N E W QUALITY C O N T R O L REQULREh4ENTS

FOR SURFACE INTEGRITY

John F. K a h l e s , V i c e P r e s i d e n t , and Michae l F i e l d , P r e s i d e n t M e t c u t R e s e a r c h A s s o c i a t e s Inc. , Cincinnat i , Ohio

f o r

1972 ASM M a t e r i a l s E n g i n e e r i n g C o n g r e s s C leve land , Ohio

October 16 -19 , 1972

I N T R O D U C T I O N

D u r i n g the p a s t s e v e r a l y e a r s , a t t e n t i o n h a s been d r a w n s h a r p l y t o m a t t e r s

of s a f e t y a n d r e l i ab i l i t y a s a r e s u l t of changing a t t i t udes and t r e n d s in m a n y

s e c t o r s of o u r soc i e ty . F o r e x a m p l e :

T h e l a w c o u r t s have handed down d e c i s i o n s which m a k e i t e s s e n t i a l

f o r m a n u f a c t u r e r s and d i s t r i b u t o r s t o r e c o n s i d e r t h e i r pos i t ion on

m a t t e r s c o n c e r n i n g p r o d u c t l i a b i l i t y a s appl ied to a l l t y p e s of c o n -

s u m e r p r o d u c t s and e s p e c i a l l y c a p i t a l equ ipmen t , such a s n ~ a c h i n c

t o o l s , which wil l b e i n a l i a b i l i t y s i t ua t ion f o r m a n y y e a r s .

T h e D e p a r t m e n t of Defense a n d the c o r n m e r c i a l a i r l i n e s a s wel l a r e

c a l l i n g f o r g r e a t e r r e l i a b i l i t y a n d s i m u l t a n e o u s l y spec i fy ing m o r e

c r i t i c a l a e r o s p a c e componen t d e s i g n s .

T h e au tomot ive i n d u s t r y h a s b e e n u n d e r p r e s s u r e t o i n c r e a s e s a f e t y

and r e l i a b i l i t y a s ev idenced by e x t e n s i v e r e c a l l p r o g r a m s , s a fe ty c a r

d e s i g n p r o g r a m s , an t ipo l lu t ion d e v i c e s , and new type eng ines which

a l m o s t c e r t a i n l y wil l i n c o r p o r a t e m o r e c r i t i c a l l y s t r e s s e d componen t s .

G r o u n d t r a n s p o r t a t i o n i n t h e f o r m of h igh speed t r a i n s a n d r evo lu t iona ry

t y p e v e h i c l e s i s r e c e i v i n g w o r l d w i d e a t t en t ion in i n d u s t r y and gove rnmen t .

Key i s s u e s undoubtedly wil l i n c l u d e m a t t e r s of s a f e t y and r e l i ab i l i t y .

A t o m i c p o w e r p l an t s have a l r e a d y s u f f e r e d f r o m a d v e r s e e x p e r i e n c e s ,

a n d t h e r e f o r e i n c r e a s e d p r e c a u t i o n s wi l l b e taken i n m a t e r i a l s and

p r o c e s s e s a s s o c i a t e d with p l an t d e s i g n and cons t ruc t ion .

T h e Occupa t iona l Sa fe ty and H e a l t h Ac t (OSHA) i s be ing i m p l e m e n t e d

s o wide ly t h a t a l l equ ipmen t u s e d i n i n d u s t r i a l p l a n t s m u s t be r e -

a s s e s s e d f r o m a s a f e t y and r e l i a b i l i t y s tandpoint .

C o n c e r n s f o r i n c r e a s e d s a f e t y and r e l i a b i l i t y r e l a t i v e t o a r e a s noted above

h a v e a l r e a d y in i t i a t ed m a n y new r e s e a r c h and deve lopmen t planning e f f o r t s .

