Substructure of austenite formed by a partial reverse martensitic transformation in an Fe-Pt alloy
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Fig. 4--Enlargement from a negative movie film taken through the microscope of the top surface of the foil during directional solidification at 1.9 x 10 -4 cm per sec. Liquid is to the right; solid is to the left with Sn-rich lamellae, light, and composite Pb-, Cd-, Pb-rich lamellae, dark. p l a n a r l i q u i d - s o l i d i n t e r f a c e , which is p e r p e n d i c u l a r to the s u r f a c e of the foil and whose v e l o c i t y is c o n t r o l l a b l e , can be obtained by h e a t i n g the f o i l with an e l e c t r i c c u r r e n t through p a r t of a w i r e loop u s e d to s u p p o r t the foil. The s o l i d m i c r o s t r u c t u r e of a s o l i d i f i e d foil of the P b - S n - C d t e r n a r y e u t e c t i c is the s a m e at the s u r f a c e of the f o l l as it is in the i n t e r i o r of the foil and as it is in l a r g e r c a s t i n g s .
Fig. 3--Micrograph of transverse section of foil after directional solidification showing topography produced by microstructure at top surface of foil. Nital etch. s e e n . Unfortunately, the ~ and y l a m e l l a e could not be i n d i v i d u a l l y d i s t i n g u i s h e d . The ~T~ c o m p o s i t e a p p e a r s to be a s i n g l e l a m e l l a when v i e w e d on the top s u r f a c e . F o r this alloy, the a p p r o x i m a t e shape of the m a c r o s c o p i c l i q u i d - s o l i d i n t e r f a c e was v e r y n e a r l y p l a n a r and p e r p e n d i c u l a r to the top s u r f a c e of the foil, This was d e t e r m i n e d by r a p i d l y i n c r e a s i n g the s o l i d i f i c a tion r a t e and s u b s e q u e n t l y e x a m i n i n g the m i c r o s t r u c t u r e i n s i d e the f o i l at the p o s i t i o n w h e r e the r a t e was i n c r e a s e d . The m i c r o t o p o g r a p h y of the s u r f a c e of the foil is shown in the t r a n s v e r s e s e c t i o n of the foil shown in Fig. 3. The ~ l a m e l l a e a r e h i g h e r on the s u r f a c e than the ~y~ c o m p o s i t e s . T h e r e f o r e , the ~ a r e light and the ~y~ a r e d a r k when the top s u r f a c e of the foil i s v i e w e d in oblique i l l u m i n a t i o n . A t y p i c a l e n l a r g e m e n t f r o m a m o v i e f i l m taken through the m i c r o s c o p e of the top s u r f a c e of the foil d u r i n g s o l i d i f i c a t i o n is shown in Fig. 4. In c o n c l u s i o n , a s u r f a c e r e l i e f is p r o d u c e d on the f r e e s u r f a c e of a s o l i d i f y i n g f o i l of the P b - S n - C d t e r n a r y e u t e c t i c through which the l i q u i d - s o l i d i n t e r f a c e and the l a m e l l a r m i c r o s t r u c t u r e can be c o n t i n u o u s l y o b s e r v e d when e x a m i n e d through an o p t i c a l m i c r o s c o p e using b r i g h t - f i e l d , oblique i l l u m i n a t i o n . A r e l a t i v e l y 1988-VOLUME 4, AUGUST 1973
1. A. Rosenbergand W. C. Winegard:Acta Met., 1954,vol.2, p. 342. 2. M. E. Glicksmanand R. L Schaefer:ActaMet., 1966, vol. 14, p. 1126. 3. M. E. Glicksman
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