Causes of the yield-point phenomenon in commercial beryllium products

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The variables of iron content, texture, and grain size are studied as a function of solutionizing, aging, and strain-aging heat treatments. Results show that the yield point is caused by precipitate pinning. Furthermore, precipitation is enhanced by pre-strain, which can be introduced by elevated- temperature working, rapid cooling, or tensile elongation at room temperature. Aging is effective between 400 and 760 deg C, depending on the type of pre- strain, iron content, and texture. Cottrell-type solute pinning is not observed, and the Rahn model for yield drops in bcc metals best explains these results. Texture increases the likelihood of a ... continued below

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Pages: 70

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Floyd, D. R. February 1, 1974.

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The variables of iron content, texture, and grain size are studied as a function of solutionizing, aging, and strain-aging heat treatments. Results show that the yield point is caused by precipitate pinning. Furthermore, precipitation is enhanced by pre-strain, which can be introduced by elevated- temperature working, rapid cooling, or tensile elongation at room temperature. Aging is effective between 400 and 760 deg C, depending on the type of pre- strain, iron content, and texture. Cottrell-type solute pinning is not observed, and the Rahn model for yield drops in bcc metals best explains these results. Texture increases the likelihood of a yield point occurring. In the case of extruded-flat stock, texture causes a 3-fold increase in the amount of hardening accompanying the yield point when compared to hot-pressed block. Yield points appear on aging and strain-aging for orientations favoring either prism or basal flow. Fine grain size is a necessary condition for the occurrence of a yield point. A yield point can occur if: the average grain size is less than 10 microns, the microstructure is duplex and has a large number of grains less than 5 microns in size, a substructure exists with subgrains less than 5 microns in size. Grain-growth anneals can irreversibly eliminate a yield point. Differences in the frequency of appearance of yield points can be explained by the above factors, and a strong yield point can be developed in material supplied by Brush and KBI by appropriate treatment. The solid-solution hardening effect of iron on yield stress is linear with a slope of 2.3 psi per ppM in the range of iron from 840 to 5850 ppM. The grain-size effect, in the range from 8 microns to 45 microns, is seen to be linear for a Hall--Petch plot of yield stress versus inverse square root of grain size. The magnitude of the effect is 138 ksi (microns)/sup 1/2, which is the slope of the plot. (26 figures, 20 tables, 77 references) (DLC)

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Pages: 70

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  • Other Information: Orig. Receipt Date: 30-JUN-74

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  • Report No.: RFP--2061
  • Grant Number: AT(29-1)-1106
  • DOI: 10.2172/4309095 | External Link
  • Office of Scientific & Technical Information Report Number: 4309095
  • Archival Resource Key: ark:/67531/metadc1022714

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  • February 1, 1974

Added to The UNT Digital Library

  • Oct. 15, 2017, 10:09 p.m.

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  • Oct. 27, 2017, 4:53 p.m.

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Floyd, D. R. Causes of the yield-point phenomenon in commercial beryllium products, report, February 1, 1974; Golden, Colorado. (digital.library.unt.edu/ark:/67531/metadc1022714/: accessed November 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.