Materials Sciences and Applications, 2010, 1, 158-161
doi:10.4236/msa.2010.13025 Published Online August 2010 (
Copyright © 2010 SciRes. MSA
Effect of Microstructures and Material
Compositions on Blister Formation
Yunan Prawoto Jern Phye Tan, Choon Yong Loh
Faculty of Mechanical Engineering, University Technology Malaysia, Johor, Malaysia.
Received May 10th, 2010; revised June 13th, 2010; accepted June 25th, 2010.
One of the early failures of coating is blister. Here two different coatings were applied on various materials and micro-
structures. The formation of the blister, and its microstructural and material dependencies were evaluated. It is con-
cluded that general organic coating forms more severe blisters than that of the metallic effect coating. General organic
coating protects the samples by insulation film while metallic coating protects by acting as galvanic protection. There-
fore, the failure modes are also different, namely blister and filiform corrosion. The dependencies on the microstruc-
tures and on material types also follow the insulation film concept and galvanic protection concept.
Keywords: General Organic Coating, Metallic Effect Coating, Corrosion, Blister
1. Introduction
Organic coating is among the most widely used surface
engineering modifications. This corrosion protection met-
hod allows one to choose the type of the coating accord-
ing to the application. Manufacturers design substrates
with the desired physical and mechanical properties. The
users can choose and utilize a coating that is resistant to
the environment to which the part is to be exposed acco-
rding to their predictions.
Besides engineering application, coating is also widely
used in non-engineering applications. Due to its wide app-
lication and availability, their usage is often erroneous;
many practitioners and engineers are not careful enough
to consider the composition of the base materials to be
painted let alone to consider the microstructures.
This research aims to clarify the first step of the corros-
ion failure mode in general organic coating, which is bli-
stering. General organic coating was applied on both fer-
rous and non-ferrous materials, in different microstruct-
ures. The specimens were subsequently tested using com-
pound corrosion test mode. The formation of the blister,
and its microstructural and material dependency were
then evaluated.
1.1 Coating Protection
Coating is a method of corrosion protection by applica-
tion of paint films to a metal in order to protect or insul-
ate the metal from corrosive environment, water and oxy-
gen. Coating also can be adjusted by using less noble
metal so that the less noble coating such as zinc coating
corrodes instead of the metal itself. Thus, corrosion can
be prevented.
Organic coating is a paint containing organic elements
such as plastic and rubber. The main purpose of this co-
ating is to isolate the metal from corrosive environment
such as seawater, or daily moist environment. An exam-
ple of organic coating is sheet linings, which use vinyl,
organisols, or plastisols. The most common form of org-
anic coating is in the form of liquid-applied paint. This
kind of paint can be applied easily to a surface by using
brush, roller, or spray. This paint consists of four basic
components: resin, solvent, pigments, and miscellaneous
compounds. Resin is also known as binder which is the
most influential in determination of resistance. Solvent
can be water or organic acrylic. Pigments are added as
rust inhibition, to decrease permeability, and provide co-
lor or increase the ultraviolet and weathering resistances.
Normally, pigments used include zinc phosphate, zinc
molybdate, zinc phosphorus silicate, zinc chromate and
strontium chromate [1]. Some organic coatings use metal
flake to achieve their metallic appearance. It ranges from
aluminum to chromium flake. This type of coating is
called metallic effect coating [2].
1.2 Blister in Organic Coating
In general, there are six types of corrosion related to gen-
eral organic coatings. Those are: blistering, early rusting,
Effect of Microstructures and Material Compositions on Blister Formation159
flash rusting, anodic undermining, filiform corrosion, and
cathodic delamination. These are in addition to other de-
teriorations such as loss of adhesion. Blistering is cons-
idered as the first failure mode of corrosion in coated
It is also widely known that alternating between dry
and wet accelerates the formation of the blister. Cycling
of the dry and wet can be perfectly achieved by comp-
ound corrosion test (CCT) test that combines drying and
immersions. This cycle provides more internal stress that
leads to creating easy formation of blister [3].
2. Experimental Method
In this research, both ferrous and non-ferrous materials
were used. For ferrous material, steel was selected. The
variation of the heat treatment was also used as a param-
eter. For the non-ferrous materials, copper and alumin-
um-based alloys were used.
2.1 Adhesion Test
Adhesion test is an important test for any paint film. Poor
adhesion means that the paint can be comparatively re-
moved readily from the substrate; this is generally con-
sidered to indicate the existence of a potential problem.
In this research, adhesion test was performed using cross
cut method according to ASTM D 3359-05 [4]. A series
of 11 parallel cuts each 1 mm apart, was made through
the coated film to the specimen substrate of a specimen
by using cutter knife or razor blade. A new cutter knife
was used for next specimen in order to maintain the
sharpness of the knife. Peel a piece of adhesive tape on to
the cross cut area by pressing with uniform force. This
can prevent bubbles from the entire area of cross cut.
