Optics & Laser Technology 86 (2016) 136–144
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Optics & Laser Technology
journal homepage: www.elsevier.com/locate/optlastec
Full length article
An empirical-statistical model for coaxial laser cladding of NiCrAlY
powder on Inconel 738 superalloy
M. Ansari a,n, R. Shoja Razavi b, M. Barekat b
a
b
Young Researchers and Elite Club, Najafabad Branch, Islamic Azad University, Najafabad, Iran
Department of Materials Engineering, Malek Ashtar University of Technology, Shahin Shahr, Isfahan, Iran
art ic l e i nf o
a b s t r a c t
Article history:
Received 11 May 2016
Received in revised form
12 June 2016
Accepted 28 June 2016
Available online 2 August 2016
In this study, coaxial laser cladding of NiCrAlY powder on a nickel-based superalloy is investigated from
an experimental point of view so as to propose an empirical-statistical model for the process. The correlations between main processing parameters (i.e. scanning speed, powder feeding rate, and laser
power) and geometrical characteristics (i.e. width, height, penetration depth, dilution and wetting angle)
of single clad tracks have been predicted and are discussed using regression analysis (RA). The validity of
the predictions is confirmed by providing correlation coefficient and analysis of the residuals. The corα β γ
relations are established as a combined parameter (P V F ) for each studied characteristic of single clad
tracks. These correlations finally lead to the design of a processing map that can be practically used to
select proper processing parameters for laser cladding of the particular material.
& 2016 Elsevier Ltd. All rights reserved.
Keywords:
Coaxial laser cladding
NiCrAlY powder
Inconel 738 superalloy
Geometrical characteristics
Regression analysis
1. Introduction
Laser cladding is a noble technique for surface engineering by
which thick protective coatings with high quality and strong metallurgical bonding can be deposited on various substrates. The
process can be applied in three different implementations: using a
pre-placed layer, wire feeding, and powder injection. However,
using pre-placed layer and wire feeding can be time-consuming,
difficult to adjust and control on complex geometries, and lead to
high dilution rates. The powder injection implementation is more
attractive and offers the most benefits [1,2].
In laser cladding with powder injection, the powder stream is
blown under the laser beam by a carrier gas while the laser beam
is scanning the surface of the substrate and melting both the
substrate material and the powder to form a single clad track.
Then, side by side and consecutive overlapping single clad tracks
can produce a fully dense cladding layer on the substrate. The
process needs minimum surface preparation and can be a feasible
solution for utilizing on complex geometries. There are two
methods of feeding powder. The first method is off-axial powder
injection, and the second method is coaxial powder injection that
is the subject of this paper. The technique of off-axial powder injection depends extensively on the cladding direction and the
change of cladding direction leads to different powder delivery
n
Corresponding author.
E-mail address: m.barekat@mut-es.ac.ir (M. Ansari).
http://dx.doi.org/10.1016/j.optlastec.2016.06.014
0030-3992/& 2016 Elsevier Ltd. All rights reserved.
efficiencies, and hence local cladding conditions [3]. In contrast,
the coaxial laser cladding process is independent of the cladding
direction. This advantage of coaxial laser cladding can be hired in
metal additive manufacturing and 3D printing [4,5].
The laser cladding process with powder injection is operationally described in terms of three main processing parameters,
i.e. scanning speed V (mm/s), powder feeding rate F (mg/s), and
laser power P (W). However, there are other processing parameters such as laser beam spot size, laser beam energy distribution, size and speed of powder particles, and the amount and type
of carrier and shielding gas, etc. Taking into consideration the
overwhelming number of processing parameters and their mutual
dependencies, optimization of the process is still challenging.
Furthermore, considering that the laser cladding process with injecting powder involves many interactions among laser beam/
powder/substrate and several physical phenomena, providing a
comprehensive description of it is quite complicated. Although
several physical models have been proposed to describe the laser
cladding process [6], empirical-statistical models can be used to
avoid analyzing complex physical phenomena of the process.
Therefore, empirical-statistical models of the laser cladding process with powder injection and an exploration into statistical
correlations between the main processing parameters and geometrical characteristics of single clad tracks are still vital for successful deposition of functional coatings. Most empirical-statistical
models have focused on relating the main processing parameters
to the final geometry of the single clad tracks, usually using some
P 2/3V1/2F1/2
P 2V−1/4F−1/4
P1/4V1/2F−1/2
P V−2/3
P is laser power, V is scanning speed, and F is powder feeding rate.
