark
flattened oxides (Figure 2c). The coating was
50–160 μm thick. The external specific coating of about
600 μm exhibited numerous voids with a developed line
of its external surface (Figure 2d).
The specific external coating sprayed with the 97 %
Al2O3 + 3% TiO2 powder had a hardness of 671.8–909.9
HV5. The hardness of the examined micro-areas in the
primer coating was lower, i.e., 353–469 HV01. The hard-
ness of the substrate material in the boundary zone along
the primer coating was approx. 226 HV05, as confirmed
by the occurrence of a narrow heat-affected zone (HAZ)
or by steel-surface strengthening after shot blasting. The
hardness of the external specific coating after the flame-
spraying operation involving the 70 % ZrO2 + 30 % CaO
powder was different, ranging from approx. 449–961
HV5. The hardness measured on oxides with a larger
area in the coating, in the places where oxide precipitates
occurred, was even more than 1176 HV5. Different
hardness results were due to a large number of voids in
the coating. The hardness of the primer coating was from
approx. 380 to approx. 446 HV01, and for the primer
material, it was between 109–230 HV05.
X-ray structure tests allowed us to identify the phases
existing in the structure of the coating after the flame
spraying involving the 97 % Al2O3 + 3 % TiO2 and 70 %
ZrO2 + 30 % CaO powders (Figures 4 and 5). There
were mainly Al2O3, NiAl10O16 and NiAl32O49 phases;
trace amounts of Fe- were also identified after the
spraying operation resulting in the external coating with
an aluminium matrix (Figure 4). The examinations did
not show any presence of a phase with titanium in this
coating due to its small amount in the content of the
powder for spraying (TiO2 = 3 %). The phase can be
A. CZUPRYÑSKI: PROPERTIES OF Al2O3/TiO2 AND ZrO2/CaO FLAME-SPRAYED COATINGS
210 Materiali in tehnologije / Materials and technology 51 (2017) 2, 205–212
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967–2017) – 50 LET/50 YEARS
Figure 8: View of samples after the third stage of thermal-resistance
tests: a) surface of the sample sprayed with 97 % Al2O3 + 3 % TiO2
powder, b) cracks on the surface of the coating made of 70 % ZrO2 +
30 % CaO powder, c) delamination of the coating made of 70 % ZrO2
+ 30 % CaO powder
Slika 8: Izgled vzorcev po tretji stopnji preizkusa toplotne odpornosti:
a) povr{ina vzorca z nanosom prahu s 97 % Al2O3 + 3 % TiO2, b)
razpoke na povr{ini nanosa prahu s 70 % ZrO2 + 30 % CaO, c)
odstopanje nanosa iz prahu s 70 % ZrO2 + 30 % CaO od povr{ine
identified with X-ray tests, provided it exists in the
amount of more than 4 % of mass fraction.
Ten diffraction lines from the Al2O3 phase were
shown in the diffraction pattern, including the maximum
intensity values for planes (113), (116), (124), (030) and
(1.0.10). Four diffraction lines for planes (121), (212),
(400) and (123) of the NiAl10O16 phase and for planes
(201), (321), (332), (122) of the NiAl32O49 oxide phase
were also found. The existence of diffraction lines (100)
and (211) with a small intensity, relating to Fe-, was
also confirmed. The presence of compound zirconium
and calcium oxides was also revealed in the structure of
the external surface obtained after the spraying operation
involving the 70 % ZrO2 + 30 % CaO powder. Ten peaks
relating to the planes of the CaZrO3 phase and four peaks
relating to the planes of the Ca0,15Zr0,85O1,85 phase occur
in a diffraction pattern (Figure 5). The existence of
peaks with a small intensity for planes (100) and (211),
derived from the Fe steel surface, was also found.
The results of the wear-resistance test allowed us to
conclude that the flame-sprayed 97 % Al2O3 + 3 % TiO2
coating was more resistant than the coating made with
the 70 % ZrO2 + 30 % CaO powder within the tested
range of revolutions of 100–1500 (Table 5).
