NASA Contractor Report 179529

. Grain Boundary Oxidation and Fatigue Crack Growth at Elevated Temperatures

[NASA-CR-179529) G R A I N BCUNCEPY O X I D A T I O l i N87-11873 A N D F A T I G U B CRACK G R O P 3 H A I E Z E V A ’ J E D ‘IEMPEEATUBES F i n a l SeFort [Syracuse U n i V , , N - , Y * ) 30 F CSCL 11r Unclas

G3/26 44797

H.W. Liu and Yoshiki Oshida Syracuse University Syracuse, New York

October 1986

Prepared for Lewis Research Center Under Grant NAG3-348

a

https://ntrs.nasa.gov/search.jsp?R=19870002440 2020-05-03T15:01:23+00:00Z

I. INTRODUCTION

Fatigue crack growth in the air at elevated temperatures is often

faster than the rate at room temperature.

crack growth has been attributed to creep and/or oxidation [1,2,3 1.

Creep induces grain boundary void formation and grain boundary cavi-

tation, and the formation and the growth of grain boundary voids and

cavities will accelerate fatigue crack growth.

The accelerated fatigue

Hull and Rimer 141 studied the growth of grain boundary voids

under stress in polycrystal copper wire. The nucleation of creep

cavities in a copper base alloy was observed by Fleck, Taplin, and

Beevers 15 1 . The nucleation and growth of cavities in iron during

creep deformation at elevated temperatures was studied by Cane

and Greenwood [ 6 ] . Grain boundary cavity and void nucleations

during creep under a sustained stress have been analyzed by a

number of investigators [7 to 16 1.

The cavity growth rate is related to either grain boundary

vacancy diffusion or surface diffusion.

has the form of the Arrhenius relation. However, grain boundary

cavity nucleation and growth under a cyclic load and the relation

between the growth rates of grain boundary cavities and fatigue

crack have yet to be studied.

The cavity growth rate

Gibb's free energies of metal oxide formation are negative.

When in direct contact with oxygen, metals oxidize easily, and

the rate of oxidation depends on the rate of diffusion of oxygen

or metal through the oxide layer. Grain boundary is a site

of high energy and a path of rapid diffusion. Therefore, the oxidation

1

11. GRAIN BOUNDARY OXIDATION PENETRATION

Oshida and Liu [311 have s tudied g r a i n boundary oxida t ion pene-

t r a t i o n i n a n i c k e l base superal loy, TAZ-8A, under a s t r e s s - f r e e

condi t ion.

w a s oxidized i n a i r . The oxidat ion temperatures w e r e 600, 800, and

1000°C, and t h e exposure t i m e s var ied from 100 t o 1000 hours.

ox ida t ion , each coupon w a s sect ioned, and t h e sec t ioned su r face w a s

examined under an o p t i c a l microscope.

a c ros s s e c t i o n of a test coupon.

deeper than the su r face oxide.

Edch disk coupon, 15 mm i n diameter and 5 mm i n th ickness ,

Af t e r

Figure 1 shows the p i c t u r e of

The g ra in boundary oxide pene t r a t e s

On each sec t ioned sur face , t h e g r a i n boundary oxida t ion penet ra t ion

va r i ed widely from one g ra in boundary t o another.

boundary oxida t ion pene t r a t ion depth, a of a sec t ioned su r face

w a s measured. Af t e r t h e measurement, a t h i n l a y e r of t he coupon,

approximately 80 um th i ck , w a s ground o f f , t h e new su r face w a s pol ished,

and another maximum g r a i n boundary oxida t ion pene t r a t ion depth w a s

measured. This process w a s repeated twelve t i m e s f o r each test

coupon. Altogether , 144 d a t a points w e r e c o l l e c t e d a t the t h r e e

oxida t ion temperatures, T, and a t var ious exposure t i m e s , t. The

regress ion a n a l y s i s of t h e da t a g ives the following empir ica l r e l a t i o n .

The maximum gra in

m'

n a m = a t exp(-Q/RT) (1)

where a i s i n cm; t , i n seconds; t he a c t i v a t i o n energy, Q i s 4.25 Kcal/mol;

T i n OK; and R = 1.987 cal/mou°K.

c o e f f i c i e n t of au to-cor re la t ion i s 0.96.

m . -3

a = 1 . 3 4 x 10 . n = 0.25. The

3

Reuchet e t a l . [32,331 s t u d i e d oxidized depth of MC c a r b i d e s i n

a cobalt-base supe ra l loy (Mar M509). They found a t i m e exponent

n = 0.25. S t o t t e t a l . [34 ,35 ] s tud ied i n t e r g r a n u l a r ox ida t ion i n

Ni -Cr a l l o y s , and they found n = 0.48 f o r 60Ni - 40Cr a l l o y , 0.51

f o r N i - 15.10- - 1.U a l l o y , and 0.66 f o r N i - 28.8Cr - 1 . O A 1 a l l o y .