One of t h e s e w a s sponsorec l by the Na t iona l M a t e r i a l s Advisory B o a r d ( N M A B )

of the Nat iona l R e s e a r c h Counci l on " T e s t i n g for P r e d i c t i o n of M a t e r i a l (1)<:

P e r f o r m a n c e in C o m p o n e n t s and S t r u c t u r e s . " Conclus ion N u m b e r 3

on p a g e 3 - 2 of t h i s e x c e l l e n t r c p o r t s t a t e s :

"Conclus ion :

In t h e c o u r s e of d e s i g n evolu t ion , d c s i g n o r manufac tu r ing m o d i -

f i ca t ions a r e so rne t in l e s i n t r o d u c e d which affect p e r f o r m a n c e

l i fe deduced f r o m the or ig ina l p r e d i c t i v e t e s t s which w e r e r u n

t o v e r i f y d e s i g n . S e r v i c e p e r f o r m a n c e f a i l u r e i s oftcn o b s c r v e d

t o be a s s o c i a t e d wi th the a l t e r a t i o n of t he ve r i f i ed d e s i g n ' s

m a t e r i a l s o r p r o c e s s e s without r e v a l i d a t i o n u t i l i z ing the appl i -

c a b l e p r e d i c t i v e t e s t s of t he o r i g i n a l d e s i g n p r o c e s s .

"Recommendation:

C h a n g e s i n m a t e r i a l s a n d / o r p r o c e s s e s a f t e r in i t ia l p r e d i c t i v e

t e s t i n g s h a l l on ly b e m a d e a f t e r d e s i g n r e v e r i f i c a t i o n , r epea t ing

t h e a p p l i c a b l e p r e d i c t i v e t e s t s e m p l o y e d f o r the o r ig ina l v e r i f i -

ca t ion and r e a n a i y z i n g the applicable d a t a g a t h e r e d a s in the

o r i g i n a l v e r i f i c a t i o n .

Wi th r e f e r e n c e t o t h e above va l id conc lus ion , i t i s i m p o r t a n t t o r e c o g n i z e t h a t

m o s t m a n u f a c t u r i n g p e r s o n n e l , inc luding d e s i g n and manufac tu r ing e n g i n e e r s ,

m e t a l l u r g i s t s , a n d qua l i t y c o n t r o l e n g i n e e r s , a r e not suff ic ient ly a w a r e of

s o m e of t he s e r i o u s v a r i a t i o n s in m e c h a n i c a l p r o p e r t i e s which o c c u r a s a

r e s u l t of v a r i a t i o n s i n o u r c u r r e n t p r o d u c t i o n p r a c t i c e s . I n o r d e r t o a c h i e v e

r e l i a b i l i t y and s a f e t y in a component being m a c h i n e d o r g r o u n d , i t will be

n e c e s s a r y t o s p e c i f y m a n u f a c t u r i n g p a r a m c t c r s i n m u c h m o r e de ta i l than

h a s b e e n t h e c u s t o m e v e n in o u r m o s t p r o g r e s s i v e manufac tu r ing p l an t s .

A p r o g r a m which h a s p r o v i d e d c o n s i d e r a b l e p e r s p e c t i v e conce rn ing the

p r o b l e m s i n d u s t r y i s f ac ing in achiev ing o r d e r of magn i tude i m p r o v e m e n t s

;k N u m b e r s in p a r e n t h e s e s i nd ica t e r e f e r e n c e s .

i n product qua l i t y i s t he S u r f a c e I n t e g r i t y P r o g r a m s p o n s o r e d by the

Manufac tu r ing Techno logy Divis ion of t h e A i r F o r c e M a t e r i a l s 1,aboratory. (2, 3 Sr 4 )

In r e l a t i o n s h i p t o v a r i o u s i n t e r e s t s i n i n c r e a s i n g the qua l i ty a s s u r a n c e of

s t r u c t u r a l m a t e r i a l s ( t h e sub jec t of t h i s m e e t i n g ) , s u r f a c e in t eg r i t y s tud ie s

h a v e r e v e a l e d s o m e i m p o r t a n t d a t a f o r c o n s i d e r a t i o n by anyone s e r i o u s l y

i n t e r e s t e d i n p lanning f o r t h e e n h a n c e m e n t of s a f e t y and r e l i ab i l i t y . T h e

p r i n c i p a l p u r p o s e of t h i s p a p e r , t h e r e f o r e , i s t o p r e s e n t d a t a which wil l

s u p p o r t the fol lowing conc lus ions :

M a n y s u r f a c e a l t e r a t i o n s p r o d u c e d by v a r i o u s m a t e r i a l r e m o v a l

p r o c e s s e s h a v e a d e t r i m e n t a l i n f luence on the m e c h a n i c a l p r o p e r t i e s

a n d a r e not d e t e c t a b l e by e q u i p m e n t p r e s e n t l y u s e d f o r nondes t ruc t ive

t e s t i n g a s a f i na l i n spec t ion m e t h o d .

