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Creep tests were carried out on specimens machined from heavily cold-worked Zircaloy-2 sheet material in both the rolling (longitudinal) and thickness (short-transverse) directions. The texture of the sheet was such that the majority of grains had basal-plane normals oriented 30 deg from the sheet-normal direction, and was independent of the metallurgical condition. The creep tests were carried out in the range 100 to 350 C on both as-received (cold-worked) and annealed material.
The results varied with temperature and stress. At high stresses (all temperatures) such that rupture occurred in under 1000 h, the longitudinal specimens showed higher creep rates than the short-transverse specimens. However, at lower stresses the texture had very little effect on creep either in cold-worked material throughout the temperature range investigated, or in annealed materials between 250 and 310 C. In annealed materials tested at temperatures below 250 and above 310 C the longitudinal specimens had higher creep rates than the short-transverse ones.
The material exhibited strong dynamic strain aging which reached maximum intensity around 300 C. In some tests the creep came to a complete stop after about 1000 h. Activation energy for creep determinations showed little variations with texture, but a very marked peaking in the strain-aging temperature range.
Optical and electron microscope investigations of crept specimens revealed the formation of kink bands and a cell structure, especially in heavily deformed specimens, but little or no twinning.
texture, strain aging, creep, Zircaloy-2
Metallurgist, Fuels and Materials Division, Applied Materials Research Branch, Atomic Energy of Canada Limited, Chalk River Nuclear Laboratories, Chalk River, Ont.