Self-propagating high-temperature synthesis of nanocomposite ceramics TaSi2-SiC with hierarchical structure and superior properties

Abstract

This study focuses on the investigation of the combustion kinetics and mechanisms, as well as the phase and structure formation processes, during elemental self-propagating high temperature synthesis of ceramics in Ta-Si-C system.Thermodynamic and kinetic features of SHS are discussed. Thermodynamic calculations, time-resolved XRD and investigation of stopped combustion front suggest the following chemical reactions sequence in combustion wave for the Ta-Si-C system: Ta+Sisolid+C→TaC+Sisolid+C→TaC+SiC+Siliquid+C→TaC+TaSi2+Ta5Si3+SiC+Sisolid+C→TaSi2+SiC.Significant microstructure refinement occurs due to the formation of SiC within the TaC, Ta5Si3 and TaSi2 particles during the SHS. Combustion products consist of agglomerated SiC and TaSi2 particles with the size of individual grains equal to 15–50nm. Hot pressing of TaSi2-SiC powders at 1600°C produces the bulk nanocomposites with a relative density of 97%. In comparison to similar materials reported in the literature, bulk SHS composite TaSi2-30%SiC exhibits superior hardness (19.1GPa) as well as fracture toughness (6.7MPam1/2) and shows a great potential for application as a structural material and as a precursor for ion-plasma deposition of high-temperature tribological coatings.