A s a r e s u l t of (1 ) above , i t i s a b s o l u t e l y e s s e n t i a l a t t h i s t i m e t o r e l y

upon i n - p r o c e s s c o n t r o l p r o c e d u r e s i n o r d e r t o deve lop s t r u c t u r a l

i n t e g r i t y . I t shou ld b e e m p h a s i z e d t h a t su i t ab l e nlar iufactur ing

m e t h o d s c a n b e e s t a b l i s h e d b y us ing a c c e p t e d t e s t i ng and inspec t ion

p r a c t i c e s , none of which a r e s u i t a b l e , h o w e v e r , a s NDT m e t h o d s

u n d e r p r o d u c t i o n cond i t i ons i n t h e shop .

T Y P I C A L S U R F A C E ALTERATIONS NOT D E T E C T A B L E ";Y NDT

F i g u r e s 1 t h r o u g h 5 a r e e x a m p l e s of a f e w of t h e types of s u r f a c e a l t e r a t i o n s

wh ich a r e not d e t e c t a b l e by n o n d e s t r u c t i v e t e s t i n g e q u i p m e n t ; a p p r o p r i a t e

d e s c r i p t i o n s a c c o m p a n y e a c h f igu re . T h e s e s u r f a c e condi t ions a r e t yp ica l of

t h o s e c r e a t e d d u r i n g m a t e r i a l r e m o v a l and o t h e r t y p e s of manufac tu r ing

p r o c e s s e s and a r e t h e t y p e s of d e f e c t s wh ich c a u s e t h e lower ing of fat igue

s t r e n g t h a s i l l u s t r a t e d in F i g u r e s 6 and 8. T h e s e c h a r t s show e x a m p l e s of

w ide v a r i a t i o n s in fa t igue s t r e n g t h a s a func t ion of t h e type of m a t e r i a l r e m o v a l

p r o c e s s u s e d a n d a l s o a s a funct ion of t h e s p e c i f i c p a r a m e t e r s s e l e c t e d f o r a

p a r t i c u l a r m a t e r i a l r e m o v a l p r o c e s s . E x t e n s i v e addi t iona l d a t a for o the r

m a t e r i a l s a n d p r o c e s s e s m a y be found in R e f e r e n c e s 2, 3 and 4.

F A T I G U E D A T A I N SUPI'OII T 01.' IN -13110CESS C O N T R O L

F r o m F i g u r e 6 , s e v e r a l impor tan t conclus ions can be reached , probably the

m o s t i m p o r t a n t of which i s that conventional gr inding often shows g r e a t

t endenc ies t o a c t abus ively toward a l a r g e v a r i e t y of a l loys used for production

of c r i t i c a l p a r t s . T h i s conf i rms s u s p i c i o n s held in the a e r o s p a c e indust ry for

m a n y y e a r s r e l a t i v e t o the grinding of s t r u c t u r a l m a t e r i a l s . On the other hand,

gen t l e gr inding ( s o m e t i m e s cal led "low s t r e s s " gr inding) does provide excellent

f a t igue s t r e n g t h and when applied in p roduc t ion h a s been shown t o e l iminate

c r a c k i n g of v e r y sens i t ive a l loys . Gen t l e o r low s t r e s s grinding conditions

a r e d e s c r i b e d in de ta i l i n R e f e r e n c e s 2 and 3. In g e n e r a l , they a r e es tabl i shed

i n p roduc t ion by simultaneously reduc ing gr inding wheel s p e e d s , lower ing

downfeed o r infeed r a t e s , using s o f t e r gr inding whee l s , and applying v e r y

a c t i v e g r ind ing o i l s r a t h e r than w a t e r so luble o i l s o r emuls ions . F o r o p e r a -

t i o n s such a s tu rn ing , mi l l ing , d r i l l ing , e t c . , gent le m a t e r i a l r e m o v a l conditions

a r e s e t up by us ing v e r y s h a r p tools and us ing machining p a r a m e t e r s which

y ie ld long tool l i fe .

