Materials and Design 30 (2009) 2895–2902
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Materials and Design
journal homepage: www.elsevier.com/locate/matdes
Effects of grit blasting on surface properties of steel substrates
K. Poorna Chander, M. Vashista, Kazi Sabiruddin, S. Paul, P.P. Bandyopadhyay *
Department of Mechanical Engineering, IIT Kharagpur, Kharagpur, West Bengal 721 302, India
a r t i c l e
i n f o
Article history:
Received 29 October 2008
Accepted 12 January 2009
Available online 20 January 2009
Keywords:
Surface treatments (C)
Scanning electron microscopy (G)
X-ray analysis (G)
Ferrous metals and alloys (A)
Plastic behaviour (F)
a b s t r a c t
Low carbon steel substrates have been grit blasted using alumina grits of various sizes under varying
pressure, time, angle and standoff distances and the corresponding effect on surface roughness and surface residual stress has been studied. The mechanism of material removal in grit blasting has been analyzed. The effect of blasting process parameters on substrate surface residual stress has been studied
using a statistically designed experiment. For this purpose the Barkhausen noise analysis (BNA) of the
blasted surface has been undertaken. Then the BNA results have been calibrated against and complemented using the residual stress values measured using X-ray diffraction. The correlation between BN
signal and the measured residual stress has been studied. The material removal in blasting takes place
by microcutting, indentation or by a mixed mode depending on the blasting angle. During blasting the
alumina grits themselves also undergo erosion. The analysis of the experimental results shows that
the surface roughness increases with grit size, blasting pressure and to an extent with blasting time
and blasting angle as well. The compressive residual stress of the surface and subsurface hardness
increases with blasting pressure and blasting angle. The Barkhausen noise signal has a strong correlation
with the magnitude of the compressive residual stress on the blasted surface.
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
Grit blasting is a process in which angular shaped metallic or
ceramic grits are carried by a pressurised air stream and hurled
against the surface of the work material. The sharp grits erode
the surface and a rough surface suitable for thermal spraying is created. Some of the common grits are alumina grits, silicon carbide
grits, chilled iron grits, etc. It is necessary to make the substrate
rough before thermal spraying so that the coating can stick to
the substrate by mechanical anchorage. Grit blasting is also undertaken to prepare a surface before dip coating the same, using light
metal alloys like Babbitt. It is also a routine procedure for cleaning
the surface of a green sand moulded product.The roughness obtained is dependent on the grit blasting parameters, e.g., blasting
pressure, angle, standoff distance, grit size and type, etc.
The effect of the process parameters of grit blasting on the
roughness of blasted surface has been discussed in the literature
[1–7]. It has been observed that the roughness increases with an
increase in grit blasting pressure and decreases with an increase
in standoff distance. However, below a critical standoff distance
the surface roughness is low. The surface roughness increases with
blasting angle till the angle is around 75°. Material removal in grit
blasting occurs by an erosion process, where mechanisms like
microcutting, ploughing and extrusion are active [2,8,9]. On grit
* Corresponding author. Tel.: +91 3222 282950; fax: +91 3222 282700.
E-mail address: ppb@mech.iitkgp.ernet.in (P.P. Bandyopadhyay).
0261-3069/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.matdes.2009.01.014
blasting, the surface undergoes work hardening and a nano-grain
region is said to develop on the top layer which has a typical thickness of a few lm. This low cost process is thus possibly capable of
providing a nano-structured top layer on the surface of a ductile
material, wherein the transformation from crystallites to nanocrystallites is not abrupt [10].
A grit blasted surface in general, is under compressive stress.
Mellali et al. [3] has used the curvature method to measure the
compressive residual stress on the grit blasted surface. It has been
found that the stress increases with blasting pressure and grit size.
Other methods suitable for measurement of residual stresses in
ferromagnetic material are X-ray diffraction and Barkhausen noise
analysis (BNA). BNA is a micromagnetic technique of stress measurement which is very suitable for industrial use [11,12]. The
measuring principal is based on the fact that the residual stress
influences the magnetic domains of ferromagnetic materials. A ferromagnetic body consists of ferromagnetic domains having different local magnetization directions. These domains are separated by
boundaries known as Bloch walls. An external magnetic field
causes a change in total magnetization of a ferromagnetic body
undergoing magnetic excitation and initiates the corresponding
Bloch wall movements. These movements can be detected using
a small conductive coil in the form an electric pulse, which is
known as Barkhausen noise (BN). The presence and distribution
of elastic stress in the material influences the Bloch walls to find
the direction of easiest orientation to the lines of magnetic flux.