They concluded t h a t t h e i n t e r g r a n u l a r oxide p e n e t r a t i o n depth i n N i - C r

a l l o y s followed a pa rabo l i c rate r e l a t i o n .

Grain boundary oxide pene t r a t ion i s c o n t r o l l e d by g r a i n boundary

d i f f u s i o n of oxygen, and g r a i n boundary d i f f u s i o n i s a func t ion of t h e

r e l a t i v e o r i e n t a t i o n s o f t h e two neighboring g r a i n s [36,37,38 b as

shown i n Figure 2. The v a r i a t i o n of g r a i n boundary d i f f u s i o n rate

could be one of t he causes f o r t h e s t a t i s t i c a l s c a t t e r of t h e measured

oxide pene t r a t ion depths.

A t any given combination of temperature , T, and exposure t i m e , t ,

t h e va lue of a can be c a l c u l a t e d from t h e measured a - va lue by us ing i m i

Equation (1) . The v a r i a t i o n of t h e c a l c u l a t e d a-values r e f l e c t s t h e

s t a t i s t i c a l s c a t t e r of the measured a -values. Thc Weibul l p l o t of

a l l of t h e L44 va lues of ai i s shown i n Figure 3 .

bu t ion func t ion is

m

The Weibull d i s t i i -

where P(a.) is t h e p r o b a b i l i t y of f ind ing an a-value less than ai

on a sec t ioned su r face . a is the l o c a t i o n parameter. I t is t h e

h o r i z o n t a i s h i f t f o r each of t he d a t a po in t s so t h a t a l l o f the

po in t s w i l l b e on a s t r a i g h t l i n e i n the p l o t . b is t h e s l o p e o f

t he l i n e , and i t is c a l l e d shape parameter o r Weibull modulus.

Q and no = a set the scale f o r t he Weibull d i s t r i b u t i o n . a. is

the value of (ai - a ) a t In l n { l / f l - P(pi>J} = 0. -3 Figure 3 , a u = 0.53 x 10

experimental d e t a i l s and a more

1

U

b 0 0

For t h e d a t a i n ' - 3 U

, b = 1.85, and a = 0 . 5 1 x 10 . The 0

4

detailed discussion on the oxide formation and the statistical scatter

.

are given in Reference [31].

If the grain boundary oxidation penetration rate is controlled

by the grain boundary diffusion rate, and if grain boundary diffusion

can be considered as a one-dimensional flow, the oxidation penetration

depth can be written as

0.5 a - at exp (-Q /2RT) m gb

(3)

is the activation energy of grain boundary diffusion. This result Qgb is certainly different from the empirical relation, Equation (1).

The coefficient of grain boundary diffusion is several orders of

magnitude higher than that of lattice diffusion. Nevertheless, the

grain boundary diffusion kinetics are affected by lattice diffusion.

Whipple [39] has analyzed the effects of lattice diffusion on grain

boundary diffusion. These effects for TAZ-8A have yet to be assessed

quantitatively.

The kinetics of grain boundary oxide penetration will certainly

be related to the morphology of the oxide. Grain boundary oxides

have two different shapes: pancake type and cone type. Furthermore,

the detailed chemical processes of oxidation have also to be taken into

consideration in a theoretical analysis. Grain boundary oxide penetration

is further complicated by the internal stresses caused by the oxide

forma tion.

For the moment, Equation (1) can be treated as an empirical

relation. Perhaps, the oxide penetration depth at a crack tip can be

written in the form

5

where D is diffusion coefficient, and C is the magnitude of the

diffusion jumping vector or interatomic spacing.

the function, F, are unknown. Assuming a simple power relation, we have

The details of

a = f3C(Dot/C)n exp(-nAH/RT) = atn exp(-Q/RT) (5) m

D is the diffusion coefficient at T = 0. a, B , and n are

constants. The apparent activation energy, Q, for grain boundary

oxide penetration is not necessarily equal to the activation energy

of diffusion, AH. If the penetration depth is dependent on both

grain boundary and bulk diffusions, am is related to both (D

0

t/C) gb

and (Dbt/C). D and D are grain boundary and bulk diffusion

coefficients.

gb b

.

6

111. THE INTERMITTENT MICRO-RUPTURE MODEL FOR HIGH TEMPERATURE FATIGUE CRACK GROWTH

Fatigue crack growth at elevated temperatures is sensitive to

both frequency and temperature. Figures 4a [40, 411 and 4b [421

show the frequency and temperature effects on the fatigue crack

growth in IN-100. The data merge onto two limiting lines, one

on the right and one on the left of the data band. Along these

two limiting lines, the fatigue crack growth rate is independent

of frequency and temperature. The right hand side limiting line

is for high frequency and low temperature. The left hand side

limiting line is for high temperature and low frequency. However,

it is not certain that the left limiting line always exits. Between

these two limiting lines, da/dN is sensitive to both frequency and

temperature. "da/dN" increases with temperature and decreases

with an increase in frequency.

