Transactions on Engineering Sciences vol 33, © 2001 WIT Press, www.witpress.com, ISSN 1743-3533
Improvement of corrosion fatigue strength
of materials by various surface treatments
R. Ebara
Department of Advanced Materials Science.
Kaganla University. Japan.
Abstract
In this paper it is summarized on improvement of corrosion fatigue strength of
materials by various kind of surface trcatrnents mainlv based upon the author's
experimental data. It is described on the effect of synthetic resins. thermalsprayed coatings and ion plating on corrosion fatigue strength of structural
materials. The emphasis is focussed upon the tar epoxy resin coating for ship
structural steels and thermal-sprayed coatings for machne structural steels. The
mechanism of the improvement of corrosion fatigue strength of materials by
' be concluded that the improvement of
surface coatings are also described. It cm
corrosion fatigue strength is not effective when an interception effect disappear
due to the breakage or degradation of the tar epoxy resin coating. It can also be
concluded that the effective thermal-sprayed coating to improve corrosion
fatigue strength should be of very low porosity and finnly adhesive to the base
metal.
l Introduction
Surface trcatmcnt is one of the effective method to improve corrosion fatigue
strength of structural materials in service environments. So far many papers have
been reported on the effect of surface treatments such as metal coating [ l ] and
shot peening 121 to improve corrosion fatigue strength of steels. The coating
effect is expected to retard corrosion fatigue crack initiation andfor decelerate
corrosion fatigue crack propagation rate of materials. In this p7per it is briefly
reviewed on the effect of synthetic resins such as epoxy resin coating and tar
epoxy resin coating. thermal-sprayed coatings such as plasma sprayed coatings
and cermet coating and ion plating for various structural materials mainly based
Transactions on Engineering Sciences vol 33, © 2001 WIT Press, www.witpress.com, ISSN 1743-3533
upon the author's experimental data.
2 Effect of synthetic resins on corrosion
fatigue strength of various materials
2.1 EtTeel of epoxy resin coating on environmental fatigue
strength of various materials
Since Gilde et a1 [3] have reported on the effect of an epoxy resin coating over
the weld reinforcement in improving the fatigue strength of welded joints ,this
effect has been confirmed by other experiments [J.] [S] [6] .
'liyo factors were to be considered: first the protective effect of the coating
against atmosphere and, secondly decrease the stress concentration at the toe of
the weld reinforcement. It was clarified that oxygen and relative humidity in air
significantly affect the fatigue strength of steels and aluminurn alloy [7] [8] .
While fatigue crack initiation was not affected by the atmosphere, the crack
propagation rate was more rapid in atmosphere which contains oxygen and water
vapor. Therefore the effect of epoxy resin coating in improving the fatigue
stren@h ot welded joints can be strongly attributed to this protectike effect
against air. In fact the fatigue crack propagation rate was decelerated by epoxy
resin coating with 2 mm thickness as shown in Fig.1 [7] .
In this figure it is also den~onstratedthat the coating eEect disappear if the
0
2
6
8
Number of
10
12
11.
16
cycles
Figure l ('rack propagation rate of plastic coated mild steel in air
[ ~ a s u m o t oet al."] alternative bending stress: 217.7MPa
Note:
4
;*
and
show break of coating
18
m05
Transactions on Engineering Sciences vol 33, © 2001 WIT Press, www.witpress.com, ISSN 1743-3533
coating should break. In this experiment it was clarified that the coating eEect
was ineffective by the epoxy resin coating with thickness less than 1.5mm. It was
concluded that the most effective coating among the synthetic resins was epoxy
resin coating cured with poly-amid and had poor air permeability, flexibility and
good adhesion for metal surface [g] .
2.2 Effect of tar epoxy resin coating on corrosion fatigue strength
of ship structural steel
The ship ballast tank members are exposed to the atmosphere with high
temperature and high relative humidity or sea water environment. Therefore the
tar epoxy resin coating has been applied to ballast tank members against these
aggressive environment. In order to evaluate the ballast tank life an evaluation of
an effect of tar epoxy resin coating and its thickuess on corrosion fatigue stren@h
is absolutely necessary. Fig.2 shows the effect of 2 0 0 , m
~ tar epoxy resin coating
on the corrosion fatigue strength of the ship strt~cturalsteel KA32(TMCP) plate
notched specimen by push-pull fatigue testing [l01 .
It is clear that the effect of tar epoxy resin coating is observed in lower nominal
stress range. The lower the nominal stress range the coating effect increased.
n
a
r 300
U
I
'J)
aJ
C?
\\--\-
ZOO
X-
-
\
C
\
m
L
m
VI
KA32(TblCP), A r t ~ f ~ c ~sea
a i flater
(298K)
\
'
U
v1
.-3
G
100
L
O1iHz.R
70
.
