4.7 Article

Two-step hydrogen reduction of oxides for making FeCoNiCu high entropy alloy: Part I - Process and mechanical properties

Journal

MATERIALS CHARACTERIZATION
Volume 193, Issue -, Pages -

Publisher

ELSEVIER SCIENCE INC
DOI: 10.1016/j.matchar.2022.112271

Keywords

High-entropy alloys; Hydrogen; Reduction; Mechanical property

Funding

  1. National Natural Science Foundation of China [52004342]
  2. Innovation-Driven Project of Central South University [150240015]
  3. Natural Science Fund for Outstanding Young Scholar of Hunan Province, China [2021JJ20065]

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This study presents a novel process for fabricating crack-free high-entropy alloys through two-step hydrogen reduction. The resulting alloy exhibits excellent mechanical properties, including hardness, compression strength, and tensile strength.
Iron-based 3d-transition group high-entropy alloys (HEAs), with remarkable wear resistance, high hardness, and excellent mechanical properties, are usually produced by a multiple-step high-energy-consumption smelting process. This study offers a novel process for fabricating FeCoNiCu HEAs by two-step hydrogen reduction using a mixture of Fe2O3, CoO, NiO, and CuO, after which a nearly full dense crack-free HEA was successfully produced. The alloy has a face-centered cubic (FCC) structure and an oxygen level as low as 0.10 wt%. After the first hydrogen reduction at 500 degrees C for 2 h, the oxygen level decreased from 23.30 wt% to 2.05 wt% and the powder obtained consisted of the elemental metal powder with some minor alloying. A second hydrogen reduction occurred during sintering at temperatures above 800 degrees C, in which near-full densification (> 99% relative density) was achieved at temperatures as low as 900 degrees C. All the compositions were homogeneously distributed in the alloy when the temperature was >900 degrees C, and a Cu-enriched FCC-structured secondary phase with two types of shapes was precipitated in the alloy. The final alloy showed excellent mechanical properties at room temperature, with a hardness of similar to 150 HV, compression strength up to 2.2 GPa, compression strain of >12%, tensile strength of 475 MPa, and tensile elongation of 7.9%.

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