studies on hvof sprayed coatingsconference.bonfring.org/papers/msr_iccomim2012/mep17.pdf · 2018....

International Conference on Challenges and Opportunities in Mechanical Engineering, Industrial Engineering and Management Studies 318

(ICCOMIM - 2012), 11-13 July, 2012

ISBN 978-93-82338-04-8 | © 2012 Bonfring

Abstract--- Boilers are extensively used in the thermal power plants. These are very conducive to corrosion and

lead to wall thinning and premature failure. Further, in boilers the combustion product changes their state of matter,

becomes salt at high temperature and generates corrosive media near the superheated tubes. These compounds

easily liquefy at operating temperature of boilers and cause accelerated corrosion.

Coatings play a major role in preventing the corrosion of the materials. These provide a protective surface by a

scale deposition helping to improve the corrosion resistance, long term stability to cracking under mechanical and

thermal stresses. Different coating techniques namely Chemical vapor deposition, Physical vapor deposition,

Thermal spray technique are commonly employed. Further Flame spraying with a powder, Plasma spraying, High

Velocity Oxy-Fuel spraying are gaining importance.

In the present investigation, HVOF spraying has been carried out using HIPOJET 2700 equipment. This utilizes

super charging jet generated by combustion of liquid petroleum gas and oxygen mixture. Two types of feed stock

powders namely WC-Co+65%NiCrAlY and Cr3C2-NiCr+Si has been HVOF sprayed on boiler tube alloys.

Microstructure, physical and mechanical properties of coatings has been studied and characterized.

Keywords--- Boilers, Hot Corrosion, HVOF Coating, Thermogravemetric Studies

I. INTRODUCTION

OMPONENTS in energy production systems required to operate at high temperatures may suffer a variety of

degradation processes as a consequence of complex multicomponent gas environment [1, 2, 3]. These include

oxidation, mixed oxidant attack, molten salt-induced attack and erosion. The development of corrosion and high

temperature oxidation protection systems in industrial boilers is a very important topic from both engineering and

economic perspective [4,5,6].

Hot corrosion is the accelerated oxidation when the surfaces covered with a thin film of few salts are exposed to

elevated temperature conditions [7,8]. This form of corrosion is commonly seen in gas turbines, boilers, internal

combustion engines etc. To minimize such corrosion, coating materials have been developed and different coating

techniques have also been investigated [9,10]. In this investigation, an attempt has been made to study the

microstructure, physical properties, and mechanical properties of the high velocity oxy fuel sprayed on boiled tube

steels. Two types of feed stock powders namely Cr3C2-NiCr+Si and WC-Co+NiCrAlY have been sprayed on the

boiler tubes and thermogravimetric studies have been carried out.

II. EXPERIMENTAL PROCEDURE

2.1 Substrate Materials

The substrate boiler tube steels for the study was procured from M/S Mishra Dhatu Nigam Limited (MIDHANI),

Hyderabad and Guru Gobind Singh Super Thermal Plant, Ropar. The Fe-based super alloy (designated as Superfer

800,Midhani Grade), chrome moly steel (designated as ASTM-SA213-T22) and MDN 310 (Midhani Grade) which

is being

S. Hanumanthlal, PG Scholar, Department of Mechanical Engineering, M S Ramaiah Institute of Technology, Bangalore

[email protected]

Dr.N.D. Prasanna, Professor, Department of Mechanical Engineering, M S Ramaiah Institute of Technology, Bangalore. E-mail: [email protected]

Dr.M.R. Ramesh, Associate Professor, Department of Mechanical Engineering, M S Ramaiah Institute of Technology, Bangalore. E-mail:

[email protected]

PAPER ID: MEP17

Studies on HVOF Sprayed Coatings

S. Hanumanthlal, Dr.N.D. Prasanna and Dr.M.R. Ramesh

C


(ICCOMIM - 2012), 11-13 July, 2012

ISBN 978-93-82338-04-8 | © 2012 Bonfring

used as material for water wall, super heater and reheater tubes in coal fired thermal power plants in northern part of

India has been used as a substrate material in the present study. The composition of the boiler tube steels is given in

Table 2.1.

