Abstract
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) Ni44Fe20Cr20Al16 and (iii) Ni34.4Fe16.4Co16.4Cr16.4Al16.4. Samples in form of cylindrical bars, dia. 10 mm x 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 BCC-B2 and FCC in order to facilitate phase characterization by energy dispersive x-ray analysis (SEM / EDS) 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.
Highlights
The intermetallic compound NiAl has long been proposed as a potential alloy for high temperature structural applications due to its high melting-point, good thermal conductivity and excellent corrosion resistance (Miracle, 1993; Noebe et al, 1993; Liu, 1995)
Summarizing, we found that FCC/BCC-B2 eutectics with lamellar microstructure were reported for ternary Al-Ni-Fe, quaternary
The aim of this study was to take up the early work by Misra and Gibala (1997), Misra et al (1998), Misra and Gibala (1999), and Misra et al (2005) and compare the microstructure and properties of ternary FCC/BCC-B2 eutectics to the recent eutectic high-entropy alloy (EHEA) reported by Lu et al (2014), Gao et al (2017), Jin et al (2019)
Summary
The intermetallic compound NiAl has long been proposed as a potential alloy for high temperature structural applications due to its high melting-point, good thermal conductivity and excellent corrosion resistance (Miracle, 1993; Noebe et al, 1993; Liu, 1995). Because of the relatively low density (5.7 g/cm3) it was especially considered for lightweight applications (Bei and George, 2005). Resulting from a high degree of order in the crystal structure and corresponding limitations in slip transfer, NiAl suffers from low room temperature ductility and low fracture toughness.
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