Effect of high current pulsed electron beam surface irradiation on the microstructure and electrochemical behavior of zircaloy-4

The microstructure and electrochemical behavior of zircaloy-4 prior and after high-current pulsed electron beam (HCPEB) irradiation were investigated. The microstructures of the surface layer were studied by means of X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Observation results indicated that, martensitic phase transformation was induced by HCPEB irradiation and formed plate martensitic structures containing a high density of ultrafine twins. When the number of pulse was increased, these structures were constantly refined along with their parent beta grains. Besides, second-phase particles (SPPs) in the modified layers were completely dissolved into the substrate and formed Fe, Cr-containing supersaturated solid solution. The electrochemical behavior was characterized by using electrode impedance spectroscopy (EIS) and potentiodynamic polarization curves. Electrochemical results demonstrated that, compared to the initial specimen, all the irradiated specimens showed better corrosion resistance in 0.01 mol LiOH solution, among which 25-pulsed specimen possessed the best corrosion resistance. Surface selective purification, supersaturated Fe, Cr elements in substrate and abundant structure defects jointly promoted the improvement of the corrosion resistance.