Enhanced Fracture Toughness in Diamond/B₄C Composites Through Residual-Stress-Induced Crack Deflection

Area of Science:

• Materials Science
• Ceramic Engineering
• Nanotechnology

Background:

• Boron carbide (B4C) is a promising material for protective and wear-resistant applications due to its low density and high hardness.
• However, B4C's inherent brittleness and crack sensitivity, stemming from strong covalent bonding, limit its reliability in demanding conditions.
• Achieving simultaneous densification and toughness enhancement in B4C composites, especially with reinforcements like diamond, remains a challenge.

Purpose of the Study:

• To investigate the synergistic effects of diamond reinforcement and rapid high-temperature and high-pressure (HTHP) sintering on boron carbide (B4C) composites.
• To systematically analyze the influence of sintering temperature and diamond content on phase evolution, densification, microstructure, and mechanical properties.
• To elucidate the toughening mechanisms in diamond/B4C composites and identify optimal processing parameters for enhanced performance.

Main Methods:

• Diamond particles were incorporated into a B4C matrix.
• The composites were consolidated using rapid high-temperature and high-pressure (HTHP) sintering.
• Systematic investigation of varying sintering temperatures and diamond content (up to 20 wt.%) was performed.
• Mechanical properties (hardness, fracture toughness) and microstructure were characterized.

Main Results:

• Hardness generally increased with higher sintering temperatures and diamond content.
• The primary toughening mechanisms identified were diamond particle pull-out and crack deflection due to residual stresses.
• A composite with 10 wt.% diamond sintered at 1450 °C under 5.3 GPa for 4 min achieved optimal properties: 98.85% relative density, 40.72 GPa Vickers hardness, and 9.20 MPa·m^1/2 fracture toughness.
• Higher diamond content (20 wt.%) led to increased hardness but also severe macroscopic cracking.

Conclusions:

• Combining diamond reinforcement with HTHP sintering is an effective strategy for simultaneously enhancing densification and fracture toughness in B4C-based composites.
• The study provides a viable pathway for developing high-performance, lightweight protective ceramics with improved reliability.
• Optimal processing parameters (10 wt.% diamond, 1450 °C, 5.3 GPa, 4 min) were identified for balancing densification and toughness.