Multi-component boron coatings on low carbon steel AISI 1018

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Chromium can modify the structure and the properties of boride layer. The
solubility of chromium in the Fe2B phase causes the replacement from iron to chromium
and forms (Fe, Cr)B and (Fe, Cr)2B on the surface. The incorporation of chromium may
increase the microhardness of boride layer but it also causes <strong>boron</strong> to diffuse along the
grain boundaries. The diffusion leads to the decreasing of thickness of boride layer and
the increasing of the smooth boride layer/substrate interface [11]. Chromium also
promotes the formation of <strong>boron</strong>-rich phase, such as FeB phase, onto the boride layer.
Manganese, Tungsten, Molybdenum, and vanadium are typically used to reduce
the boride thickness and to flatten out the saw-tooth morphology.
2.4.2 Characteristics and Properties of Boride Layer on Various Metals and Alloys
The characteristics and properties of both <strong>boron</strong>ized ferrous and nonferrous metals and
alloys are widely interested topics due to a need to increase the value of metals and alloys
in terms of wear performance, corrosion and high temperature properties.
99.97 wt. % pure iron was investigated by Ozdemir et al. [12] and Asthana et al.
[13]. The Fe2B phase was formed with the hardness of 1700 HV and the fracture
toughness of about 3 - 4 MPa m 1/2. The preferred crystallographic orientation was in the
(002) direction.
The <strong>boron</strong>izing of AISI 1020 and AISI 5115 were investigated and compared to
carburizing [14] and carbonitriding [15]. Friction coefficients obtained under the same
conditions was at 0.45 - 0.62 for carburized, 0.36 - 0.57 for carbonitrided and 0.36 - 0.62
for <strong>boron</strong>ized AISI I020 steels, and 0.35 - 0.70 for carburized, 0.32 - 0.54 for
carbonitrided and 0.12 - 0.24 for <strong>boron</strong>ized AISI 5115. As well, the kinetics and fracture
toughness of AISI 1040 and P20 were investigated. Fe2B and FeB phases were formed