A mechanism of interfacial reactions between boron nitride and nickel aluminide

Abstract

The interfacial reaction between boron nitride and nickel aluminide was studied by diffusion bonding at 1000 °C. Samples annealed in air or vacuum yield the same results. The interdiffusion zone is enriched with Al. An ex situ fractured boron nitride interface shows predominantly BN, featured by granular microstructure, and a minor amount of BOx Ny . A very small amount of Al, but no Ni, is detected. On the other hand, the nickel aluminide interface shows three-dimensional Ni clusters embedded in an alumina matrix. Interactions of Ni and Al thin films with boron nitride substrates were studied to clarify the mechanism. Thermodynamic calculations of Gibbs free energy and reaction enthalpy of various possible reactions between boron nitride and nickel aluminide were carried out. The partition of Ni atoms from nickel aluminide is discussed based upon the grain-boundary diffusion of Ni atoms, chemical potential of the diffusion environment, and chemical activities of Ni and Al atoms in the presence of boron nitride.