In other words, residual stress present in a body influences the
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K. Poorna Chander et al. / Materials and Design 30 (2009) 2895–2902
Bloch wall movements and consequently, the BN. A tensile stress
registers an increase in BN and a compressive stress shows a decrease. Hence the surface residual stress of a ferromagnetic component can be measured using BNA technique. This is an on-site and
quick method of stress determination.
The objective of the present work has been to study the mechanism of material removal during grit blasting of low carbon steel
using alumina grits. The effect of various grit blasting parameters
on the material removal mechanism, roughness and residual stress
of the grit blasted surface has been investigated. The residual stress
measurement has been undertaken using both X-ray diffraction
and Barkhausen noise analysis. The fact that grit blasting creates
a nano-structured layer has been established.
2. Experimental procedure
The experimental conditions for grit blasting are listed in Table
1. Test coupons of size 25 25 5 mm are sliced from a low carbon steel plate. The samples are held in a vise inside the grit blasting cabinet and the required angle is obtained in the vise. The
nozzle is held in position by a stiffener of adjustable length, using
which the standoff distance between the job and the nozzle can be
set. Once the angle and the standoff distance are fixed, blasting of
the small sample is carried out without moving the nozzle. Blasting
is undertaken on a round area on the centre of the sample and further analysis of the surface, e.g., roughness, X-ray is done on that
area only. The roughness of the grit blasted surfaces has been measured using a Taylor Hobson surtronic 3+ surface roughness tester.
For each data point corresponding to the roughness of grit blasted
surface using a particular combination of process parameters, three
coupons have been grit blasted. Then the roughness measurements
have been taken at four to six places on each sample and an average of these readings taken from all the three samples is reported
in each case. The grit blasted sample has been cross sectioned and
polished metallographically for hardness measurement using a
Leco LM 700 microhardness tester. The hardness has been measured in a direction away from the blasted surface along the thickness of the sample starting from a depth of about 25 lm. A load of
10 gf has been used for each hardness measurement. An average of
six hardness data has been reported. The morphology of the
blasted surface and the grits has been observed using a JEOL JSM
5800 scanning electron microscope. X-ray diffraction of the samples, other than the samples used for stress measurement, has been
done using Co Ka radiation in a Phillips diffractometer (PW 1729
generator, and PW 1710 diffractometer controller). The grain size
of the grit blasted and deformed layer has been estimated using
peak broadening. For measurement of peak broadening two samples have been annealed at 500 °C for 2 h and furnace cooled. Both
of them have been polished again for cleaning the oxide layer and
subsequently only one of them has been grit blasted for 1 min
using grits of mesh 24. Both of these have been used for X-ray diffraction. The annealed and as polished sample has been tested so
that the peak width of the grit blasted sample can be compared
with it.
The Barkhausen noise (BN) measurement has been carried out
with a 100 Hz excitation frequency of the external magnetic field
and 3.5 V magnetizing voltage using commercially available sys-
tem, Rollscan 300 BN. The data acquisition during Barkhausen
noise measurement and the subsequent analysis of the BN signal
have been undertaken using commercially available l-scan software. Fig. 1 shows typical representation of BN superimposed with
external magnetic excitation field. Fig. 2 on the other hand shows
the rectified BN signals for positive and negative magnetization cycles. In the present investigation, rms and peak values of the BN
signals have been employed to characterize the change in the micromagnetic response of the work piece upon grit blasting.
The state of stress of the grit blasted surface has been measured
using X-ray diffraction technique. For this purpose a PW1710 Philips X-ray diffractometer with five tilt angles from 45° to +45° has
been used. Fe has served as the target material. Scan parameters
have been collected using Philips X’pert Data Collector software
with 2h values (2h is the angle between source and diffracted Xray beam) chosen to encompass the Fe Ka doublet for the {2 1 1}
planes, where, 110 6 2h 6 113. The resulting spectra have been
analyzed using Philips X’pert stress software to determine uniaxial
residual stress. The well known sin2 W technique has been used to
obtain absolute stress value, where W is the angle between the surface normal and the bisector of source and diffracted X-ray beam.
Pearson VII technique has been used to calculate the peak position
on the diffracted intensity plots. Young’s modulus and Poisson ratio used for stress calculation are 211.9 GPa and 0.29, respectively.
