Ordering in copper-titanium alloys
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(c) Fig. 1 - - E l e c t r o n diffraction p a t t e r n s of a Cu-5.17 wt pct Ti as quenched s p e c i m e n (a) [002] diffraction p a t t e r n showing s a t e l lites around the fundamentals. (b) [002] diffraction p a t t e r n which was overexposed to detect faint s u p e r l a t t i c e reflections.
(c) Schematic of the observed [002] diffraction pattern of the as quenched Cu-5.17 wt pct Ti alloy. The positions of the satellites spots are not to scale. The open and filled circles are super-lattice positions for two variants of the Dla structure. METALLURGICAL TRANSACTIONS
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TITANIUM
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Fig. 2 - - C u - 5 . 1 7 wt p e t Ti s p e c i m e n aged 15 s at 450~ [002] d i f f r a c t i o n p a t t e r n , s h o w i n g the Dla s u p e r l a t t i c e r e f l e c t i o n s . Also v i s i b l e a r e faint r e f l e c t i o n s f r o m Cu20 epitaxial film. See text.
Fig. 3--A d a r k field e l e c t r o n m i c r o g r a p h of a Cu-5.17 wt pct alloy aged at 450"C for 1000 rain. The i m a g e was f o r m e d f r o m one of the s u p e r l a t t i c e r e f l e c t i o n s . The foil n o r m a l is [002], and the p a r t i c l e s lie along the [020] and [200] d i r e c t i o n s . (1000 n m = 1pro).
and the third type occurs from the diffraction of the {220} matrix reflections, by {110} oxide planes. After further aging, the ordered Cu4Ti particles could be imaged by using a superlattice reflection. Fig. 3 shows the ordered particles that exist after aging a 5.17 wt pct Ti alloy 1000 min at 450~ The 1.55 and 3.08 wt pct alloys both have been observed z to o r d e r after aging at temperatures above 375~ Comparison of satellite and superlattice intensities implies that the spinodal reaction occurs METALLURGICAL TRANSACTIONS
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Fig. 4 - - T h e c o p p e r r i c h s i d e of the c o p p e r - t i t a n i u m p h a s e d i a g r a m . The e q u i l i b r i u m s o l v u s w a s d e t e r m i n e d by S a a r i v i r t a and Cannon. 9 The line t h r o u g h the s q u a r e s i s the c o h e r e n t s o l v u s for t h e m e t a s t a b l e Dla p h a s e . T e m p e r a t u r e s m a r k e d by f i l l e d s q u a r e s w e r e d e t e r m i n e d by Hakkarainen 5 T h o s e m a r k e d by open s q u a r e s w e r e d e t e r m i n e d in this i n vestigation.
first. The ordering reaction begins in the titanium enriched regions probably after a certain critical titanium composition is reached in them. The two reactions then occur together. The Cu-Ti binary is therefore an example of an alloy in which both phase separation and ordering occur simultaneously, consistent with recent theoretical predictions, v The Cu4Ti phase is metastable. Upon prolonged agi
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