Table 2.1: Chemical Composition (Wt %) for Various Substrate Alloys

2.2 Coating Materials

Two types of commercially available feedstock materials has been used in the powder form. This has been used

as a spray coating material on three different types of substrate materials using High velocity oxy fuel coatings

(HVOF). The details of the chemical composition and particle size of powder is reported in Table 2.2.

Table 2.2: Chemical Composition and Particle Size of Coating Powders

Sl. No Coating powder Chemical Composition

(Wt %) Particle size

1 [Cr3C2-35%(NiCr)]+5%Si [Cr - 30Ni - 9.5C] + 5%Si -45 + 15 μm

2 [WC-12%Co]+65%[NiCrAlY]

28.49W - 4.55Co – 14.95Cr

- 42.12Ni – 7.15Al – 1.96C

– 0.78Y

-45 + 5 μm

2.3 Deposition of the Coatings

HVOF spraying technique has been carried out using a HIPOJET 2700 equipment (M/S Metalizing Equipment

Co.Pvt.Ltd, Jodhpur, India) has been used in the present investigation. This equipment utilizes supersonic jet

generated by the combustion of liquid petroleum gas and oxygen mixture. The schematic of the HIPOJET 2700

system is shown in Figure 2.3. The spraying parameters selected during the HVOF deposition are listed in Table 2.4.

The process parameters namely spray distance and all other process parameter (listed in Table 2.4) were kept

constant throughout coating process. The substrate materials were grit-blasted using Al2O3 (Grit 45) before the spray

coating to develop better adhesion between the substrate and the coating.

Figure2.3: HIPOJET 2700

Sl. No. Alloy Grade

(ASTM code)

Chemical Composition (wt. %))

Fe Ni Cr Ti Al Mo Mn Si C

1 Superfer 800 Bal. 32 21.0 0.3 0.30 - 1.50 1.00 0.10

2 SA213-T22 Bal. - 2.55 - - 1.10 0.52 0.43 0.14

3 MDN 310 Bal. 21 25 - - - 2 0.8 0.1


(ICCOMIM - 2012), 11-13 July, 2012

ISBN 978-93-82338-04-8 | © 2012 Bonfring

Table 2.4: Spray Parameters Employed for HVOF Spray Process

HVOF process parameter

Quantity

Oxygen flow rate 250 l/min

Fuel (LPG) flow rate 65-70 l/min

Air-flow rate 550 l/min

Spray distance 178 mm

Powder feed rate

[Cr3C2-35%(NiCr)]+5%Si

[WC-12%Co]+65%[NiCrAlY]

28 g/min

38 g/min

Fuel(LPG) pressure 681 kPa

Oxygen pressure 981 kPa

Air pressure 588 kPa

2.4 Experimental Setup and Procedure

Hot corrosion studies were conducted using silicon carbide tube furnace (Make Digitech, India). The studies

were carried out at a temperature of 700˚C. Photo 2.1 shows the hot corrosion study experiment setup which has

been used in the present investigation.

Photo 2.1: Hot Corrosion Experimental Setup

Procedure

Furnace was calibrated Platinum/Platinum-13% Rhodium thermocouple (fitted with a temperature indicator

of Electromek Model-1551P, India) to an accuracy of ±5°C.

The coated specimen and uncoated specimen were polished using polishing machining (1µm accuracy).

Dimension of the specimen were noted down using digital vernier caliper.

The specimen were thoroughly cleaned, washed with acetone and dried in hot air to remove moisture.

The specimen were then heated in an oven up to 250˚C, which helps in uniform application of salt mixture.

Salt mixture sample containing Na2SO4-60%V2O5 dissolved in distilled water was coated on the warm

polished specimen using a brush (thickness between 3.0 -5.0 mg/cm2).

The Alumina boats and the salt coated specimen were dried in the oven at 150˚C for 30 minutes duration-

weighed precisely.

