Atomic-scale interface structure of a Cr-coated Zircaloy-4 material

HRTEM and chemical study of an ion-irradiated chromium/zircaloy-4 interface

“…The different interfaces observed are crystalline and display atomic row matching. These results are in accordance with the paper of Ribis et al [33] on the atomic-scale structure of Cr-coated Zircalloy-4 alloy.…”

“…7c, 8 and 9b show atomic row matching between respectively, the ð220Þ fccÀZrðFe; CrÞ 2 and ð0011Þ hcpÀZrðFe; CrÞ 2 , the ð001Þ Cr and ð0111Þ hcpÀZrðFe; CrÞ 2 , the ð110Þ Cr and ð1101Þ Zr . As pointed out by Ribis et al [33] for a thicker Cr coating, this crystal continuity visible over several micrometers is a strong evidence pointing towards local heteroepitaxy. Also, they state that this high degree of local epitaxial growth achieved using the HIPIMS technique is expected to translate into strong adhesion of the overall coating.…”

“…Although these two phases are found in industrial grade Zircaloys [51e55], their presence at the interface is likely related to the iron enrichment. As confirmed by thermodynamic calculation using "Thermocalc" and "Zircobase" thermodynamic tools [56] and discussed by Ribis et al [33], the stability of C14-hcp is favored by Fe addition as it increases the average electron concentration ratio (e/a) which is defined for transition elements as the average number of (p þ d) electrons per atom. Thus, localized Fe enrichment or depletion at the interface observed on Fig.…”

“…Overall, the crystallinity of the interface is kept after irradiation as the plan continuity. This tends to ensure the residual good coating adhesion by avoiding a too sharp decrease of the elastic modulus when going from chromium to zirconium [33]. Note that investigations on the mechanical properties of ion irradiated Cr/Zirc-4 interface are in progress.…”

“…It has been shown that some of the coatings studied (especially those containing aluminium) entirely disappeared after irradiation showing the great interest of studying the Cr coating/Zr interfaces behavior upon irradiation [32]. This paper presents the first HRTEM observations and chemical analysis (EDS) done on chromium/zircaloy-4 interface before and after ion irradiation at 400 C. A first paper presenting a fine characterization of an unirradiated chromium/zircaloy-4 interface shows a polytyped structured Laves Phases in the vicinity of the interface and a preserved crystallinity throughout the Zr/Cr interface [33]. However, in order to compare directly the unirradiated material to the ion irradiated material, this fine characterization is necessary on our sample.…”