Production and characterization of the Cr35Fe35V16.5Mo6Ti7.5 high entropy alloy. (March 2022)

• Record Type: Journal Article
• Authors: Ortega, Y.; Monge, M.A.; Savoini, B.; Muñoz, A.; Pérez, P.
• Is Part Of: Nuclear materials and energy. Volume 30(2022)
• Publication Date: 2022-03
• Subjects: High entropy alloys -- Complex alloys -- Thermal diffusivity -- Nanoindentation -- Alloys; Nuclear energy -- Periodicals; Nuclear fuels -- Periodicals; Nuclear reactors -- Materials -- Periodicals; Radioactive substances -- Periodicals; 621.4833
• DOI: 10.1016/j.nme.2022.101148
• Languages: English
• ISSNs: 2352-1791

Abstract

Highlights: The as-cat Cr35 Fe35 V16.5 Mo6 Ti7.5 exhibits the microstructure with the most homogenous composition (BCC). Thermal treatments at about 1000 °C induced the formation of a σ-phase. The analyses of pop-in events reveal that the onset of plasticity is triggered by dislocation nucleation. The thermal treatments induced hardening, but a lack of thermal shock resistance after quenching. The low thermal diffusivity makes it a potential candidate to be used as a thermal barrier. Abstract: The microstructure, thermal stability, and mechanical properties of a novel Cr35 Fe35 V16.5 Mo6 Ti7.5 high-entropy alloy were studied. The mechanical properties were mapped by nanoindentation, and the results correlated with the microstructure and the Vickers microhardness measurements. The alloy was produced by arc melting in a low pressure He atmosphere. Thermal treatments were performed to study the thermal stability of the alloy. The as-cast microstructure of the alloy exhibited a body-centered cubic phase with morphology of dendrites, outlined by a very thin interdendritic phase with a crystallographic structure compatible with Fe2 Ti. The presence of the intermetallic particles was predicted by a free-energy based model, in contrast with the single solid solution alloy predicted by a parameter-based model. The volume fraction of the dendrites in the alloy is ∼ 94 % after arc melting. A small fraction of sparse Ti-rich particles, ∼0.4 vol%, was observed. The thermal treatments produced an increase of the population of Ti-rich particles, the formation of a σ-phase and nucleation of precipitates enriched with Fe and Ti into the previous dendrites. The material in as-cast condition exhibited a microhardness value of 6.2 ± 0.3 GPa, while the alloy aged at 960 °C resulted in 7.1 ± 0.4 GPa. Nanoindentations maps showed an excellent correlation with the microstructure, and their statistical analyses yielded a nanohardness mean value of 8.2 ± 0.4 GPa in the dendritic BCC regions of the as-cast and thermal treated samples and 14.1 ± 0.6 GPa for the σ-phase. The onset of the plastic behavior has been studied by analyzing the pop-in phenomenon observed in the nanoindentation loading curves. For the as-cast alloy, this analysis showed that the elastic-to-plastic transition seems to be triggered by dislocation nucleation. The alloy has a low thermal diffusivity in the measured temperature range that increases on increasing temperature.