Effect of process parameters on surface residual stress upon grit
blasting of the substrate material has been studied using statistical
design of experiments. Design of experiment enables along with
regression analysis, development of empirical models relating the
responses with the process parameters with significantly less
number of experiments. In the present investigation blasting pressure, grit size and impingement angle have been chosen as independent controllable parameters as they have significant
contribution towards grit blasting process [13–15].
As an initial attempt a linear first order model has been aimed
with total 13 trials. The levels of independent factors are shown
in Table 2, whereas Table 3 lists the combination of process parameters. The independent variables are in coded form in the developed regression models. It is a case of linear coding. The
measured values of BN parameters (rms and peak value) and surface residual stress obtained from XRD are also listed in this table.
Trial numbers 9–13 indicate the central points which enable estimation of pure experimental error and lack of fit of the model
independently.
3. Results and discussion
Fig. 3a is a secondary electron image of the surface of a low carbon steel test coupon grit blasted for only 5 s using grits of size 24,
standoff distance of 100 mm and blasting angle 20°. This figure
clearly shows traces of microcutting. The sharp edges of the particles cut into the work material, creating a fresh surface, pushing
the metal and folding it at the edge of the microcutting track
[2,9]. This is indicated by superimposing a rectangle in Fig. 3a.
Microcutting continues with blasting time, filling the surface with
microcutting tracks. Fig. 3b, taken after 60 s of blasting time bears
testimony to this fact. In this figure the traces of microcutting have
been shown using arrows. At this low blasting angle as expected,
Table 1
Experimental conditions for grit blasting.
Substrate
Grit type and size
Blasting pressure
(bar)
Stand off distance (mm)
Blasting angle
(°)
Blasting time (s)
Mild steel composition C 0.2%, Mn 0.3%,
P 0.04%, S 0.05%
Alumina, grit size 24, 48
and 60
5, 7
50, 80, 100, 130, 160 and
200
20, 50, 70, 80,
90
15, 30, 60, 90, 120, 150,
180
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K. Poorna Chander et al. / Materials and Design 30 (2009) 2895–2902
Fig. 1. The Barkhausen effect signal with excitation field taken from l-scan software.
Fig. 2. Averaged and rectified (positive and negative) impulses.
Table 2
Level of independent variables.
Levels
Low
Centre
High
Coding
Blasting pressure (bar)
Grit size
Blasting angle (°)
1
5
24
40
0
6
40
60
1
7
60
80
the microcutting is the major mechanism of material removal. A
major change in the mechanism of material removal takes place
as the angle of blasting is changed to 90°. Fig. 4a and b is the secondary electron images of a surface grit blasted at 90°. In this case
the grits get embedded in the surface and displace material. This is
also known as material removal by indentation [2]. Fig. 4a is a close
up of a typical indentation mark left on the surface after 5 s of
blasting time. One indentation is immediately followed by others.
The indentations overlap and a rough surface is created. Fig. 4b
shows a large crater created by overlapping indentations. In both
Fig. 4a and b, the indent areas have been identified using letter
‘I’. This mechanism of material removal obviously brings about a
rougher surface as compared to that created using a blasting angle
of 20°.
The grits also undergo surface damage during blasting process.
As such the grit material is brittle. During collision with the substrate the sharp edges of the grits are broken. In addition, collisions
Table 3
Experimental conditions and results for BN measurement and measured residual stresses.
Trial numbers
Blasting pressure (bar)
Grit size
Angle (°)
1
2
3
4
5
6
7
8
9
10
11
12
13
5
7
5
7
5
7
5
7
6
6
6
6
6
24
24
60
60
24
24
60
60
40
40
40
40
40
40
40
40
40
80
80
80
80
60
60
60
60
60
Coding
x1
x2
x3
1
1
1
1
1
1
1
1
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
BN (rms)
BN (peak)
r (MPa)
108
72
90
57
77
55
75
47
59
61
71
75
66
152
97
126
79
104
75
104
67
84
85
96
80
90
282
342
289
350
297
371
328
370
357
350
335
347
353
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K. Poorna Chander et al. / Materials and Design 30 (2009) 2895–2902
Fig. 3. Secondary electron image of the surfaces grit blasted using 24 grit size alumina grits at a blasting angle of 20°, standoff distance 100 mm and blasting time: (a) 5 s, (b)
40 s.
