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Laser Powder Bed Fusion and Heat Treatment of an AlCrFe2Ni2 High Entropy Alloy

: Vogiatzief, Dimitrios; Ervirgen, Alper; Gein, Sergej; Molina, Veronica Rocio; Weisheit, Andreas; Pedersen, Mikkel

Volltext ()

Frontiers in Materials 7 (2020), Art. 248, 12 S.
ISSN: 2296-8016
Zeitschriftenaufsatz, Elektronische Publikation
Fraunhofer ILT ()
Laser Powder Bed Fusion; high-entropy alloy; AlCrFe2Ni2; laser heat treatment

Recent research in the Al-Co-Cr-Fe-Ni and Al-Cr-Fe-Ni systems has shown thatnovel duplex materials composed of FCC and BCC phases can be obtained. Amongthem, alloys with a composition close to AlCrFe2Ni2 retain their structural propertieswhile being Co-free. Their strength and ductility can be tailored by adjusting thephase fractions of FCC and BCC phases, while the latter is undergoing a spinodaldecomposition into ordered and disordered BCC phases. Further improvement of theproperties is expected with the use of novel processing techniques such as laser powderbed fusion. This process stands out due to high geometric complexity capabilities, awide range of accessible processing parameters, and high cooling rates that supportmicrostructure refinement. Within the frame of the present study, alloy powder aroundthe composition AlCrFe2Ni2 was produced and coupons for material characterizationwere built with laser powder bed fusion. In this paper, the following will be presented:(i) prealloyed powder properties, (ii) laser powder bed fusion processing of the material,(iii) heat treatments and their subsequent effect on microstructure, and (iv) mechanicalproperties obtained by three-point bending and microhardness tests. A highlight ofthis study is the novel pathway to obtain an ultrafine duplex microstructure, whichforms upon heat treatment from a metastable as-built microstructure. A spinodallydecomposed BCC microstructure, retained due to solidification under high coolingrates, is used to nucleate and grow FCC micro-platelets during a subsequent heattreatment step. This ultrafine duplex material cannot be obtained under conventionalprocessing; thus, it can be considered a unique additive manufacturing material. In thecontext of the heat treatment study carried out in the present work, the influence of heattreatment parameters on the phase fraction of FCC platelets and the resulting hardnessand flexural properties will be discussed. Finally, the current challenges concerning theprocessing of the alloy and the possible optimization paths for best material performance will be discussed.