Metcocladd 21 Co–Cr–Mobased
γ-TiAl
Coaxial
V−5/4F
–
P, V , F
–
P420 stainless steel
Low carbon steel
Coaxial
Saqiba et al. (Ref. [15]) (ANOVA,
RSM)
Barekat et al. (Ref. [16]) (RA)
Titanium
Titanium
Coaxial
Ti6Al4V
Kumar et al. (Ref. [14])
P1/4V−1F1/4
V, F
P, V
–
–
–
P, F , P2
–
–
P , V , F , P 2, F2
–
)
Coaxial
Ti6Al4V
316L stainless steel
Coaxial
Coaxial
Diamalloy 2002 Ni-based
Sun et al. (Ref. [13]) (ANOVA, RSM)
P1/4V−1F3/4
P 3/4V−1/4
(
ln P 4/5F−1/4
–
P , V , F , PV , V2
P, V , F
–
P, V , F
P, V , F
V , F , PF , P 2
–
ln (P V−1/2F−1)
–
P 2V−1/2
P, F
P −1/2V−1/2F
–
P V−1/2
P , FV , F
V−1F
P, V , F
Diamalloy 2002 Ni-based
Coaxial
EuTroLoy 16006 Co-based
Cast iron
Off-axial
Ocelík et al. (Ref. [9]) (RA)
100Mn Cr W4 (DIN)
steel
100Mn Cr W4 (DIN)
steel
Low carbon steel
C45 steel
Coaxial
DIN Ck45 steel
Off-axial
Costa et al. (Ref. [7])
de Oliveira et al. (Ref. [8]) (RA)
Substrate
Paulo Davim et al. (Ref. [10]) (ANOVA, RA)
Paulo Davim et al. (Ref. [11]) (ANOVA, RA)
El Cheikh et al. (Ref. [12]) (RA)
P1/2V1/2F−1/2
P V F−1
–
P V−1/3F−1/3
V F−1
V F−1
–
P V−1/2
V−1F
P1/2V−1F1/2
Stellite 6
19E Ni–Cr-based
Penetration depth or molten
area
Wetting angle or clad
angle
Clad width
Powder
Clad height
Geometrical characteristic
137
Material
Feeding powder
method
In this study, an as-cast Inconel 738 superalloy with the dimension of 100 100 5 mm and NiCrAlY powder (PAC9620AM,
USA) with the particle size of 50–100 mm were used as the substrate and clad powder material. The chemical composition of both
substrate and clad powder obtained by Optical Emission Spectrometry (OES) is given in Table 2. Morphological evaluation of the
powder was performed by Field Emission Scanning Electron Microscopy (FE-SEM) (SIGMA VP, ZEISS). Fig. 1 shows the morphology
of the NiCrAlY powder used for laser cladding.
A coaxial laser cladding system equipped with a powder feeder
with a four-way coaxial nozzle, a 700 W pulsed Nd:YAG laser and
an XYZ-Rotation CNC machine was used for the experiments. In all
the experiments, the laser beam was defocused on the workpiece
resulting in laser beam spot diameter of 1 mm. The argon with a
flow rate of 20 L/min was used as carrier and shielding gas. Other
parameters of the pulsed Nd:YAG laser such as frequency, and
pulse duration were fixed at 35 Hz, and 3 ms, respectively. In order
to find empirical-statistical correlations between the main processing parameters of coaxial laser cladding and the geometrical
characteristics of the single clad tracks, a wide variety of processing parameters (laser power P (W), scanning speed V (mm/s) and
powder feeding rate F (mg/s)) were chosen, based upon a gradual
increase in one individual parameter while the other parameters
were kept constant. All processing parameters applied to each
single clad track are listed in Table 3. In brief, 48 single clad tracks
were applied to investigate the whole processing window.
After the coaxial laser cladding experiments, three transverse
cross-sections were cut from each laser track to prepare metallographic specimens. In order to study geometrical features of the
single clad tracks, all metallographic specimens were ground,
polished, and etched by Kalling's No. 2 reagent solution. An optical
microscope was used to characterize the geometrical features.
These geometrical features are summarized in Fig. 2, which shows
a schematic single clad track. In Fig. 2, h (mm) is the clad height
that is defined as the thickness of the clad track above surrounded
substrate surface, w (mm) is the clad width, θ (°) is the wetting
angle, and b (mm) is penetration depth that is defined as the
thickness of the substrate under the surrounded substrate surface
melted during the laser cladding process. All lengths and angles
were measured by the Clemex Vision PE image processing
Work
2. Material and methods
Table 1
Empirical–statistical relationships between geometrical characteristics of single clad tracks and processing parameters in laser cladding with powder injection.
analyses based upon regression models including analysis of variance (ANOVA), response surface methodology (RSM), and regression analysis (RA) [6]. Using these analyses, some researchers
have experimentally investigated the empirical-statistical correlations between the geometrical characteristics and the main
processing parameters for various coating/substrate combinations
in the laser cladding process with powder injection, as summarized in Table 1 [7–16].