These specimen kept in aluminum boat were preheated to maintain the weight constant for high


(ICCOMIM - 2012), 11-13 July, 2012

ISBN 978-93-82338-04-8 | © 2012 Bonfring

temperature cyclic corrosion studies (preheated at constant temperature of 1200˚C for 10hr duration).

The boat containing the specimen was introduced into hot zone in furnace whose temperature was set at

700˚C.

Holding time inside the furnace was maintained for 1 hour duration and then afterwards the boat with the

specimen was taken out and cooled to room temperature in still air.

The boat with specimen was weighed precisely again using an Electronic balance (sensitivity of 10-3

gm,

model CB-120, contech, Mumbai, India) was used to conduct the thermo gravimetric studies (this

constitutes one cycle of corrosion study).

Weight change method has been considered for the analysis.

At the end of each cycle, Visual observations were made to study the color change, the luster, formation of

oxide scale...etc.

The above study (cyclic hot corrosion studies) was carried out for 50 cycles.

III. RESULTS AND DISCUSSION

3.1 Morphology of Coating Powder

(a)

(b)

Figure 3.1: Scanning Electron Micrograph of Coating Powders: Cr3C2-NiCr+Si (b) WC-Co+NiCrAlY

The morphology of coating powders has been evaluated using the scanning electron microscopy which is shown

in Fig 3.1. It is found from this figure that the Cr3C2-NiCr+Si powder particles have irregular shapes, where as the

WC-Co+NiCrAlY have spherical morphology. The particle size distribution of powder as determined by the image

analysis of the secondary electron micrographs are found to be consistent with nominal size distribution as provided

by the manufacturer.


(ICCOMIM - 2012), 11-13 July, 2012

ISBN 978-93-82338-04-8 | © 2012 Bonfring

3.2 Measurements of Coating Thicknesses

(a)

(b)

Figure 3.2: Back Scattered Electron Image of the as-Sprayed Coating Deposited on T22 Steels Cr3C2-NiCr+Si (b)

WC-Co+NiCrAlY

Coating thickness was measured from the back scattered image obtained along the cross-section of coated

specimen (Fig 3.2). The measured values of coating thickness are tabulated in Table 3.1. The HVOF coating

parameters used could provide coatings of desired thickness range.

3.3 Evaluation of Microhardness

The micro-hardness values are the measured across the coating-substrate interface. The average values of

microhardness for the Cr3C2-NiCr+Si and WC-Co+NiCrAlY are found to be 725.43Hv and 486.08Hv respectively.

The microhardness of the coatings is found to vary along the cross-section and further considerable increase in the

microhardness values are measured on the substrate region closer to the coating-substrate interface.

3.4 Bond Strength of Coatings


(ICCOMIM - 2012), 11-13 July, 2012

ISBN 978-93-82338-04-8 | © 2012 Bonfring

(a)

(b)

Figure 3.3: Photograph of the Fractured Surfaces of a Coated Specimen after it was Pulled Apart in the Tensile Test

Machine. (a)Cr3C2-NiCr+Si (b) WC-Co+NiCrAlY

The photograph of the fractured surfaces of a coated specimen after pulling apart in the tensile test machine is

shown in Fig. 3.3. The coating failed at the coating–substrate interface while remaining attached to the adhesive.

Average bond strength of bond strength is reported in Table 3.1.

Table 3.1 Thicknesses, Porosity and Surface Roughness of Sprayed Coating

Coating type Average

thickness

(µm)

Average

Bond

Strength

(MPa)

Micro Hardness

(HVN)

Cr3C2-NiCr +Si ~400 85.565 725.43

WC-Co+NiCrAlY ~250 63.032 486.08

3.5 Corrosion Results

3.5.1 Uncoated Specimen

3.5.1.1 Thermo Gravimetric Studies

Figure 3.4: (Weight Change/Area) versus Number of Cycles Plot for Uncoated Specimens subjected to Hot

Corrosion for 50 Cycles in Na2SO4-60%V2O5 Environment at 700°C


(ICCOMIM - 2012), 11-13 July, 2012

ISBN 978-93-82338-04-8 | © 2012 Bonfring

The weight gain for the T22, MDN310 and Superfer at the end of 50 cycles are found to be 24.17, 3.974 and

3.159 mg/cm2 respectively. The T22 steel showed a maximum weight gain during the hot corrosion studies in molten

salt environment. Further the weight gain square (mg2/cm

4) data is plotted as a function of time as shown in Fig 3.4.

