MASS-TRANSFER EFFECTS IN SOME REFRACTORY-METAL--ALKALI-METAL--STAINLESS STEEL SYSTEMS. Page: 30 of 37
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specimens exhibited a very thin surface layer, less than 0.1 mil, quite
similar to the mixed carbide-nitride phase observed on specimens from
sodium and NaK tests.
Effect of Stress
To determine the effect of an applied load on the integrity of the
carbide-nitride film and hence on the rate of carbon and nitrogen trans-
fer to niobium, the test system shown in Fig. 10 was devised. A 200-lb
load was applied to a niobium rod with sections 0.4 and 0.3 in. in
diameter and resulted in stresses of 1700 and 3000 psi, respectively.
An unloaded niobium rod with sections machined to 0.4 and 0.3 in.
diameter, respectively, was suspended next to the stressed rod. The
unstressed rod was inverted so that its 0.3-in.-diam section was opposite
the 0.4-in.-diam section of the stressed rod to minimize the effect of
specimen position on the results. So that the analytical results would
not be biased by the different rod thicknesses, the chemical analyses
were determined from 0.005-in. layers turned from the specimens after
test. Results of the analyses are shown in Table 12. At 1700 psi the
amount of carbon and nitrogen transfer was less for the stressed than the
unstressed rod; at 3000 psi the stressed rod picked up less carbon but
more nitrogen than the unstressed rod. Metallographically the stressed
and unstressed samples differed little; a duplex carbide-nitride layer of
approximately the same thickness was observed on both. In view of the
small differences between the specimens, stress up to the limits of this
test appears to have little effect on the transfer of carbon and nitrogen.
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DiStefano, J.R. MASS-TRANSFER EFFECTS IN SOME REFRACTORY-METAL--ALKALI-METAL--STAINLESS STEEL SYSTEMS., report, January 1, 1966; Oak Ridge, Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc1034069/m1/30/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.