Abstract
The alloy system Al-Cr-Fe-Ni provides means for developing novel duplex materials composed of face-centered cubic (FCC) and body-centered cubic (BCC) phases with nearly equal volume fraction. We performed an alloy development study starting from the medium entropy alloy AlCrFe2Ni2 and adding small amounts of molybdenum in the following series (at.%): Al17Cr17Fe33Ni33, Al17Cr17Fe33Ni33Mo1, Al16Cr16Fe33Ni33Mo2, Al16Cr16Fe33Ni33Mo3. We focused the research on samples with an ultrafine vermicular duplex microstructure, a unique structure requiring sufficiently high cooling rates to suppress the conventional Widmanstatten colony formation. The samples were produced by arc melting in buttons of 300 g each. We characterized the microstructure of the samples using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD). The EBSD results revealed significant strain in the FCC phase, which is characteristic for the ultrafine vermicular duplex microstructure and its specific formation pathway. We investigated mechanical properties of the samples by micro-indentation and 3-point bending in a miniature testing device. The test specimens were in the as-cast condition, as well as in distinct annealed conditions. Annealing treatments were carried out at 950 °C and 1100 °C under argon. The annealing lasted from 10 minutes to 6 hours, followed by water quenching. Prolonged annealing at 950 °C of Mo-containing samples resulted in the formation of sigma-phase. Annealing at 1100 °C safely avoided sigma-phase formation, while leading to a good balance between the flexural strength and ductility of these samples. Mechanical testing also included the well-established superduplex steel 1.4517 (DIN EN 10283 / ASTM A890) as reference material.
Highlights
In the last two decades, research on high entropy alloys (HEAs) aimed at finding alloys that would allow obtaining single-phase equiatomic HEAs exhibiting face-centered-cubic (FCC), body-centered-cubic (BCC), and hexagonal-close-packed (HCP) structures while eliminating secondary phases (Kozak et al, 2015; Steurer, 2020)
The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation, to any qualified researcher
All authors contributed to the article and approved the submitted version
Summary
In the last two decades, research on high entropy alloys (HEAs) aimed at finding alloys that would allow obtaining single-phase equiatomic HEAs exhibiting face-centered-cubic (FCC), body-centered-cubic (BCC), and hexagonal-close-packed (HCP) structures while eliminating secondary (and tertiary) phases (Kozak et al, 2015; Steurer, 2020). Unique so far are vermicular duplex microstructures (Dong et al, 2016; Li C. et al, 2020) composed of an ultrafine vermicular FCC phase intertwined with a spinodally decomposed BCC in nearly equal volume fraction. They were first reported in 2016 by Dong et al (2016) in an AlCrFe2Ni2 alloy, being termed “noodle-like” and suggested to be of eutectic origin.
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