Zirconium and Hafnium Interdiffusion Study in ZrB ₂ –HfB ₂ System

ABSTRACT Interdiffusion of Zr and Hf in the diboride system was investigated. High‐purity zirconium diboride (ZrB 2 ) and hafnium diboride (HfB 2 ) were prepared by a combination of boro‐/carbothermal reduction synthesis and densification by spark plasma sintering. The bulk ceramics had relative densities of 99.3% for ZrB 2 and 99.7% for HfB 2 , and both ceramics were phase‐pure by x‐ray diffraction analysis. Diffusion couples of ZrB 2 and HfB 2 were annealed at temperatures ranging from 2000°C to 2200°C for times from 4 to 12 h. Zr and Hf elemental concentration profiles were measured using energy dispersive spectroscopy and analyzed using an algorithm based on a Boltzmann transformation of Fick's second law. The interdiffusion coefficients increased as the annealing temperature elevated, which indicates that the interdiffusion was a thermally activated process. The diffusion rate of Hf in ZrB 2 is smaller than that of Zr in HfB 2 due to the larger atomic mass and stronger bonding strength.