At a constant AK level and at a given test temperature, the

more detailed frequency effects on the fatigue crack growth rate

are shown in Figure 5 [41,43-48 1. The cyclic crack growth rates,

da/dN, of a number of materials in the low frequency region are

inversely proportional to cyclic frequency, v , and are linearly

proportional to the length of the time period per cycle. The

time rate of the fatigue crack growth, da/dt = (da/dN)(l/v), is

constant. In this region, the fatigue crack growth is intergranular.

The fatigue crack growth rate decreases as cyclic frequency in-

At a very high frequency, the fatigue crack growth rate is creases.

independent of frequency and temperature. It corresponds to the right

7

hand side limiting line. At such a high frequency, the fatigue crack

growth is transgranular, and the abserved fatigue striations on ;1 crack surface

indicate that fatigue crack growth is caused primarily by crack tip

cyclic plastic deformation.

In the intermediate frequency region, a fatigue crack grows in a

mixed mode both intergranularly and transgranularly, and the growth

rate is sensitive to both frequency and temperature.

For constant-K tests at elevated temperatures, two crack growth

features are common: (i) the time rate of crack growth is constant,

(i.e. da/dt = constant) and (ii) crack growth is intergranular. Crack

growth at constant-K is often referred to as creep crack growth.

In the low frequency region, da/dN is inversely proportional

to frequency, w , and frequency is the inverse of the time period per

cycle. Therefore, in the low frequency region, the time rate

of fatigue crack growth is also constant as the creep crack growth

rate. Furthermore, fatigue crack growth in this region is also

intergranular. Therefore, fatigue crack growth in the low frequency

region, where the intergranular crack growth rate da/dN is inversely

proportional to v , is often referred to as creep crack growth.

However, a few questions remain unclear. Does creep crack

growth imply that the fatigue accelerated crack growth is caused by grain

boundary void nucleation and growth and/or by crack tip creep

deformation? Does the inverse relation between da/dN and v

preclude the possibilty that grain boundary oxidation is the under-

lying cause for the accelerated fatigue crack growth at elevated

temperatures?

cause of the accelerated fatigue crack growth at elevated temperatures.

In this section, oxidation will be analyzed as a possible

8

i ~~ ~~

In t h e low frequency region of Figure 5, t h e f a t i g u e c rack growth

rates of Inconel 718, Inconel X-750, Astroloy a t 7OO0C and 76OoC, and

Cr-Mo steels, are i n v e r s e l y propor t iona l t o frequency. The c y c l i c

l oad ing p a t t e r n s are a l s o shown in t h e f igu re .

As t ro loy , a hold t i m e , A t H at KmX w a s appl ied .

Cr-Mo steels, and Ast ro loy a t 7OO0C, a t r i a n g u l a r loading p a t t e r n w a s used.

For Inconel 718 and

For Inconel X-750,

Antolovich et al. [ 4 9 ] found t h a t oxide i n a smooth specimen

ruptured when t h e app l i ed stress reached a c r i t i ca l value. The app l i ed

stress a t rup tu re is i n v e r s e l y r e l a t e d t o t h e oxide s ize . The c r i t i ca l

c rack t i p oxide s i z e a t r u p t u r e must b e r e l a t e d t o t h e stress i n t e n s i t y

f a c t o r , K. The oxygen a r r i v i n g a t a c rack t i p w i l l have t o d i f f u s e

a long t h e g r a i n boundary i n t o the reg ion ahead of t he c rack t i p

forming oxide. When t h e c rack t i p g r a i n boundary oxide reaches t h e

c r i t i ca l size, 6a, t h e oxide w i l l r u p t u r e and t h e c rack w i l l grow

by t h e amount of 6a.

t h i s process of g r a i n boundary d i f fus ion , g r a i n boundary ox ida t ion ,

r u p t u r i n g of t h e g r a i n boundary oxide, and crack advancing w i l l b e

repea ted again.

g r a i n boundary oxides can reoccur i n t e r m i t t e n t l y many times dur ing a f a t i g u e cyc le .

Cof f in (1) has suggested t h i s process as a mechanism of t h e a c c e l e r a t e d

f a t i g u e c rack growth a t e l eva ted temperatures. I n t h i s p a p e r , a

q u a n t i t a t i v e model of i n t e r m i t t e n t micro-ruptures of g r a i n boundary

oxide w i l l be cons t ruc ted and i t w i l l be shown t h a t t h e i n t e r m i t t e n t

micro-ruptures of g r a i n boundary oxide can l e a d t o a f a t i g u e c rack

growth rate i n v e r s e l y propor t iona l t o v .

