W-Modified TiAlN Coatings with Compact Non-Columnar Structure for Enhanced Hydrogen Barrier Protection of NdFeB...

Area of Science:

• Materials Science and Engineering
• Surface Engineering
• Corrosion Science

Background:

• Hydrogen embrittlement poses a significant threat to the performance and longevity of magnetic materials, particularly rare-earth magnets like Neodymium Iron Boron (NdFeB).
• Titanium Aluminum Nitride (TiAlN) coatings are explored for their potential as protective barriers, but their efficacy against hydrogen permeation requires enhancement.

Purpose of the Study:

• To develop and evaluate W-modified TiAlN coatings as superior hydrogen permeation barriers for magnetic materials.
• To investigate the structural and chemical modifications induced by tungsten (W) incorporation into TiAlN coatings.
• To assess the protective performance of TiAlN and TiAlN-W coatings against hydrogen embrittlement in Fe and NdFeB substrates.

Main Methods:

• Deposition of TiAlN and TiAlN-W coatings (approx. 1.5 μm thickness) onto Fe and NdFeB substrates using physical vapor deposition.
• Characterization of coating structure and morphology using Grazing Incidence X-ray Diffraction (GIXRD) and Scanning Electron Microscopy (SEM).
• Surface chemical analysis using X-ray Photoelectron Spectroscopy (XPS).
• Electrochemical hydrogen permeation tests on Fe substrates and high-pressure hydrogen exposure tests on NdFeB substrates.

Main Results:

• W modification transformed the TiAlN structure from weakly crystalline to a more compact, amorphous/nanocrystalline coating with low crystallinity.
• XPS analysis revealed W-N/Wⁿ⁺ bonding and modified surface chemistry in TiAlN-W coatings.
• TiAlN coatings reduced hydrogen permeation by a factor of ~4.7, while TiAlN-W coatings demonstrated a reduction factor >250, with no hydrogen breakthrough detected over 15,000 s.
• TiAlN-W coated NdFeB samples remained intact after 5 MPa H₂ exposure, unlike uncoated and TiAlN-coated samples which were pulverized.

Conclusions:

• W-modified TiAlN coatings offer significantly enhanced hydrogen permeation resistance compared to standard TiAlN.
• The improved barrier properties are attributed to the more compact coating morphology and altered W-modified structure.
• TiAlN-W coatings are highly effective in preventing hydrogen embrittlement, crucial for preserving the integrity of magnetic materials.