Static strain-aging in nickel 200 between 373 and 473 K
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FACE
centered cubic nickel has been observed t o strain age due to the two interstitial elements, hydrogen~-9 and carbon,l°-~4 In this metal, dynamic straina g i n g p h e n o m e n a , 4-%~1,~3,~4 such as the Portevin-LeChatelier effect, have been studied in more detail than the static yield point r e t u r n phenomena. 1-2'~°'~2 Static studies, however, can often yield information useful for determining the mechanism controlling the a g i n g process. Some observations concerning the effect of carbon on static strain a g i n g in Nickel 200 are reported h e r e . A quantitative model, postulated t o explain the kinetics and energetics of the r e t u r n of the lower yield stress, will be reported separately. In e a r l i e r work on static s t r a i n a g i n g in nickel containing carbon, Sukhovarov1° deformed compression specimens at room temperature and aged them between 433 and 493 K. H e deduced that the a v e r a g e activation energy for the r e t u r n of the l o w e r yield s t r e s s was 30,700 cab/mole. This is lower than the normally accepted activation energy of 34,800 c a l / mole for the diffusion of carbon in nickel. The kinetics of the a g i n g process were not reported. More information has been obtained concerning the effect of hydrogen on static s t r a i n a g i n g in nickel than for carbon. Thus, Boniszewski and Smiths have demonstrated that the yield s t r e s s returned approximately as t2/3 when a g i n g was due t o hydrogen and that the activation energy for the r e t u r n of the yield s t r e s s was 9,300 cab/mole. Macherauch and VShringer2 determined a yield point return activation energy of 10,200 cab/mole in n i c k e l specimens containing 0.05 wt pet of carbon which they attributed to a g i n g due t o hydrogen. S i n c e the activation e n e r g y for the diffusion of hydrogen in nickel is about 10,000 cab/ mole, 3 the a g i n g phenomena due t o hydrogen give both an activation energy and kinetics consistent with the Cottrell-Bilby model for s t r a i n aging. As will be W. R. CRIBB is Research Metallurgist with RepublicSteel Corporation Research Center, Cleveland, OH44131. R. E. REED-HILL is Professor, Department of Materials Science and Engineering, University of Florida, Gainesville FL 32611, whereW. R. Cribb was formerly Graduate Assistant. Manuscript submittedMay 11, 1976. METALLURGICAL TRANSACTIONS A
demonstrated, the a g i n g phenomena due to carbon, when measured below 473 K, do not conform t o the Cottrell-Bilby model. They are, however, analogous t o the a g i n g phenomena observed in austenitic stainless steels by Rose and Glover1~ and by Jenkins and Smith. 16 This analogy will be considered in the discussion. EXPERIMENTAL PROCEDURES The b a s i c m a t e r i a l was 19.1 mm diam Nickel 200 b a r s . The principal impurities in wt pct were C-0.10, Mn-0.18, Fe-0.01, S-0.005, Si-0.04, and Cu-0.01. A secondary m a t e r i a l was higher p u r i t y Nickel 270 containing in wt pct C-0.01, Mn
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