Surface microstructures and corrosion behavior of Zircaloy-4 induced by the composite action of micro electrical discharge machining and high current pulsed electron beam

Abstract

In present study, the Zircaloy-4 was subjected to a composite surface modification induced by a micro electrical discharge machining (μEDM) device and a high current pulsed electron beam (HCPEB) device. The results showed that after μEDM-HCPEB composite action (using the μEDM device for main cutting and 7 times of trimming, followed by 25 times surface irradiation with the HCPEB device), the sample surface became extremely flat and compact, and Cu alloying was successfully achieved. The alloying layer featured significant refinement of grains and martensites, along with the formation of extensive areas consisting of nanocrystalline grains. Also in this layer, except for most Cu atoms that being uniformly dissolved in the matrix, some others together with Fe and Cr atoms formed a few Zr(Fe, Cr, Cu)₂ second phase particles (SPPs) which sizes were smaller than 20 nm. On the contrary, large-sized Zr(Fe, Cr)₂ SPPs with a size range of 100–250 nm that originally existed in the matrix dissolved throughout the remelted layer and the heat-affected zone. Corrosion behavior test was conducted in 500 °C/10.3 MPa superheated steam, and the results indicated that the aforementioned surface microstructural changes endowed the 7-trimmed+25-pulsed sample with extremely excellent corrosion resistance.