Subsequently, adhesive tape is then peeled.
2.2 Corrosion Test with Scribe
Before testing, X-cut on the coating was made with the
blade of cutter knife vertically to the test piece coated
surface. The length is 40 mm long cut in the shape of “X”,
with the intersection forming an angle of 30˚. The sam-
ples were then tested using compound corrosion testing
mode. This consists of 15 minutes immersion in 5% NaCl
and 11.5 hrs dry off periods. Total test was 60 cycles.
After the testing, rinse the coating surface with clean
running water, and the samples were evaluated.
3. Results and Discussions
3.1 Adhesion Test
After the cross-hatches test, it can be clearly seen that the
quality of general organic coating is very good compared
to that of metallic effect coating. However, as they ap-
peared in Figure 1, the general organic coating performs
better than metallic effect coating. The paint cracks when
the knife blade is applied on the coating. Therefore, the
adhesive quality is weak while applying the adhesive tape
(see Figure 2). The destruction of metallic coating when
it is applied to non-ferrous materials is more severe. This
is due to the base material hardness and not due to the
microstructure or materials compositions.
Figure 1. Appearance of the adhesion test results
Figure 2. The effect of cutting on (a) General organic coat-
ing (b) Metallic effect coating
Copyright © 2010 SciRes. MSA
Effect of Microstructures and Material Compositions on Blister Formation
3.2 Blistering Test Results
Figures 3(a) and 3(b) show the conditions of the blistering
for ferrous materials after 60 cycles. The blister for
quenched materials shows that high carbon produces fewer
Figure 3. (a) Appearance of the annealed samples before
and after 60 cycles of CCT; (b) Appearance of the quenched
samples before and after 60 cycles of CCT
blisters. This phenomenon was not observed for the an-
nealed samples. Materials dependency on the blistering
can be seen in Figure 4. It shows that aluminum pro-
duces fewer blisters than that of brass. Furthermore, with
copper as the base material, blisters were found inde-
pendent of the scribes.
Figure 5 shows the cross section of the blistering near
and originated from the scribes. It is clear that majority of
the blister is formed by corrosion product originated
Figure 4. Appearance of the non-ferrous samples before and
after 60 cycles of CCT
Figure 5. Cross section of scribed area in micrograph shows
undercut corrosion
Copyright © 2010 SciRes. MSA
Effect of Microstructures and Material Compositions on Blister Formation
Copyright © 2010 SciRes. MSA
from the scribes. Some blisters occur independent of the
scribes. Among materials tested, copper produces most
blisters that are independent of the scribe. To explore
further on the mechanism, more cross sections were
evaluated. Figure 6 shows the summary of the results.
The figure shows that moisture can penetrate inside the
coating without passing the scribe. Once the moisture and
the chloride penetrate, they create corrosion that has a
larger volume than the crystalline one. This large volume
is the one that push the coating outside causing the blister
to occur.
Figure 7 shows that regardless of the coating, the me-
chanism of the corrosion remains the same. Microscopi-
(b) (c)
Figure 8. (a) Coating before corrosion; (b) Metallic coating
after corrosion (sacrificial); (c) Organic coating after corro-
cally, the microstructure dependency is driven by the
galvanic corrosion, where cementite phase corrodes more
than the ferrite phase, as they work as anode and cathode.
(a) (b)
For the metallic effect coating, blistering was not obs-
erved. This is because the metallic flake works like sacri-
ficing anode. Therefore, the failure mode is filiform cor-
rosion (Figures 3(a), 3(b) and 4). Graphical explanation
on the difference between metallic effect coating and
general organic coating is shown in Figure 8.
(c) (d)
4. Conclusions
Figure 6. Blistering. (a) Normal coating; (b) Blistering for-
med; (c) Pressure exert Two representative coatings, namely organic and metallic
effect coatings, were evaluated. For all based materials
used, the general organic coating formed more severe
blister than metallic effect coating. General organic coa-
ting protects the samples by protecting film while metal-
lic coating provides galvanic protection. As a result, the
failure mode is also different. The former forms blister
while the latter forms filiform corrosion. Consequently,
the dependencies on the microstructures and on material
compositions are different. General organic coating fol-
lows the protecting film concept, while the metallic effect
coating follows the concept of galvanic cell.
[1] J. R. Davis, “Surface Engineering for Corrosion and Wear
Resistance,” American Society for Materials International,
Materials Park, 2001.
[2] K. Stevens, “Surface Engineering to Combat Wear and
Corrosion: A Design Guide,” The Institute of Materials,
London, 1997.
[3] Z. W. Wicks, “Organic Coatings: Science and Technol-
ogy,” Wiley-Interscience, Haboken, 2007.
[4] “ASTM Standard: D3359-07,” ASTM Annual Book of
Standards, ASTM Publisher, West Conshohocken, 2007.
Figure 7. Corrosion mechanism in two different phases un-
derneath the coating