Theoretical and experimental study of combustion synthesis of microgradient ULTRA high-temperature ceramics in Zr-Ta-Si-B system

Abstract

The macrokinetic features and phase and structure formation mechanisms are investigated in the Zr-Ta-Si-B system in the framework of the fractal theory of combustion. The reaction mechanisms are explored using ab initio grand potential modeling and Ellingham diagrams and then verified via direct in situ time-resolved XRD and quenching of combustion fronts in a copper block. The tendency of the Zr-TaSi-B system to form tantalum boride Ta3B4 and a transient tantalum silicide Ta5Si3 and release elemental Si and Zr in the combustion front is suggested based on the developed models and verified using a quenched combustion front and timeresolved XRD analysis. Investigation of hot-pressed combustion products shows that despite slightly higher relative density, TaSi2-rich ceramics have relatively lower mechanical properties and oxidation resistance under plasma torch as compared to single-phase (Zr,Ta)B2 solid solution.