Influence of the cooling rate on the texture and the microstructure of Zircaloy-4 studied by means of a Jominy end-quench test

When zirconium alloys are used for fuel cladding in nuclear plants, they are β quenched and then extruded and rolled in the upper α range. At the start of this mechanical process, the alloys possess a lamellar, Widmanstätten microstructure. When the quenching is applied to large billets, the difference of cooling rates between the outer surface and the core of the piece produces variations in the microstructure. To investigate this phenomenon, the Jominy end-quench device has been adapted here to Zircaloy-4. The width of the lamellae, the size of the colonies and of the precipitates, the hardness are shown to depend strongly on the cooling rate. Other features of the quenched material are less rate-dependent: the sharp texture provoked by the α→β→α transformation, the disposition of the lamellae (intricated or parallel) and the number of the principal variants found within the former β grains.