Mechanism of formation of Fe–N alloy in the solid-state reaction process between iron and boron nitride

Abstract

Processes and resulting products of solid-state reaction between Fe and hexagonal boron nitride (h-BN) were studied by ball milling a mixture of Fe and h-BN with an Fe to h-BN volume ratio of 1:12.5 and/or heat-treating under normal or high pressure. The 30h-milled mixture was annealed for 1h under an atmospheric pressure at 770 and 1170K, respectively. A small amount of γ′-Fe4N was observed in the mixture annealed at 770K and a little γ-Fe(N) was obtained at 1170K. All Fe atoms in the mixture reacted with N atoms in the BN to form a single phase of ε-FexN when the mixture was milled for 60h or annealed for 1h under 4GPa at temperatures of 690–800K. However, no Fe–B phase was observed in the present experiment. Formation and phase transition of Fe–N alloy in the solid-state reaction process as well as effect of pressure on the reaction and resulting products are discussed in the present paper. The mechanism of formation of Fe–N and Fe–B alloys in the reaction processes are also investigated in terms of the Miedema model and thermodynamics and kinetics.