Deformation faulting in the premacroyield region of polycrystalline nickel
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FROM a consideration of its electronic structure there is no reason why nickel, situated between cobalt and copper (stacking fault energies of 10 and 40 erg per sq cm, respectively) in the periodic table, should have a high stacking fault energy. The overlap of 3d electrons of neighboring atoms is small at the end of the third long period, as is the difference in the energy between the stacking orders ABCABC and ABABAB of closed packed planes as suggested by Seeger." In fact Reimer2 obtained a hexagonal phase of nickel by condensation from the vapor at low temperatures. The large frequency of twins in nickel also suggests a low stacking fault energy, because the energy of the twin boundary is closely related to the stacking fault energy
(~). S m a l l m a n and W e s t m a c o t t a d e t e r m i n e d the s t a c k i n g fault p r o b a b i l i t y (from the X - r a y line shift method) of n i c k e l to be about half of that for copper i n d i c a t i n g 7Ni > 7Cu. C h r i s t i a n and S p r e a d b o r o u g h 4 f r o m X - r a y line s h i f t s and e l e c t r i c a l r e s i s t i v i t y m e a s u r e m e n t s on d e f o r m e d n i c k e l , concluded that copper and n i c k e l b e long to the s a m e c l a s s as f a r a s s t a c k i n g fault e n e r g y is c o n c e r n e d . Seeger, 1 a f t e r i n t e r p r e t i n g the data on the p l a s t i c p r o p e r t i e s of n i c k e l , concluded that ~Ni s = 80 e r g p e r sq cm, in good a g r e e m e n t with H a a s e n ' s c a l c u l a t e d v a l u e of 90 e r g p e r sq c m by the r i i I m e t h o d . However, H a a s e n ' s v a l u e is not an a b s o l u t e d e t e r m i n a tion p e r se, b u t is ~Ni = 2.2YCu w h e r e rCu was t a k e n a s 40 e r g p e r sq c m . In a r e c e n t r e v i e w , G a l l a g h e r s c o n c l u d e d that 7Cu is of the o r d e r of 55 e r g p e r sq c m which would r e s u l t in a ~Ni v a l u e of 120 e r g p e r s q c m . It is of i n t e r e s t to note that, in l a t e r works e m p l o y i n g the TIII method, Seeger 7 e t a l . o b t a i n e d 7Ni = 410 e r g p e r sq c m and H a a s e n and King s o b t a i n e d 7Cu = 102 to 165 e r g p e r s q c m . More r e c e n t l y ~Ni v a l u e s f r o m the r o l l i n g t e x t u r e data b y B e e s t o n e t a l . ~ and f r o m the e x t r a p o l a t i o n of t e t r a h e d r a data by C I a r e b r o u g h e t a l . ~~ have b e e n r e p o r t e d as 240 and 160 e r g p e r sq c m , r e s p e c t i v e l y . Thus, it s e e m s likely that ~Ni is i n the high SFE r a n g e , p r o b a b l y of the s a m e o r d e r a s a l u m i n u m , though it is obvious that s e r i o u s d i f f e r e n c e s of opinion s t i l l e x i s t as to the exact m a g nitude of the s t a c k i n g fault e n e r g y of n i c k e l . Stacking faults w e r e o b s e r v e d d u r i n g the c o u r s e of R. N. SINGH formerly Graduate Student, University of Manitoba, Winnipeg,Manitoba, Canada, is Graduate Student, Department of Metallurgy and Materials Science, M.I.T., Cambri
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