Synthesis and Mechanical Character of Hexagonal Phase δ-WN

Area of Science:

• Materials Science
• Solid State Chemistry
• Crystallography

Background:

• Tungsten nitride (WN) is a transition metal nitride with potential applications in various fields.
• Understanding the synthesis and properties of different WN phases is crucial for materials development.
• Previous synthesis methods for high-quality bulk WN have limitations.

Purpose of the Study:

• To synthesize high-quality bulk WC-structured WN (δ-WN) using an unconventional method.
• To accurately determine the crystal structure of the synthesized δ-WN.
• To investigate the mechanical properties, including bulk modulus and Vickers hardness, of δ-WN.

Main Methods:

• Synthesis of δ-WN using W2N3 as the tungsten source and melamine as the nitrogen source.
• Structure determination via X-ray diffraction and Rietveld refinement.
• In situ high-pressure X-ray diffraction and Vickers microhardness testing for mechanical property evaluation.
• Analysis of chemical bonding using electron localization function (ELF), density of states (DOS), and Mulliken population.

Main Results:

• Successfully synthesized high-quality bulk δ-WN, demonstrating an effective synthesis route.
• Determined the crystal structure of δ-WN accurately.
• Measured a bulk modulus of 373 ± 8.3 GPa and a Vickers hardness of 13.8 GPa (at 4.9 N load).
• Identified the primary chemical bonds in δ-WN as W-W metallic and W-N ionic, lacking strong W-N covalent bonds for a 3D network.

Conclusions:

• The novel synthesis method provides an effective route for producing high-quality bulk δ-WN.
• δ-WN possesses significant hardness comparable to established hard materials like c-BN.
• The bonding characteristics explain the observed hardness, guiding future design of superhard transition metal nitrides.