Fig. 4. Secondary electron image of the surfaces grit blasted using 24 grit size alumina grits at a blasting angle of 90°, standoff distance 100 mm and blasting time: (a) 5 s, (b)
40 s.
occur between the impacting and ricocheting grits as well. With
each collision grits wear out from the surface by microbrittle fracture. The loss of grit volume is a function of grit usage time. Eventually the grits loose their effectiveness and needs replacement.
Fig. 5a and b is the secondary electron images of a fresh grit and
a grit used for 40 s, respectively. The used grit shows pitting on
the surface as a result of removal of tiny particles from the surface
of the grit owing to microfracturing.
Fig. 6 is the plot showing the variation of surface roughness
against a wide range of blasting time (Fig. 6a), standoff distance
(Fig. 6b) and angle of impact (Fig. 6c), respectively. The roughness
is found to increase as the blasting time (Fig. 6a) is increased from
30 to 60 s and thereafter no significant variation in roughness with
increase in blasting time is recorded. The roughness value is found
to decrease a little when the blasting time approaches 3 min. The
initial increase in roughness is owing to the attack of grits on previously unaffected areas. After some time the surface layer is work
hardened and significant increase in roughness by plastic deformation is not possible. Beyond this point of saturation, with over
blasting, some of the plastically deformed parts and folded over attached chip material (Fig. 3a) are removed, flat areas are created
and there is a decrease in overall surface roughness. All subsequent
blasting trials have been conducted for 1 min only. The roughness
is found to increase initially with standoff distance (Fig. 6b) up to
Fig. 5. Secondary electron images of (a) fresh alumina grit of size 24 and (b) the same grit after 40 s of blasting time.
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K. Poorna Chander et al. / Materials and Design 30 (2009) 2895–2902
Ra in microns
Angle of impact 90 degree
SOD 100 mm
Time of blasting 1 min
Grit Alumina
Grit size 24, 48 and 60
5 bar
6
7 bar
4
2
0
10
30
50
70
grit size in mesh no
Fig. 7. Variation of roughness in grit blasted surface with grit size and blasting
pressure.
Fig. 8. Variation of cross sectional hardness of the grit blasted surface along the
thickness of the sample and away from the grit blasted surface.
Fig. 6. Variation of surface roughness of grit blasted mild steel surfaces under a
wide range of variation in (a) blasting time, (b) standoff distance, (c) angle of
impact.
100 mm for this experiment, and no further increase in roughness
has followed a further increase in standoff distance. Below 100 mm
the impacting particles collide with the ricocheting particles
resulting low blasting efficiency [3]. At 130 mm of standoff distance, the kinetic energy of the grits is reduced owing to entrainment of air and flaring of the jet and hence, the corresponding
blasted surface roughness is lower than that that at 100 mm. Beyond 130 mm the roughness value does not show a major change
with a further increase in standoff distance up to 200 mm. It can be
speculated that an increase beyond this standoff distance is likely
to cause a reduction in the roughness value since this standoff distance will correspond to a still lower kinetic energy of the particles
during impact. In subsequent trials a standoff distance of 100 mm
has been used. The roughness is found to increase with blasting angle (Fig. 5c) up to 80°. A further increase in blasting angle to 90° has
caused a decrease in roughness. Blasting at a lower angle causes
material removal mainly by microcutting where in the blasting
particle grazes on the blasted surface keeping the roughness low.
With increase in angle of impact the indentation effect becomes
more predominant. The roughness of an indented surface tends
to be higher. The roughness attains the highest value when the
blasting angle is around 80°. In this regime, a limited microcutting
and mainly indentation mechanisms are active and these two together brings about a change in the geometry of the asperities
keeping the roughness high. The asperities are more hook shaped
when blasted using blasting angle near 80°.
Fig. 7 shows the variation of surface roughness with blasting
pressure and grit size. Blasting has been done under two pressures
5 bar and 7 bar. At a higher blasting pressure the grit velocity is always higher and as a result a higher surface roughness is obtained.
A larger grit on the other hand can bring about more damage and
create larger craters on the blasted surface and hence the roughness is higher with larger grit.