Once t h e crack t i p advances t o i t s new p o s i t i o n ,

This process of micro-ruptures of c rack t i p

The tests with ho:d time w i i i be anaiyzed first. h r i n g t h e

9

hold time, AtHaC

take place.

to the "tip" of the oxide. Therefore, the time increment, 6t,

necessary for the oxide starting from the crack tip, to reach the

critical rupture size, 6a, is given by Equations 44) and (5).

simple power relation, we have

KmX, a number of intermittent micro-ruptures will

Assume that every micro-rupture will advance the crack

For a

The number of micro-ruptures during At is H

1/ n m = AtH/6t = (At D /C)(BC/6a) H gb

I1 I 1 m is proportional to At Both m and At are inversely

proportional to frequency , W .

H' H

Fatigue crack growth per cycle is the sum of the rapid and

intermittent micro-ruptures per cycle.

(7) Y

- = a a dN

Substituting Equation (7) into Equation (8), we have

da/dN are inversely proportional to V .

3 For n = 0.25, da/dN is inverse ly p ropor t iona l t o 6a . Fatigue

c rack growth rate i n c r e a s e t a p i d l y as 6a becomes s m a l l . b a is

smaller i f t h e oxide is more b r i t t l e .

For a given material,6a and m are func t ions of K dur ing max

t h e hold t i m e . Therefore , w e have

as shown by t h e d a t a i n t h e low' frequency reg ion i n Figure 5.

For t h e t r i a n g u l a r loading p a t t e r n , l e t us assume t h a t

t h e c r i t i ca l c rack t i p oxide s i z e , 6a, a t rup tu re is a func t ion of

t h e c rack t i p f i e l d , t h e c rack t i p f i e l d can be cha rac t e r i zed by t h e

stress i n t e n s i t y f a c t o r , K, and t h e c rack t i p f i e l d is independent of

t h e c y c l i c frequency, V .

Figure 6 shows t h e t r i a n g u l a r loading a t two d i f f e r e n t f requencies .

(We use t h e t r i a n g u l a r loading a s an i l l u s t r a t i o n , bu t t h e fol lowing

a n a l y s i s is a p p l i c a b l e t o any o the r wave shape). I f t h e c rack t i p

f i e l d s a t K. are t h e same a t both of t hese two Erequenices, t h e c r i t i c a l

oxide p e n e t r a t i o n depths , 6a. a t rup tu re must be t h e same. During t h e

t i m e i n t e r v a l A t . a t K a number of i n t e r m i t t e n t micro-ruptures w i l l

t ake place. A t t h e same K. l eve l , t h e t i m e increment, 6 t i , necessary

f o r t h e oxide t o reach t h e c r i t i ca l s i z e , is d i r e c t l y r e l a t e d t o

1

1

1 i'

1

6ai, Equation (6) . The number of micro-ruptures , mi, dur ing t h e t i m e

i n t e r v a l , A t . a t Ki is simply A t i / 6 t i . "m" ' is p ropor t iona l t o A t and

i n v e r s e l y p ropor t iona l t o frequency, v . This inve r se r e l a t i o n between

1

m A t i , and u is t r u e a t any Ki-level.

The f a t i g u e c rack growth r a t e is the sum of t h e r ap id and i n t e r -

i'

mittent micro-ruptures a t a l l the K - l e v e l s dur ing one cycle . i

1 1

11 i i m is inve r se ly p r o p o r t i o n a l t o V a t any K-level. Therefore , da/dN

is i n v e r s e l y p r o p o r t i o n a l t o V .

The crack growth rate a t a frequency V can a l s o be w r i t t e n as

da -) is t h e c rack growth rate a t a r e f e r e n c e frequency, v . Equations

(11) and (12) f o r a r b i t r a r y wave shapes are de r ived w i t h t h e assumption

t h a t K is capable o f c h a r a c t e r i z i n g t h e c rack t i p f i e l d and the c rack

t i p f i e l d i s n o t a f f e c t e d by c y c l i c frequency. However, t h e c reep

stress r e l a x a t i o n a t a c rack t i p and the i n t e r n a l stress caused by

o x i d a t i o n have n o t been taken i n t o account. They could be t h e reasons

why some o f the d a t a i n t h e low frequency reg ion i n F igure 5 do not

obey t h e inve r se r e l a t i o n . No such assumption i s necessary fL)r the

d e r i v a t i o n of Equation (8) f o r t h e c rack growth rate wi th a holdtime

at Kmax*

dN vo 0

In t h e l o w frequency reg ion , when t h e r e i s enough t i m e f o r repea ted

g r a i n boundary ox ida t ion p e n e t r a t i o n s and r epea ted micro-ruptures

of t h e oxides t o t ake place, t h e f a t i g u e c rack growth rate along

an embr i t t l ed g r a i n boundary i s i n v e r s e l y p r o p o r t i o n a l t o t h e

f r e q u e n q , and crack grovth is i n t e r g r a n u l a r . Therefore , t hese

two c rack growth f e a t u r e s of i n v e r s e r e l a t i o n of da/dN wi th frequency

and i n t e r g r a n u l a r c rack growth can be caused by g r a i n boundary

ox ida t ion , and they cannot be a t t r i b u t e d t o creep cracking wi thout

1 2

I -

a d d i t i o n a l s u b s t a n t i v e experimental evidence. Such inve r se r e l a t i o n -

s h i p in t h e low frequency region i s shown i n Figure 5 f o r Inconel

718, Inconel X-750, Astroloy, and Cr-Mo steels.

