Microstructure and Hydrogen Permeability of Nb-Ni-Ti-Zr-Co High Entropy Alloys

Area of Science:

• Materials Science
• Chemical Engineering
• Hydrogen Technology

Background:

• Hydrogen separation membranes are crucial for hydrogen purification.
• High-entropy alloys (HEAs) offer a promising approach due to their unique elemental interactions and structural properties.
• Preventing hydride formation and maintaining high permeability are key challenges in HEA development for membranes.

Purpose of the Study:

• To investigate the fabrication and hydrogen separation performance of equimolar and non-equimolar Nb-Ni-Ti-Zr-Co high-entropy alloys.
• To analyze the influence of composition and microstructure on hydrogen permeability and embrittlement resistance.
• To correlate ab initio calculations of hydrogen binding energy with experimental observations.

Main Methods:

• Fabrication of Nb-Ni-Ti-Zr-Co HEAs using arc melting.
• Microstructural and phase composition analysis via scanning electron microscopy and X-ray diffraction.
• Hydrogen permeation experiments conducted at 300-500 °C and 4 bar pressure.
• Ab initio calculations using virtual crystal approximation to determine hydrogen binding energies.

Main Results:

• Nb-enriched and near equimolar BCC phases were observed in Nb20Ni20Ti20Zr20Co20 HEA.
• Nb-enriched BCC and B2-Ni(Ti, Zr) phases formed in Nb40Ni25Ti18Zr12Co5 alloy.
• Nb20Ni20Ti20Zr20Co20 HEA exhibited lower activation energy, higher permeability at lower temperatures, and improved resistance to hydrogen embrittlement.

Conclusions:

• The composition and resulting microstructure significantly impact the hydrogen separation performance of Nb-Ni-Ti-Zr-Co HEAs.
• The Nb20Ni20Ti20Zr20Co20 HEA demonstrates superior potential for hydrogen separation applications.
• Understanding hydrogen binding energies is crucial for optimizing HEA design for membranes.