Discussion of the intergranular embrittlement of iron-carbon alloys by impurities
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p e a r a n c e of c e l l s , f r o m which the vein m a r k i n g s a p p a r e n t l y o r i g i n a t e , w e r e also noted by Leamy et al. 3 However, t h r e e d i f f e r e n c e s in the behavior p a t t e r n s of the alloys a r e noted. F i r s t l y , Pd-Si and the Ni and N i - F e alloys containing l a r g e amounts of P and C exhibited a s m a l l amount of ductility, w h e r e a s no d u c t i l ity was found in the Cu-40 at. pct Zr alloy at c o m p a r a ble t e m p e r a t u r e s . Secondly, the f r a c t u r e s u r f a c e s of Pd-Si alloys exhibited r e g i o n s with f e a t u r e l e s s f r a c ture s u r f a c e s , i.e., without vein p a t t e r n s . No evidence for this type of s u r f a c e was found in Cu-40 at. pct Z r ; the unveined r e g i o n in Fig. 2 was o b s e r v e d only in one of m o r e than 8 f r a c t u r e d t e s t s p e c i m e n s . Thirdly, in the Pd-Si a l l o y s , the f r a c t u r e s u r f a c e s w e r e found to be inclined at 45 deg to the t e n s i l e axis w h e r e a s in the C u - Z r alloy, the initial f r a c t u r e s u r f a c e was found to be n o r m a l to the t e n s i l e axis. Whether these d i f f e r ences a r e a t t r i b u t a b l e to e x p e r i m e n t a l condition, f r a c ture mode, or m a t e r i a l s t r u c t u r e s s'6 cannot be d e t e r mined at the p r e s e n t time. The authors wish to acknowledge the financial s u p p o r t of this work by NASA, under Grant NGL22-009003. The helpful d i s c u s s i o n s with P r o f e s s o r Regis Pelloux at MIT a r e also acknowledged.
1. J. M. Vitek, J. B. Vander Satlde, and N. J. Grant: ActaMet., 1975, vol. 23, p. 165. 2. D. E. Polk and C. A. Pampillo: Scr. Met, 1973, vol. 7, p. 1161. 3. H. J. Leamy, H. S. Chen, and T. T. Wang: Met. Tran~, 1972, vol. 3, p. 699. 4. T. Masumoto and R. Maddin: ActaMet., 197l, vol. 19, p. 725. 5. J. Logan: Scr. Met., 1974, vol. 8, p. 727. 6. J. Logan: CALT-822-63, August 1974.
Discussion of 'The Intergranular Embri.lement of Iron-Carbon Alloys by Impurities"* R. L. SCHUYLER, III Fig. 4 - - S E M v i e w of c e l l u l a r p a t t e r n on f r a c t u r e f a c e ( m i n o r s t r u c t u r a l f e a t u r e ) . Note f i n e r s t r u c t u r e w i t h i n t h e c e i l s . M a g n i f i c a t i o n 1660 t i m e s .
c o n f i r m s the lack of high s e n s i t i v i t y of f r a c t u r e to tiny flaws. Such flaws a r e not uncommon in piston and anvil s p l a t foils. Fig. 3 p r e s e n t s a higher m a g n i fication photo of the vein p a t t e r n s in the fiat region. As seen in the figure, the m a r k i n g s a p p a r e n t l y o r i g i nate from s e v e r a l c e l l s within the s a m p l e , implying c r a c k initiation f r o m within the s a m p l e . Fig. 4 shows extensive c e l l s in c o n t r a s t to the vein p a t t e r n s . The changes in f r a c t u r e conditions leading to the s t r u c t u r e s in Figs. 3 and 4 a r e not known. Of p a r t i c u l a r i n t e r e s t is the fine s t r u c t u r e within the c e l l s of Fig. 4, wh
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