Effect of low frequency mechanical vibration on structure of modified aluminum-silicon eutectic
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loops generated around second phase particles decorat i n g t h e t w o - d i m e n s i o n a l d e f e c t . T h e o b s e r v a t i o n of fringe contrast within the defect indicates that the region has a stacking fault associated with it. The g r o w t h of t h e s e f a u l t s o c c u r s b y t h e g e n e r a t i o n of p a r tial dislocations around second-phase particles, movem e n t of t h e p a r t i a l s t o r e e s t a b l i s h p o i n t d e f e c t e q u i librium and further precipitation inside the newlycreated faulted region and on the dislocations. New loops are generated around the precipitates and loops f r o m d i f f e r e n t s o u r c e s l i n k up to f o r m l a r g e r l o o p s . A l l t h e s e f e a t u r e s a r e e v i d e n t i n F i g . 2. F i g s . 3(a) a n d 3(b) s h o w (220> t w o - b e a m m i c r o g r a p h s of t w o f a u l t s a l o n g ( I i 0 > d i r e c t i o n s o n i n c l i n e d ( i i i ) p l a n e s . T h i s s a m p l e w a s h e a t e d f o r 30 r a i n a t 9 0 0 ~ All the features associated with Fig. 2 are observed here. The dislocations generated are pure edge-type s i n c e t h e d i s l o c a t i o n s a r e o u t of c o n t r a s t w h e n t h e operating vector is parallel to them while the segments normal to g exhibit the characteristic double image and dotted contrast. ~ The dislocation-generation mechanism shown differs in its detail from the classical Bardeen-Herring concept. The dislocations generated are heavily jogged, F i g s . 2 a n d 3, a n d n o t s m o o t h l y c u r v e d a s p o s t u l a t e d in the original mechanism. Furthermore, new sources
are constantly created due to the added phenomenon of precipitation of second-phase particles at the dislocations and faults. A m o r e detailed study of the mechanism of dislocation generation and fault growth of the type presented here will be reported in a separate paper. 1. W. C. Dash: J. Appl. Phys., 1956, vol. 27, p. 1193;/Appl. Phys., 1956, vol. 27, p. 1387. 2. J. Bardeen and C. Herring:Imperfections in Nearly Perfect Crystals, W. Shockley, ed., p_ 261, John Wiley and Sons, Inc., New York, 1952. 3. A. S. Parasnisand J. W. Mitchell:Phil. Mag., 1959, vol. 4, p. 171. 4. W. Bontinck and S. Amelinckx:Phil. Mag., 1957, vol. 2, p. 94. METALLURGICAL TRANSACTIONS
5. T. Iizuka and M. Kikuchi: Lattice Defects in Semiconductors, R. R_ Hasiguti, ed, p. 500, Universityof Tokyo Press,Tokyo, 1968. 6. M. L. Joshi: Acta Met., ] 966, vol. 14, p. 1157. 7. J. E. Lawrence:J. Appl. Phys., 1969, vol. 40, p. 360. 8. G. R. Booker andW. J. Tunstall: Phil. Mag., 1966, vol. 13, p. 71. 9. P. B. Hirsch,A. Howie, R. B. Nicholson, D. W. Pashley, and M. J. Whetan:Electron Microscopy of Thin Crystals, p. 178, Butterworth, London, 1965.
Effect of Low Frequency Mechanical Vibration on Structure of Modified Aluminum-Silicon Eutectic N . R. P I L L A I THE literature on solidification contains many refere n c e s to t h e e f f e c t of v i b r a t i o n on t h e s t r u c t u r e of solidifying metals and alloys.'-3 The main
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