Surface Degradation of Ductile Metals in Elevated

7/30/2019 Surface Degradation of Ductile Metals in Elevated

http://slidepdf.com/reader/full/surface-degradation-of-ductile-metals-in-elevated 1/14

Wear, 111 (1986) 173 - 186 173

SURFACE DEGRADATION OF DUCTILE METALS IN ELEVATED

TEMPERATURE GAS-PARTICLE STREAMS

ALAN LEVY and YONG-FA MAN

Materi als and Molecular Research Di vision, L awrence Berkeley Laboratory, Berkeley,

CA 94720 (U.S.A.)

(Received February 15, 1985; revised November 5, 1985; accepted December 20,1985)

Summary

The mechanisms and rates of erosion and combined erosion-corrosion

of SCr-1Mo steel (where the composition is in approximate weight per cent)

and type 310 stainless steel at elevated temperatures were investigated to

understand better the behavior of piping steels in fluidized bed combustor

environments. Tests were performed in a partially inert gas atmosphere to

study erosion behavior and in an air atmosphere to study combined erosion-

corrosion behavior. I t was determined that the erosion rate remained con-

stant or decreased with increasing temperature in nitrogen unti l a temper-ature was reached at which the tensile strength started to decrease more

rapidly with increasing test temperature. Above this temperature the erosion

rate increased rapidly with temperature.

In an erosion-corrosion environment, corrosion was the. dominant

mechanism at all test conditions. At higher temperatures and velocities the

material loss mechanism changed from low loss rate chipping of the scale to

high loss rate periodic spalling. The continuous scale formed on SCr-1Mo

steel in air appeared to protect the metal surface, decreasing its loss rate in

(Y= 30” tests compared with that of type 310 stainless steel tested in the

same conditions in nitrogen where a continuous scale did not form.

1. Introduction

The surface degradation of metals that occurs in aggressive environ-

ments containing both corrosive and erosive media has been an important

design consideration in the construction of equipment for several different

industries. The loss of sound structural metal by erosion-corrosion can be

experienced in such diverse equipment as gas turbines [l 1 and fluidizedbed combustors [ 41. There are major differences in the operating environ-

ments of key components in the two equipment examples referred to [5,6].

However, both the turbine blades in the gas turbine and the heat exchanger

0043-1648/86/$3.50 @ Elsevier Sequoia/Printed in The Netherlands



174

tubes in the fluidized bed combustor can lose sound metal by a combined

erosion-corrosion mechanism in an elevated temperature env~onment,

It is the purpose of this paper to describe the material loss mechanisms

which have been observed to occur in structural metal alloys tested in condi-tions which lie between those of the bed of a fluidized bed combustor and

the turbine stage of a gas turbine. The test conditions were selected for

several reasons, major among them being the need to use rates that were

neither too fast nor too slow so that the behavior could be reasonably well

observed in a laboratory test. It is felt that the results of the investigations

reported herein are more applicable to the fluidized bed combustor case

than they are to the gas turbine case. However, it is possible that the types

of metal and scale surface morphology described have been observed on gas

turbine components and might be of use in helping to understand their

erosion-co~osion degradation.

The tests performed in this investigation were carried out in sulfur-free

gases because of limitations of the test equipment to contain toxic gases.

However, the oxide scale morphologies that were developed on the test

surfaces of the metals were very similar to the sulfide scales observed in

multi~omponent gas corrosion tests [ 71. Since the corrosion mechanism was

dominant over the erosion mechanism in ah the erosion-corrosion tests

reported herein, it is felt that the observations made have at least some

applicability to erosion-corrosion in oxygen- and sulfur-bearing gas atmo-

spheres.

2. Test conditions

The experiments were carried out in the elevated temperature erosion

tester described in the previous paper [ 81. It can use a variety of erodents

and air, argon or nitrogen carrier gases. Temperatures T from 20 to 900 “C

are achievable with a ~mpera~re variation not exceeding &15 “C over the

test range. The tests were performed at three different impingement angIes:

(II= zoo, o!= 30” and CY 90”. Angular Sic or rounded agglomerates of A1,03erodent particles with mean diameters of 100 - 250 pm were used [2, 33.

