Microstructure of warm worked zircalloy-4

Abstract

The microstructure of commercial purity Zircalloy-4 (Zry-4) compressed at temperatures 650°C and 750°C up to strains of 0.8 was characterized over a wide range of scales, using optical metallography, scanning (SEM) and transmission (TEM) electron microscopy. The typical microstructure after warm deformation consisted of the α-phase matrix and the second phase particles (SPP) enriched in Fe and Cr. Two kinds of these particles were observed. The large isolated SPP were situated along boundaries of lamellae of α-phase, whereas very fine intermetallic particles were nearly homogeneously distributed inside the lamellae. The intensity of recrystallization was main factor deciding on microstructure development in this material. The efficiency of that process increased quite rapidly with temperature or decreasing strain rate. The appearance of twins was the second important feature of the 'warm deformed' structure with the prevailing {11̄02} - type system of twins. They were occasionally observed in all samples after the deformation at 650°C and 750°C temperatures.