On the one hand, the MCrAlY coatings (where the M stand for
Ni and/or Co) are functional and prevalent coatings that are being
frequently used to protect high-temperature and high-pressure
gas turbine blades and vanes made of nickel-based superalloys,
Inconel 738 in particular. On the other hand, the geometrical
characteristics of single clad track play a crucial role in controlling
the characteristics of the optimum clad layer (thick, dense and
well-bonded) formed by overlapping single clad tracks. Therefore,
this study aims to relate the main processing parameters to the
geometrical characteristics of single clad tracks using the regression analysis method so as to propose an empirical-statistical
guideline for coaxial laser cladding of NiCrAlY powder on Inconel
738 superalloy and reduce the needs for extensive and time-consuming experiments.
Dilution
M. Ansari et al. / Optics & Laser Technology 86 (2016) 136–144
138
M. Ansari et al. / Optics & Laser Technology 86 (2016) 136–144
Table 2
Chemical composition of clad powder and substrate.
Material
NiCrAlY
Inconel 738
Form
Powder
Plate
Element (wt%)
Ni
Cr
Al
Y
Co
W
Ti
Ta
Mo
Nb
C
Other
Bal.
Bal.
21.02
13.6
9.92
2.9
0.95
–
–
9.1
–
4.9
–
4.4
–
3.1
–
1.7
–
0.1
–
0.1
o0.20
o 0.11
Table 3
Processing parameters and mean geometrical measurements for each single clad
track.
Track
Fig. 1. SEM micrograph of NiCrAlY powder.
software from cross-sectional optical digital images. The mean
measurement of geometrical characteristics for each single clad
track is reported in Table 3. Another important property of the clad
track is called the geometrical dilution D (%) that is defined by the
Eq. (1) [17]:
D (%) =
b
h+b
(1)
The laser cladding process is based on integrated parameters
including laser power, scanning speed and powder feeding rate to
form an appropriate single clad track with desired coating properties. Therefore, the examination of the process can be simply
α β γ
defined based on a combined parameter as P V F . In our study,
the combined parameter was assumed to be capable of predicting
the different single clad track geometrical characteristics. By employing Microsoft Excel software and “trial and error” approach,
the linear regression analysis is used to determine α, β and γ. A
mathematical formula was finally established as y¼ a(x)þb where
y is one of the geometrical characteristics of the single clad track,
α β γ
and x is the combined parameter (P V F ) while a and b are
constants.
3. Results and discussion
Fig. 3 represents cross-sectional optical micrographs of the
single clad tracks for different values of P, V and F. Some qualitative
features of the main processing parameters on the geometrical
characteristics of the single clad tracks can be concluded from this
figure. At the first glance, well-bonded single clad tracks were
formed at almost all processing parameters. However, some of
them, especially those with low scanning speed, had an inappropriate clad bead shape with a weak bond, which resulted in
the detachment of the edge of clad tracks. These imperfect single
clad tracks were finally rejected and omitted from our measurements. In general, from the Fig. 3 it can be seen that the clad
1
2
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4
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9
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31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
Processing parameters
Geometrical measurements
P (W)
V (mm/s)
F (mg/s)
h (mm)
w (mm)
θ (°)
b (mm)
D (%)
150
150
150
150
150
150
150
150
150
150
150
150
200
200
200
200
200
200
200
200
200
200
200
200
250
250
250
250
250
250
250
250
250
250
250
250
300
300
300
300
300
300
300
300
300
300
300
300
2
4
6
8
2
4
6
8
2
4
6
8
2
4
6
8
2
4
6
8
2
4
6
8
2
4
6
8
2
4
6
8
2
4
6
8
2
4
6
8
2
4
6
8
2
4
6
8
150
150
150
150
200
200
200
200
250
250
250
250
150
150
150
150
200
200
200
200
250
250
250
250
150
150
150
150
200
200
200
200
250
250
250
250
150
150
150
150
200
200
200
200
250
250
250
250
0.183
0.121
0.057
0.046
0.243
0.122
0.072
0.053
0.298
0.141
0.090
0.073
0.251
0.149
0.099
0.075
0.310
0.174
0.088
0.067
0.423
0.204
0.120
0.075
–
0.184
0.124
0.081
–
0.214
0.114
0.084
–
0.253
0.167
0.122
–
0.216
0.145
0.113
–
0.286
0.151
0.104
–
0.383
0.197
0.117
1.553
1.520
1.480
1.468
1.553
1.518
1.476
1.427
1.576
1.494
1.443
1.415
1.750
1.690
1.654
1.566
1.757
1.727
1.662
1.580
1.834
1.706
1.592
1.569
–
1.884
1.785
1.708
–
1.900
1.818
1.740
–
1.903
1.829
1.760
–
2.019
1.918
1.906
–
1.976
1.900
1.899
–
1.999
1.960
1.860
24
11
7
5
33
14
12
6
33
19
13
9
35
19
10
8
42
22
16
11
45
23
18
11
–
22
16
14
–
25
19
10
–
24
18
13
–
24
20
16
–
33
21
15
–
37
20
16
0.047
0.057
0.065
0.070
0.033
0.047
0.050
0.056
0.035
0.042
0.040
0.054
0.054
0.076
0.095
0.105
0.041
0.060
0.064
0.081
0.033
0.050
0.060
0.064
–
0.084
0.117
0.125
–
0.068
0.087
0.112
–
0.068
0.093
0.103
–
0.119
0.134
0.143
–
0.099
0.126
0.138
–
0.085
0.093
0.109
20
32
53
60
12
28
41
51
11
23
31
43
18
34
49
58
12
26
42
55
7
20
33
46
–
31
49
61
–
24
43
57
–
21
36
46
–
36
48
56
–
26
46
57
–
18
32
48
height significantly increased with increasing laser power and
powder feeding rate, or decreasing scanning speed. It can also
show that the penetration depth noticeably increased with increasing scanning speed. At high laser power with high powder
feeding rate and low scanning speed, high and wide clad tracks
with a low amount of dilution happened. Whereas, at low laser
power with low powder feeding rate and high scanning speed, low
and narrow clad tracks with a high amount of dilution took place.
