The Surface Self-Diffusion of Mo, Cb (Nb), and Re
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r e l a t i v e l y h i g h d e n s i t y of t h e t i t a n i u m a l l o y i n q u e s t i o n , m e a s u r e d to b e a b o u t 0.2 l b m i n -a, t h e above quoted strengths compare favorably with r e s p e c t t o t h o s e of t h e m o r e c o n v e n t i o n a l a-/3 t i t a n i u m a l l o y s , s u c h a s T i - 6 2 4 2 a n d T i - 6 4 . Of special interest may be the elevated temperature s t r e n g t h of t h e a l l o y i n q u e s t i o n . F o r e x a m p l e , i t s yield strength at ll00~ e v e n a f t e r 100 h a t t h a t t e m p e r a t u r e , i s a b o u t 90 k s i w h e n t h e p r e c i p i t a t e s a r e c u b o i d s a n d a b o u t 120 k s i w h e n W i d m a n s t a t t e n platelets strengthen the alloy. We conclude by simply stating that precipitate shape can be altered by controlled mechanical treatment during precipitation. As such, this treatment must be considered as an additional dimension in microstructural design. I. C.S. Smzth: Trans.Amen. Soc. Metals, 1953, vol. 45, p. 533. 2. H. I. Aaronson: Decomposition of Austenite by Diffusional Processes, p. 453, H. I. Aaronson and V. F. Zackay, eds., J. Wileyand Sons, New York, 1962. 3. J. K. Tien, P. G. Shewmon, and L S. Foster: Met. Trans., 1971, vol. 2, p. 1193. 4. J. C. Williams,and M. J. Blackburn: OrderedAIloys-StructualApplicat~ons and PhysicalMetallurgy:p. 425, B. H. Kear, C. T. Szms,M. S. Stoloff, and J. H. Westbrook, eds., Claitor's PubhshingDivision,Baton Rouge, 1970. 5. M. Gell, G. R. Leverant, and C. H. Wells:Amen Soc. Test. Mater, Special Tech. PubL ASTM-STP 467: 1970. 6. J. B. Zeldowtch.ActaPhysicochim. URSS, 1843, vol. 18, p. 17.
Co
Sn Cu ( a / o l
Fig. 1--Alloys studied in C u - S n - M n s y s t e m .
Table I, Enahalpies of Formation as a Function of Composition in the Cu2 Sn-Mn System
Chemical Unit
Cu2.~4sMnz.oSnonls
The Enthalpies of Formation of Ferromagnetic Cu-Mn-Sn Alloys M. A. MEYERS
AND
M. T. HEPWORTH
THE enthalpies of formation at 298.16 K of five alloys closely approaching the composition Cu2MnSn were determined by solution calorimetry with tin as a solvent. The alloys are in the ferromagnetic /3 phase range; their compositions, as well as the maximum range for the ~ phase are shown in Fig. I. This phase is ordered and presents reasonably high magnetizations (up to 660 emu/cm3). The /3 phase decomposes upon cooling below 400~ Alloys were prepared by arc melting. They were homogenized and quenched to retain the B phase at room temperature. The liquid-metal solution calorimeter used in this investigation has been described elsewhere. I At the start of each series of measurements, the solvent bath consisted of about 0.4 g-atom of 99.9+ pet pure Sn. The heat capacity of the calorimeter was determined by two tin drops before each series of experiments. The only heat effect due to a tin drop is the sensible heat of the specimen. The heat content of tin is well established and is presented in the compilation of Hultgren et all T h e c a l c u l a t i o n of t h e e n t h a l p i e s of f o r m a t i o n o
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