Dorn, J.E.

Mohamed, P.A.

Murty, K. Linga.

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Lawrence Berkeley National LaboratoryRecent WorkTitleON THE KINETICS OF ORDERING IN Cu3AUPermalinkhttps://escholarship.org/uc/item/8gd4p7gsAuthorsMohamed, P.A.Murty, K. Linga.Dorn, J.E.Publication Date1971-10-01eScholarship.org Powered by the California Digital LibraryUniversity of CaliforniaSubmitted to Materials Science and Engineering ON THE KINETICS OF ORDERING IN Cu3Au UCRL-19121 Rev. Preprint C'.~ .-' .: c ;::: ' \. :.:: c ' . . ... . . ·-..,,... r •. ,\- 4~ OOCUM~lo..; ·,-s SE..;·ri0"-1 F. A. Mohamed, K. Linga Murty and J. E. Dorn October 1971 AEC Contract No. W -7405-eng-48 TWO-WEEK LOAN COPY This is a Library Circulating Copy which may be borrowed for two weeks. For a personal retention copy, call Tech. Info. Division, Ext. 5545 c (') :::0 l' I ~ "' ~ N ~ .n :::0 y~ DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain cotTect information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or the Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or the Regents of the University of California. f.' . ; ·-~ • -1- UCRL-19121 Rev. On the Kinetics of Ordering in cu3Au t F. A. Moham~d, K. Linga Murty and J. E. Dorn Inorganic Materials Research Division, Lawrence Berkeley Laboratory and Department of Materials Science and Engineering, College of Engineering; University of California, Berkeley, California · Several resistometric studies l-lO have been made on the kinetics of·ordering in cu3Au following quenching. Minor discrepancies exist in some of the reported data and some differences in opinions have been expressedregarding interpretation of these data. Furthermore, several facets of the subject have not been adequately explored. Nevertheless there now appears to be a fair agreement on all major issues. The research of Benci et a1. 10 is most pertinent to the present discussion: Following quenching thin wires .04 mm in diameter from a series of temperatures covering the range Tc. < T < 1073°K, they determined ~~~ -- where R is the resistivity measured at room temperature and .the subscripts refer to the temperature from which the specimens were quenched. (RT - ~)/~ decreased as Twas first increased above Tc' c reached a minimum value at about T = 723°K, and increased as T was increased above 723°K. Obviously at least two factors are responsible for the variation of the resistivity of quenched eu3Au as a function of the quenching temperature. The resistivity of cu3Au is known to 1 increase with both increasing vacancy concentration and increasing 4 absolute degree of short-range order, and it decreases with increasing t deceased, Sept. 1971. . ' -.-11 degree oflong-range order. The possibility that increasing degrees of long-range order can account for the decreasing values of (RT - Rrj/RT \ with increasing values ofT over the range T <.T < 723°K can be c disqualified on the basis of several observations, the most direct being the fact that isothermal annealing of quenched specimens at 438°K results first in a decrease in the resistivity followed by an increase in resistivity. The latter can only be due to predominance of short-range ordering over other factors. 2 Furthermore as shown by Dugdale specimens quenched from just below T = 663°K exhibit upon annealing c only decrease i~ resistivity coincident with elimination of excess vacancies and long-range ordering. Consequently, the variations of (RT -~)/~with quenching temperature must be ascribed to short-range c order and vacancy effects. Over the lower range of quenching tempera-tures where T < T < 723°K the predominant factor appears to be the c decreasing value of the quenched-in absolute degree of short-range order with increasing quenching temperature, whereas above 723°K the effect of increasing excess vacancies plays the predominant role. These conclusions are also in agreement with those presented earlier by 12 Damask. Th~s cu3Au can be quenched sufficiently rapidly from above T = 663°K to avoid long-range ordering. Furthermore the absolute c degree of short-range order under equilibrium conditions :at the quenching ~emperature must be frozen into the as-quenched cu3Au with ' no, or at most, negligible increases in value. .. • -3-Whether excess quenched-in vacancies can be retained over several days in as-quenched specimens might be estimated from annealing kinetics. In the light of the previous discussion the early stages of annealing could involve two simultaneous trends, a decrease in resistiv-ity arising from migration of excess vacancies to sinks and an increase in resistivity due to short-range order. Since the resistivity is more sensitive to vacancy concentration, this effect will predominate at first, resulting in a decrease in resistivity, followed subsequently, when the excess vacancy concentration is small, by an increase in resistivity due to an increase in the absolute degree of short-range order. Only following much longer times will the resistivity decrease again as a result of transformation from short-range to long-range order. Such general trends upon annealing have been reported by Benci et a1. 