The deformation microstructure and creep mechanisms of Zircaloy-4 have been investigated. Four Zircaloy-4 specimens were tested at different temperatures and stress levels and the deformation microstructures of these specimens were analyzed using transmission electron microscopy. On the basis of microstructural observation of a-type screw dislocations in prismatic slip systems, the modified jogged-screw model has been applied as a rate controlling mechanism for creep of Zircaloy-4. In addition, the stress dependency of dislocation density, jog spacing, and jog height has been evaluated via modeling and experimental observations. The purpose of this study is to provide a detailed understanding of the creep deformation of Zircaloy-4 and prediction of creep rates in this alloy based on the microstructural information obtained from TEM analysis.

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Ductile Ni3Al-based alloys offer unique properties. However, their use has been limited because information is lacking regarding their processing into various product forms. This paper describes the recent progress made toward melting, electroslag remehing, and the processing of large-scale ingots of one of the Ni3Al-based alloys.Microstructural data are presented after various homogenization treatments. Both as-cast and homogenized samples were subjected to hot-compression testing. The hotcompression data for the commercial-size ingot showed the same behavior as previously reported on the experimental heats. The status of industrial applications of nickel-aluminide alloys is also described.

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