The separation of hafnium and zirconium, required for nuclear use of zirconium, is generally performed by liquid-liquid extraction in organic solvents. The paper describes a new process based on extractive distillation of zirconium chloride (ZrCl4) and hafnium chloride (HfCl4) in a solvent made of molten potassium chloride-aluminum chloride (KCl-AlCl3) mixture above 350°C at atmospheric pressure. The corresponding process is now in full-scale industrial production.

Starting from the extrusion billet, different reduction sequences were used to fabricate tubing to the same final dimensions. The fabrication sequences varied in the reductions of area, wall thickness, and diameter and also in the number of rolling steps (five to three), corresponding to area reductions in the range from 38% to 90%. They included common reduction routines as well as experimental reduction procedures. The microstructural properties and the corresponding textures were measured in each sequential pass for the as-rolled and for the annealed conditions, respectively. The results show that the reduction parameters of the final step predominantly determine the microstructure and texture in the final tube. The parameters governing the texture development, such as the reductions in wall thickness, diameter, and area as well as the intermediate annealing conditions, are determined after each reduction step. Maximum intensities and spread of basal and prism pole orientations, f-factors, etc., describing the texture are correlated with the microstructural parameters, such as grain size, degree of recrystallization, and hardness. After the final cold reduction step, different annealing temperatures were applied in order to follow up and correlate the changes in microstructure and texture for The final tube condition. The results of these measurements allow conclusions about the recrystallization kinetics, as a function of cold deformation, annealing temperature, and annealing time. Their correlation with the factors determining the texture, resulting from the investigated reduction parameters, lead to an understanding of the control and improvement of the properties of the final tube.

The precipitation of intermetallic compounds in Zircaloy-4 has been studied by transmission electron microscopy. The classical precipitates with a ZrCr2 lattice have been observed. In addition to these precipitates, a hexagonal phase with lattice parameters a = 7.9 Å and c = 3.3 Å can be developed by quenching from the temperature range 840 to 870°C. This phase is metastable and transforms into a zirconiumiron compound by aging at 600 to 650°C.