Formation of boride layers at the Fe–25% Cr alloy–boron interface

Two boride layers based on the FeB and Fe₂B compounds are formed at the interface between a Fe–25% Cr alloy and boron at 850–950 °C and reaction times up to 12 h. The characteristic feature of both layers is a pronounced texture. Each of two boride layers is compositionally two-phase. The outer layer consists of the (Fe,Cr)B and (Cr,Fe)B phases. The inner layer comprises the (Fe,Cr)₂B and (Cr,Fe)₂B phases. The diffusional layer-growth kinetics are close to parabolic and can alternatively be described by a system of two non-linear differential equations, also producing a fairly good fit to the experimental data. Annealing of a borided Fe–Cr sample in the absence of boriding media results in the disappearance of the (Fe,Cr)B–(Cr,Fe)B layer, with the (Fe,Cr)B phase disappearing first. Microhardness values are 21.0 GPa for the outer layer, 18.0 GPa for the inner layer and 1.35 GPa for the alloy base. The abrasive wear resistance of the (Fe,Cr)B–(Cr,Fe)B layer, found from mass loss measurements, is more than 150 times greater than that of the alloy base.