Fig. 8 shows the variation of cross sectional hardness of the grit
blasted surface along the thickness of the sample and away from
the grit blasted surface. The hardness is highest at a point nearest
to the surface and hardness decreases with distance from the surface. Grit blasting involves considerable work hardening of the surface and the high hardness value near the surface is attributed to
this work hardening. The effect of work hardening gradually reduces with distance from the affected surface and hence the hardness also decreases. Under orthogonal impact the degree of
indentation (i.e., plastic deformation) is more than that of the surface blasted using a blasting angle of 60°. As a result the degree of
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K. Poorna Chander et al. / Materials and Design 30 (2009) 2895–2902
ð1Þ
peak ¼ 95:5 21:0p 6:75n 12:8h;
ð2Þ
where p is blasting pressure, n is the grit size and h is the blasting
angle.
Tables 4 and 5 provide the ANOVAs for rms and peak values of
BN, respectively. For the purpose of analysis, a confidence level of
95% has been chosen, which means the associated a-error is 0.05. It
is the low probability of finding a significant association amongst
the BN signal and blasting parameters when one does not really exist. F-ratios (Fisher test ratios) of all factors (regression, lack of fit
and process parameters) as obtained have been compared with
the statistical values of F-ratio for 95% level of confidence.
Both the ANOVAs clearly indicate that the blasting pressure and
impingement angles have significant effects on BN parameters as
the F-ratio of corresponding coefficients is significant. On the other
hand, the effect of grit size seems to be statistically insignificant
within the present experimental domain. Earlier investigators have
indicated in case of solid impact erosion significant effect of blasting pressure and angle of impingement on erosion rate [1–3]. Tables 4 and 5 also reveal the insignificance of lack of fit with
respect to pure experimental error.
Fig. 9a and b shows the effect of blasting pressure and impingement angle on rms and peak of BN signal. As the blasting pressure
and impingement angle are increased, there is an associated decrease in the BN parameters. An increase in either pressure or angle
of impingement (towards 90°) increases the momentum of the
individual impacting particle in a direction orthogonal to the
Total
Regression
b1(blasting
pressure)
b2 (grit size)
b3 (blasting
angle)
Error
Lack of fit
Pure error
a
Degree of
freedom
Sum of
square
Mean of
square
F-ratio
(calc.)
F-ratio
(table)
12
3
1
6298.4
5206.4
3507
5249
1735.5
3507
44.4794
89.8847
6.59
7.71
1
1
355.1
1344.2
355.1
1344.2
9.1014
34.4519
7.71
7.71
10
5
4
1092.1
936
156.1
109.2
187.2
39
4.7979
6.26
120
40 degree
60 degree
80 degree
80
rms
rms ¼ 70:2 14:9p 5:37n 9:13h;
Table 5
Summary of ANOVA results for BN (peak).
40
Grit: alumina, 24 mesh
Blasting time 1 min
SOD 100mm
0
4.5
5.5
6.5
7.5
pressure in bar
b
160
40 degree
60 degree
120
Peak
work hardening of the surface under orthogonal impact is higher
and this is reflected in its higher hardness value.
Surface integrity is a term that collectively reflects the state of
stress on surface and subsurface of a component along with information on microhardness, microstructure and presence of other
damages like cracks, etc. Micromagnetic techniques like Barkhausen noise analysis (BNA) can estimate the surface integrity, particularly state of stress and change in hardness and microstructure of
a component [11,12]. Table 3 shows the peak and rms (root mean
square) values of Barkhausen noise (BN) for different combinations
of process parameters used in this experiment. Trial numbers 9–13
are the repeated trials at the central point and they reflect the
repeatability and robustness of the experimental technique. Analysis of variance (ANOVA) has been undertaken to quantitatively
analyze the adequacy of model and significance of each regression
coefficients of the linear models.
Eqs. (1) and (2) are the linear models obtained through regression analysis of the data presented in Table 3. These models exhibit
the effect of process parameters, namely, the blasting pressure, the
grit size in mesh number and the impingement angle on the two
BN parameters under study, namely rms and peak values of BN
signal:
80 degree
80
Grit Alumina, 24 mesh
40
Blasting time 1 min
SOD 100mm
0
4.5
5.5
6.5
7.5
Pressure in bar
Fig. 9. The plot showing the effect of blasting pressure and impingement angle on
(a) rms and (b) peak of BN signal.
Table 4
Summary of ANOVA results for BN (rms).
Total
Regression
b1 (blasting
pressure)
b2 (grit size)
b3 (blasting
angle)
Error
Lack of fit
Pure error
Degree of
freedom
Sum of
square
Mean of
square
F-ratio
(calc.)