.

In o rde r t o accelerate f a t i g u e c rack growth, t h e oxygen atoms must

reach t h e . c r a c k tip d u r i n g the process of c rack growth r a t h e r than

a f t e r . Therefore , t h e acce le ra t ed f a t i g u e c rack growth is c l o s e l y

r e l a t e d t o t h e rate of t h e t r a n s p o r t of oxygen.

For a given material a t a given app l i ed K level, t h e r e e x i s t s

an i n t r i n s i c c rack growth rate, (da/dN)f, which is caused by t h e

f a t i g u e process of c y c l i c crack t i p p l a s t i c deformation a lone , without

t h e e f f e c t of oxidat ion.

s p e c i e s does not have enough t i m e t o travel i n o rde r t o fo l low t h e

c rack t i p .

f a t i g u e c rack growth.

c y c l i c p l a s t i c deformation, and t h e growth is t r ansg ranu la r . The

da/dN is n o t l i m i t e d by the t r anspor t p rocess , and i t is independent

of frequency and temperature, so t h a t t h e c rack growth rate d a t a i n

F igures 4a and 4b w i l l merge t o t h e r i g h t hand s i d e l i m i t i n g l i n e

of h igh frequency and low temperature and t h e d a t a i n Figure 5 w i l l

level o f f i n t h e high frequency region.

deformation is dependent on frequency and temperature , da/dN

w i l l be weakly dependent on frequency and temperature.

A t a very high frequency, t h e d i f f u s i n g

Therefore , ox ida t ion does not have much e f f e c t on t h e

The f a t i g u e c rack growth is caused by

I f t h e c y c l i c p l a s t i c

I n Figure 5, between the low-frequency f a s t e r i n t e r g r a n u l a r

f a t i g u e c rack growth caused by t h e i n t e r m i t t e n t micro-ruptures, and

t h e high-frequency slower t r ansg ranu la r i n t r i n s i c f a t i g u e c rack

growth due t o c y c l i c p l a s t i c deformation, t h e r e e x i s t s a reg ion

of mixed mode of bo th in t e rg ranu la r and t r ansg ranu la r c rack growth,

as observed by Pe l loux and Huang [ 4 6 1 .

13

IV. DISCUSSIONS

The accelerated fatigue crack growth at elevated temperatures has

been attributed to either oxidation o r creep damage. Both oxidation

and creep have been shown as possible mechanisms for the high temperature

fatigue damage. Grain boundary void formation and cavitation are the

result of surface diffusion and/or grain boundary vacancy diffusion,

while grain boundary oxidation is primarily caused by the diffusion

of oxygen. The kinetics of the diffusions of vacancies and

oxygen atoms is shown schematically in Figure (7). The figure

indicates that one mechanism dominates in the high temperature region

and the other dominates in the low temperature region. Therefore,

the question is not which one of these two mechanisms causes high

temperature fatigue damage. The problem is to define the different

regions dominated by these two different mechanisms.

The quantitative relations between the diffusion rates and

the rate of oxide rupture and the rate of nucleation and growth of voids

and cavities, and their relations with fatigue crack growth have not

yet been established. It is obvious that fatigue crack growth rate

is not necessarily linearly proportional to the diffusion rates,

therefore, the activation energy for diffusion may not be equal to

the "activation energy" for fatigue crack growth.

relationships between da/dN and the diffusion rates of vacancies

and oxygen atoms depend on the detailed physical processes of

fatigue crack growth. If a simple power relationship exists between

da/dN and diffusion rate, then the rate, R (in Figure 7) can also be

interpreted as the crack growth rate caused by the diffusion process.

The functional

14

Without a clear understanding of the underlying reasons for

the observed fatigue crack growth behaviors, it is difficult and

unsafe to extrapolate a limited amount of experimental data to make

fatigue life predictions. For example, to extrapolate the

crack growth data in Figure 5, from the l o w frequency region into the

high frequency region or vise versa will underestimate the crack

growth rate. Therefore it is unsafe.

If creep is the damage mechanisms for high temperature fatigue,

and if grain boundary creep cavitation is induced by a tensile stress

together with vacancy diffusion, the tensile stress in a redundant

structure will decrease by creep stress relaxation, and the decreased

tensile stress will reduce the rate of cavitation. Thermal stress

is a transient stress. Thermal stress will be relaxed as creep

deformation takes place. In a sense, it is "redundant". Therefore,

creep damage may not be as important in thermal fatigue or thermal-

mechanical fatigue in structural components, where creep relaxation

takes place.

Multidisciplinary studies based on empirically observed physical

processes are needed to develop mechanistic and quantitative models

5or oxidation damage and creep damage in high temperature fatigue.

