Structure and properties of nitrided binary Fe-Al, Fe-V, and Fe-Ti alloys

Abstract

1. The formation of phases with nitrogen in the diffusion layer of binary alloys of iron with aluminum, vanadium, and titanium after nitriding at 500° for 1h occurs in the conformity with the Fe-N phase diagram. 2. With increasing amounts of aluminum in the alloy the amount of e phase decreases, while the amount of γ′ phase increases and it extends into the grains in the form of whiskers. 3. Aluminum has a slight effect on the hardness of the α solid solution; titanium and vanadium substantially increase the hardness after nitriding at 500°. 4. Sectioning and electron microscopic and electron diffraction analysis of the diffusion layer on nitrided Fe-Al alloys showed that the surface consists of e phase, with γ′ phase alloyed with aluminum beneath it. The sublayer contains two excess nitride phases-Fe4N and Fe16N2. 5. Besides e and γ′ phases on the surface of nitrided Fe-Al alloys, we observed separate crystals of Al2O3. 6. No precipitates of stable hcp AlN were observed on the surface of Fe-Al alloys after nitriding. 7. The diffusion sublayer of Fe-V and Fe-Ti alloys nitrided at 500° contains a second nitride phase-Fe16N2 — that is isomorphous with the matrix, in addition to precipitates of γ′ phase. The effect of diffusion scattering is noticeable on the matrix reflections in the form of streaks, indicating the formation of coherent GP zones.