Particle velocities v from 10 to 70 m s-i were used at a solids loading of 2.5

g min-‘. Particle velocities were established by setting a pressure drop across

the nozzle using a metering system that was connected to a shop air supply.

The air or nitrogen pressures for a desired velocity were determined using the

computer calculation developed in ref. 9 to take elevated temperatures into

account. Undried nitrogen was used as the carrier for the erodent particles

in the type 310 stainless steel test to prevent corrosion from occurring

during the test.

Test durations t of 30 min and 5 h were used, depending on the nature

of the test. Both times were sufficient to produce steady state degradation

rates, The impact of small erodent particles on the test surface during the

corrosion process modified the effects of elemental diffusion through the



175

scale. This overcame the parabolic reaction rates which make the degradation

process much more time dependent in straight corrosion testing.

The data reported and analyzed in this paper are a part of a compre-

hensive program to investigate the elevated temperature behavior of a

number of alloys [ 8, lo]. The steels tested.in the total program were com-

mercial alloys commonly used in steam boiler and chemical process plant

components. Their designations are as follows: 1018; 2iCr-1Mo; 5Cr-+Mo;

SCr-1Mo; type 410 stainless steel; type 304 stainless steel; type 310 stainless

steel; 17-4PH. Their compositions are listed in ref. 10.

The two alloys reported on herein, type 310 stainless steel and 9Cr-

1Mo steel, behaved in a manner that was representative of all the alloys

investigated. The type 310 stainless steel was selected because it forms a

protective Cr,03 scale at the selected test conditions. The SCr-1Mo steelwas selected because its lower chromium content is marginal for forming a

protective scale at the test conditions. The erosion of the other alloys is

reported in ref. 10. They are comparatively simple alloys of iron having their

major variable element, chromium, in the range from 0 to 25 wt.%. This

range of chromium contents was selected because the oxide scales that form

on the metals in straight elevated temperature corrosion tests provide from

none to a fully protective Cr,Os scale.

The size of the specimens tested in the nozzle tester was 17.5 mm X

17.5 mm X 2 mm. The degradation rates of the test specimens were deter-

mined either by mass loss or thickness loss. To prevent oxidation of the testsurface prior to the tests in the elevated temperature erosion tester, undried

nitrogen was passed through the erosion tester until the specimen reached

the test temperature. After the test the specimen was quickly removed from

the furnace section of the tester and placed under a protective flow of

nitrogen until it had cooled to approximately 300 “C to prevent further

oxidation. Some spalling of the scale on the test surface occurred during

cooling. Optical and scanning electron microscopes were used to observe the

specimens’ surfaces and cross sections. Energy-dispersive X-ray analysis and

X-ray diffraction were used to determine the composition of the scales.

3. Results and discussion

3.1. Effect of t emperat ure on t he st rai ght erosi on of t ype 310 stai nl ess st eel

Figure 1 shows the erosion rate as a function of test temperature of

the highest chromium content most-corrosion-resistant steel tested, type

310 stainless steel [lo]. Each data point was obtained from a separately

tested specimen. The alloy was tested in a nitrogen carrier gas to prevent

corrosion from occurring. Four different test series were carried out to

determine the reproducibility of the data generated in the elevated tem-

perature erosion tester. At Q = 30” the erosion rate did not change as the

temperature was increased until 400 “C was reached. Above this temper-

ature the erosion rate increased with higher test temperatures at an increas-

ing rate.



176

'.'O 200 400 600 800 1000

Temperature PC)

Fig. 1. Erosion rate of type 310 stainless steel us. test temperature (20 pm Sic; u = 30m s-l) at (Y= 30” (A, 0, 0, 0) and (Y= 90” (A, m, 0, 4): A, A, run 1; 0, ., run 2; 0, 0, run 3;

0, +, run 4.

The shape of the curve for the CY 90” tests is somewhat different from

the cr = 30” curve. The erosion rate decreased from ambient temperature to

400 “C and then increased with temperature at an increasing slope. All the

alloys listed above showed this type of behavior with the decrease in erosion

rate at the lower elevated temperatures varying from essentially 0% to 60%less than the rate at room temperature.

The temperature at which the alloy steels started to undergo an increas-

ing erosion rate with test temperature correlated well with the temperature

at which their short-time tensile properties started to decrease at an increas-

ing rate. The decrease in erosion rate with test temperature at the lower

temperature showed the same trend as increases in the impact strength of

the alloys as the test temperature was increased above ambient temperature.