The first step in the development of such models for oxidation damage

is a quantitative analysis of grain boundary oxidation.

The high temperature fatigue crack growth model of intermittent

micro-ruptures of grain boundary oxides gives an inverse relationship

. between fatigue crack growth rate, da/dN and the cyclic frequency, v .

This inverse relation is observed for a number of high temperature alloys

1 5

in the low frequency region.

possible mechanism for the accelerated fatigue crack growth at elevated

temperatures.

Grain boundary oxidation is certainly a

Grain boundary oxidation was studied for samples free of stress.

The effects of an applied stress and an imposed cyclic strain on the

diffusion of oxygen and oxidation still need to be addressed.

Equation (1) is for grain boundary bulk oxide penetration. It

is conceivable that even a monolayer of oxide will reduce the grain

boundary cohesive strength and will accelerate fatigue crack growth.

As indicated by the above discussion on the needs for additional

knowledge, the work on the effects of oxidation on high temperature

fatigue life is far from completed.

the initial steps to construct a mechanistic and quantitative model

based on the empirical data of grain boundary oxide penetration.

This study is only one of

16

v. SUMMARY

Grkn

at elevated

AND CONCLUSIONS

boundary oxidation may accelerate

temperatures. The grain boundary

fatigue crack growth

oxidation kinetics

was studied.

from one grain boundary to another. The measured grain boundary

oxide penetration data agree well with the Weibull distribution.

A model of intermittent micro-ruptures of the grain boundary oxide

is constructed for the accelerated fatigue crack growth at elevated

temperatures.

model agrees well with the observed inverse relation between da/dN

f o r a number of high temperature alloys.

Grain boundary oxide penetration depth varies widely

The derived fatgiue crack growth rate based on the

1 7

References

L.F. Coffin, Jr., "Fatigue a t High Temperature - P r e d i c t i o n and I n t e r p r e t a t i o n , " P ~ c . 2 ~ 4 ~ 3 1 . Me&. Enghb. 1 8 8 , 109 (1974).

S.S. Manson, G.R. Halford, and M.H. Hirschberg, " Creep-Fatigue Analysis by Stra inrange Par t i t ion ing" , NASA TM X - 6 7 8 3 8 (1971).

S.S. Manson, G.R. Halford, and M.H. Hirschberg, "S t r a i n r a n g e P a r t i t i o n i n g - A Tool for Character iz ing High Temperature, Low Cycle Fatigue", NASA TM X-71691.. (1975).

D. Hul l and D.E. Rimer, "The Growth of Grain-Boundary Voids under Stress", Pkce. Mag. 4 , 6 7 3 (1959).

R.G. Fleck, D.M.R. Tapl in , and C . J . Beevers, "An I n v e s t i g a t i o n o f t h e Nucleation of Creep Cavities by IMV Elec t ron Microscopy", A& M d . 2 3 , 415 (1975).

B. J. Cane and G. W. Greenwood, "The Nucleation and Growth of Cavities i n I ron during Deformation a t Elevated Temperatures", M& S C i . 9, 55 (1975).

T.-J. Chuang, and.J.R. Rice, "The Shape of I n t e r g r a n u l a r Cracks Growing by Surface Diffusion", A& M e t . 2 1 , 1625 (1973).

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M.V. Speight and W. Beere, "Vacancy P o t e n t i a l and Voids Growth on Grain Boundaries'1, M a S G . 9 , 190 (1975).

W. Beere and M.V. Speight , "Creep Cavi ta t ion by Vacancy Diffusion i n P l a s t i c a l l y Deforming Solid", M& S G . 72, 172 (1978).

Non- I 1 T.-J. Chuang, K . I . Kagawa, J .R . Rice, and L.B. S i l l s , Equilibrtum Models f o r Di f fus ive Cavi ta t ion of Grain In t e r f aces" , A& M e t . 2 7 , 265 (1979).

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A. Needleman, and J . R . Rice, " P l a s t i c Creep Flow E f f e c t s i n Dif fus ive Cavi ta t ion of Grain-Boundaries" , D i v h i o n 0 6 Engh. RepohX, Bmwn U ~ v e h b L t g (1980).

A . S . Argon, I . W . Chen, and C.W. Lau, 11 I n t e r g r a n u l a r Cavi ta t ion i n Creep : ed. by P&oux, R . M . and S.takk66, N.S. , A l M E , 46 (1980).

Theory and Experiments", "Cheep- Fatigue- Envhonmertt 7n.tehaction"

J. L. Bassani, and A. Saxena , "Time-Dependent Fat igue Crack Growth Behavior a t Elevated Temperature'', Aknnawbhooh Condmence on "Li d i d o n @ R High Tempehatwre Gas T h i n e M a t d a h " , EPRZ, (198

18

[17] Y. Oshida and H.W. Liu, "Oxidation and Low Cycle Fatigue Life Prediction", Pmc. 06 the Tkitrd A n n u l Wo&hop on T h i n e f fo t S e c t i o n JechnoLogy (HOST) Pmject, 32 1 (1984).

