Structurally modulated Zr(Fe,Cr)2 secondary phase particles in Zircaloy-4 alloy subjected to cyclic deformation at room temperature

Phase stability of the fine dispersed secondary phase nanoparticles (SPPs), which is the key to ensure the mechanical properties, corrosion and neutron irradiation resistances of zirconium alloys, is tightly linked with their intrinsic microstructrues. Here we found structurally modulated SPPs were frequently observed in the Zircaloy-4 alloy under cyclic deformation. By using transmission electron microscopy techniques, a modulation structure containing Zr(Fe,Cr)2 SPP, which located at alpha-Zr grains boundaries, has been systematically investigated, for its particular substructure and location. Results indicated modulation structure in this C14 structured SPP was incommensurate with a modulation vector of q = 0.117 b* + 0.289 c*. And the modulation structure was likely to be induced by the periodic Zener pinning effect of grain boundary during fatigue test. This study is expected to offer an important basis for reliable crystallographic and micro-structural characterizations on SPPs, so as to understand and optimize their phase stability under service conditions.