Go _
50
1
l
o4
,
Uncoated
90.
80 -
Ooi
-a
alr
1
\,
\
1111
Uncoated , A r t ~ r i c i a l sea w a t e r ] K o b a ~ a s h l
Tar e p o x y (200 urn)
1
'
" I
:0'
L
-
L
A
1
,
1 0;
1 oi
Number of cycles to fadure
Figure 2 S-N, curve for tar epoxy coated notched specimen in artitkid
sea water [ ~ b a r aet al.'"')
Transactions on Engineering Sciences vol 33, © 2001 WIT Press, www.witpress.com, ISSN 1743-3533
144
h i Icic c
i i l iiiiilcill
It can be also observed that the thicker the coating thickness the longer the
fatigue life is [F'ig.3] . It was observed that corrosion pits initiated on the base
metal after breakage of coating caused by deterioration of the tar epoxy resin.
Then corrosion fatigue crack initiated and propagated in association with
1000
I
KA32(TMCP), Artificial sea water (298K), 0 17Hz, R=O 05
500 -
i
i
Number of cycles tc failure
Figure 3 Relation between tar epoxy coating thickuess and
number of cycles to failure (Ebara et al."")
striation.
Impedance1 time curve for tar epoxy resin. coated specimen with 50 to 3 0 0 p m
thickness is shown in Fig.4. Impedance of tar epoxy resin coated with 50 p m
thickness drops tremendously after few days exposure into au artificial sea water.
The same phenomenon is seen on 100,um tar epoxy resin coated specimen.
While the impedance of 2 0 0 p m aud 3 0 0 , ~ mtar epoxy resin coated specimen
never drops after exposure for 6000 hrs. The impedance drops slightly after 10''
hrs. exposure and the dropping rate is not prominent. Thus it can be mentioued
that tar epoxy resin deteriorate due to the change of water absorption. In this
study it was also observed that the deterioration ot the tar epoxy resin coating
occurs at the notched area influenced by repeated stress. Aud impedance
decrease of the uotched portion was bigger than that of a plane portion I:Fig.5) .
From afore mentioned results the mechanism ofthe deterioration of the tar epoxy
resin coating can be concluded as follows. In higher stress lcvel corrosion fatigue
crack initiate earlier at the notched area where stress coucentratth and an
improving effect oT corrosion fatigue strength is not expected when an
interception eKect disappear. The lower the stress an improving efiect becomes
to be recognized by an interception effect due to the difficulty or crack
Transactions on Engineering Sciences vol 33, © 2001 WIT Press, www.witpress.com, ISSN 1743-3533
l ! ! !L / / L ! l ' l /
0
1200
2400
Time
3600
(h)
4800
145
6000
Coating r h c k n e r s 3 0 0 n m
...
0
l200
. . . . . . . . .L
,
2400
3600
Tme (h)
4800
6000
Figure 4 ImpedancelTime curve for tar epoxy coated specimen with various
coating thickness, Artificial sea water,200Hz ( ~ b a r aet al.""]
[
F
A
F
i
I
,
'
,
"
'
/
.
I
I
,
.
~
F
-
,
Coating thickness 50um , Artificial sea water
Frequency 200Hz, AS 2 1 OMPa
Ji,
\,
\.'.
l
3
.-.
C..
'3~.
\.
>.
F
?
......
....
.:.
.':-....- .
notch
E
1
2
t
l
1 0 ' L _
.
_
l
. . .8
, . .
. ,.
0
2x10'
4x10'
0
34
68
6x10'
8x10'
Number o f cycles
102
136
Time (h)
1x10'
170
.
1 . 2 ~ 1 01~. ~ ~ 1 0 '
204
238
F i g m 5 Impedance/number of cycles curve for tar epoxy resin coated
tatigw test specimen with 5 0 p m coating thickuess (f.,bm et al.'")
Transactions on Engineering Sciences vol 33, © 2001 WIT Press, www.witpress.com, ISSN 1743-3533
initiation 011 the coating. However an improving effect becomes to be small
when water absorption rate increases and the coating deteriorate as times goes by.
EKective coating thickness is an extent of 2 0 0 m.