1181 L.F. Coffin, Jr., "The Effect of High Vacuum on the Low Cycle Fatigue Law", Thand. 7, 17771 (1972).

JOWL. 06 M a t s . 7, 299(1972). [19] H.D. Solomon,. "Low Cycle Fatigue Crack Propagation in 1018 Steel",

1201 H.D. Solomon, "Frequency Dependent Low Cycle Fatigue Crack Propagation", Met. T/cans. 4, 341 (1973).

[21] H.D. Solomon, and L. F. Coffin, Jr. , "Effects of Frequency and Environment on Fatigue Crack Growth in A286 at llOO°F", ASTM STP 520 on "FaaXgue at ELevctted Tempcmu3,ae" (1973).

[22] L.A. James, and R.L. Knecht, "Fatigue-Crack Propagation Behavior of Type 304 Stainless Steel in a Liquid Sodium Environment", M e t d T m . 6, 109 (1975).

[23] L.A. James, "Some Questions Regarding the Interaction of Creep and Fatigue", ,Tout. 06 Eng. Ma,?&&- and Technology, A S M E , 98, 235 (1976).

[24] M.W. Mahoney and N.E. Paton, "The Influence of Gas Environments on Fatigue Crack Growth Rates in Types 316 and 321 Stainless Steels", Nu&m Tech., 23, 290 (1974).

[25] G.J. Hill, -' "The Failure of Wgought 1% Cr-M-V Steel in Reverse- Bending High Strain Fatigue at 530 C", Thetunae and High-Stmin Fatigue, The M c t u O and Metaeeurrgy TUX, 3 1 2 (1967).

[26] D.J. White, "Effect of Environment and Hold Time on the High Strain Fatigue Endurance of 1/2 percent Molybdenum Steel", Puke. TmX. 06 Me&. E n g i n e m , P& I , 184, 2 2 3 (1969).

[27] A.J. Nachtigal, S.J. Klima, J.C. Freche and C.A. Hoffman,. "The Effect of Vacuum on the Fatigue and Stress-Rupture Properties of S-186 and Inconel 550 at 1500°F", NASA Tech. Note U-2898 (1965)-

[28] H.W. Liu and J.J. McGowan,. "A Kinetic Analysis of High Temperature Fatigue Crack Growth", SU&JU Met. 15 , 507 (1981)-

[29] J.J. McGowan and H.W. Liu, "A Design Approach for Correlating High Temperature Fatigue Crack Growth Over a Wide Range of Papameters", JOWL. 06 Eng. M a . and Tech. Tmm. ASME, 203, 246 (1981).

6

[30] S.D. Antolovich, S. Liu and R. Baqr, . "Low Cycle Fatigue Behavior of Rene 80 at Elevated Temperature", M a . i 6 i i t A . IZA, 373 (1981).

[31] Y. Oshida and H.W. Liu, "Grain Boundary Oxidation and an Analysis of the Effects of Pre-Oxidation on Subsequent Fatigue Life", ASTM Sympodium on "Low Cyde Fatigue - D h e c t i o n 604 &e FuZwre" (1985).

19

[ 34

[ 35

J. Reuchet and L. Remy,"High Temperature Fatigue Behavior of a Cast Cobalt-Base Superalloy", F d g u e 06 Engk. M a t ~ ~ i d ~ and S k u c W ~ e \ l , 2, P * 5 1 (1979).

J. Reuchet and L. 'Remy,"Fatigue Oxidation Interaction in a Superalloy- Approach of Life Prediction in High Temperature Low Cycle Fatigue", M&. Tw. , 14A, p. 141 . (1983).

F.H. .Stott, G.C. Wood, Y. Shida, D.P. Whittle, and B.D. Bastow, "The Development of Internal and Intergranular Oxides in Nickel- Chromium-Aluminum Alloys at High Temperature", COWL. s&., 2 1 , p. 599 (1981).

Y. Shida, G.C. Wood, F.H. Stott, D.P.. Whittle and B.D. Bastow "Intergranular Oxidation and Interal Void Formation in Ni-40% Cr Alloys", COWL. Sci., 2 1 , p.561, (1981).

L. Couling and R. Smoluchowshi, "Anisotropy of Diffusion in Grain Boundaries", J. AppL PhqA. 25, 1538. (1954)

W.R. Upthegrove and N.J. Sinnot, 11 Grain Boundary Self- Diffusion of Nickel", T W . ASM, 50, ( 1 9 5 8 ) -

D. Turnbull and R. Hoffman, "The Effect of Relative Crystal and Boundary Orientations of Grain Boundary Diffusion Rates", A c b M e t . 2 , 4 1 9 . (1954)-

R.T.P. Whipple, "Concentration Contours in Grain Boundary Diffusion", Pkie. Mug. 45, 1 2 2 5 . (1954).

