Production and characterization of the Cr_35Fe_35V_16.5Mo_6Ti_7.5 high entropy alloy

© 2022 The Authors. Published by Elsevier Ltd. This research has been supported by the Agencia Estatal de Investigación of Spain (PID2019-105325RB-C33/AEI/10.13039/ 501100011033) and by the Regional Government of Madrid through the program TECHNOFUSI´ON(III)CM (S2018/EMT-4437), project cofinancing with Structural Funds (ERDF and ESF). The support of the Madrid Government (Comunidad de Madrid-Spain) through the Multi-annual Agreement with UC3M ( Excellence of University Professors – EPUC3M14 and in the context of the V PRICIT - Regional Programme of Research and Technological Innovation) is also acknowledge.
The microstructure, thermal stability, and mechanical properties of a novel Cr_35Fe_35V_16.5Mo_6Ti_7.5 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 Fe_2Ti. 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 sigma-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 ºC 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 sigma-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.
Ministerio de Ciencia e Innovación (MICINN)
Comunidad de Madrid
Comunidad de Madrid / Universidad Carlos III
Depto. de Física de Materiales
Fac. de Ciencias Físicas
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