Plasticity Mechanisms in Nanostructured Cubic Boron Nitride: Internal Defects and Amorphous Layers

Area of Science:

• Materials Science and Engineering
• Nanotechnology
• Computational Materials Science

Background:

• Nanostructured cubic boron nitride (NS-cBN) exhibits high hardness and thermal stability.
• A systematic approach to balance strength and toughness in NS-cBN through structural design is needed.
• Understanding the role of defects like twin boundaries (TBs), stacking faults (SFs), dislocation networks, and amorphous interfacial layers (AILs) is crucial.

Purpose of the Study:

• To elucidate the size-dependent roles of various internal defects and AILs in NS-cBN.
• To establish design principles for balancing strength and toughness in NS-cBN.
• To guide the development of next-generation superhard materials.

Main Methods:

• Integration of plasticity theory with large-scale atomistic simulations.
• Analysis of defect mechanisms including dislocation penetration, grain-boundary sliding, and destacking fault mechanisms.
• Investigation of the effects of AIL thickness, density, and bond strength on mechanical properties.

Main Results:

• Competition between slip modes and grain-boundary sliding governs strength and crack-initiation strain in TBs and SFs.
• Cross-slip of dislocations and destacking fault mechanisms enhance strength and toughness.
• Dislocation networks increase failure strain by 76% and induce a metal-like plastic plateau.
• A 0.5 nm-thick AIL simultaneously enhances strength and toughness by homogenizing stress and suppressing crack initiation.

Conclusions:

• Synergistic tailoring of internal defects and AILs can achieve NS-cBN with combined high strength and toughness.
• General design principles are established for developing advanced superhard materials.
• Atomistic structural design is key to optimizing the mechanical performance of NS-cBN.