All of these changes can be controlled by the combined parameter.
M. Ansari et al. / Optics & Laser Technology 86 (2016) 136–144
139
Hence, the dependence of different geometrical characteristics of
single clad tracks on the combined parameter was examined via
statistics for the purpose of quantifying the qualitative
observations.
Fig. 4 represents the dependence of the clad height (h) on the
main processing parameters when it is plotted out as a function of
powder feeding rate (F), laser power (P), and scanning speed (V). In
this figure, a weak linear dependence of clad height on powder
feeding rate is noticeable for all laser power and scanning speed
values. From Fig. 4 it can be concluded that the laser power can be
considered as a strong parameter for predicting the clad height. If
the laser power had a negligible influence on the clad height, the
clad heights with different values of laser power, and the same
values of powder feeding rate and scanning speed would have
been approximately equal to each other (they would have been
overlapped). However, the single clad tracks in the same values of
powder feeding rate and scanning speed had by far different
heights. In fact, the effect of the laser power on the clad height can
be seen by the scattering of the data points with the same values
of powder feeding rate and scanning speed. When the data points
overlap, the effect of the laser power is actually negligible; on the
other hand, when the data points are at distant point from each
other, the effect of the laser power is significant. For example,
square markers in the same values of powder feeding rate and
scanning speed were scattered around because of the significant
influence of the laser power. Therefore, only the combined parameter derived from P, F, and V could mainly control the clad
height. The height of the clad tracks varied from 50 mm, observed
at the highest scanning speed, and the lowest powder feeding rate
Fig. 2. A schematic view of single clad track showing the geometrical features.
Fig. 4. The clad height as a function of the main processing parameters.
Fig. 3. Cross-sectional optical micrographs of the single clad tracks for different processing parameters. For each laser power the scanning speed (V) increases from left to
right and the powder feeding rate (F) increases from up to down.
140
M. Ansari et al. / Optics & Laser Technology 86 (2016) 136–144
Fig. 6. The clad width as a function of the main processing parameters.
Fig. 5. (a) Dependence of the clad height on the combined parameter P2V-3/2F1.
(b) Residual plot.
and laser power, to the values close to 1.5 mm, observed at the
lowest scanning speed, and the highest powder feeding rate and
laser power.
In the next step, the combined parameter derived from P, F, and
V was found, which could linearly depend on the clad height.
Fig. 5a shows the statistical dependence of the single clad height
(h) on the combined parameter. It is noticeable that the clad height
is directly proportional to P2V-3/2F1 with a linear regression coefficient R ¼0.98 (R2 ¼0.96). The high amount of the linear regression coefficient can confirm the statistical linear model, together
with the residual plot (Fig. 5b).
Although the combined parameter can be different in various
combinations of substrate/powder, the combined parameter found
in the present study for the statistical dependence of the clad
height is in agreement with the majority of previous works on
empirical–statistical model of laser cladding with powder injection, which reported combined parameters derived from P, F and V
for the clad height. Nevertheless, some works described the clad
height just as a function of F and V (See Table 1).
The powder material is melted in the first contact with the
laser beam. Therefore, the higher laser power can induce the
higher temperature and melt the more amount of powder that
results in the increase of the clad height. Moreover, powder particle size distribution and the laser beam attenuation can influence
on the absorbed energy level during the cladding process [18–20].
These might be the explanation why the laser power is an important determinant of the clad height.
