YIELD AND FRACTURE IN POLYCRYSTALLINE NIOBIUM

Journal Article · Sun May 01 04:00:00 EDT 1960 · Acta Met.

DOI:https://doi.org/10.1016/0001-6160(60)90118-8· OSTI ID:4149422

Adams, M A; Roberts, A C; Smallman, R E

Tensile tests on specimens prepared from an ingot of electron- bombardment melted niobium showed that the material undergoes a ductile-brittle transition and can be made to twin. The variation of yield stress sigma /sub y/ with grainsize 2d was used to determine the effect of temperature (293 to 20 deg K at a strain-rate of 2.02 x 10/sup -4/ sec/sup -1/) and strain-rate (2.02 x 10/ sup -4/ sec/sup -1/ -6.18 x 10/sup -2/ sec/sup -1/ at 77 DEK) on the values of sigma /sub i/ and k/sub y/ in a Petch type equation sigma /sub y/ = ss/sub i/ + k/sub y/d/sup -1/2/. Results indicated that the ductile-brittle transition characteristics are in accordance with Cottrell's transition equation ( sigma / sub i/d/sup 1/2/ + k/sub y/)k/sub y/ = beta mu gamma . Niobium shows a greater resistance to brittleness than carburized alpha -iron because it has a smaller k/sub y/ value, and the reluctance of the material to twin except under extreme conditions of low temperature or high strain-rate is also attributed to a low value of k/sub y/. The mechanical behavior of niobium relative to that of other body-centered cubic transition metals was discussed. (auth)

• Research Organization: Materials Research Corp., Yonkers, N.Y.
• NSA Number: NSA-14-023311
• OSTI ID: 4149422
• Journal Information: Acta Met., Journal Name: Acta Met. Vol. Vol: 8
• Country of Publication: Country unknown/Code not available
• Language: English

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METALS, CERAMICS, AND OTHER MATERIALS