R.M. Wallace, C.G. Annis, Jr., and D.L. Sims, Ap p 1 i cat i o n o f Fracture Mechanics at Elevated Temperatures". AFML-TR- 76- I 7 6 (1976).

Cumulative J.M. Larsen, B.J. Schwartz and C.G. Annis, Jr. 11

Damage Fracture Mechanics Under Engine Spectra", AFML-TR- 7 9 - 4 7 5 9 (1980).

D.E. Macha, , "Fatigue Crack Growth Retardation Behavior of IN-100 at Elevated Temperature", Eng. F t r a a e M e c h a n i c n , 1 2 , 1 (1979).

T. Weerasooriya and T. Nicholas, "Hold-Time Effects in Elevated Temperature Fatigue Crack Propagation", AFWAL-TR- 64-4 164 I (1985).

F. Garrielli and R.M. Pelloux, 11 Effect of Environment on Fatigue and Creep Crack Growth in Inconnel X-750 at Elevated Temperature", M d . Ttravtb. 13A, 1083 (1982).

M. Zhou and F. Gabrielli, 11 Some Aspects of Frequency on High Temperature Fatigue in Inconnel X-750", Z. M c t d X h d e , 7 4 , 6 3 9 (1983).

R.M. Pelloux and J.S . Huang, II Creep-Fatigue-Environment Inter- actions in Astroloy","Cteep- Fatigue- EnvhnmevLt lntmaci2on" ed . by R.M. P&oux and N.S. SXolodd, AIME, 151 (1980).

20

[471 K.M. Nikbin and G.A. Webster, "Prediction of Crack Growth Under Creep-Fatigue Loading Conditions", ASTM Sympaaium an I' Law C y d e Fa t igue - D ~ ~ c L I Z O ~ 604 Rhe Fu--twre" (1985).

The Effect of Frequency upon the Fatigue-Crack I t [ 4 8 ] L.A. James, Growth of Types 304 Stainless Steel a t 1000°F" ASTM STP 513 an " S i x m Anaeybd and G/raw;th 0 6 Cnachn", 2 1 8 . (1972).

[ 4 9 ] S.D. Antolovich, E . Rosa, and A. Pineau, "Low Cycle Fatigue of Rene 77 a t Elevated Temperatures", Mat. SCi. and Engk , 47, 4 7 . (1981).

21

Figure 1 Cross-sec t ion of oxidized coupon of TAX-8A a! 1000°C f o r 500 h o u r s

22

Boundary angle, (deg.)

Figure 2 Grain boundary angle effect on the penetration of radioactive nickeloalong nickel bicrystals grain boundaries at 1050 C (37)

23

"I "I ( ! D ) d - 1 I

I

d I rn

I

I l l I '

I-

-F

- I

\ 0

\ --

I + N ! W

24

n n v

E ri \ 2 E c

x Q

I . I I I ni cu m ' b' &"

0 I - 0 I '0 -

-0 Y

0

d (0

g,

P a

0 N

0

0 0 - cu 0 \

m o o o o o o o o o N I o r n O I n - l o r n - -

U

x a

8

8

b

-J W z

i<

z

t

c %

1 1 I I I I " I I I B 1 I 1

O

a 4- 0

D -Q

OQ

n 0

K

Ki

. -

Figure 6 Cyclic loading at t w o different frequencies

27

I

In R

Figure 7 The schematic plot of t w o rate processes

28

1. Report No.

NASA CR-179529

Gra in Boundary Ox ida t ion and Fat igue Crack Growth a t E levated Temperatures

- .-

2. Government Accession No.

7. Author@)

H.W. L i u and Yoshik i Oshida

16. Abstract

9. Performing Organization Name and Address

Syracuse U n i v e r s i t y Dept. o f Mechanical and Aerospace Engineer ing Syracuse, New York 13244

Nat iona l Aeronaut ics and Space Admin is t ra t ion Lewis Research Center Cleveland, Ohio 44135

12. Sponsoring Agency Name and Address

IY. Security Ciassii. (ui ihis iepuiij

u n c l a s s i f i e d

3. Recipient's Catalog No

- 20. Socuriiy Ziassii. (oi ihis payuj 2 i . Go. of pages LL. riiLe

j 29 Unc lass i f i ed

5. Report Date

October 1986 6. Performing Organization Code

8. Performing Organization Report No.

None

10. Work Unit No.

533-04-1 1 11. Contract or Grant No

NAG3- 348

13. Type of Report and Period Covered

Contractor Report F i n a l

14. Sponsoring Agency Code

15. Supplementary Notes

P r o j e c t Manager, Jack Telesman, St ructures D i v i s i o n , NASA Lewis Research Center.

.. - 17. Key Words (Suggested by Author@)) 118. Distribution Statement

Ox ida t ion Fat igue crack growth Elevated temperatures

I

U n c l a s s i f i e d - u n l i m i t e d STAR Category 26

.