The reasons for these correlations are not known.

The effect of particle velocity on the erosion rate of type 310 stainless

steel tested at 800 “C is shown in Fig. 2. The velocity exponent of 1.23 isapproximately one-half of that reported for ductile metals at room temper-

ature [ll] in the range of velocities used in these tests. This indicates that

the relationship between the kinetic energy of the impacting particles andthe amount of material removed from the eroded surface that has been

observed in room temperature tests [ll] and modeled extensively is mod-

ified at elevated temperatures.

The erosion rate for the type 310 stainless steel in Figs. 1 and 2 for the

same test condition, particle velocity u = 30 m s-l at 800 “C, differs becauseof the impingement angle used. The erosion rate of 0.25 X lo-” g g-l in

Fig. 2 is greater than the value of 0.13 X 10m4g g-l in Fig. 1 because the data

in Fig. 2 were obtained at (x = 20”. This angle was nearer the peak rate im-pingement angle for type 310 stainless steel than was the (II= 30” angIe used

in the tests plotted in Fig. 1.



I

40 80 100

Velocity, m/s

Fig. 2. Erosion rate of type 310 stainless steel us. particle

T = 800 “C; cz = 20”).

velocity (240 Sic; nitrogen;

The appearance of the eroded surface of the type 310 stainless steel at

several test temperatures and two impingement angles is shown in F ig. 3. The

surfaces are filled with platelets and shallow craters which are representative

of the platelet mechanism of erosion [X2]. It can be seen that the erodedsurface texture was the same at all temperatures and both impingement

angles even though the erosion rates were significantly different. The dif-

ferences in the erosion rates are due to the size of the platelets that are

formed and knocked off the surface 1131. They are much larger at higher

particle velocities. The same eroded surface texture has been observed in

tests carried out at the highest possible velocity in the erosion tester, 130 m

s-i [13]. Whether this mechanism of erosion also occurs at the 300 m s-’

velocities that are common on turbine blade surfaces is not known.

The absence of any corrosion product can be seen on all the surfaces

pictured except the ~1s 30*, T = ‘775 “C test micrograph. The small nodules

that can be seen on the surface in this test condition are the beginning of the

formation of oxide scale. The scale formed on the type 310 stainless steel

was not continuous, even at the top test temperature, 900 “C. Once condi-

tions are right for a continuous corrosion scale to form, the nature of the

combined erosion-corrosion process enhances the growth of the scale and

corrosion becomes the dominant mechanism [ 141.

3.2. Combined erosion-corrosion of SCr-1iWo steel scale morphologyThe ability of impacting solid particles to promote the growth of the

scale is seen in Fig. 4. SCr-1Mo steel was selected for this series of tests

because it had a marginal chromium content for producing a continuous

protective Cr20s scale under ideal corrosion conditions but not enough

chromium to produce such a scale under all corrosion conditions. Thus the



(a) (b)

Fig. 3. Micrographs of an eroded type 310 stainless steel surface at various test temper-atures (nozzle tester; erosion; 240 pm Sic; u = 30 m s-l; t =: 30 min).

Figure 01 deg) T WI

3(a) 30 775

3& f 90 710

3(c) 30 397

3(d) 30 25

3(e) 90 25

(d)



(clFig. 4. Scale morphology on QCr-1Mo steel at (a), (b) 750 “C and (c) 900 “C (nozzle

tester; 130 firn A&03; air; U = 70 m s-l; t = 30 min; or = 90”) showing (a), (c) dynamic

corrosion and (b) erosion-corrosion.

effect of erosion-corrosion could be observed more readily. Figure 4(a)

shows the surface of a SCr-1Mo steel specimen that was exposed to dynamic

corrosion in a u =70 m s-l air blast without any erodent particles in it at

750 “C. Tbe smooth thin scale that formed is typical protective Cr,Os that

forms on chromium-containing steels in oxidizing atmospheres.

When 130 pm Al,Os particles were added to the air blast, the Fe203

scale shown in’ Fig. 4(b) resulted. This scaIe is several microns thick and has

a segmented domain type of microstructure [15]. The micrograph in Fig.

