Experimental study of the reaction zone at boron nitride ceramic–Ti metal interface

In the present work, solid state interaction between boron nitride (BN) ceramic and Ti metal was studied on BN plates immersed into a loose Ti powder and on BN particles embedded into a dense Ti matrix. The samples were vacuum annealed at 1000–1200°C, and the reaction zones formed at BN/Ti interfaces were characterized employing X-ray diffraction, scanning electron microscopy with electron probe microanalysis, high resolution SEM, and transmission electron microscopy with parallel electron energy loss spectroscopy. Similar but not identical multi-phase reaction zones were formed at both types of interfaces containing Ti borides (TiB and TiB2), Ti nitride (TiN1−x) and solid solution of nitrogen in Ti (α-Ti(N)). In both cases, α-Ti(N) constituted the major part of the reaction zone, its grains containing fine Ti2N/α-Ti(N) precipitates with the lamellar structure formed during cooling from the annealing temperature. The phase sequences at both BN–Ti powder and BN–Ti matrix interfaces were in a good agreement with the equilibrium B–N–Ti ternary diagram and could be plotted as diffusion paths on the isothermal section of the diagram. The differences between the two reaction zones were explained based on the different conditions of mass transfer at BN interface with a loose Ti powder and with a dense Ti matrix.