Fig. 6 shows the behavior of the clad width (w) as a function of
the three main processing parameters. In the case of the clad
width, there is a strong linear dependence on laser power for all
values of scanning speed and powder feeding rate. The clad widths
with the same values of laser power and scanning speed, and
different values of powder feeding rate are approximately equal to
each other. The effect of the powder feeding rate on the clad width
can be seen by the overlapping of the data points with the same
Fig. 7. (a) Dependence of the clad width on the combined parameter P3/2V-1/3.
(b) Residual plot.
values of laser power and scanning speed. When the data points
overlap, the effect of the powder feeding rate is actually negligible.
For example, square data points in the same values of laser power
and scanning speed have overlapped with each other because the
powder feeding rate did not have a strong influence in scattering
them. The laser power and the scanning speed appear to be indispensable parameters and the powder feeding rate appears to be
a dispensable parameter. Therefore, only the combined parameter
derived from P and V could mainly control the clad width. The clad
width is mainly proportional to the laser power, while the scanning speed is a parameter with less influence. The width of the
clad tracks varied from the minimum value of 1.4 mm to the
maximum value close to 2.2 mm. The detailed linear statistical
analysis (Fig. 7a) showed the dependence of the single clad width
(w) on the combined parameter as P3/2V-1/3 with a linear regression coefficient R¼0.98 (R2 ¼0.96). The high amount of the linear
regression coefficient and the residual plot (Fig. 7b) can confirm
that the statistical linear model is valid. It is good to note that the
combined parameter found in the present study for the statistical
dependence of the clad width is in agreement with the majority of
M. Ansari et al. / Optics & Laser Technology 86 (2016) 136–144
previous works, which reported combined parameters derived
from P and V for the clad width (See Table 1).
During laser-material interaction when a melt pool is formed
by the laser beam, there are multiple driving forces for the melt
pool that can change the depth and width of the melt pool:
buoyancy force, shear stress triggered by surface tension gradient
(Marangoni convection), and shear stress triggered by plasma jet
[21]. On the other hand, all of the driving forces involve several
physical phenomena that can be induced by different processing
parameters. In the present work, it seems the driving forces are in
balance so that just two parameters (laser power and scanning
speed) are sufficient to control the clad width.
For successfully depositing a well-bonded clad layer, some dilution between the clad track and substrate is required to make
sure a good metallurgical bond is formed. Furthermore, the wetting angle is required not to be too large to avoid porosity formation in the clad track. Therefore, dilution and wetting angle as
two important parameters for achieving desired coating properties
are predicted and discussed in the next part of the paper.
Dilution relies on the penetration depth (b) and the clad height
(h). Since the statistical dependence of the clad height on the
combined parameter was predicted, it is enough to determine the
statistical dependence of the penetration depth on the combined
parameter and then, the dilution can be predicted. Fig. 8 shows the
statistical correlation between the penetration depth and the
combined parameter. The penetration depth was found to be
proportional to the combined parameter P1V2/3F-2/3 with regression coefficient R¼0.97 (R2 ¼0.94). The penetration depth of the
clad tracks varied from 35 mm, observed at the lowest laser power,
scanning speed and the highest powder feeding rate, to the values
close to 145 mm, observed at the highest laser power, scanning
speed and the lowest powder feeding rate. The combined parameter found in the present study for the penetration depth is in
agreement with the majority of previous works, which reported
combined parameters derived from P, V and F (See Table 1).
Fig. 8. (a) Dependence of the penetration depth on the combined parameter P1V2/
3 -2/3
F . (b) Residual plot.
141
Fig. 9. The dilution as a function of the main processing parameters.
According to the fundamentals of laser cladding, both additional powder and substrate absorb laser beam energy and the
energy is shared between them. If the powder feeding rate and the
scanning speed are assumed to be constant, an increase of the
laser power leads to a large portion of the shared energy transfer
to the substrate material causing an increase in the penetration
depth. On the other hand, if the laser power is assumed to be
constant, an increase of the powder feeding rate and/or a decrease
of the scanning speed or altogether an increase of the amount of
powder material delivered per unit length of the clad track (F/V)
result in a decrease in the penetration depth. Since there is more
incoming powder per unit length of the clad track, a major portion
of the shared energy is consumed for melting of the incoming
powder and leaves a minor portion of energy available for melting
the substrate.