The plot shows that the three materials T22, MDN310 and Superfer follow parabolic behaviour. The parabolic rate

constants, Kp (g2 cm

-4 S

-1) for T22, MDN310 and Superfer specimens are 0.349×10

-8, 0.010×10

-8 and 0.0061×10

-8

respectively.

3.5.1.2 X-Ray Diffraction Analysis

The X-ray diffraction patterns of the upper oxide scale, after its exposure to the molten salt environment at

700°C for 50 cycles for superfer substrate specimen is shown in Fig 3.5. The oxide scale on all the specimen under

study consisted of Fe203 as a main constituent. MDN and Superfer substrates showed the presence of Cr2O3 in the

oxide scale.

Figure 3.5: X-Ray Diffraction Patterns of Superfer Substrate Subjected to Hot Corrosion for 50 cycles in Na2SO4-

60%V2O5 Environment at 700°C

3.5.1.3 Uncoated Steels -Discussion

The results of thermogravimetry data demonstrates the accelerated kinetics induced due to Na2SO4-60%V2O5

eutectic mixture. Thick oxide scale formed on T22, MDN and Superfer steels mainly consists of iron oxide. T22

steel shows a higher corrosion rate and intense spalling of oxide scale in comparison to MDN and Superfer.

The uncoated T22 steel showed intense spalling, peeling of scale and enormous weight gain. The higher

corrosion rate during initial hours of study, which might be attributed to the rapid oxygen pick up by diffusion of

oxygen through the molten salt layer, is identical to the results reported by investigators [1, 2, 3] during their hot

corrosion studies.

Intensive spalling/sputtering of the scale of the bare steels can be attributed to severe strain developed due to the

precipitation of Fe2O3 from the liquid phase and interdiffusion of intermediate layers of iron oxide as has been

reported by investigator [1]. Further, the presence of different phases in a thin layer might impose severe strain on

the film, which may result in cracking and peeling of the scale. The cracks may have allowed the aggressive liquid

phase to reach the metal substrate.

The weight gain graph, shows that the weight gained by bare superalloys increases continuously, although the

rate of increase is relatively high during the initial period of exposure. This can be attributed to the formation of

NaVO3. At a temperature of 700°C, the Na2SO4–60% V2O5 will combine and form NaVO3 having a melting point of

610°C as proposed by researcher [4] .Na2SO4+V2O5 = 2NaVO3 (1) +SO2 + 1/2O2.

This NaVO3 acts as a catalyst and also serves as an oxygen carrier to the base alloy, which will lead to the rapid


(ICCOMIM - 2012), 11-13 July, 2012

ISBN 978-93-82338-04-8 | © 2012 Bonfring

oxidation of the basic elements of the superalloy to form the protective oxide scales. The rapid increase in weight

gain during the initial period was also reported by investigators [1, 2] in their studies of the hot corrosion behaviour

of nickel-based superalloy. The slower increase in weight gain after an initial rise is probably due to the

simultaneous growth and dissolution of oxide scale in the molten salt due to the reaction Cr2O3 + 4NaVO3 +3/2O2

→ 2Na2CrO4 + 2V2O5. Investigator [5] has suggested that this Na2CrO4 gets evaporated as a gas. The superior

corrosion resistance shown by the bare MDN and Superfer might be ascribed to the formation of Cr2O3 and nickel

vanadate

3.5.2 Cr3C2-NiCr+Si Coating


It can be seen from the thermo gravimetric data that the necessary protection against hot corrosion has been

provided by the Cr3C2-NiCr+Si coating, as the weight gain values for the coated steels are smaller than those for

respective uncoated steels as reported in section 3.4.1.1. The total weight gain values for the coated T22, MDN and