4(c) shows a similar segmented domain type of scale morphology to that

shown in Fig. 4(b). However, this scale occurred as the result of a dynamic

corrosion test without particles in the gas at a test temperature of 900 “C.

Thus the impact of erodent particles on the corroding surface at 750 “C

produced a scale which occurred in a dynamic corrosion test at a temper-

ature 150 “C higher.The morphology of the scale formed on the surfaces of steels has a

strong relation to the metal loss rates which occur in erosion-co~osion

environments [ 8,15,16]. The effect of the test temperature on the scale

morphology in erosion-corrosion tests carried out at a particle velocity u of



(a)

(c)

Fig. 5. Effect of test temperature on the scale morphology of SC&1Mo steel at L’= 70 m

s-l (nozzle tester; erosion-corrosion; 130 pm Al,Os; air; t = 30 min; Cx= 90”): (a) T =

750 “C; (b) T = 850 “C; (c) T = 90 0 C.

70 m s-l is shown in Fig. 5. At 750 “C the scale was segmented into domains

as was shown in Fig. 4. At 850 “C the scale has been condensed and con-

solidated somewhat by what is speculated to be a hot isostatic pressing type

of action from the impacting particles. This consolidation is more pro-

nounced in the scale that formed at 900 “C (Fig. 5(c)).The great difference in the scale morphology as the result of particle

impacts can be seen by comparing the appearance of dynamic corrosion scale

formed on the SCr-1Mo steel at 900 “C in Fig. 4 with F ig. 5(c). The scale

formed on the erosion-corrosion specimen at 900 “C is essentially contin-

uous, having no sharply defined segments as occurred on the 900 “C speci-

men in the dynamic corrosion test or the 750 “C specimen in the erosion-

corrosion test (Fig. 5(a)).

The same type of transition of the scale morphology from segmented

domains to a consolidated densified continuous scale was also observed to

occur as a function of increasing velocity at the higher temperature. Figure 6

shows a sequence of scales that formed on SCr-1Mo steel as the particle

impact velocity was increased from 10 to 70 m s-l in 850 “C tests. At the

10 m s-r velocity the force of the impacting particles was not sufficient to



181

(a) (b)

(c) (d)

Fig. 6. Effect of particle velocity on the scale morphology of SCr-1Mo steel in 5 h testsat (Y= 90” (nozzle tester; erosion-corrosion; 130 pm Al203; air; T= 850 “C; primaryzone): (a) u = 10 m s-l; (b) u = 30 m s-l; (c) u = 45 m s-l; (d) IJ = 70 m s-l.

consolidate the scale and the segmented domain type of morphology re-

sulted. At a particle velocity of 30 m s-i a transition in the morphology can

be seen. The scale still has segments, but they appear to be more densified

with smoother surfaces. In the 45 m s-l test the distinctly separated domainshave essentially disappeared and in the 70 m s-l test there is no evidence that

segmented domains remain. The differences in the morphology discussed

can be clearly seen in the original glossy micrographs, but in the printed

photographs these important differences are much harder to see.



182

3.3. Metal loss rates

The effect of the differences in the scale morphology in erosion-corro-

sion tests as a function of velocity and temperature on metal loss rates is

seen in Fig. 7 and Fig. 8 respectively. Figure 7 plots the metal thickness lossas a function of velocity at two impingement angles: Q!= 90’ and (x = 30”.

The (Y= 90” curve is a classic S-shaped transition curve, indicating that a

marked difference occurred in the erosion-corrosion mechanism in the

velocity region around v = 30 m s-l. Below the transition velocity, the

scale was eroded by a comparatively slow mechanism of chipping of small

pieces of scale [ 171. Above the transition velocity, the scale was removed

by a much faster mechanism, the periodic spalling of relatively large pieces

of scale [ 81. The scale loss rates on the corrosion-dominated surface trans-

lated into the underlying metal loss rates that were measured by an optical

micrometer on a specimen cross section, The curve for the CY 30” tests

will be discussed later.

