Indian Journal of Engineering & Materials Sciences
Vol. 19, August 2012, pp. 253-259
Microstructural development on AISI 1060 steel by FeW/B4C composite coating
produced by using tungsten inert gas (TIG) process
Serkan Islaka*, Soner Buytozb & Muzaffer Karagözc
a
Cide Rifat Ilgaz Vocational High School, Kastamonu University, 37600 Kastamonu, Turkey
b
Department of Metallurgy and Materials Engineering, Faculty of Technology, Firat University, 23100 Elazig,Turkey
c
Department of Metallurgy and Materials Engineering, Faculty of Engineering, Bartin University, 74100 Bartin,Turkey
Received 18 August 2011; accepted 16 July 2012
This study discusses the effects of B4C addition on the morphologies of primary carbides and eutectic colonies in FeW
weld-surfacing alloys. Results reveal that a series of FeW weld-surfacing alloys with different B4C contents are successfully
fabricated onto AISI 1060 steel by using tungsten inert gas (TIG) arc welding. SEM observations show that the obtained
coating sheet has a smooth and uniform surface, as well as a metallurgical combination with the AISI 1060 steel substrate
without cracks and pores at the interface. Fe23(C,B)6, Fe3(C,B), FeW2B2 and FeW3C boride and carbides are determined in
the microstructure. The microhardness values of the coating results show a difference depending on the rate of B4C and
coating conditions. The maximum microhardness value of the coating is about 1095 HV.
Keywords: TIG process, Composite coatings, Microstructure
Surface coating techniques have been successfully
applied on different substrates to provide a better
surface property in recent years.1,2 The most common
surface coating techniques are vapor deposition (PVD
and CVD), sol-gel, electrolytic coating and hardfacing
process (welding and thermal spray). Hardfacing
primarily involves deposition of a hard and wear
resistant material to the specific areas of the surface of
the components by any of the techniques such as
welding and thermal spraying.3
Welding cladding processes contain oxyacetylene
gas welding (OAW), tungsten inert gas welding (TIG),
submerged arc welding (SAW), plasma transferred arc
welding (PTA) and laser beam welding (LBW)
methods. These techniques create an excellent bond
between the coating and substrate.4-7 Among the weld
cladding procedures, tungsten inert gas (TIG) surfacing
process is a cost-effective approach applied when
reactive materials (as coatings or substrates) are
involved.8 In this method, substrate surface and powder
or hard filler wire used for coating were melted down
using arc source and then solidified, which resulted in
the formation of a new composite layer.9-12
Composite coating is generally made up from a
ductile matrix and a hard ceramic material as
——————
*Corresponding author (E-mail: serkanislak@gmail.com)
reinforcement.13 While nickel, cobalt, iron and
titanium based alloys are used as matrix in the
production of these composite coatings, in terms of
reinforcement elements, hard reinforcement particles
such as SiC14, TiC15, B4C16,17, WC18,19, TiB220 and
Cr3C221,22 are preferred.
In recent years, the application of B4C in the
surface coating processes has attracted more and
more attention for its super hardness, thermal stability,
high melting point (2450°C), low density (2.52 g/cm3)
and super mechanical properties.23 Boron carbide (B4C)
is one of the hardest materials known, ranking third
behind diamond and cubic boron nitride (cBN). Due to
its high hardness, boron carbide powder is used as an
abrasive material and it shows perfect wear resistance.2426
Chao and et al.16 investigated the characterization of
B4C particulate reinforced nickel composite coatings on
A3 steel substrate by laser cladding. The composite
coating gave very high hardness of 1400 HV which was
seven times higher than that of A3 steel and excellent
wear resistance. Meng et al.27 produced TiB2/TiC–Ni
composite coatings by laser cladding of pre-placed
B4C+NiCrBSi powders onto Ti–6Al–4V substrate. The
composite coating mainly consists of γ-Ni matrix phase,
TiB2, TiC and CrB reinforcements. The average
hardness of the coating is four times as big as that of
Ti–6Al–4V substrate.