Superfer specimens at the end of 50 cycles of hot corrosion studies are found to be 0.4088, 0.7492 and 0.618

mg/cm2 respectively. Further the weight gain square (mg

2/cm

4) data were plotted as a function of time shown in the

Fig 3.6. The T22, MDN and Superfer steels followed parabolic behaviour and the parabolic rate constants kp

calculated are 0.00011×10-8

, 0.00037×10-8

and 0.00023×10-8

g2 cm

-4 S-

1 respectively.

Figure 3.6: (Weight Change/Area) versus Number of Cycles Plot for Cr3C2 NiCrSi Coated Steels subjected to Hot

Corrosion for 50 Cycles in Na2SO4-60%V2O5 at 700°C.


The XRD result reveals presence of Cr23C6, SiO2, NiO and Cr2O as major phases along with minor phases of

NiSiO4, Ni3V2O8 and Fe2O3.


(ICCOMIM - 2012), 11-13 July, 2012

ISBN 978-93-82338-04-8 | © 2012 Bonfring

Figure 3.6: X-Ray Diffraction for Cr3C2-NiCr+Si Coated Superfer Substrate Subjected to Hot Corrosion for 50

Cycles in Na2SO4-60%V2O5 Environment at 700°C

3.5.2.3 Cr3C2- NiCr+Si Coating Discussion

The Cr3C2-NiCr+Si coated specimen shows lower weight gain in comparison to the uncoated specimens as

reported in section 3.4.1.1, when exposed to Na2SO4-60%V2O5 molten salt environment.

The presence of minor phase such as Fe2O3 on the surface of hot corroded Cr3C2–NiCr+Si indicates the

diffusion of Fe from the substrate during hot corrosion of the specimens at temperature about 700°C. The formation

of Fe2O3 in the spalled scale has also been reported to be non-protective by investigator [6].

The initial high oxidation rate of the coated specimens might be ascribed to the rapid formation of oxides at the

splat boundaries and within open pores due to the penetration of the oxidizing species.

During hot corrosion, initially the corroding species reacts with the top surface of the coating and starts

migrating through the inter splat interface and diffusion of elements of substrate for example iron moves upward

along this inter splat space at the coating substrate interface, as the oxidation proceeds elements basically chromium

get oxidised and forms a continuous Cr2O3 layer below the top oxide layer. The continuous band of Cr2O3 in the

subscale and Cr2O3 along the splat boundaries will not allow any further transport of the oxidizing species and the

metallic ions. The presence of these elements at the coating surface will decrease oxygen availability in the

underlying alloy and favors the formation of most thermodynamically stable oxide, i.e. Cr2O3. With the passage of

time coating get partially oxidised along the splat boundaries with this further oxidation become negligible. This

partially oxidised coating provides protection to the substrate.

Cr2O3 and NiO nuclei at the coating surface react to form NiCr2O4 spinel, as it is evident from XRD analysis. So

the reaction is confined mainly to the top of the coating. Some minor spalling of the oxide scale of coated specimens

especially on the edges and corners during cooling periods of the thermal cycles may be due to different values of

thermal expansion coefficients of the coatings, substrate and oxides. Initial spallation and sputtering might be due to

the different values of thermal expansion coefficients of the coatings, substrate and oxides.

The NiCr coating has provided the best protection to the substrate steel, which may be due to the formation of

NiO, NiCr2O4and Cr2O3 as confirmed by XRD analysis, which are reported to be the protective oxides by

researchers [3, 7].

3.5.2.4 WC-Co-NiCrAlY Coating


Cumulative weight gain at the end of the 50 cycles of hot corrosion studies for coated T22, MDN and Superfer

steels are found to be 1.849, 1.958 and 1.731 (mg/cm2)

respectively. Further the weight gain square (mg2/cm

4) data

plotted as a function of time is shown in Fig 3.7. The coated T22, MDN and Superfer followed linear rate up to 50


(ICCOMIM - 2012), 11-13 July, 2012

ISBN 978-93-82338-04-8 | © 2012 Bonfring

cycles and the linear rate constants are 0.0019×10-8

, 0.0021×10-8

and 0.0016 ×10-8

g2 cm

-4 S-

1 respectively.