F-ratio
(table)
12
3
1
3088.3
2667.4
1770.1
257.4
889.1
1770.1
19.8465
39.511
6.59
7.71
1
1
231.1
666.1
231.1
666.1
5.159
14.868
7.71
7.71
10
5
4
420.9
241.7
179.2
42.1
48.3
44.8
1.0792
6.26
blasted surface. This is expected to provide a larger crater size
and a greater degree of plastic deformation of the blasted surface.
Such plastic deformation of the work material in turn, results compressive residual stress. Compressive residual stresses diminish the
level of BN parameters as shown in Fig. 9a and b.
Further, as stated earlier, a lower angle of impact tends to provide microcutting or scratching actions (Fig. 3). Similar observations have also been reported earlier in solid impact erosion [13–
15] and abrasive water jet machining [16]. Such microcutting action expectedly introduces less compressive stresses than near
orthogonal impacts. This observation is also corroborated from
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K. Poorna Chander et al. / Materials and Design 30 (2009) 2895–2902
r ¼ 336:23 þ 29:625p þ 5:625n þ 12:875h;
ð3Þ
where p is pressure, n is grit size and h is the blasting angle.
F-ratio for the coefficient of blasting pressure and impingement
angle indicate their significant association with residual stress.
Also the regression equation is significant in explaining the relationship between process parameters with residual stress. Table
6 also indicates the adequacy of the model by revealing insignificance of lack of fit with respect to pure experimental error. Eqs.
(1)–(3) also show the existence of similarity between significant
coefficients of process parameters on their respective responses.
Fig. 10 demonstrates that the compressive residual stress increases
with an increase in blasting pressure and impingement angle. As
stated before, an increase in these two parameters indicates a rise
in momentum of the impacting particles in a direction orthogonal
to the substrate. This explains a rise in plastic deformation and
residual compressive stress of the substrates. Figs. 11 and 12 exhibit the correlation between BN parameters (rms and peak) and the
induced residual stress. A close almost linear relation between BN
parameters and XRD residual stress measurement has been
established.
Measurement of grit size has been done using Scherer’s
formula:
dg ¼ 0:9 k=ððD2hÞ cos hÞ;
where dg = grain (crystallite) size, k = wavelength of the X-ray in
use, for Co Ka it is 0.161 nm, h = diffraction angle, D2h = full width
half maxima.
Fig. 13 shows the peaks from both the as annealed and the annealed and grit blasted surfaces. The peak corresponding to the grit
blasted surface shows a broadening and a shift. The factors affecting this broadening and shift are grain size, residual stress and
125
100
BN (rms)
Fig. 8, where it is found that a near orthogonal impact brings about
more plastic deformation on a surface and hence a surface with a
greater degree of work hardening and corresponding higher hardness results.
Grit blasted samples have also been characterized using X-ray
diffraction complementing Barkhausen noise analysis. The measured stress values are compressive throughout the experimental
domain. Table 6 presents the ANOVA for residual stress.
Eq. (3) represents the linear model for compressive residual
stress obtained through regression analysis to capture the effect
of process parameters on residual stress:
75
50
Table 6
Anova for residual stress.
Degree of
freedom
Total
Regression
Blasting
pressure
Grit size
Angle
Error
Lack of fit
Pure error
Sum of
square
Mean of
square
12
3
1
370
8600
7021.1
864
2867
7021.1
1
1
10
5
4
253.1
1326.1
1770
1491
279
253.1
1326.1
177
298
70
F-ratio
(calc.)
25
-400
F-ratio
(table)
-350
-300
-250
residual stress (MPa)
41.0715
100.5892
6.59
7.71
3.6264
18.9989
7.71
7.71
4.2714
6.26
Fig. 11. Variation of BN (peak) with residual stress.
175
150
BN (peak)
Compressive residual stress in
MPa
400
370
340
125
100
310
75
80 degree
280
60 degree
40 degree
250
4.5
5.5
6.5
7.5
Pressure in bar
Fig. 10. Variation of residual stress with blasting pressure and impingement angle.
50
-400
-350
-300
residual stress (MPa)
Fig. 12. Variation of BN (rms) with residual stress.
-250
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K. Poorna Chander et al. / Materials and Design 30 (2009) 2895–2902
owing to collisions with the target and with other grits. The surface
residual stress of the grit blasted surface has been measured using
both X-ray diffraction and Barkhausen noise analysis techniques.
