STRAIN AGING OF REFRACTORY METALS
The available data on strain-aging behavior of twelve refractory metals (vanadium, niobium, tantalu, chromium, molybdenum, tungsten, ruthenium, rhodium, palladium, osmium, iridium, and platinum) were reviewed and interpreted in terms of the dislocation models proposed by Cottrell. Cottrell pictares the strain- aging phenomenon as a result of the diffusion of interstitial solute atoms to positions of lowest energy in the stress fields of dislocations in body-centered- cubic metals. A segregation of interstitial solute atoms at dislocation lines (Cottrell Atmosphere) restricts their movement and is the cause of yield-point discontinuities. The return of a yield point in strained specimens is associated with the diffusion of interstitial solute atoms back to the dislocation lines after the specimen has yielded and the dislocations have been pulled free of their locking atmospheres. Maximum points in strength vs. temperature curves and serrated stressstrain curves are attributed to the continuous diffusion of interstitial solute atoms to the vicinity of moving dislocation as a specimen is being strained. It is thought that substitutional solute atoms are responsible for the strainaging behavior of face-centered-cubic and hexagonalclose-packed metals. The body-centered-cubic metals in Group V-A (tantalum, niobium, and vanadium) tend to exhibit greater strain-aging effects and a lower transition temperature than do taose in Group VI-A (tungsten, molybdenum, and chromium). Available data indicate that strain aging is a result of the interaction of dislocations with oxygen and carbon in tantalum, oxygen and possibly hydrogen in niobium, carbon in molybdenum, and nitrogen in chromium. The interstitial solute atoms responsible for the strain aging of vanadium and tungsten are urknown. The face-centered-cubic (rhodium, palladium, iridium, and platinum) and hexagonal- close-packed (ruthenium and osmium) metals in Group VIII-A exhibit strain-aging effects similar to those observed in the two groups of bodycentered-cubic refractory metals. However, the available data do not permit the determination of the identity of the substitutional solute atoms causing the strain-aging effects. (auth)
- Research Organization:
- Battelle Memorial Inst. Defense Metals Information Center, Columbus, Ohio
- DOE Contract Number:
- AF18(600)-1375
- NSA Number:
- NSA-14-025931
- OSTI ID:
- 4126244
- Report Number(s):
- DMIC-134; PB-151092
- Resource Relation:
- Other Information: Orig. Receipt Date: 31-DEC-60
- Country of Publication:
- United States
- Language:
- English
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