Structural study of borided layers obtained on synthetic Fe-Ni alloys

Carbon free Fe-Ni alloys (12 and 20 wt.% Ni) have been analysed by X-ray diffraction and surface Mössbauer spectroscopy (CXMS and CEMS) after boriding treatment at 1273 K for 20 hours. Some (FexNil-x)2B and FexNil-xB samples, with different values of x, obtained by heating at 1073 K mixtures of elements in powder form, were used as reference. Besides (FexNil-x)2B and FexNil-xB, a third boride phase rich in boron has been detected in the outer borided layers of the alloy specimens. A third phase appears also in the corresponding X-ray patterns. A comparison between CXMS and CEMS data show that (FexNil-x)2B is present only in the deeper part of the borided layers and that the outer surface layer is a mixture of a nickel and boron rich boride and of a superparamagnetic oxide.