EFFECTS OF COLD WORK AND NEUTRON IRRADIATION ON THE TENSILE PROPERTIES OF ZIRCALOY-2

Technical Report · Mon Apr 01 04:00:00 EST 1963

OSTI ID:4690313

Bement, Jr, A L

An investigation was made of the effects of cold work and neutron irradiation on the plastic behavior and fracture mechanisms of Zircaloy-2. Tensile tests of annealed and cold-rolled Zircaloy-2 both before irradiation and after fast neutron exposures at about 80 deg C to 10/sup 19/, 10/sup 20/, and 10/ sup 21/ taken both from the transverse and rolling directions of sheet containing 0, 10, 20, 40, and 70% cold work. The preferred orientations imparted by cold rolling were characterized by x-ray diffraction pole figures. The results of this investigation showed that anisotropy in the tensile properties of Zircaloy-2 with stress direction is due to the inhomogeneity of plastic deformation. Plastic deformation occurred both by slip and twinning, and the amount of twinning varied with stress direction in accordance with preferred orientation. Directional effects were also observed both in the plastic instability associated with necking and in fracture. After the onset of necking, microcracks formed at inclusions and opened into pores. Porosity distributions depended on the confinement of plastic deforiration during necking and inclusion distributions due to rolling. Transverse specimens necked primarily along shear zones and exhibited extensive shear lips in their fracture. The effects of preferred orientation on tensile properties were modified by neutron irradiation. Directionality effects on plastic instability were increased in annealed Zircaloy- 2 by differences in radiation hardening mechanisms. Transverse specimens exhibited a yield point and necked at plastic strains less than 5% after exposures of 10/sup 19/ n/cm/sup 2/. This instability was accredited to the source hardening of twinning dislocations from neutron damage to the crystal lattice. Changes in tensile properties due to this type of hardening did not saturate at exposures less than 10/sup 21/ n/cm/sup 2/, the highest exposure attained. Some strain hardenability in the longitudinal direction of annealed Zircaloy-2 was retained after neutron irradiation. Radiation damage impedance to moving dislocations had the major influence on properties in this direction. Changes in tensile properties saturated at about 10/sup 20/ n/cm/sup 2/ exposure in longitudinal, cold-worked specimens. At higher exposures, reversals in strengih and ductility were observed. This apparent recovery occurred at temperatures below the thermal recovery ranges for both cold work and radiation damage and was attributed to interactions between dislocations and radiation- induced defects. Twinning modes other than {1012} twinning were not active in significant amounts after neutron irradiation. Variations in the inhomogeneity of deformation with stress direction were as dominant after irradiation as before. Mode s of fracture and pore formation were unchanged by irradiation; however, deformation during necking in the transverse direction was more confined to shear zones. This greater confinement of necking deformation plus the decrease in strain hardenability accounted for a large decrease in fracture energy with irradiation. (auth)

• Research Organization: General Electric Co. Hanford Atomic Products Operation, Richland, Wash.
• DOE Contract Number: AT(45-1)-1350
• NSA Number: NSA-17-032665
• OSTI ID: 4690313
• Report Number(s): HW-74955
• Country of Publication: United States
• Language: English

Related Subjects

ANISOTROPY
ANNEALING
COLD WORKING
DEFECTS
DEFORMATION
DISLOCATIONS
DUCTILITY
FAILURES
FAST NEUTRONS
HARDNESS
IMPURITIES
IRRADIATION
LOW TEMPERATURE
MECHANICS
METALS, CERAMICS, AND OTHER MATERIALS
RADIATION DOSES
RADIATION EFFECTS
ROLLING
TENSILE PROPERTIES
X RADIATION
ZIRCALOY