Irradiation resistant high entropy alloys – HERIA

HEA (high entropy alloys), along with their multiphase recent developments, CCA (complex concentrated alloys), are new classes of metallic materials in which exceptional and improved properties are expected due to the several-element-rich composition of metallic matrix. These alloys are promised for future applications in different demanding areas like in the nuclear industry. The purpose of HERIA project is to evaluate the interest of applications of HEAs/CCAs in this field. The project takes advantage on its members’ expertise: (i) original single phase HEAs, recently designed and developed; (ii) successful development of methodology of numerical design of HEA/CCA alloys. This approach will be used to extend the range of possible applications through design and optimization of new multiphase CCAs, “HE-superalloys”. The whole set of alloys will cover a wide range of industrial interests (defined by project’s industrial partners), as possible substitutes for nowadays used 316SS, but also for more resistant precipitation hardened alloys like A286 or alloy 718.
The criteria of success will be determined through an in-depth evaluation of selected alloys, from the point of view of their mechanical properties (yield strength YS, ultimate tensile stress UTS, elongation to fracture, formability) in parallel with their irradiation behaviour. Since very low stress relaxation is expected under irradiation, the stress corrosion resistance could be also an issue for high strength applications encountered in fuel design applications: the alloys that will be developed have to be also optimized for this property. The principal hypothesis is based on bibliographic data suggesting an improved radiation resistance of complex HEA matrices.
The project goals are considered in two different fields. The technical objectives deal with the development of new HEAs/CCAs. The scientific objectives focus on: (i) in depth analysis and understanding of irradiation mechanisms and behaviour of HEA matrices, at atomic and microscopic level, including the confirmation of an improved irradiation resistance; (ii) application and improvement of existing alloy design methods to the case of CCAs.
HERIA consortium is composed of five academic research labs (or “grand organisme” like DNM-CEA) and one industrial R&D entity, EDF R&D. The two other industrial partners are respectively in charge of (i) HEA elaboration and pre-industrialisation (Aperam); (ii) definition of alloys specification (Framatome); (iii) stress corrosion tests of HEAs/CCAs (Framatome). In this project, structured into five interconnecting work-packages, the consortium applies both experimental and computational approaches. It covers the whole necessary chain of development and evaluation of novel alloys: (i) elaboration, both in industrial-lab (Aperam) and by a unique high-purity cold crucible method laboratory melting (Armines, MINES St-Etienne); (ii) computational design of original and optimised grades (IMN) on the bases of thermodynamic and physical modelling associated to in-house developed genetic algorithms; (iii) access and expertise to use the unique JANNuS platforms associated to long-lasting experience of TEM quantitative analyses (DNM-CEA and CSNSM) to study irradiation defects; (iv) high-level expertise in TAP atomic scale chemical analyses, necessary to understand the phenomena of segregation and pre-precipitation (GPM); (v) long-lasting expertise in atomic scale computational modelling of alloys (DNM-CEA and EDF R&D MMC) especially those considered as “reference materials” in the project. The project will be performed with strong implication of Framatome, the unique European designer and producer of nuclear fuel assemblies.