The statistical dependence of the clad height and the penetration depth on the combined parameters were successfully
predicted and the dilution of the single clad tracks can be predicted based on them. Fig. 9 shows the behavior of the dilution (D)
as a function of scanning speed (V), powder feeding rate (F), and
laser power (P). In this figure, a strong linear dependence of the
dilution on scanning speed can be observed for all laser power and
powder feeding rate values. From Fig. 9 it can be concluded that
the laser power can be considered as a dispensable parameter for
predicting the dilution. The amounts of dilution in the same values
of powder feeding rate and scanning speed and different values of
laser power are approximately equal to each other. The dispensable effect of the laser power on the dilution can be seen by
the overlapping of the data points in the same values of powder
feeding rate and scanning speed. For example, triangular data
points in the same values of powder feeding rate and scanning
speed have overlapped with each other because the laser power
did not have a strong influence in scattering them. Therefore, only
the combined parameter derived from F and V could mainly control the dilution. The dilution of the clad tracks varied from the
minimum value of 5% to the maximum value close to 60%. The
combined parameter as V1F-1 with a linear regression coefficient
R¼0.96 (R2 ¼ 0.93) was found according to the linear statistical
dependence of the dilution (see Fig. 10a). The high amount of the
linear regression coefficient can confirm the statistical linear
model, together with the residual plot (Fig. 10b).
The combined parameter found in the present study for the
statistical dependence of the dilution is not in agreement with the
previous works on empirical–statistical model of laser cladding
with powder injection, which reported combined parameters derived from P, F and V (See Table 1). However, the combined
parameter found in the present study describes the dilution just as
a function of F and V.
The reason for this disagreement can be explained by the
presence of the laser power factor in both combined parameters of
142
M. Ansari et al. / Optics & Laser Technology 86 (2016) 136–144
Fig. 10. (a) Dependence of the dilution on the combined parameter V1F-1.
(b) Residual plot.
the clad height and the penetration depth. As it is mentioned
earlier, the dilution is defined by the Eq. (1) and depends on the
penetration depth (b) and the clad height (h). Since the factor of
laser power exists in both numerator and denominator in the dilution fraction, it is possible that its effect to be eliminated by
simplifying the fraction. Therefore, the dilution could be just
proportional to F and V.
Concerning the last geometrical property of single clad track,
the same statistical analysis for the wetting angle (θ) leads to the
combined parameter as P1V-1F1/2 with a linear regression coefficient R ¼0.98 (R2 ¼0.96), together with the uniform distribution of
the residuals (See Fig. 11). The wetting angle varied from 5°, observed at the highest scanning speed, and the lowest laser power
and powder feeding rate, to the values close to 86°, observed at the
lowest scanning speed, and the highest laser power and powder
feeding rate. The combined parameter found in the present study
for the wetting angle is in agreement with the majority of previous
works, which reported combined parameters derived from P, V
and F (See Table 1).
If the cross section of the single clad track is assumed to be a
segment of a circle [22], the wetting angle can be simply calculated
from the clad height and width as θ ¼ 2arctan(2h/w). It is noticeable that the values calculated from the clad width and the
clad height are significantly close to the experimental measurements of the wetting angle. The similarity of these values can
show the validation and robustness of our measurements and
assumptions.
All predicted combined parameters in the present study with
the best correlations with measured geometrical characteristics of
single clad tracks are summarized in Table 4. All combined parameters with relatively high values of the linear regression coefficient (R 40.95) were found showing the robustness of all the directly measured quantities.
For achieving a fully dense clad layer, dilution should be kept
Fig. 11. (a) Dependence of the wetting angle on the combined parameter P1V-1F1/2.
(b) Residual plot.
Table 4
All predicted combined parameters in the present study with the best correlations
with measured geometrical characteristics of single clad tracks.
Quantity (y)
Combined parameter (x)
R
a
b
4.3007E 02
h (mm)
P 2V −3/2F 1
0.98
1.0902E 07x
w (mm)
P 3/2V −1/3
0.98
2.5103E 04
1.2263
b (mm)
P 1V 2/3F −2/3
0.97
0.0034
0.0129
θ (degree)
P 1V−1F 1/2
0.98
0.0288
0.0672
D (%)
V 1F −1
0.96
1.1633Eþ03
3.6888
between 5% and 10%, and the wetting angle is advised to be
smaller than 80°, leading to a free-porosity and perfect-bonded
clad layer [7]. Since overlapping of side by side single clad tracks is
employed to cover all the surface of the specimen, some circumspections should be considered in the selection of optimum processing parameters for single clad tracks that can result in a freeporosity, well-bonded and dense clad layer with overlapping
tracks. For instance, a clad layer formed by overlapping tracks is
usually 20–35% thicker than that of a single clad track. Moreover,
using overlapping tracks reduces the amount of dilution due to the
consumption of a portion of the laser energy for re-melting adjacent clad material that previously cladded at the side [3]. However, the reduction in dilution is not always a constant value and
can change for various substrate/powder combinations. Therefore,
in this study, the value of dilution for single clad tracks is operationally advised to be between 15% and 25% just to assure wellbonded clad layer with overlapping tracks.