~
3 Effect of thermal-sprayed coating on
corrosion fatigue strength of steels
Fig.6 shows plasma-sprayed coating effect on the corrosion fatigue strength of
13Cr stainless steel (12) . In this experiment rotating bending corrosion fatigue
tests were conducted on WC-CO, ZrO,,Cr,C,, Co-Cr-Ni-W plasma-sprayed
specimens in 3% NaCl aqueous solution at a testing ~ p e e dof 60Hz. 7l1e WC-CO
and ZrO, coating with low porosity improved corrosion fatigue strength at 10cycles by about 704%.While no improvement of corrosion fatigue strength was
observed by the Cr,C, and Co-Cr-Ni-W coatings with relatively high porosity. In
these specimeus corrosion fatigue cracks initiated Gom corrosion pits at the
surface of the base metal and propagated predominantly through the
intergranular path. Corrosion fatigue mechanism of the plasma sprayed 12Cr
stainless steel in 3% NaCl aqueous solution cau be schematically depicted as
shown in Fig.7.
a
z
V)
500
400
V)
2
4-
V)
m
300
.-c
U
c 200
Q)
D
0
m
--,'J-. - - * - -
.-Cc 100
m
*
0
a
2'
4
68105
2
4
6 B I 0 6
2
4
6 O l 0 7
2
4
6
8
Number of cycles
Figure 6 S-N curves of various plasma sprayed specimens in air and in 3% NaCl
aqueous solution [Ebara et al.'',)
It was also found that the corrosion fatigue strength of the WC-Cr-Ni cerniet
thermal-sprayed specimen with 1 0 0 , ~ mthickness was about three times larger
than that of the S K D l l base metal at 2x107 cycles in 2 mass % h S O , aqueous
solution [~;ig.8] [13]. The effective thickness of the WC-Cr-Ni cermet thcrmalsprayed coating to improve the corrosion fatigue strengflh of SKDll steel was
about 100@m [Fig.9]. Ln this case the principal cause of the improvemeut of the
corrosion fatigue strength of steel by thermal-sprayed WC-Cr-Ni cennet is the
Transactions on Engineering Sciences vol 33, © 2001 WIT Press, www.witpress.com, ISSN 1743-3533
insulation of SKDll steel surface horn the permeation of ZnSO, aqueous
solution. Lmpreguation of fluorine-contained resin into the thermal-sprayed WCCr-Ni cermet was found to be effective to improve corrosion fatigue strength of
SKD l l in lower stress region.
........................... ---3% NaCl aqueous solution ---- - - - - - W - - - - - - - - - - - - - - - - - - - - - - - - -
---m--
-
-
:G.
------------------------v--
Cr3C2coating
under coating
~ ~ 3 NaCl
° aqueous
/ ~ solution
-.
'%G
porosity
13 Cr stainless
steel
orrosion pit
intergranular
crack
l
I
Figure 7 Schematic illustmtion of corrosion fatigue mechanism of plasmasprayed 13Cr stairiless steel in 3 % NaCl aqueous solutiou ( ~ b a r aet ali")
-m
2
l
SKD11 Base metal
(WC-Cr-NI) Cermet (100 y m)
(WC-Cr-Ni) Cermet t Fluonne resin(lC0 p m)
Air(6OHz) Pmass%ZnSO4aqueous solution (16.7Hz)-
o
a
A
A
1600 -
a
2,
1400-
F
.-
1200
-
1000-
=---:t.....
0,
.-5
m
4-
0
LT
---.__
-
600400 200
-
i 6:'
O
103
10'
1 d
Q;' 1
d 8;'
105
1o6
1
'
4
10'
Number of cycles
Figure 8 S-N curves of WCCr-Ni thcr~nal-sprayedspecimen in
2 rnass'i; 7nSO, aqueous solutiou (Ebara et
$ $
Transactions on Engineering Sciences vol 33, © 2001 WIT Press, www.witpress.com, ISSN 1743-3533
/
(WC-Cr-Ni) Cermet thermal spray
2rnass%ZnS04 aqueous solution, 16.7Hz, 342.5MPa
Number of cycles
Figure 9 Intlt~enceof coating thickuess on corrosion fatigue like of WC-Cr-Ni
thermal-sprayed specimen ,2mass% ZnSO, aqueous solution,332.5MPa
[Ebara et al.13']
4 Effect of Ion plating on corrosion fatigue strength of steels
The ceramic coating has been applied to the substrate material by new
techniques, such as chemical vapor deposition (CVD), or physical vapor
deposition (PVD), the latter method being more precise than the former.
The compressor drive turbines for petrochemical plants are cllrrently expected,
from the stand point of saving energy and maintenance, to withstand long term
continuous operation of more than 5 years. Cr-TiN multilayer coating was
successti~lly applied for actual turbine moving blade to prevent drain
erosion[l.t].
In order to evaluate the mechanical properties of Cr-TiN multilayer coating
fatigue and corrosion fatigue tests were also conducted on Cr-TiN coated
specimens in air and in 3%NaCI aqueous solutions. It was observed that fatigue
and corrosion fatigue strength of Cr-TiN multilayer coated specimen is almost
same as that of the base metal[ I;ig.lOJ[lS]. It can be concl~ldedthat Cr-TiN
multilayer coating is an efXective surface treatment for turbine blade against
drain erosion without causing a decrease in its fatigue strength which is
frequently encountered with stellite soldering. Improvement of corrosion fatigue
strength can be expected if corrosion resistant coating without pir~holeshould be
developed.