There is an almost linear correlation between the Barkhausen noise
signal and the measured compressive residual stress of grit blasted
low carbon steel surfaces. Grit blasting has been found to produce a
surface with a compressive residual stress. This stress increases
with both blasting pressure and blasting angle, since these two
parameters brings about a greater degree of plastic deformation
on the surface. Also, upon grit blasting a nano-structured surface
is produced.
10000
as annealed
Intensity (arbitrary units)
annealed and grit blasted
8000
Co K alpha
6000
4000
References
2000
0
50
51
52
53
54
55
Diffraction angle (degree)
Fig. 13. Selective peaks from XRD patterns showing peak broadening of as annealed
and grit blasted low carbon steel surfaces.
instrumental broadening. The as annealed peak also shows a
broadening which is attributed to instrumental broadening only.
The measured grain size of the as annealed sample is found to be
20 lm and that of the grit blasted surface as calculated using
Scherer’s formula after background correction and correction for
instrumental broadening is 80 nm. Hence, it is observed that grit
blasting in this case produces a nano-structured surface [10].
4. Conclusions
In this paper, the mechanism of material removal during grit
blasting of low carbon steel surface using alumina grits of different
sizes has been discussed thoroughly. Two mechanisms, namely,
microcutting and indentation, were identified. The effect of varying
the grit blasting parameters like blasting pressure, blasting angle,
grit size, standoff distance, etc. on the blasted surface roughness
has been addressed. Grit erosion during blasting has been detected.
This attributed to microfracturing of the brittle grit at the surface
[1] Wigren J. Technical note: grit blasting as surface preparation before plasma
spraying. Surf Coat Technol 1988;34(1):101–8.
[2] Griffiths BJ, Gawne DT, Dong G. The erosion of steel surfaces by grit-blasting as
a preparation for plasma spraying. Wear 1996;194(1):95–102.
[3] Mellali M, Grimaud A, Leger AC, Fauchais P, Lu J. Alumina grit blasting
parameters for surface preparation in the plasma spraying operation. Therm
Spray Technol 1997;6(2):217–27.
[4] Amada S, Hirose T. Influence of grit blasting pre-treatment on the adhesion
strength of plasma sprayed coatings: fractal analysis of roughness. Surf
Coatings Technol 1998;102:132–7.
[5] Day J, Huang X, Richards NL. Examination of a grit-blasting process for thermal
spraying using statistical methods. J Therm Spray Technol 2005;14(4):471–9.
[6] Varacalle DJ, Guillen DP, Deason DM, Rhodaberger W, Sampson E. Effect of gritblasting on substrate roughness and coating adhesion. J Therm Spray Technol
2006;15(3):348–55.
[7] Mohammadi Z, Ziaei-Moayyed AA, Sheikh-Mehdi Mesgar A. Grit blasting of Ti–
6Al–4V alloy: optimization and its effect on adhesion strength of plasmasprayed hydroxyapatite coatings. J Mater Process Technol 2007;194:15–23.
[8] Bellman Jr R, Levy A. Erosion mechanism in ductile metals. Wear
1981;70:1–27.
[9] Momber AW, Wong YC, Budidharm RIJE. Hydrodynamic profiling and grit
blasting of low-carbon steel surfaces. Trib Int 2002;35:271–81.
[10] Guan XS, Dong ZF, Li DY. Surface nanocrystallization by sandblasting and
annealing for improved mechanical and tribological properties.
Nanotechnology 2005;16:2963–71.
[11] Tonshoff HK, Friemuth T, Becker JC. Process monitoring in grinding. Ann CIRP
2002;51:551–71.
[12] Brinksmeier E, Schneider E, Theiner WA, Tonshoff HK. Nondestructive testing
for evaluating surface integrity. Ann CIRP 1984;32:489–509.
[13] Bitter JGA. A study of erosion phenomena: Part I. Wear 1963;6:5–21.
[14] Hutchings IM. Deformation of metal-surfaces by oblique impact of square
plates. Int J Mech Sci 1977;19:45–52.
[15] Finnie I. Some observations on the erosion of ductile metals. Wear
1972;19:81–90.
[16] Paul S, Hoogstrate AM, Van Praag R. Abrasive water jet machining of glass fibre
metal laminates. Proc Inst Mech Eng – Part B: J Eng Manuf 2002;216:1459–69.