254
INDIAN J. ENG. MATER. SCI., AUGUST 2012
In this study the microstructural characteristics of
FeW overlays with B4C powder have been
investigated. The results obtained from the deposition
process and the investigation of the tracks and
surfaces produced have been characterized by means
of scanning electron microscopy (SEM), X-ray
analysis (EDS), X-ray diffraction (XRD) and energy
dispersive analysis, and by microhardness testing.
Microstructural properties and change of hardness of
samples which had different wt. % of B4C powders
were discussed.
Experimental Procedure
In coating processes from an AISI 1060 steel
produced samples were used, which had dimensions
of 20 mm × 10 mm × 80 mm. In order to place
coating powders, holes with 8 mm of width and
1.5 mm of depth were drilled on substrates. Prior to
the modification of surfaces by using TIG method,
surfaces of steel material were cleaned with acetone.
Metallic powders were mixed, wetted and, then
placed in the surface holes, thus metallic powders do
not lifted from the surface by the shielding gas. Then,
samples were left to dry at 50°C temperature for
30 min. Figure 1 illustrates the SEM images for every
powder. Table 1 gives chemical compositions of the
powders and the substrate used in coating process.
FeW powder was modified by addition of B4C
particles. B4C particles were added to the powder
alloys used for obtaining coating layers, in a range of
10 wt% to 40 wt%. The average sizes of the FeW
powder were from 10 to 75 µm, and the B4C particles
were less than 10 µm. The coating powders with
various B4C content are given in Table 2.
Coating process was carried out using production
parameters given in Table 3. Figure 2 shows principle
scheme of surface coating process via TIG method.
For microstructure examinations, 10 mm × 10 mm
× 10 mm samples were extracted from the middle part
of coating material. Coating materials undergoing
metallographic procedures were etched in 5 mL
HNO3 + 200 mL HCl + 65 g FeCl3 solution used as
etchant for microstructure examinations. While a
scanning electron microscope (SEM) was used for
microstructure examinations, X-ray diffraction (XRD)
and X-ray energy dispersive spectrometer (EDS) were
used for phase analyses. Hardness measurement was
conducted throughout a line from superstrate of the
coating through substrate at intervals of 250 µm, in
waiting time of 10 s and with a load of 200 g using a
Future-Tech FM 700 brand micro-hardness device.
Fig. 1—SEM image of metal powders used in coating; (a) FeW
powder and (b) B4C powder
Table 1—Chemical compositions and physical properties of
substrate and coating powders
Substrate & Powder
Composition (wt%)
AISI 1060
C
Mn
Si
Ni
Cr
Fe
B
W
Melting point (°C)
Density (g/cm3)
Size (µm)
0.60
0.67
0.22
0.19
0.059
Balance
-
FeW powder B4C powder
0.20
0.25
0.50
Balance
60.0
2425
14.50
-75+10
20.5
0.1
0.05
79.0
2450
2.52
≤ 10
ISLAK et al.: MICROSTRUCTURAL DEVELOPMENT OF AISI 1060 STEEL
255
Fig. 2—Schematic diagram of TIG cladding system
Table 2—The coating powders with various B4C contents
Samples
Powder ratios
Production speed *Heat input
(mm/s)
(kJ/cm)
S1
S2
S3
S4
FeW
FeW-10 wt% B4C
FeW-20 wt% B4C
FeW-40 wt. % B4C
1.05
0.85
0.79
0.75
52.26
63.96
68.64
72.54
*Heat input Q = η.U.I.60/(ν.1000) U: voltage, I: current, ν: travel
speed, η: productivity coefficient ( for TIG process η: 0.65).28-30
Table 3—Production parameters
Electrode
Protective gas
Electrode diameter
Gas flow rate
Current
Voltage
Production speed
Heat input
W-2% ThO2 electrode
99.9 % pure argon
2.4 mm
10 L/min
140 A
20 V
0.75 - 1.05 mm/s
52.26 - 72.54 kJ/cm
Results and Discussion
In order to compare the microstructure of FeW/B4C
coatings fabricated using TIG process, different
powder mixtures were used. Coating thickness has
been varied between 2000 µm and 2400 µm. The
coatings were well formed without cracking. In Figs
4-10, the typical dendritic microstructure can be
found clearly. According to the microstructure
characteristics, the districts of the TIG process can be
generally divided into deposited coating and substrate.