10 and Brinkman et al.1 Annealing data at a series of temperatures from 363°K to 473°K were obtained by Benci et al10 following quenching frpm 803°K. The ratio R/R , of the instantaneous to initial resistivity initially 0 decreased rapidly, reached a minimum value and then increased very slowly with time. Obviously over the ini.tial stages of annealing the decrease in resistivity due to migration of excess quenched-in vacancies to sinks predominated over the minor concomitant increase in resistivity resulting from short-range ordering, whereas in the final stage the excess vacancy concentration was so low that the effects of short-range ordering on the resistivity predominated. The fact that about the same minimum value of R/R0 was obtained regardless of the ann.ealing I' -4-temperature can be attributed to the fact that the differences in the equilibrium concentration of vac~cies over the range of annealing temperatures was negligibly small iri contrast to the excess quenched-in vacancy concentration. Since both·the migration of excess vacancies to sinks and short-range ordering are dependent on the,migration of vacancies, the annealing data for all temperatures should correlate as shown in Fig. 1 to give a single curve ·in terms of the temperature compensated time, t (-E /RT), where E = 16.6 kcal/mole is the activa-e m · m tion energy for migration of vacancies. Similar. values for E have m been obtained by a number of investigators. 2 'lO,l3,l4 The upper scale in Fig. 1 gives an extrapolation of these data in terms .of the time of anneal at 290°K. Assuming that most of the excess vacancies have been eliminated when R/R reaches its minimum value, it is noted 0 ' that the excess vacancy concentration in quenched eu3Au becomes small after a 3000 hr hold at room temperature. It is well known that following the previously described initial period of adjustment, cu3Au quenched from above Tc' can be held for very long periods of time at room temperature withou~ material changes in its ordering-sensitive properties. This shows that the equilibrium concentration of vacancies is so low and their rate of migration at room temperature is so slow that they provide infinitely slow rates of short-range ordering. Consequently the terminal slow increase in ·resistivity documented in Fig. 1 must be due to excess vacancies. Such order will continue until the excess vacancy concentration reach~s some terminal residual value. ( t..l A j -5-ACKNOWLEDGMENTS This work was supported by the United States Atomic Energy Commission through' Inorganic Materials Research Division of Lawrence Berkeley Laboratory of the University of California, Berkeley, California. REFERENCES 1. J. A. Brinkman, C. E. Dixon, and C. J. Meechan, Acta Met.£, 38 (1954 ). 2. R. A. Dugdale, PhiL Mag. 1, 537 (1956) 3. John B. Gibson, J. Phys. Chern. Solids 1, 27(1956). 4. A. C. Damas~, J. Phys. Chem. Solids 1, 23(1956) 5. B. M. Korevaar, Acta. Met • .2_, 297(1961). 6. E. Nagy and I. Nagy, J. Phys. Chem. Solids 23, 1605(1962). 7• H. Elknoly and E. Nagy, J. Phys. Chem. Solids 23, 1613(1962). 8. E. Nagy and J. Toth, J. Phys. Chem. Solids 24, 1043(1962). 9. M. T. Beal, J. Phys. Radium 23, 843(1962) 10. S. Benci, G. Gaspa.i"rini and E. Germagnoli,Nuovo Cimento 31, 1165 (1964). 11. E. W. Jones and C. Sykes, Proc. Roy. Soc. Al66, 377(1938) •. · 12. A. C. Damask, z. A. ~·am and E. Germagnoli, J. Phys. Chem. Solids .!2_, 265 ( 1961) • 13 •. Norman W. Lord, J. Chem. Phys. 21, 692(1952). 14. F. A. Mohamed, K. Linga Murty and J. E. Dorn, "I;>iscontinuous yielding in Cufu," to be published. . \ lj b [C ' '; 0::: Tl._,,~ i>'d.::. 0 ':- r, t._, \ 1 ;. t\ I I (··I' I • ,__ • -co tO C\1 ..;-f() \ 0 C\1 ~ .. 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I 0 r-----------------LEGALNOTICE-------------------, This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor the United States Atomic Energy Commission, nor .any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights. 0 -.. ·~1.~, TECHNICAL IN FORMA TIOI'TDIVISION LAWRENCE BERKELEY LABORATORY UNIVERSITY OF CALIFORNIA BERKELEY, CALIFORNIA 94720 .:::_•• t I) •t 

ON THE KINETICS OF ORDERING IN Cu3AU

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