Figure 3.7: (Weight change/area) versus Number of Cycles plot for WC-Co-NiCrAlY Coated Steels Subjected to

Hot Corrosion for 50 Cycles in Na2SO4-60%V2O5 at 700°C


The XRD reveal presence of Cr2O3, NiO, Al2O3 and CoO as major phase along with minor phase of NiWO4,

CoCr2O4, NiCr2O4 and Ni3V2O8

Figure 3.8: X-ray Diffraction Patterns for WC-Co-NiCrAlY Coated Superfer Substrate Subjected to Hot Corrosion

for 50 cycles in Na2SO4-60%V2O5 Environment at 700°C

3.5.3.3 WC-Co-NiCrAlY Coating Discussion

The WC-Co-NiCrAlY coated specimen shows lower weight gain in comparison to the uncoated specimens as

reported in section 3.4.1.1, when exposed to Na2SO4-60%V2O5 molten salt environment.

The mechanism of scale formation during the oxidation of Ni-Cr-Si alloy has been proposed by investigator (8)

in three steps. Initially, an external scale is formed consisting of NiO and SiO2 with Cr2O3 precipitates at the grain

boundaries. The formation of SiO2 lowers the oxygen potential, promoting the lateral growth of Cr2O3 rather than


(ICCOMIM - 2012), 11-13 July, 2012

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nucleation. After completion of the Cr2O3 external scale, more stable binary oxide formation replaces ternary oxides

such as NiCr2O4 or Ni2SiO4, which are formed during the intermediate stages of oxidation. Researcher [9] suggested

that SiO2 affords a better protection than that of Cr2O3 scales which, in addition, becomes susceptible to

vaporization loss via CrO3 at a temperature of about 1000°C.

The above process occurs more rapidly at high temperatures. This means that a protective glassy film of silica

forms rapidly during the present oxidation studies at 700°C. Figure 3.8 shows a transient stage of oxidation where

rapid weight gain of the coating has been observed in the initial oxidation period up to 10 cycles of study due to the

formation of oxides of each and every active element present in the coating. Thereafter, the oxidation rate drops

drastically due to the formation of glassy SiO2 and Cr2O3 layer.

Protective layer rich in silicon oxide is formed in the topmost layer of the coating and a band of chromium oxide

is formed in the subscale, which restricts the further penetration of corrosive species into the coating. The formation

of spinel NiCr2O4 has also been detected in the surface scale of both the coated specimens. The oxides of chromium

and silicon are protective oxides [10] and offer better protection against hot corrosion due to their slow growth rate,

strongly bonded compositions, and ability to act as effective barriers against ionic migration [11].

According to investigator [12], in service environments the coating forms an oxide surface layer which ideally

inhibits corrosion. Thus, the coating is designed to serve as a reservoir for the element forming the surface oxide.

The oxide required for the purpose of corrosion and oxidation resistance are Al2O3, Cr2O3 and SiO2 and coating

compositions are selected accordingly to allow oxides to form in service. In the present study, XRD analysis showed

the formation of protective oxides such as NiO, Cr2O3 and Al2O3 in case of the NiCrAlY

In this way, the coatings provided the base alloy with a reservoir of elements such as Ni, Cr, Al and Co, which

form the protective oxide scales. This behaviour further tends to reduce the depletion of these elements from the

base metal, and hence increases the life of the alloy.

The formation of phases CoO, CoCr2O4, and Cr2O3 revealed by XRD in accordance with the studies of

researchers [13, 14, 15]. The protection shown by this coating may be due to the formation of oxides of chromium

and spinels of chromium and cobalt. Investigator [14] reported that the formation of spinels might stop the diffusion

activities through the cobalt oxide (CoO), which in turn suppresses the further formation of this oxide. He further

opined that increases in the growth of CoCr2O4 and Cr2O3 in competition with CoO and Co3O4 formation increases

the corrosion resistance of alloys.

