Microstructural characterization of Zr1Nb alloy after hot rolling

Abstract

The nuclear industries have large interest on the development of new alloys involving zirconium (Zr) because this material presents extraordinary mechanical properties, outstanding resistance to corrosion and high permeability to thermal neutrons, being suitable for applications in areas such as energy and human health. The alloy studied in this paper is formed by Zr and niobium (Nb), normally expressed as Zr1Nb. These two elements have large chemical affinities with oxygen, carbon, and nitrogen, elements that normally are responsible for a series of damages in the alloy. The principal goal of this work is to obtain Zr1Nb alloys and to perform microstructural characterizations before and after the hot rolling process. The resulting alloys were subjected to a process of heat treatment, the temperature was increased at a rate of 10 K/min up to 1273 K and maintained for 2 h, after which it was cooled down at −10 K/min until room temperature, with the only purpose of relieving residual stresses. The next step was to apply the hot rolling process to the alloy. The sample initially measured, approximately, 1.5 cm of thickness when it was inserted into the furnace at 1203 K to start the hot rolling. Every pass on the hot rolling reduced the thickness by 0.5 mm, originating uniform and homogeneous samples of 2.5 mm thickness. Auxiliary technical tools, such as XRD (X-Ray Diffraction), SEM (Scanning Electron Microscopy), and EDS (Energy Dispersive X-Ray Spectroscopy), were used to analyze the microstructure of the samples before and after the hot rolling process. The XRD results show the formation of only a single α-HCP (Hexagonal Close Packed) phase for our samples, indicating that they are free of other phases that can damage the material. This result is consistent and coherent with both SEM and EDS analysis. The observed homogeneity of our samples is very good; proving that both techniques employed to obtain Zr1Nb as well as the hot rolling process was well succeeded. Therefore, the obtained alloy can be directly used in the pipes of nuclear combustible industries.