The alloy system Al-(Co)-Cr-Fe-Ni contains compositional ranges where a solid state BCC-FCC phase transformation leads to dual-phase materials composed of face-centered cubic (FCC) and body-centered cubic (BCC) phases with nearly equal volume fraction. The microstructure arising from this transformation at slow cooling rates is the classical Widmanstätten structure, with FCC-laths and colonies growing from grain boundaries into the parent BCC-B2 grain. Very distinct microstructures are obtained, when Widmanstätten growth is kinetically suppressed e.g., during continuous cooling with high cooling rates. These novel microstructures are associated with the spinodal decomposition of the parent BCC-B2 such that FCC growth occurs during the spinodal decomposition or upon annealing from a metastable, fully spinodal state. We review the microstructures at case as function of the imposed cooling regimes for the Co-free medium entropy alloy AlCrFe₂Ni₂. One of them, termed ultrafine vermicular microstructure, involves a characteristic and novel crystal orientation relationship (OR) between FCC and BCC. We identify the common planes and directions of this OR using electron backscatter diffraction maps to be ${\{111\}}^{FCC}\parallel {\{12\overline{1}\}}^{BCC}$ and ⟨$\overline{1}01⟩{}^{FCC}\parallel ⟨\overline{1}0\overline{1}$⟩^BCC, respectively. Embedded is a second OR with ${\{1\overline{3}\overline{1}\}}^{FCC}\parallel {\{\overline{1}03\}}^{BCC}$ and ⟨101⟩^FCC∥⟨010⟩^BCC. We further show that the vermicular FCC phase contains a high amount of lattice strain and sub-grain boundaries with disorientation angles in the range from 2 to 12°, as a result of the solid-state phase transformation.

While repair is mainly used to restore the original part geometry and properties, hybrid manufacturing aims to exploit the benefits of each respective manufacturing process regarding either processing itself or resulting part characteristics. Especially with the current implementation of additive manufacturing in the production of TiAl, turbine blades for both hybrid manufacturing and repair new opportunities are enabled. One main issue is the compatibility of the two or more material types involved, which either differ regarding composition or microstructure or both. In this study, a TNM^TM-alloy (Ti-Nb-Mo) was manufactured by different processes (casting, forging, laser additive manufacturing) and identically heat-treated at 1290 °C. Chemical compositions, especially aluminum and oxygen contents, were measured, and the resulting microstructures were analyzed with Scanning Electron Microscopy (SEM) and High-energy X-ray diffraction (HEXRD). The properties were determined by hardness measurements and high-temperature compression tests. The comparison led to an overall assessment of the theoretical compatibility. Experiments to combine several processes were performed to evaluate the practical feasibility. Despite obvious differences in the final phase distribution caused by deviations in the chemical composition, the measured properties of the samples did not differ significantly. The feasibility of combining direct energy deposition (DED) with either casting or laser powder bed fusion (LPBF) was demonstrated by the successful build of the dense, crack-free hybrid material.

This study aimed at understanding the structure and properties of dual-phase eutectics in ternary, quaternary, and quinary alloys of the Al-Co-Cr-Fe-Ni system. The alloys at case were i) Ni₄₈Fe₃₄Al₁₈, ii) Ni₄₄Fe₂₀Cr₂₀Al_16, and iii) Ni_34.4Fe_16.4Co_16.4Cr_16.4Al_16.4. Samples in the form of cylindrical bars, diameter 10 mm × 150 mm, were produced by arc melting and suction casting from pure elements (>99.9 wt%). Bridgman solidification at low growth velocity was used to produce additional samples with large eutectic spacing and lamellae thickness of the two phases body-centered cubic (BCC)-B2 and face-centered cubic (FCC) in order to facilitate phase characterization by energy-dispersive X-ray analysis (scanning electron microscopy/energy-dispersive spectroscopy) and nano-indentation. In agreement with thermodynamic calculations, each of the phases was found to be multi-component and contain all alloying elements in distinct amounts. The mechanical properties of the individual phases were analyzed in relation to their composition using nano-indentation experiments. These measurements revealed some insights into “high-entropy effects” and their contribution to the elastoplastic response to indentation loading. Further analysis focused on as-cast as well as heat-treated samples comprising phase fraction measurements, micro-indentation, and miniature testing in three-point bending configuration. For optimum heat treatment conditions, a good balance of strength and ductility was obtained for each of the investigated alloys. Further work is necessary in order to assess their capability as structural materials.