Morphologies des nitrures β-Nb 2N et γ-Ta 2N. Relations d'orientation avec la matrice α-Nb(N); α-Ta(N)

Abstract

Thin foils of niobium and tantalum have been nitrided by heating in a flow of gaseous ammonia over the temperature range 600–700°C. The three phases β-Nb 2N, β-Ta 9N and γ-Ta 2N formed have been studied by electron microscopy and diffraction. The two hexagonal nitrides, β-Nb 2N and γ-Ta 2N, appeared as twinned precipitates with a (011̄1) cph twinning plane parallel to one of the matrix α-Nb(N) or α-Ta(N) {110} bcc planes. The angle between the close-packed (0001) cph and (110) bcc planes is ~2°. A similar relationship has been observed by Potter between the V 3N phase and the α-V(N) phase. However, some precipitates of γ-Ta 2N are in a different orientation with respect to the matrix and are best described by the relationship of Pitsch and Schrader. The crystal structures of the nitrides are in agreement with previous results.