It is thought that the change in thickness loss rate of the SCr-1Mo steel

at the higher particle velocities in the Q!= 90” tests is due to the change in

the manner in which the scale is removed rather than because of a change

from primarily corrosion to a synergistic combined erosion-corrosion

mechanism. Corrosion was observed as the dominant mechanism on all

surfaces of the specimens in all the tests at all velocities. The sharp increase

IO 20 so 40 so 80 70 80

Vek@ty of Pdcle m/s

I

I

760 800 860 900

Temperature 'C

Fig. 7. Effect of particle velocity on the metal thickness loss of SCr-1Mo steel in TE850 “C tests at a! = 30” (A) and a! = 90” (0) (130 pm Al,O,; air; t = 5 h).

Fig. 8. Effect of test temperature on the metal thickness loss of $Cr-1Mo steel in u = 70ms-1testsat&=900(130~Alz0~;air;t=5h).



183

in metal loss could not be the result of a sudden increase in erosivity of the

particles between 30 and 40 m s-i because the erosivity is a function of the

kinetic energy which increases uniformly as a function of the velocity (see

Fig. 2). The initiation of loss of larger pieces of scale by spalling at u = 30 ms-l was observed and this is thought to account for the increased metal loss.

The difference between the scale loss mechanism at the lower andhigher velocities is postulated to be due to the difference between the scale

morphologies. As seen in Fig. 6, at about u = 30 m s-l the force of the im-

pacting particles begins to densify and consolidate the segmented domainsof scale which occurred at the lower velocities. In its more continuous form

at the higher velocities, the scale can develop sufficiently high internal stresslevels to cause periodic spalling. At the lower velocities the scale’s separate

domains prevent these high stress levels from occurring and scale removalcan only occur by the chipping mechanism.The behavior is thought to be similar to that of plasma-sprayed thermal

barrier ceramic coatings on gas turbine components. They are purposelymicrocracked during application to reduce thermal fatigue failures by coat-

ing spallation [ 18,191. The large number of subcritical microcracks reducethe elastic modulus and, therefore, minimize the stresses that can develop

in the coating layer for a given strain level. This results in a strain accom-modation that reduces the spalling tendency of the coatings.

3.4. Protective scaleOn the right-hand ordinate in Fig. 7 the approximate mass loss of the

specimen was plotted. It was calculated from the eroded area, the metal thick-ness loss and the metal density. It is approximate because the contour of the

eroded area varies somewhat. Comparing the erosion rates for the type 310

stainless steel in Fig. 1 at 800 - 850 “C with the rates plotted in Fig. 7 for the

SCr-1Mo steel shows that the rates based on mass loss were the same at(Y= 90” and 3.0 X lop6 g g-l. At CY 30” the type 310 stainless steel had an

erosion rate that was five times that of the SCr-1Mo steel.There are several factors regarding the erosion behavior of the two

steels that indicate that the corrosion scale that formed on the SCr-1Mosteel in the 850 “C test could have provided some protection to the basemetal in the small-angle (a = 30”) tests.

(1) The type 310 stainless steel was tested in a nitrogen gas atmosphereand did not form a continuous corrosion scale.

(2) The general erosion behavior of brittle material such as the com-paratively thick continuous scale which formed on the SCr-1Mo steel is toundergo their highest erosion rate at a! = 90” and, by comparison, to be muchmore erosion resistant at o = 30”.

(3) In other investigations [ 201 it has been observed that austeniticstainless steels are more erosion resistant than ferritic steels.

(4) The tensile strength of the type 310 stainless steel at 850 “C is17.5 kgf mmP2 (25000 lbf in-‘) while that of the SCr-1Mo steel is 7 kgfmmm2 (10 000 Ibf inM2).



184

Erosion rates have been observed to increase as tensile strength de-

crew% i n elevated temperature tests [ 12 1. I tems (3) and (4) indicate that

the type 310 stainless steel should have had a lower erosion rate than the

SC%-1Mo steel.All these factors can be used to explain the higher erosion rate for

the type 310 stainless steel than for the SCr-1Mo steel when tested at

850 “C, u = 30 m s-’ and LY= 30”. I t appears that the decrease in the metal

loss rate of the SCr-1Mo steel was the result of the formation of a protective

scale on the surface of the steel at a formation rate that was enhanced by

the impacting erodent particles [16]. The equal erosion rate for the two

steels tested at LY= 90” indicates that the scale on the SCr-lM0 steel is

eroding at a faster rate because it is a brittle material and did not provide

as much protection to the metal as it did in the Q!= 30” tests. If the scale

on the SC+-1Mo steel was not providing some protection, the generally

higher corrosion resistance of austenitic stainless steels compared with

ferritic steels and the higher elevated temperature strength of the type 310

stainless steel at the 850 “C test temperature compared with that of 9Cr-

1Mo steel should have made the SC%--1Mo steel erode at a faster rate.

