PROCESSING MAP FOR HOT-WORKING OF ALPHA-ZIRCONIUM

The hot deformation characteristics of alpha-zirconium in the temperature range of 650-degrees-C to 850-degrees-C and in the strain-rate range of 10(-3) to 10(2) s-1 are studied with the help of a power dissipation map developed on the basis of the Dynamic Materials Model.[7,8,9] The processing map describes the variation of the efficiency of power dissipation (eta = 2m/m + 1) calculated on the basis of the strain-rate sensitivity parameter (m), which partitions power dissipation between thermal and microstructural means. The processing map reveals a domain of dynamic recrystallization in the range of 730-degrees-C to 850-degrees-C and 10(-2) to 1 s-1, with its peak efficiency of 40 pct at 800-degrees-C and 0.1 s-1, which may be considered as optimum hot-working parameters. The characteristics of dynamic recrystallization are similar to those of static recrystallization regarding the sigmoidal variation of grain size (or hardness) with temperature, although the dynamic recrystallization temperature is much higher. When deformed at 650-degrees-C and 10(-3) s-1, texture-induced dynamic recovery occurred, while at strain rates higher than 1 s-1, alpha-zirconium exhibits microstructural instabilities in the form of localized shear bands which are to be avoided in processing.