Relationship between alpha grain size and crack initiation fatigue strength in Ti-6Al-4V

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0.6

0.5

0.4

0,3

02

0.1

[ 2

i 4

I 6

I 8

I tO

i t2

I t4

[ t6

] 18 20 Wt% M

Fig. 7--Logf0 vs wt pet M. tn Yo 12

i

/

I

I

I

i

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t w e e n p u r e c o p p e r and p u r e n i c k e l . T h e i r r e s u l t s s h o w e d t h a t EoNi at 1550~ = - 4 . 2 6 and EoNi at 1500~ = - 3 . 9 1 w h i c h i n d i c a t e s t h a t CoNi i n c r e a s e s r a p i d l y ( b e comes less negative) as the temperature decreases. A l i n e a r e x t r a p o l a t i o n b a s e d on s u c h r a t e of c h a n g e w o u l d p r e d i c t t h a t toni at 1200~ m a y be c l o s e to z e r o o r e v e n p o s i t i v e a s found in t h i s w o r k . W i t h a l l o y s r i c h in n i c k e l t h e s a m e r e s e a r c h e r s 3 found t h a t t h e a d d i t i o n of c o p p e r to n i c k e l i n c r e a s e s t h e o x y g e n s o l u b i l i t y w h i c h is o p p o s i t e to w h a t m i g h t be e x p e c t e d on t h e b a s i s of n o b i l i t y c o n s i d e r a t i o n a l o n e but p e r h a p s in l i n e w i t h t h e "electron capture" theory cited above. E~g c a l c u l a t e d f r o m the r e s u l t s of F r u e h a n and R i c h a r d s o n 4 n e a r 1200~ i s a b o u t 4.6 w h i c h is l e s s t h a n t h e v a l u e of 13 found in t h i s w o r k . T h e r e i s no e x p l a n a t i o n at t h i s t i m e f o r t h e d i f f e r e n c e . T h e a u t h o r s w i t h to e x p r e s s t h e i r t h a n k s to t h e N a tional Science Foundation for their financial support of t h i s w o r k .

I

1. M. M. A. E1-Naggarand N. A. D. Padee: Met. Trans., 1970, vol. 1, pp. 2975-77. 2. C. Lupis and J. Elliot: Trans. TMS-AIME, 1965, vol. 233, pp. 257-58. 3. E. S. Tankins, J. F. Erthal, and M. K. Thomas, Jr.: J. Electrochem. Soc., 1965, vol. 112, pp. 446-50. 4. R. Fruehan and F. Richardson: Trans. TMS-AIME, 1969, vol. 245, pp. 1721-26.

1.0

08

06

04

Relationship between Alpha Grain Size and Crack Initiation Fatigue Strength in Ti-6AI-4V

02

OOl

002

005

004

006

017 0 08 Mole traction M

Fig. 8--Ln 3'o vs N M .

J . J . LUCAS AND 1a. P. KONIECZNY

Table I. The Interaction Coefficients at 1200~

DURINGthe course of investigating the effects of

e~t = a logfo/a %M; eoM = a In "yo/aNM AlloyingElement

eM

eoM Calculated*

eoM

Gold Platinum Silver Nickel

0.0318 0.0300 0.0335 0.0375

20.6 19.1 12.4 8.0

23 21 13 9

*Usingthe formula givenin Ref. 2, see Eq. [I].

p e r a t u r e c o n d i t i o n s . O n t h e o t h e r h a n d , it w a s e x p e c t e d that nickel would probably increase the oxygen solub i l i t y s h o w i n g a n e g a t i v e eoM , b e c a u s e it is c o n s i d e r a b l y l e s s n o b l e t h a n c o p p e r . T h i s w a s not f o u n d , h o w e v e r , a n d p o s s i b l y c a n b e e x p l a i n e d a s b e i n g due to n i c k e l d e c r e a s i n g t h e a c t i v i t y of f r e e e l e c t r o n s on t h e a s s u m p t i o n t h a t o x y g e n u n d e r g o e s i o n i z a t i o n upon d i s s o l u t i o n a c c o r d i n g to +

2e-

= o=

[2]

T h e n i c k e l a t o m