3.5. Erosi on-corrosion at CY 30”

The morphology of the scale on the SCr-1Mo steel as well as its thick-

ness were considerably different at an impingement angle (Y of 30” than ata = 90” [16]. Segmented domains of scale with different morphologies were

presented at all velocities up to u = 70 m s-i at a = 30”. The scales at the

higher velocities were observed to be relatively thin. Almost no spalled

regions were found on the specimens after the a! = 30” tests while major

spalling was observed on the LX=90” test specimens. The resulting metal

thickness loss curve for the 01 = 30” tests is shown in F ig. 7, I ts shape indi-

cates that metal loss is occurring only as the result of the slower scale-

chipping mechanism at all velocities.

3.6. Effect of t est t e~~er~t ~re

The effect of the test temperature on the metal thickness loss is plotted

in Fig. 8. The three available data points are connected by straight lines to

get an idea of the basic shape of the curve to compare with the particle

velocity effect curve. The curve has a steep slope between 750 and 850 “C

and a smaller slope between 850 and 900 “C. The shape of the curve together

with micrographs of the morphology of the scale at each temperature (Fig.

5) indicate that the curve in Fig. 8 is the transition portion of the same type

of S-shaped curve shown for the cy= 90” tests in Fig. 7. As in the effect of

velocity on scale morphology, the effect of the test temperature at the

higher velocities on consolidating the scale is thought to be responsible for

the change in the metal loss rates as the test temperature was increased.



185

4. Conclusions

4.1. Elevated temperature erosion

(1) An increase in the erosion rate of steels as a function of temperature

occurs at the temperature at which the tensile strength uersus temperature

curve of the steel increases its downward slope.

(2) The initial decrease in the erosion rate of some steels as a function

of temperature at lower elevated temperatures appears to be related to

increasing impact strength.

(3) The velocity exponent for the erosion of type 310 stainless steel at

800 “C is one-half of its exponent at 25 “C.

(4) At all test temperatures and velocities, erosion occurred by the

platelet mechanism of erosion in the absence of a continuous scale layer onthe metal surface.

4.2. Elevated temperature erosion-corrosion

(5) Corrosion was the dominant mechanism at all test conditions,

producing a scale layer on the metal surface.

(6) Impacting erodent particles on a surface in an oxidizing atmosphere

effectively increase its scale formation temperature by about 150 “C.

(7) At higher test temperatures and velocities the scale is consolidated

and densified by the impacting erodent particles.

(8) When the scale is consolidated, the erosion-corrosion loss mecha-nism of the scale changes from low loss rate chipping to high loss rate peri-

odic spa&g.

(9) Different erosion-corrosion mechanisms occur at (Y= 30” and (Y=

90” at the higher temperatures and velocities.

(10) The scale on the SCr-1Mo steel appears to be protective in the

(Y= 30” test at 850 “C compared with the base metal erosion of type 310

stainless steel under the same test conditions.

Acknowledgment

This research was sponsored by the U.S. Department of Energy under

DOE/FEAA 15 10 10 0, Advanced Research and Technical Development,

Fossil Energy Materials Program, Work Breakdown Structure Element

LBL-3.5, and under Contract DE-AC03-76SF00098.

References

1 W. Tabakoff, Review - turbomachinery performance deterioration exposed to solidparticulate6 environment, J. Fluids Eng., IO6 (1984) 125 - 134.

2 R. H. Barkalow and F. S. Pettit, Corrosion-erosion of materials in coal combustion

gas turbines, Proc. NACE Conf. on Corrosion- Erosi on of coal conversion syst em



186

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

mat eri al s, Berkeley, CA, Januar y 1979, National Association of Corrosion Engineers,Houston, TX, 1979, pp. 139 - 173.