Transactions on Engineering Sciences vol 33, © 2001 WIT Press, www.witpress.com, ISSN 1743-3533
-
Base metal
Cr-TIN Ion plated
Cr-TIN ion piated
(eroded)
Q
'A
'
a'
Number
of
Air
3"/,Nacl
0
D
A
A
Cycles
Figure 10 S-N curves of Cr-TiN iou plated steel in air and in 3% NaCl aqueous
solution [Ebara et al. ' '1
5 Concluding remarks
In tlus paper it is briefly summarized on the effect of surface treatments to
improve corrosion fatigue strength of structural materials. It can be concluded
that the effective coating to improve corrosion fatigue strength should be of very
low porosity and firmly adhesive to the base metal. However corrosion fatigue
is a time dependent phenomenon. Therefore more microscopic studies are
needed to develop a corrosion resistant coating in surely improving long-term
corrosion fatigue strength of materials.
References
Hirakawa, K.& Kitaura, I., Corrosion fatigue of steel in sea water, The
Surnitonzo Search, 26, pp.136-151.1981.
[2] Kurihara,Y., Takasaki,S., Kobayashi, M,, Ebara, R., Yamaday. &
Murakmi.Y., Corrosion fatigue behavior of automobile suspension spring
steels, Iinpact of Improved Material Quality on Properties, Product
Performance, and Design, .tfD- 28. ASME, pp.5 1-62, 199 1.
[3] Gilde, W., Increasing the fatigue strength of butt welded joints, British
Welding Journal. 7. pp.208-2 11. 1960.
[l]
Transactions on Engineering Sciences vol 33, © 2001 WIT Press, www.witpress.com, ISSN 1743-3533
Gilde, W., Muller, G. & Schwarz, H., Erhohung der Dauerfestigkeit von
durch Plastiiberzuge,
dynamisch beanspruchten Konstructionen
Schweisstechnik, 12, pp.6448,1962.
[5] Weller, J. & Weissgerber, R., Uber den Elnfluss von Kunstaraz-Uberziigen
auf die Dauerfestigkeit von A1:Mg-Legierungen Aluminurn, 40, pp.760762,1964.
[6] Schwarz, H., Erhohung der Dauerfestigkeit von Schweisskonstmktionen
durch Plastiiberzuge, Schweisstechnik (Vienna), 17, pp.61-66, 1963.
[7] Masumoto, I., Ebara, R., & Ueda, K., Effect of atmosphere on the fatigue
strength of steels, Metal Construction and British Welding Journal 2.
pp.423-426,1970.
[8] Masumoto, I., & Ebara, R., Effect of atmosphere and epoxy resin coating
on fatigue strength of aluminum alloq; Journal of Japan Welding Sociew,
41, pp.379-384,1972.
[9J Masumoto, I. & Ebara, R., Reason of fatigue strength improving effect
of epo,q resin coating steels, Journal ofJapan R'elding Society, 41, pp.283290, 1972.
[l01 Ebara R., Yamada,Y., Kino, T., Tada, M., Haslumoto. K.. Imajo,Y. &
Hushimi, K., Corrosion fatigue belmiour of tar epoxy resin coated
structural steel, Journal of the Society ofh'avalArchitects o f J a p m , 180,
pp521-530, 1996.
[l11 Kobayashi. S., Corrosion fatigue testing results under standard testing
condition, SR220 Report, Corrosion Fatigue of Ballast Tank, Japan Ship
Research Committee pp. 37-50,1996.
[l21 Ebara, R., Shigemura, S. & Yamane, T., Influence of plasma-sprayed
coating on corrosion fatigue strength of 13Cr stainless steel. Journal ofthe
Society of Materials Science , Japan, 13,pp.88 1-887. 1994.
[l31 N a k a l m . H., Harada,Y., Tani,K., EbaraR. & Yamada, Y., Tmprovement of
corrosion fatigue strength of high strength steel by thermal-spmyed (WCCr-Ni) cermct coating, Journal qf the Sociep of Llaterials Science, Japan
43, pp.880-894, 1994.
[l41 Ebara, R., Nakagawa,Y., YamadaY, Wada,T. & Osaki. H., Tmprovement of
drain erosion resistance of steam turbine blade by ceramic coating,
Mitsubishi Technical Bulletin, 202, pp. 11.1997.
[ l 51 Ebara, R., Nakajima H., Odohim. H., Wada, T. & Hatano. M,, Application
of ion-plated Cr-TiN multilayer coating to steam turbine blades.
Proceedings ?f the ldhTurhornachinety Svmpnsiutn. pp.3-8, 1987.
[4]