Structural-disorder and its effect on the mechanical properties in single-phase TaNbHfZr high-entropy alloys

By S. Maiti, W. Steurer. 2015

299 citations recorded by the source corpus.

Equiatomic TaNbHfZr refractory high-entropy alloys (HEAs) were synthesized by arc-melting. The HEAs were annealed at 1800{\deg}C for different times, at maximum up to 8 days. Their on average body-centered cubic (bcc), solid-solution structure was confirmed by X-ray (XRD) and neutron (ND) diffraction, respectively. The HEAs are characterized by high average values of the static atomic displacements from the ideal lattice positions and the local internal strain. The short-range clustering (SRC) of a subset of atoms, enriched in Hf and Zr takes place perpendicular to the directions. Furthermore, it becomes increasingly interconnected as a function of the annealing time. This is revealed by the evaluation of diffuse XRD intensities, high-resolution transmission electron microscopy (HRTEM) images, and atom probe tomography (APT). The local structural disorder and distortions at the SRC were modeled by molecular dynamics (MD) relaxations. The hardness and compressive yield strength of the as-cast HEA is found to be many times of what can be expected from the rule of mixture. The yield strength further increases by 76 % after 1 day of annealing, which can be explained by a strengthening mechanism resulting from the SRC. With further annealing to 4 days, a minor phase with hexagonal close packed (hcp) structure and rich in Hf and Zr nucleates at the larger connecting nodes of the SRCs.

Subfields: Aerospace Engineering, Biomedical Engineering, Mechanical Engineering

View Paper: https://www.semanticscholar.org/paper/cf48b57fb5431a22d6e3391cce8583c6f4700e08

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Citations in the corpus

Lattice distortion in a strong and ductile refractory high-entropy alloy (2018, background): “For instance, many HEAs exhibit not only elemental seg-regations in the as-cast condition, but also the formation of small amounts of ordered phases after the heat treatment [27,34 e 36].”
Development and exploration of refractory high entropy alloys—A review (2018, background): “In the initial BCC HfNbTaZr alloy, heat treatment at 1800 °C caused the formation of short-range clusters and consequently the increase of strength with a decrease in ductility.(53) These results indicate that the strength and ductility of some RHEAs can be controlled over broad ranges by thermomech”