With r e f e r e n c e t o i n - p r o c e s s con t ro l , l ow s t r e s s gr inding h a s been shown to

be a n e x t r e m e l y r e l i a b l e finishing p r o c e s s and one which i s capable of producing

v e r y h igh qual i ty s u r f a c e s . I t has b e e n employed in l a r g e - s c a l e production

o p e r a t i o n s t o e l i m i n a t e c r a c k i n g of c a s t and wrought n ickel b a s e high t e m p e r a -

t u r e a l loys u s e d for b lades in a i r c r a f t engine and e l e c t r i c power genera t ion

equ ipment . F i g u r e 7 ( 5 ) shows zyglo ve r i f i ca t ion of the qual i ty of s u r f a c e

p r o d u c e d b y l o w s t r e s s grinding. T h e zyglo indica t ions i n F i g u r e 7a, 7b and 7c

r e v e a l the p r e s e n c e of c r a c k s , voids , and o t h e r s u r f a c e d e f e c t s caused by l e s s

t h a n o p t i m u m gr inding condit ions.

F i g u r e 8 p r o v i d e s s o m e v e r y in te res t ing d a t a with r e f e r e n c e t o fatigue s t rength

of a widely u s e d a e r o s p a c e nickel b a s e high t e m p e r a t u r e al loy. The al loy i s

v e r y p r o n e t o w a r d d a m a g e i n conventional g r ind ing but , a s notcd e a r l i e r , i t

r e s p o n d s w e l l when low s t r e s s grinding p a r a m e t e r s a r e u sed . EDM p r o c e s s i n g

d r o p s f a t igue s t r e n g t h s h a r p l y to a l e v e l of 22, 000 p s i both in roughing and

f in i sh ing o p e r a t i o n s . D u r i n g the finis11 o p e r a t i o n , the r e c a s t l a y e r p roduced

w a s o n l y . 0001 in . to .0002 in. t h i c k . F o r c r i t i c a l l y s t r e s s e d applications,

i t i s o f ten n e c e s s a r y to r e m o v e the E D M s u r f a c e l a y e r by I-means of convent iona l

m a c h i n i n g o p e r a t i o n s , s u c h a s g r ind ing , r e a m i n g , and honing. It i s p o s s i b l e

t o r e s t o r e t he f a t i gue s t r e n g t h of a n EDM s u r f a c e by shot peening, a s shown

i n F i g u r e 8 . A w o r d of caut ion i s i n o r d e r , f o r i t r e m a i n s to be p roved

w h e t h e r s h o t peen ing w i l l p rov ide a s i m i l a r r e s t o r a t i o n of p r o p e r t i e s i n

p r o d u c t i o n p a r t s i n s e r v i c e .

E n g i n e e r s h a v e f r e q u e n t l y r e g a r d e d e l e c t r o c h e m i c a l mach in ing ( E C M ) a s a n

o p e r a t i o n which would m i n i m i z e s u r f a c e a l t e r a t i o n s . Most a l l o y s show l o w e r

f a t i g u e s t r e n g t h a f t e r E C M . R e f e r r i n g to F i g u r e 8 , Inconel 718, f o r example ,

s h o w e d a l o w e r i n g f r o m 60, 000 p s i f o r low s t r e s s g r ind ing to 39, 000 p s i a f t e r

E C M . I t i s c u s t o m a r y p r a c t i c e i n i n d u s t r y t o shot peen a f t e r E C M on c r i t i c a l

s u r f a c e s . T h e d a t a i n F i g u r e 8 c o n f i r m the adv i sab i l i t y of t h i s p r a c t i c e on bo th

e l e c t r o p o l i s h e d ( E L P ) a n d E C M s u r f a c e s .

