Study of the FCC+L12 two-phase region in complex concentrated alloys based on the Al-Co-Cr-Fe-Ni-Ti system

International audienceNew face-centered cubic (FCC) multicomponent alloys designed through the high-entropy (HEA) concept and strengthened with L12 ordered precipitates are promising material solutions for high temperature (HT) structural applications. However, as the design strategy is based on multi-principal elements, the research of alloy compositions exhibiting a stable and well-controlled FCC+L12 microstructure at HT is particularly challenging. Among the critical issues, those relative to the extent and the stability of the FCC+L12 two-phase region in the wide compositional space have to be addressed. Here, we performed high-throughput Calphad calculations in the senary Al-Co-Cr-Fe-Ni-Ti system in the 800°C-1000°C range to screen alloy compositions exhibiting duplex FCC+L12 microstructures. From the 79 695 analyzed compositions, we show that roughly 6% of the total own duplex microstructure at 800°C and 1000°C. Calculations suggest that Cr and Fe additions destabilize the two-phase region. Interestingly we found that Fe is a good candidate to substitute Co or Ni in the FCC phase and potentially induce some solid solution strengthening effects. Finally, the present results allow to propose an original 2D visualization method of the two-phase FCC+L12 region in the complex compositional space. The method is based on the relative influence of the alloying elements on the formation of such microstructure. To assess the reliability of calculations, six alloys were designed and characterized. A good agreement is found between predictive calculations and experimental results except for Cr-and Al-free alloy compositions in the quaternary Co-Fe-Ni-Ti system, due to the absence of description of the τ phase with (Ni0.5Co0.5)3Ti composition in the selected thermodynamic database

Combining experiments and modeling to explore the solid solution strengthening of high and medium entropy alloys

International audienceThe mechanical properties due to solid solution strengthening are explored within the single phase fcc domain of the Co-Cr-Fe-Mn-Ni high entropy alloy (HEA) system. This is achieved by combining an efficient and reproducible metallurgical processing of alloys to X-ray diffraction and nanoindentation characterization techniques, thus enabling to get access to 24 different bulk alloys. Large variations of nanohardness are seen with composition. Experimental results are rationalized in terms of lattice misfit and elastic constant variations with alloy-composition, through the use of an analytical mechanistic theory for the temperature-, composition-and strain-rate-dependence of the initial yield strength of fcc HEAs, with predictions made using only experimental inputs. The good agreement obtained by comparing model predictions to experiments provides the basic framework for mechanical properties optimization within the Co-Cr-Fe-Mn-Ni system; the approach could be systematically applied to all classes of fcc HEAs

Combining tensile tests and nanoindentation to explore the strengthening of high and medium entropy alloys

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Influence of ball-milling and annealing conditions on nanocluster characteristics in oxide dispersion strengthened steels

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Microstructure and mechanical properties of a CoCrFeMnNi high entropy alloy processed by milling and spark plasma sintering

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Influence of ball-milling and annealing conditions on nanocluster characteristics in oxide dispersion strengthened steels

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