THE EFFECT OF HYDROGEN ON THE MECHANICAL PROPERTIES OF COLUMBIUM

Thesis/Dissertation · Tue Jan 01 04:00:00 EST 1963

OSTI ID:4745417

Wood, T W

The mechanical properties of Nb-H alloys, as a function of H content, temperature and strain rate, were investigated. H embrittles Nb even at concentrations below the limit of solubility. The concentration of H necessary to effect a given degree of embrittlement increases with increasing temperature in a roughly exponential manner. When not masked by a high ductile-brittle transition temperature caused by other factors (e.g., grain structure or other embrittling impurities), a restoration of ductility is observed at low temperatures. The ductility minimum occurs at about --78 deg C, which temperature appears to be that of H-strain aging during the tensile test The embrittlement associated with the presence of H can be removed by vacuum dehydrogenation. H solubility in Nb increases with increasing temperature. The H concentrations necessary to cause embrittlement vary with temperature in a manner similar to that of the solubility but are somewhat less than the gross solubility. At H contents above the limit of solubility a second phase forms with a volume expansion of 10%. This expanded second phase constitutes prestressed Griffith crack on (100) planes and is the evident cause of embrittlement. At H concentrations below the limit of solubility, H is believed to segregate at microcrack vertices during plastic straining. The repulsive forces consequent to the segregation increase the stress concentration at the crack vertices. The applied stress required for fracture is thus lowered. It is found that the fracture stress of Nb decreases, with increasing H content, most rapidly at the strain-aging temperature. It is at this temperature, during straining, that H is delivered at a maximum rate to microcracks by the dislocations. (M.P.G.)

• Research Organization: Originating Research Org. not identified
• NSA Number: NSA-17-016728
• OSTI ID: 4745417
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

BRITTLENESS
CRACKS
DEFECTS
DEFORMATION
DISLOCATIONS
DISTRIBUTION
DUCTILITY
EXPANSION
FAILURES
GRAIN SIZE
HYDRIDES
HYDROGEN
IMPURITIES
LOW TEMPERATURE
MECHANICAL PROPERTIES
METALS, CERAMICS, AND OTHER MATERIALS
NIOBIUM
QUANTITY RATIO
RECOVERY
SEGREGATION
SOLUBILITY
STRESSES
TEMPERATURE
TRANSITION TEMPERATURE
VACUUM
VOLUME