B a s e d upon M e t c u t ' s s u r f a c e i n t e g r i t y e x p e r i e n c e ga ined a s a r e s u l t of con-

t r o l l e d t e s t i n g p r o g r a m s a n d app l i ca t ion e x p e r i e n c e i n r e l a t i o n t o p roduc t ion

p r o b l e m s , i t a p p e a r s bo th e s s e n t i a l a n d f e a s i b l e to r e l y upon i n - p r o c e s s

c o n t r o l t o i m p r o v e t h e q u a l i t y of m a n u f a c t u r e d p r o d u c t s . By c o n t r a s t , s o m e

of t h e f i n a l i n s p e c t i o n p r o c e d u r e s c u r r e n t l y be ing used a r e of ten not app l i cab le

b e c a u s e t h e y l a c k s e n s i t i v i t y t o i s o l a t c t he t y p e s of s m a l l d e t r i m e n t a l a l t e r a t i o n s

s h o w n i n F i g u r e s 1 t h r o u g h 5.

MISC ELLANEOUS CONS1 DEIIATIONS CONC EIINING

QUALITY ASSURANCE O F S T R U C T U R A L MATERIALS

Sur face F i n i s h

Frequen t ly , des ign and manufac tu r ing e n g i n e e r s s p e c i f y s u r f a c e finish

r e q u i r e m e n t s f o r c o n t r o l of quali ty. The accep ted s t andard fo r Surface

T e x t u r e in the U . S . i s ANSI 1346. 1. (6) F r o m e x p e r i e n c e gained to da te , i t

a p p e a r s tha t i n d u s t r y and government should r e a s s e s s careful ly the ro le of

s u r f a c e f in ish i n des ign and manufac tu re of s t r u c t u r a l components . F r o m

s u r f a c e i n t e g r i t y d a t a developed t o da te , i t a p p e a r s that f o r s t r u c t u r a l

components having a s u r f a c e f in ish i n a r ange of 10- 125 m i c r o i n c h e s AA,

s u r f a c e f in i sh cannot i t s e l f b e used a s a m e a s u r e of o r f o r con t ro l of s u r f a c e

i n t e g r i t y a s eva lua ted b y fat igue t e s t ing . Unt i l addi t ional m u c h needed data

a r e m a d e ava i l ab le , m a n u f a c t u r e r s of c r i t i c a l components a r e encouraged to

develop e x p e r i m e n t a l p r o g r a m s fo r the p u r p o s e of opening up s u r f a c e f inish

r e q u i r e m e n t s , t h e r e b y reduc ing c o s t s .

F i g u r e 9 shows d a t a upon which the above c o m m e n t s w e r e m a d e . These data

show tha t f o r t h r e e d i f fe ren t c l a s s e s of m a t e r i a l s t e s t ed , even though fine

f in i shes w e r e developed, the endurance l i m i t w a s not i n c r e a s e d . Only when

gen t l e gr inding condi t ions w e r e employed w a s s o m e ' i m p r o v e m e n t noted with

f ine f in i shes and e v e n then the i m p r o v e m e n t was d i sp ropor t iona te ly s m a l l . I t

should b e noted, however , t h a t c lose d i m e n s i o n a l t o l e r a n c e s cannot be speci f ied

without c o n s i d e r i n g s u r f a c e f inish. In addi t ion , s u r f a c e f in ish i s of cons iderable

i m p o r t a n c e i n the des ign , manufac tu re , and s e r v i c e p e r f o r m a n c e of mat ing

s u r f a c e s s u c h a s i n b e a r i n g s , c a m s , g e a r s , e t c .

Eng inee r ing Design Data

T h e fat igue d a t a shown i n F i g u r e s 6, 8 and 9 prov ide in fo rmat ive data on the

e n d u r a n c e l i m i t s a s s o c i a t e d with v a r i o u s t y p e s of p r o c e s s i n g . This s e t of da ta ,

typ ica l of a m u c h l a r g e r s e t a l r e a d y ava i l ab le , r a i s e s thought- provoking ques t ions

i n r e l a t ionsh ip to des ign data . T h e s e da ta sugges t the urgent need fo r a

r e q u i r e m e n t to develop handbook da ta f o r impor tan t engineer ing m a t e r i a l s

f o r a l l c o m m o n l y used p r o c e s s e s f o r f inishing the s u r f a c e s of c r i t i c a l p a r t s .