The coating layer and the substrate were bonded
metallurgical with interface layer each other. From
Fig. 3—Ternary phase diagram of Fe-C-B33
the interface to coating surface, cellular and dendritic
solidification were observed in opposite direction to
the heat flux. On the other hand, the planar
solidification was observed at the interface. The
structural change is associated with the solidification
rate (V) of the metallic liquid in the PTA melt pool
and the temperature gradient (∆T). The ∆T/V ratio of
the interface between the coating layer and the
substrate, whose temperature gradient is high and its
solidification rate is low, is significantly high; hence,
the interface displays a planar structure. The fact
that the interface having a planar structure proves that
the metallurgical bonding between the substrate and
the coating layer is perfect. The solidification
rate increases rapidly after planar solidification, and
the temperature gradient that was at its maximum
value at the beginning, starts to decrease rapidly.
In conclusion, the ∆T/V ratio decreases causing
the formation of a cellular structure. Dendritic
solidification occurs after cellular solidification.16,31,32
Theoretically, the possible products of the reaction
between liquid B4C and Fe may be Fe3(C,B),
Fe23(C,B)6, Fe2B, α-Fe / Fe3(C,B), Fe23(C,B)6, Fe2B
according to the Fe–C–B ternary phases diagrams
(Fig. 3).
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INDIAN J. ENG. MATER. SCI., AUGUST 2012
The SEM image of FeW coating which was
produced without B4C was given in Fig. 4. Generally,
Fe2C, Fe3C and FeW3C carbides were formed in the
microstructure of coating. This situation was
supported by both EDS analysis (Table 4) and XRD
pattern (Fig. 5). These carbides in α-Fe matrix were
found as reinforcement. FeW powder was converted
into Fe and W with the given energy in the melt pool.
A small amount of W3C hard phase was obtained
from the combination of the carbon in the substrate
and tungsten in the FeW powder (Fig. 5).
The SEM image of FeW-10 wt% B4C composite
coating was shown in Fig. 6 and its XRD pattern was
given in Fig. 7. It was understood from the SEM
image in Fig. 6b the borides and carbides formed with
the dissolution of B4C with the given energy. The
formation of Fe3(C,B), Fe23(C,B)6 and FeW2B2 phases
prove the dissolution of B4C and this situation is
supported with the XRD pattern in Fig. 7. In Fig. 6b,
the EDS analysis of dark structure in SEM image is
5.81% B, 14.07% W and 80.12% Fe. This analysis
demonstrates the formation of FeW2B2 phase.
The substrate, the interface and the coating layer
regions of FeW-20 wt% B4C composite coating were
given in Fig/. 8a. The center and upper regions of
coating layer were shown in Figs 8b and 8c,
respectively. The growth of most dendrites is
observed to be upwards towards the alloyed layer
surface, and their direction is almost perpendicular to
the interface (Fig. 8b). However, in the upper region,
due to the effect of polycrystalline, the microstructure
becomes untidy dendrites (Fig. 8c).16 The EDS
analysis of A zone (Fig. 8a) of coating layer is 3.78%
C, 9.79% B, 14.21% W and 72.22% Fe. The dendrites
consist of Fe2W and interdendrites eutectics are
composed of α-Fe/Fe23(C,B)6 phases. The formation
Table 4—Chemical composition (wt%) of coating layers
Samples Microstructures
C
B
W
Fe
Cladding layer
0.58
-
40.84
Balance
Dendrite
Interdendritic
(eutectic)
0.25
0.38
-
57.71
19.45
Balance
Balance
S2
Cladding layer
Dendrite
Interdendritic
(eutectic)
2.62
1.13
1.78
9.06
5.81
14.35
16.56
14.07
Balance
Balance
Balance
S3
Cladding layer
Dendrite
Interdendritic
(eutectic)
3.78
1.60
2.23
9.79
7.54
14.21
11.66
14.09
Balance
Balance
Balance
S4
Cladding layer
Dendrite
Interdendritic
(eutectic)
4.27
1.68
2.44
11.16
10.02
6.01
4.10
3.39
Balance
Balance
Balance
S1
Fig. 4—SEM morphologies of specimen S1 (a) general appearance
and (b) interface (cross-section) and planar solidification
Chemical composition (wt%)
Fig. 5—XRD pattern of S1 sample (coated with FeW)
ISLAK et al.: MICROSTRUCTURAL DEVELOPMENT OF AISI 1060 STEEL
257
Fig. 6—SEM morphologies of specimen S2 (a) general appearance
and (b) top surface of clad
Fig. 7—XRD pattern of S2 sample (coated with FeW+10% B4C)
of these phases is supported with the XRD analysis
(Fig. 9).
