Abstract
Abstract Boriding of pure iron was investigated using the powder pack method with boriding powder mixtures containing different weight fractions of ZrB2 (5 %, 10 %, 15 % and 20 %). The samples were borided in an electric resistance furnace for an exposure time of 4 h at 1,173 K temperature under atmospheric pressure. Borided samples were characterized by optical microscopy, X-ray diffraction analyses and microhardness tests. Results showed that the boride layers consisted mainly of FeB and Fe2B phases. No significant difference in boride layer thicknesses (average 140 μm) could be observed as a function of ZrB2 content. The needle-like morphology of the boride layer became more prominent with increasing weight fraction of ZrB2 in the boriding powders. The average microhardness of the boride layer decreased with increasing ZrB2 content due to changes in the morphology of the boride layer.
Highlights
Iron is the second most abundant metal in Earth’s crust, after aluminium
The main goal of the current study is to investigate the microstructure and morphology of boride layers grown on the surface of pure iron by pack boriding using powders containing ZrB2 in different concentrations as the boron source
Two distinct regions are identified in the cross-sections of the borided pure iron surfaces: the double-phase boride layer and the substrate unaffected by boron diffusion
Summary
Iron is the second most abundant metal in Earth’s crust, after aluminium. When reduced from its ore, pure iron is soft and susceptible to corrosion. The use of surface coatings opens up the possibility for material design in iron and steel for which certain properties such as surface hardness and corrosion resistance can be improved. One such surface coating technique is boriding, a thermochemical surface treatment in which boron atoms diffuse into the surface of the workpiece to form hard borides with the base material. In the literature [11,12,13], it has been shown that borided materials exhibit significantly higher surface hardness compared to their untreated counterparts and improved abrasive and adhesive wear resistance, due to the hard boride phases grown on the surface and due to diffusion of boron into the substrate. The thickness of the boride layer increases with decreasing particle size of the boriding powders and increasing boriding temperature
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