Such da ta could be incorpora ted into the "Aerospace S t r u c t u r a l M a t e r i a l s

Handbook" (79 . At p r e s e n t , s o m e d a t a a r e a l r e a d y avai lable f r o m the

Manufactur ing Technology Divis ion ' s S u r f a c e In tegr i ty P r o g r a m fo r inclusion

i n f u t u r e s u p p l e m e n t s of the above handbook. E n g i n e e r s cannot be expected

t o d e s i g n highly s t r e s s e d p a r t s f o r s t r u c t u r a l p u r p o s e s without in i t ia l ly

f ac to r ing i n the se lec t ion of specif ic manufac tu r ing p r o c e s s e s and contro l of

s p e c i f i c manufac tu r ing p a r a m e t e r s f o r a l l c r i t i c a l p a r t s .

In- P r o c e s s Speci f ica t ions

E a r l i e r i n th i s p a p e r i t was s t a t ed tha t i n - p r o c e s s con t ro l can b e and h a s been

u s e d s u c c e s s f u l l y f o r manufac tu r ing p u r p o s e s in Lieu of f inal inspect ion p r a c t i c e s .

S u c c e s s of i n - p r o c e s s c o n t r o l s e e m s to b e b a s e d upon the intel l igent s t ruc tu r ing

of a c o n t r o l s y s t e m which inc ludes a t l e a s t : 1) Set t ing up a s y s t e m a t i c rne ta l lurgica l

and m e c h a n i c a l t e s t ing p r o g r a m f o r m a t e r i a l s and p r o c e s s e s f o r which data a r e

not ava i l ab le . With r e g a r d to th is r e c o m m e n d a t i o n , i t should be emphasized

t h a t t h e r e is no diff icul ty in identifying s u r f a c e a l t e r a t i o n s and m e a s u r i n g the i r

inf luence , but t h i s r e q u i r e s m e t a l l u r g i c a l sect ioning f o r m i c r o s c o p i c examination.

A s noted e a r l i e r in th i s p a p e r , ident i f ica t ion of s u r f a c e de fec t s is difficult when

NDT condi t ions a r e r e q u i s i t e . 2 ) Wri t ing and publishing i n - p r o c e s s speci f ica t ions .

3 ) Developing educa t iona l p r o g r a m s t o acqua in t pe r sonne l with s u r f a c e in teg r i ty

d a t a and new qua l i ty c o n t r o l r e q u i r e m e n t s .

1. N a t i o n a l R e s e a r c h C o u n c i l . May 1 9 7 2 . T e s t i n g f o r p r e d i c t i o n o f m a t e r i a l p e r f o r m a n c e i n c o m p o n e n t s

a n d s t r u c t u r e s . P u b l i c a t i o n No. NMAB 288 . W a s h i n g t o n , D . C . : N a t i o n a l Academy o f S c i e n c e s - N a t i o n a l Academy o f E n g i n e e r i n g .

2 . Kos ter , W . P . ; F i e l d , M i c h a e l ; F r i t z , L . J . ; e t a l . March 1 9 7 0 . S u r f a c e i n t e g r i t y o f m a c h i n e d s t r u c t u r a l

c o m p o n e n t s . AFML-TR-70-11. C i n c i n n a t i , O h i o : M e t c u t R e s e a r c h A s s o c i a t e s I n c .

3. Koster , W . P . ; e t a l . A p r i l 1 9 7 2 . M a n u f a c t u r i n g m e t h o d s f o r s u r f a c e i n t e g r i t y o f m a c h i n e d s t r u c t u r a l compo-

n e n t s . AFML-TR-71-258. C i n c i n n a t i , O h i o : M e t c u t R e s e a r c h A s s o c i a t e s I n c .

4 . Koster , N. P . May 1 , 1 9 7 2 - J u l y 3 1 , 1 9 7 2 . S u r f a c e i n t e g r i t y o f m a c h i n e d m a t e r i a l s . P r o j e c t No. I R 7 2 1 - 2 ( I ) . Con-

t r a c t No. F33615-72-C-1385. C i n c i n n a t i , O h i o : M e t c u t R e s e a r c h A s s o c i a t e s I n c .