Based on the above-mentioned considerations, the processing
map for the coaxial laser cladding of NiCrAlY powder on Inconel
738 superalloy can be constructed that relates geometrical characteristics of the single clad tracks to their applied processing
parameters. Fig. 12 represents such a map in terms of laser power
(P) on the vertical axis and the amount of powder material
M. Ansari et al. / Optics & Laser Technology 86 (2016) 136–144
143
Fig. 12. The processing map for coaxial laser cladding of NiCrAlY powder on Inconel 738 superalloy in terms of P vs. F/V representation.
delivered per unit length (F/V) on the horizontal axis. Considering
the linear relation between the dilution (D) and F/V parameter, the
second horizontal axis can be drawn for the dilution. The dilution
can be directly derived from each combination of processing
parameters. The two solid vertical lines on the processing map
mark the advisable values of dilution for single clad tracks (15–
25%). The statistical relations between the clad height (h) and the
combined parameter P2V-3/2F1 forms the parabolic-dashed curves
for eight constant values of clad height (h ¼0.1, 0.2, 0.3, 0.4, 0.6,
0.8, 1 and 1.4 mm). The statistical relations between the clad width
(w) and the combined parameter P3/2V-1/3 forms the other parabolic-dashed curves for four constant values of clad width (w ¼1.5,
2, 2.5, and 3 mm). To take the wetting angle (θ) into account, the
combined parameter P1V-1F1/2 allows the solid parabolic curves on
the processing map as a mark of the advisable values of wetting
angle for single clad tracks (30–70°). It should be mentioned that h,
w, θ, and D represent the geometrical characteristics of the single
clad tracks, not the final clad layer with overlapping tracks.
The shaded region on the processing map represents plausible
limits to acquire free-porosity clad tracks with good metallurgical
bonding to the substrate and low dilution. The clad height and
width can be adapted to this region in order to obtain required
values of the clad height and width. It is the processing map to
successfully deposit clad material, which can be employed as a
guideline for selecting the processing parameters of coaxial laser
cladding of NiCrAlY powder on Inconel 738 superalloy. The map
clearly demonstrates the robustness of the laser cladding process,
which allows obtaining high quality clad layer within a wide range
of the processing parameters.
characteristics of single clad tracks to the main processing parameters. The high correlation coefficients for all studied characteristics of single clad tracks, together with residual plots, substantiated the validity of such an empirical-statistical model. The
main results are as follows:
The clad height statistically depended on the laser power, while
the scanning speed and powder feeding rate were parameters
with less impact. This statistical relation could be written as
P2V-3/2F1 .
The clad width was mainly controlled by the combined parameter derived from the laser power and scanning speed so that
the powder feeding rate was a dispensable parameter. The
combined parameter as for the clad width could be written as
P3/2V-1/3.
The penetration depth was mainly proportional to the combined parameter as P1V2/3F-2/3. However, the dilution was found
to be proportional to the combined parameter as V1F-1, which
laser power was an ineffective parameter.
The wetting angle was controlled by the combined parameter as
P1V-1F1/2 . Moreover, the calculated values of the wetting angle
from the clad width and height showed the accuracy and robustness of experimental measurements.
The processing map of the process was modeled on empiricalstatistical relations to reduce the needs for extensive and timeconsuming experiments. A wide plausible processing window
was observed in the process to acquire a thick, dense and wellbonded clad layer.
References
4. Conclusions
In this experimental study, coaxial laser cladding of NiCrAlY
powder on Inconel 738 superalloy was performed in order to establish an empirical-statistical model to relate the geometrical
[1] R. Vilar, Laser cladding, J. Laser Appl. 11 (1999) 64–79, http://dx.doi.org/
10.2351/1.521888.
[2] R. Vilar, Laser powder deposition, in: S. Hashmi, G.F. Batalha, C.J. Van Tyne, B.
S. Yilbas (Eds.), Comprehensive Materials Processing, Elsevier, Oxford, 2014,
pp. 163–216, http://dx.doi.org/10.1016/B978-0-08-096532-1.01005-0.
144
M. Ansari et al. / Optics & Laser Technology 86 (2016) 136–144
[3] W.M. Steen, V.M. Weerasinghe, P. Monson, Some aspects of the formation of
laser clad tracks, in: Proc. SPIE 0650, High Power Lasers and Their Industrial
Applications, 1986, pp. 226–234. doi: http://dx.doi.org/10.1117/12.
938104http://dx.doi.org/10.1117/12.938104.
[4] W.E. Frazier, Metal additive manufacturing: a review, J. Mater. Eng. Perform.
23 (2014) 1917–1928, http://dx.doi.org/10.1007/s11665-014-0958-z.
[5] J.J. Lewandowski, M. Seifi, Metal additive manufacturing: a review of mechanical properties, Annu. Rev. Mater. Res. 46 (2016) 151–186, http://dx.doi.
org/10.1146/annurev-matsci-070115-032024.