The EDS analysis of the coating layer deposited
with the FeW + 40% B4C is 4.27% C, 11.16% B,
6.01% W and 78.56% Fe. The unremelted boron
carbide (B13C2) phase was observed in the coating
layer (Fig. 10a). This situation showed that the energy
Fig. 8—SEM morphologies of specimen S3 (a) general
appearance, (b) center region and (c) upper region of clad
given was not sufficient for dissolving B4C totally.23
The eutectics as a vein-like phase formed among the
dendrites (Fig. 10b). The eutectic structure just in like
other coatings is composed of α-Fe/Fe23(C,B)6 phase.
The formation of this phase is supported with the
XRD pattern in Fig. 11. While the α-Fe matrix
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INDIAN J. ENG. MATER. SCI., AUGUST 2012
Fig. 9—XRD pattern of S3 sample (coated with FeW+20% B4C)
Fig. 11—XRD pattern of S4 sample (coated with FeW+40% B4C)
Fig. 12—Microhardness profile of the cladding layer across the
depth
Fig. 10—SEM morphologies of specimen S4 (a) upper region and
(b) dendrites and interdendrites eutectics
provides toughness, the Fe23(C,B)6 phase enhances the
strength to the coating layer.
The tungsten inert gas (TIG) cladding of FeW-B4C
powder with AISI 1060 steel is anticipated expected
to significantly increase hardness in the cladding
layer. The microhardness of the coating layer was
measured along the coating depth from the surface; all
of the data were an average of five measurements.
The microhardness profiles of the coatings across the
depth are depicted in Fig. 12. Average hardness
values of S1, S2, S3 and S4 specimens were measured
as HV 480, 810, 880 and 1095, respectively.
The FeW-B4C composite coating demonstrates a
microhardness 4-5 times higher than the AISI 1060
steel (substrate). The carbide and boride formed in
microstructure contributed to obtaining microhardness
values stated above. The amount of carbide and
boride increases with an increase in B4C content. The
undissolved or resolidified B13C2 and WC1-X occured
substantially in the microstructure of the cladding
layer produced by increasing of B4C powder rate.
B13C2 and WC1-X carbides contribute to a extra
hardness and strength.28,34 While hardness of coating
area is in maximum level in the hardness change
ISLAK et al.: MICROSTRUCTURAL DEVELOPMENT OF AISI 1060 STEEL
between coating area and substrate, it reduces in small
amount towards interface and reduces dramatically in
the interface. This situation is associated with the
fact that the Fe content is scarce in coating area, and
that it is higher in interface area.35-38
Conclusions
The microstructural and compositional investigations
have been carried out on cross-sections of FeW-B4C
based coatings obtained by tungsten inert gas (TIG)
process with different boron carbide (B4C) powder
rate. The coating thickness produced on AISI 1060
steel with FeW-B4C powder by the TIG process was
measured as 2000-2400 µm using the optical
microscope. The SEM examinations results showed
that no evidence of microcrack and gas porosity
formation was found in all production parameters.
The microstructure of the coating surfaces consists of
α-Fe, Fe3(C,B), Fe23(C,B)6 and FeW2B2, Fe2W, WC1-x
and B13C2 phases. The dendrite structures have been
observed from the interface to the alloyed layer
surface. The hardness of coating alloyed with B4C
powder enhanced significantly. The FeW-B4C
composite coating demonstrates microhardness 45 times higher than the AISI 1060 steel. The average
hardness was between HV 480 and 1052. The
maximum microhardness value was measured as 1095
HV in the coating which produced with 40% B4C
powder rate. This is attributed to the presence of
Fe3(C,B) and Fe23(C,B)6 carbides dispersed in the
eutectic matrix.
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