5, - a n d K o h l s , J o h n B . 1 9 7 2 . R e l a t i o n o f s u r f a c e i n t e g r i t y t o cost a n d r e l i a b i l i t y o f s t r u c t u r a l c o m p o n e n t s . P a p e r

N o . IQ72-207 . D e a r b o r n , M i c h i g a n : S o c i e t y of M a n u f a c t u r i n g E n g i n e e r s .

6 . S u r f a c e t e x t u r e . 1 9 6 2 . ASA B46 .1 -1962 . New Y o r k , N e w York : T h e A m e r i c a n S o c i e t y o f M e c h a n i c a l E n g i n e e r s .

7. M e c h a n i c a l P r o p e r t i e s D a t a C e n t e r . 1 9 7 2 . VOLS. I - I V . A e r o s p a c e s t r u c t u r a l m e t a l s h a n d b o o k . AF'ML-TR-68-115.

T r a v e r s e C i t y , M i c h i g a n : B e l f o u r S t u l e n , I n c .

ABUSIVE GRIND 4340, 50R, lOOOX

T H E TI-ILN WHITE MARTENSITIC LAYER IN T H E ABOVE PHOTO-

MICROGRAPH IS O F T E N FOUND IN T H E SURFACES O F HARDENED

A L L O Y S T E E L S A F T E R GRINDING. I T HAS B E E N FOUND THAT

E V E N ISOLATED P A T C H E S O F U N T E M P E R E D OR O V E R T E M P E R E D

M A R T E N S I T E AS THIN AS . 0 0 0 2 IN. CAN R E D U C E FATIGUE

S T R E N G T H O F HIGH S T R E N G T H S T E E L S AS MUCH AS 3570 T O 40%.

F i g u r e 1

F A C E M I L L I N G

MACHINING O P E R A T I O N S SUCH AS TURNING, DRILLING, MILLING,

E T C . , E S P E C I A L L Y UNDER POOR MACHINING CONDITIONS, A R E

P R O N E T O PRODUCING S U R F A C E S WITH A B U I L T - U P E D G E . THIS

P H O T O M I C R O G R A P H SHOWS T H A T P O R T I O N O F T H E B U I L T - U P

E D G E WHICH WAS L E F T ON T H E W O R K P I E C E . F R A C T U R E ANALYSES

O F F A I L E D P A R T S H A V E SHOWN T H A T CRACKS ASSOCIATED WITH

T H E B U I L T - U P E D G E HAVE S E R V E D AS ORIGINS O F T H E F R A C T U R E .

F i g u r e 2

D R I L L I N G Ti -6A1-6V-ZSn lOOOX

C R A C K - L I K E C R E V I C E S , AS SHOWN I N T H E ABOVE S U R F A C E ,

A R E COMMONLY F O U N D I N D R I L L E D AND R E A M E D HOLES.

THE S E C T I O N SHOWN IS A B U R R ON T H E W O R K P I E C E S U R F A C E

B U R R S H A V E B E E N SHOWN T O B E R E S P O N S I B L E FOR A P P R E -

C I A B L E R E D U C T I O N O F F A T I G U E S T R E N G T H IN S T E E L AND

T I T A N I U M ALLOYS.

F i g u r e 3

E L E C T R I C A L T Y P E I32 lOO0X DISCHARGE T O O L S T E E L MACHINING 6 1 R

C

N O T E S H O U L D B E T A K E N OF T H E THIN R E C A S T LAYER

A P P R O X I M A T E L Y . 0001 -. 0002 IN. THICK. SUCH THIN

L A Y E R S A R E A S D E T R I M E N T A L AS THOSE WFICH A R E

T E N TLMES T H I C K E R AND NAVE B E E N SHOWN T O R E D U C E

F A T I G U E S T R E N G T H O F T E N AS M U C H AS 30% T O 70% IN

HIGH S T R E N G T H AND TIHERMAL R E S I S T A N T MATERIALS .