D. R. Spriggs and R. P. Brobst, The effect of PFBC particulate on the high velocity

erosion-corrosion of gas turbine materials,Proc. NACE Conf on Corrosion -Erosion

of Coal Conversi on System M at eri al s, Berkeley, CA, Januar y 1982, National Associa-tion of Corrosion Engineers, Houston, TX, 1982, pp. 799 - 831.

J. B. Gilmour, D. C. Briggs, A. Sui and H. Hindam, Preliminary results of the CanadianAFBC materials test, NACE Corrosion’ 85, Boston, M A, M arch 1985, NationalAssociation of Corrosion Engineers, Houston, TX, 1985, Paper 341.

M. F. Hussein and W. Tabakoff, Dynamic behavior of solid particles suspended bypolluted flow in a turbine state, J. A i rcr. 10 (7) (1973) 434 - 440.S. Jansson, Erosion and erosion-corrosion in fluidized bed combustor systems, hoc.NACE Conf. on Corrosi on-Erosion-Wear i n Emergi ng Fossi l Energy Syst ems, Berk el ey,

CA, Januar y 1982, National Association of Corrosion Engineers, Houston, TX, 1982,pp. 548 - 560.

H. Hindam and D. P. Whittle, Corrosion behavior of CraOs former alloys in Hz-H+H20 atmospheres, NA CE Corrosion’ 81, Toront o, Apr i l 1981, National Associa-tion of Corrosion Engineers, Houston, TX, 1981, Paper 93.A. V. Levy and Y.-F. Man, Elevated temperature erosion-corrosion of 9CrlMo steel,

Proc. AI M E Conf. on Hi gh Temperat ure Corrosion in Energy Systems, D et roi t , MI ,

Sept ember 1984, Metallurgical Society of AIME, New York, 1984.D. M. Kliest, One dimensional, two phase particulate flow, Rep. LBL -6967, 1977

(Lawrence Berkeley Laboratory, University of California, Berkeley, CA); M.S. Thesis,

University of California, Berkeley, CA, 1977.A. V. Levy, J. Yan and J. Patterson, Elevated temperature erosion of steels, Proc. Int.

Conf. on Wear of M at eri al s, Vancouver, Apr i l 1985, American Society of MechanicalEngineers, New York, 1985, in Wear, 108 (1) (1986) 43 - 60.

I. Finnie and D. H. McFadden, On the velocity dependence of the erosion of ductilemetals by solid particles at low angles of incidence, Wear, 48 (1) (1978) 181.

A. V. Levy, The erosion of metal alloys and their scales, Proc. NACE Conf. on Cor-

rosion- Erosi on-W ear of M at eri al s i n Emergi ng Fossi l Energy Systems, Berkel ey, CA,

January 1982, National Association of Corrosion Engineers, Houston, TX, 1982, p.

298.A. V. Levy, M. Aghazadeh and G. Hickey, The effect of test variables on the platelet

mechanism of erosion, Wear , 108 (1) (1986) 23 - 4 1.A. V. Levy, E. Slamovich and N. Jee, Elevated temperature combined erosion-corrosionof steels, Wear, 110 (2) (1986) 117 - 149.A. V. Levy and Y.-F. Man, The effect of temperature on the erosion-corrosion of

SCk-1Mo steel, NA CE Corrosion’ 85, Boston, M A, M arch 1985, Paper 337, in Wear,111 (1986) 161 - 172.A. V. Levy and Y.-F. Man, Elevated temperature erosion-corrosion of SCr-1Mo steel,

Wear, 111 (1986) 135 - 159.G. Zambelli and A. V. Levy, Particulate erosion of NiO scales, Wear, 68 (3) (1981)

305 - 331.T. E. Strangman, Thermal barrier coatings for turbine airfoils, AVS Int. Conf. on

Met all urgical Coati ngs, San Di ego, CA, Apri l 9 - 13, 1984, in Thin Solid Films, 127

(1985) 93 - 105.

I . E. Sumner and D. Ruckle, Development of improved durability plasma sprayedceramic coatings for gas turbine engines, AZ AA Paper 80-l 193, 1980 (AmericanInstitute for Astronautics and Aeronautics).

T. Foley and A. V. Levy, The erosion of heat-treated steels, Wear, 91 (1) (1983) 45 - 64.

Documents

Surface Degradation of Ductile Metals in Elevated