Multi-component boron coatings on low carbon steel AISI 1018

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The following sections address the overview of <strong>boron</strong>izing processes that are
applied to both ferrous and non-ferrous materials. Despite that, this dissertation will focus
only on two-<strong>component</strong> <strong>boron</strong>izing processes of ferrous materials.
2.2.1 Boronizing of Ferrous Materials
The boride layer can be formed in either single phase or double phases on iron and steel,
corresponding to a definite chemical composition from the Fe-B phase diagram, as
illustrated in Appendix A. The single-phase boride layer consists of Fe 2B, while the
double-phase boride layer consists of the exterior phase of FeB and the interior phase of
Fe2B. The morphology of the boride layer is a saw-tooth structure as depicted in Figure
2.1. The saw-tooth structure helps improving the mechanical adherence at the
Fe2B/substrate interfaces.
Figure 2.1 The saw-tooth structure of boride layers with the exterior phase of FeB and
the interior phase of Fe2B on AISI 1018.
During <strong>boron</strong>izing, Fe2B phase is formed under high compressive stress, while
FeB phase is formed under high tensile stress. At the end of <strong>boron</strong>izing when
temperature is being reduced to an ambient temperature, if Fe2B and FeB phases are
formed in the boride layer, stresses from the two phases can lead to the crack formation at