F i g u r e 4

E L E C T R O C H E M I C A L CAST R E N E ' 41

37R, MACHINING AGED -

THE ABOVE PHOTOMICROGRAPH SHO' J R F A C E HAVING A

PRONOUNCED TENDENCY TOWARD INTERGRANULAR ATTACK

DURING A N E C M PROCESS. S M A L L D E F E C T S , SUCH AS SHOWN,

ARE D I F F I C U L T T O D E T E C T B U T THEY A R E DETRIMENTAL AND

CAN BE AVOIDED THROUGH T H E USE O F P R O P E R LN-PROCESS

C O N T R O L O F E C M CONDITIONS.

F i g u r e 5

AISI 4 3 4 0 Q L T , 5 0 R,

4 3 4 0 M O D . Q & T , 5 3 R , 2

G R A D E 3 0 0 MARAGIh'G S T E E L

S T A . 54 R,

TI- 6A1-4V, B E T A R O L L E D . 3 2 R,

T I - 6 ~ 1 - 6V-2Sn S T A , 4 2 R,

T I - 6 A 1 - 2 S n - 4 Z r - 2 M o

S T A , 3 6 R,

IIVCONEL 718 STA, 4 4 R,

A F 9 5 S T A , 50 R,

R E N E ' 8 0 C O N V E N T I O N A L S T A , .40 R,

A F 2 - I D A S T A , 46 R,

0 2 0 6 0 8 0 100 120 -- -. .. -

ENDURANCE LLMIT, KSI

l o 7 C Y C L E S F U L L Y R E V E R S E D BENDING

SUMMARY O F HIGIH C Y C L E F A T I G U E RESPONSE: SURFACE GRINDING

F i g u r e 6

WI-IEEL S P E E D - 6 0 0 0 S F M GRINDING F L U I D - DRY WI-IEEL DRESSED - F I N E

ABUSIVE GRIND

W I I E E L S P E E D - 4 8 0 0 S F M GRINDING F L U I D - O I L W H E E L DRESSED - F I N E

C O N V E N T I O N A L G R I N D

C O N V E N T I O N A L G R I N D

L O W S T R E S S GRIND

W H E E L S P E E D - 4 8 0 0 S F M GRINDING F L U I D - O I L W H E E L D R E S S E D - C O A R S E

W H E E L S P E E D - 2000 S F M GRINDING F L U I D - O I L W H E E L D R E S S E D - C O A R S E

Z Y G L O INDICATIONS O N C A S T N I C K E L B A S E A L L O Y

R E S U L T I N G F R O M D I F F E R E N C E S IN GRINDING P R A C T I C E

F i g u r e 7

. . . . . . . . . . . . . . SURFACE G R I l m

T U R NING 60 ( F A C N G ) 6 0

ECM t

E C M 2 7

3 9

7 8 P E E N

E D M

EDM + P E E N I . 7 5

ELP + P E E N 1 7 8

E N D U R A N C E LLMIT, KSI

l o 7 C Y C L E S FULLY R E V E R S E D B E N D I N G

S U M M A R Y O F HIGI1 C Y C L E F A T I G U E REI-IAVIOEI

O F T N C O N E L 718 (SOLUTION T R E A T E D AND A G E D , 44 Rc)

4 3 4 0 ( Q & T , 5 0 R,) T R A N S V E R S E : S U R F . G R I N D

S U R F A C E FINIS11 MICR OINCIIES

4 3 4 0 (08; T , 50 R,)

L O N G I T U D I X A L S U R F . G R I N D

4 3 4 0 ( Q L T, 5 9 Rc) P ,

T I - 6 - 6 - 2 (STA, 4 2 R,)

117

END MILL END C U T

! I N C O N E L 7 18 (STA, 4 4 R,)

T U R N I N G ( F A C i N C )

L O N G I T U D I N A L 65 1 1 1 0

i N C G N E L 7 i 8 (STA, 4 4 R,) T U R N I N G (FACING)

S U R F A C E G R I X D 127

1 1 5 8 -- 1 l o o

E N D U R A N C E LIMIT, KSI

l o 7 CYCLES F U L L Y R E V E R S E D BENDING

: ?,,

I I I I

.SUMMARY O F F A T I G U E S T R E N G T H S - S U R F A C E FINISH

I 0 0

F i g u r e 9