IV. CONCLUSIONS

High velocity oxy-fuel thermal spraying with liquid petroleum gas as the fuel gas has been used

successfully used to deposit Cr3C2-NiCr+Si and WC-Co-NiCrAlY alloy coatings on boiler tube materials.

Under the given spray parameters, seemingly dense laminar structured coating with thickness in the desired

range of 250 to 400 µm and porosity less than 3.45% has been achieved.

The cumulative weight gain for all the HVOF coated T22, MDN 310 and Superfer 800H boiler materials

are significantly lower than that of uncoated specimen subjected to hot corrosion in Na2SO4-60%V2O5

molten salt environment for 50 cycles at 700°C. Uncoated specimen suffered a higher corrosion rate and

intense spalling of oxide scale was observed. The main constituent of oxide scale formed on all specimens

is iron oxide. The acidic fluxing of the oxides by the molten salt mixture resulted in massive, porous oxide

scale.

Based on the Thermogravimetric data, the relative oxidation resistance of the Cr3C2-NiCr+Si is higher than

WC-Co-NiCrAlY.

Cr3C2-NiCr+Si>WC-Co-NiCrAlY

All the coated specimen exhibit characteristic thick protective oxide scale, composed of oxides and spinel

oxide of the active elements of the coating and imparted resistance to the hot corrosion in the given salt

environment.

REFERENCES

[1] T. S. Sidhu, R. D. Agrawal, and S. Prakash, “Performance of high velocity oxy-fuel sprayed coatings on a Fe-

based superalloy in H2 SO4–60% V2 O5 environment at 900°C. Part II: Hot corrosion behavior of the

coatings,” J. Mater. Eng. Perform. (2005), (to be published).

[2] S. N. Tiwari, Investigations on Hot Corrosion of Some Fe-, Ni- and Co-Base Superalloy in Na2SO4-V2O5


(ICCOMIM - 2012), 11-13 July, 2012

ISBN 978-93-82338-04-8 | © 2012 Bonfring

Environment under Cyclic Conditions (Ph. D.Thesis, Met. Mat. Engg. Dept., University of Roorkee, Roorkee,

India,1997).

[3] UI-Hamid, Mater. Chem. Phys. 80 (2003) 135.

[4] Kolta GA, Hewaidy IF, Felix NS. Thermochim Acta 1972;4:151.

[5] Fryburg GC, Kohl FJ, Stearns CA. J Electrochem Soc 1984;12:2985.

[6] D.A. Stewart, P.H. Shipway, Surf. Coat. Technol. 105 (1998) 13.

[7] T. Sundararajan, S. Kuroda, T. Itagaki, ISIJ Int. 43 (2003) 104.

[8] R.A. Rapp, Kinetics, Microstructures and Mechanism of Internal Oxidation, Its Effect and Prevention in High-

Temperature Alloy Oxidation, Corrosion, 1965, 21, p 382.

[9] Wood GC, Hodgkiess T. Nature 1996;211:1358.

[10] F.H. Stott: Mater Sci Technol, 1989, vol. 5, pp. 734–40.

[11] U.K. Chatterjee, S.K. Bose, and S.K. Roy: Environmental Degradation of Metals, Marcel Dekker, New York,

NY, 2001.

[12] Wahl, G. and Nicoll, A.R. (1983), “ICMS, San Diego”, Thin Solid Films, Vol. 5, pp. 35 43.

[13] S. Prakash, S. Singh, B. S. Sidhu and A. Madeshia, In: Proc. National Seminar on Advances in Material and

Processing, Nov., 9-10 (2001) (IITR, Roorkee, India,2001) 245.

[14] K. L. Luthra and H.S. Spacil // J. Electrochem. Soc. 129 (1982) 649.

[15] G.J. Santoro, Oxid. Met. 13 (5) (1979) 405– 435.

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