Rigid three-dimensional networks of hafnium diboride for improving mechanical and wear properties of boron carbide

Abstract

Being one of the hardest materials known in nature, boron carbide (B4C) suffers from severe degradation of mechanical properties when subjected to external pressure or shear stress, which hinders its application in metal forming and machining industries. Herein, based on the phase diagrams, a new strengthening strategy consisting of constructing three-dimensional hafnium diboride (HfB2) networks was proposed to reinforce B4C using the molten-salts method followed by spark plasma sintering (SPS). It was found that the surface amorphization and subsequent decarburization were the main wear regime of pure B4C. Incorporating hard HfB2 networks in B4C resulted in enhanced mechanical properties and reduced wear rates, as the deformation and decarburization of B4C grains were effectively restrained. The excessively high Hf contents, however, made the composites prone to severe adhesive wear following the material transfer from mating materials during the inception of sliding contact, which led to deteriorated wear performances. Thus, the optimal molar ratio of Hf to B4C was determined with the underlying wear mechanisms delineated. The presented results not only show the feasibility of B4C-HfB2 composites as tool materials but also provide a novel designing strategy employing hard networks rather than conventional compliant binders to fabricate wear-resistant composite materials.

Keywords

• Boron carbide
• Hafnium diboride
• Three-dimensional networks
• Mechanical properties
• Wear resistance