It was confirmed, based on erosion-resistance tests,
that the coating made with the 97 % Al2O3 + 3 % TiO2
powder exhibits a higher erosion resistance (determined
with the mass loss) than the coating made with the 70 %
ZrO2 + 30 % CaO powder, except in the case of testing it
at the angle of 90°. In the cases of the erosion tests at the
angles of (45, 30 and 15)°, the mass loss of the sample
with the 93 % Al2O3 + 3 % TiO2 coating was 0.0218,
0.0279 and 0.0179 g, respectively, while for the sample
with the 70 % ZrO2 + 30 % CaO coating, it was higher
by about 50 % (Table 6).
The substrate adherence of the flame-sprayed coat-
ings made with the 97 % Al2O3 + 3 % TiO2 and 70 %
ZrO2 + 30 % CaO powders, determined with a static-
stretching test, involving a detachment of the coating
from the substrate, showed that the adherence of the
coating made of the 97 % Al2O3 + 3 % TiO2 powder was
higher than that of the coating made of the 70 % ZrO2 +
30 % CaO powder, being 6.5 MPa and 3.3 MPa, respecti-
vely (Table 7). The difference between the tensile-
strength and adhesion values was confirmed by inhomo-
geneous microsections of the samples’ surfaces after the
tensile test.
The thermal resistance was investigated with the
method of cyclic heating the samples coated on one side
with the 97 % Al2O3 + 3 % TiO2 coating and 70 % ZrO2
+30 % CaO coating to 1050 °C and cooling them down
at rates of 40 °C/h (in an oven), 25 °C/s (air cooling) and
100 °C/s (water cooling). After heating the samples to
1050 °C and cooling them down using an oven in the
first cycle of the test, compressed air in the next nine
cycles and water after the last cycle, the coating made of
the 70 % ZrO2 + 30 % CaO powder delaminated from
the substrate and cracks were identified on it, along with
the detached coating (Figure 8c). No damages in the
form of delamination were identified for the coating
made of the 97 % Al2O3 + 3 % TiO2 powder; however,
small cracks without broken-out sections were recorded
(Figure 8a).
4 CONCLUSIONS
The following conclusions were formulated based on
the investigations performed and the outcomes obtained
and analysed:
1. Flame spraying with the 97 % Al2O3 + 3 % TiO2 and
70 % ZrO2 + 30 % CaO powders carried out within
the range of the selected parameters allowed us to
achieve high-quality ceramic coatings of approx. 500
μm applied to a steel substrate.
2. The structure of the coating flame-sprayed with the
97 % Al2O3 + 3 % TiO2 powder consisted mainly of
aluminium oxide and a small amount of the
NiAl10O16 and NiAl32O49 phases, while the coating
made of the 70 % ZrO2 + 30 % CaO powder showed
a structure of oxide zirconium phases with calcium.
3. The bonding of the primer coating made of the
Ni-Al-Mo powder with the steel substrate and of the
external coatings made of the 97 % Al2O3 + 3 % TiO2
and 70 % ZrO2 + 30 % CaO powders was of the
mechanical adhesion nature. The ceramic coatings
including the aluminium-matrix powder and zirco-
nium-matrix powder were characterised by their
adhesion to the substrate, being 6.5 MPa and 3.3
MPa, respectively.
4. The coatings achieved, consisting of the 97 % Al2O3 +
3 % TiO2 powder and 70 % ZrO2 + 30 % CaO pow-
der, exhibited the average hardness values of approx.
780 and approx. 720 HV, respectively.
5. The abrasive-wear resistance of the coating made of
the 97 % Al2O3 + 3 % TiO2 powder was higher than
the resistance of the coating made of the 70 % ZrO2 +
30 % CaO powder, and the average erosion-wear
resistance for an erodent incidence angle of less than
90° was higher by approx. 50 %.
6. The coating made of the 97 % Al2O3 + 3 % TiO2 pow-
der exhibited cyclical-heat-stroke resistance, while
the coating made of the 70 % ZrO2 + 30 % CaO pow-
der, heated and cooled in the same conditions,
revealed cracks, chippings and delamination.
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