[6] A.J. Pinkerton, Advances in the modeling of laser direct metal deposition, J.
Laser Appl. 27 (2015) S15001, http://dx.doi.org/10.2351/1.4815992.
[7] L. Costa, I. Felde, T. Réti, Z. Kálazi, R. Colaço, R. Vilar, B. Verő, A simplified semiempirical method to select the processing parameters for laser clad coatings,
Mater. Sci. Forum 414–415 (2003) 385–394, http://dx.doi.org/10.4028/www.
scientific.net/MSF.414-415.385.
[8] U. de Oliveira, V. Ocelík, J.T.M. De Hosson, Analysis of coaxial laser cladding
processing conditions, Surf. Coat. Technol. 197 (2005) 127–136, http://dx.doi.
org/10.1016/j.surfcoat.2004.06.029.
[9] V. Ocelik, U. de Oliveira, M. de Boer, J.T.M. de Hosson, Thick CO-based coating
on cast iron by side laser cladding: analysis of processing conditions and
coating properties, Surf. Coat. Technol. 201 (2007) 5875–5883, http://dx.doi.
org/10.1016/j.surfcoat.2006.10.044.
[10] J. Paulo Davim, C. Oliveira, A. Cardoso, Laser cladding: an experimental study
of geometric form and hardness of coating using statistical analysis, Proc. Inst.
Mech. Eng. Part B: J. Eng. Manuf. 220 (2006) 1549–1554 ⟨http://pib.sagepub.
com/content/220/9/1549⟩.
[11] J. Paulo Davim, C. Oliveira, A. Cardoso, Predicting the geometric form of clad in
laser cladding by powder using multiple regression analysis (MRA), Mater.
Des. 29 (2008) 554–557, http://dx.doi.org/10.1016/j.matdes.2007.01.023.
[12] H. El Cheikh, B. Courant, S. Branchu, J.-Y. Hascoët, R. Guillén, Analysis and
prediction of single laser tracks geometrical characteristics in coaxial laser
cladding process, Opt. Lasers Eng. 50 (2012) 413–422, http://dx.doi.org/
10.1016/j.optlaseng.2011.10.014.
[13] Y. Sun, M. Hao, Statistical analysis and optimization of process parameters in
Ti6Al4V laser cladding using Nd:YAG laser, Opt. Lasers Eng. 50 (2012)
985–995, http://dx.doi.org/10.1016/j.optlaseng.2012.01.018.
[14] S. Kumar, V. Sharma, A.K.S. Choudhary, S. Chattopadhyaya, S. Hloch, Determination of layer thickness in direct metal deposition using dimensional
analysis, Int. J. Adv. Manuf. Technol. 67 (2013) 2681–2687, http://dx.doi.org/
10.1007/s00170-012-4683-1.
[15] S. Saqiba, R.J. Urbanica, K. Aggarwal, Analysis of laser cladding bead morphology for developing additive manufacturing travel paths, Procedia CIRP 17
(2014) 824–829, http://dx.doi.org/10.1016/j.procir.2014.01.098.
[16] M. Barekat, R. Shoja Razavi, A. Ghasemi, Nd:YAG laser cladding of Co–Cr–Mo
alloy on γ-TiAl substrate, Opt. Laser Technol. 80 (2016) 145–152, http://dx.doi.
org/10.1016/j.optlastec.2016.01.003.
[17] E. Toyserkani, A. Khajepour, S. Corbin, Laser Cladding, CRC Press, Boca Raton,
2004.
[18] Y. Fu, A. Loredo, B. Martin, A.B. Vannes, A theoretical model for laser and
powder particles interaction during laser cladding, J. Mater. Process. Technol.
128 (2002) 106–112, http://dx.doi.org/10.1016/S0924-0136(02)00433-8.
[19] I. Tabernero, A. Lamikiz, S. Martínez, E. Ukar, L.N. López De Lacalle, Modelling
of energy attenuation due to powder flow-laser beam interaction during laser
cladding process, J. Mater. Process. Technol. 212 (2012) 516–522, http://dx.doi.
org/10.1016/j.jmatprotec.2011.10.019.
[20] W. Devesse, D. De Baere, P. Guillaume, Modeling of laser beam and powder
flow interaction in laser cladding using ray-tracing, J. Laser Appl. 27 (2015)
S29208, http://dx.doi.org/10.2351/1.4906394.
[21] S. Kou, Welding Metallurgy, Second ed., John Wiley & Sons, Hoboken, New
Jersey, 2003.
[22] H.-J. Bartsch, Geometry, in: Handbook of Mathematical Formulas, Academic
Press, New York, 1974,
p. 155, http://dx.doi.org/10.1016/B978-0-12-080050-6.50007-5.