THE EFFECT OF INTERSTITIAL ATOM-DISLOCATION INTERACTIONS ON THE DEFORMATION BEHAVIOR OF SOME BODY-CENTERED-CUBIC METALS
The strain aging behavior of arc-melted niobium and tantalum, 1020 steel, and hydrogenated niobium was investigated using yield-point return and dynamic modulus of elasticity measurements to study the aging process. Comparison of activation energies for strain aging with those for interstitial diffusion revealed that hydrogen was responsible for dislocation locking in niobium, and probably in tantalum, in the temperature ranges studied. The studies on 1020 steel reconfirmed the fact that nitrogen and carbon cause dislocation locking in mild steel, and validated the accuracy of the yield point return and dynamic modulus techniques for studying the strain aging process. The elastic interaction, U, between hydrogen atoms and dislocations in niobium is quite small as compared to U for carbon in alpha-iron (U for H in Nb ses appear to c 0.03 ev, U for C in alpha --Fe =0.5 ev). It is suggested that there may be a significant electrical interaction between hydrogen atoms and dislocations in Nb. It was concluded that hydrogen locking of dislocations in Nb occurs to some extent by Cottrell-Bilby segregation, but probably more strongly by the formation of microprecipitates aiong dislocation lines. Harper's modification of the Cottrell-Bilby analysis was applied to the dynamic modulus strain aging data for 1020 steel, niobium, and hydrogenated niobium to determine dislocation densities in these materials. Densities so determined were compared with values obtained by direct observations using etchpitting techniques. In order to obtain a measure of the degree of dislocation locking in niobium as a function of hydrogen content, the lower yield stress of electron beam melted niobium was measured as a function of grain size and hydrogen content (7, 15, 61, and 78 ppm H). In the Petch equation, olytic C and /sub y/ = olytic C and /sub y/ + k/sub y/d/sup -1/2/, the paramete r k/sub y/ a measure of the dislocation locking strength, was found to increase with increasing hydrogen content. The lattice friction stress, olytic C and /sub i/, decreased with increasing hydrogen content, probably because the hydrogenating treatments caused the removal of oxygen and nitrogen from solid solution. The effective surface energy, , for crack propagation in hydrogen embrittled niobium (367 ppm H) was found to be less than 1410 ergs/cm/sup 2/ using Cottrell's fracture criterion. Using Johnson's ductile cleavage fracture theory, was found to be less than 4650 ergs/cm/sup 2/. (Dissertation Abstr. 23: May 1963)
- Research Organization:
- Originating Research Org. not identified
- NSA Number:
- NSA-17-025827
- OSTI ID:
- 4698045
- Resource Relation:
- Other Information: Thesis. Orig. Receipt Date: 31-DEC-63
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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Related Subjects
ATOMS
BRITTLENESS
CARBON
CARBON STEELS
CRACKS
DEFECTS
DEFORMATION
DIFFUSION
DISLOCATIONS
DISTRIBUTION
DUCTILITY
ELASTICITY
ELECTRIC ARCS
ELECTRON BEAMS
EQUATIONS
ETCHING
EXCITATION
FAILURES
FRICTION
GRAIN SIZE
HEAT TREATMENTS
HYDROGEN
HYDROGENATION
INTERACTIONS
INTERSTITIALS
LATTICES
MEASURED VALUES
MELTING
MOTION
NIOBIUM
NIOBIUM HYDRIDES
NITROGEN
QUANTITATIVE ANALYSIS
QUANTITY RATIO
SEGREGATION
SOLID SOLUTIONS
STEELS
STRESSES
SURFACES
TANTALUM
TENSILE PROPERTIES