Nitriding response of ferritic Fe-Ti-Cr alloys

摘要

Specimens of ferritic iron-based Fe-Ti-Cr alloys, containing a total of 0.30 at.% alloying elements, Ti and Cr with varying Ti/Cr atomic ratio (0.45, 0.87 and 1.90), were nitrided in a NH_3/H_2 gas atmosphere at 580℃. The microstructure of the nitrided zone was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Nitride -platelets (length ≤ 30 nm and thickness ≤ 1 nm) developed in the nitrided zone. Particularly clear for the larger Ti/Cr atomic ratios, a tetragonally distorted ferrite develops next to the cubic ferrite, as evidenced both by XRD and TEM. The absence of separate TiN and CrN diffraction spots in the selected area electron diffraction patterns suggests the development of mixed Ti_xCr_(1-x)N nitride precipitates. The mixed T_xCr_(1-x)N nitride precipitates are of rock-salt crystal structure type and obey a Bain orientation relationship with the ferrite matrix.