a b s t r a c t The effects of orientation and lamellar spacing on the interface microstructure and corrosion behavior of a directionally solidified (DS) Fe-B alloy in a hot-dip galvanization bath were investigated. The results indicated that the microstructure of the DS Fe-B alloy consisted of oriented a-Fe and Fe 2 B grains. The oriented Fe 2 B with [002] preferred growth orientation displayed low-angle grain boundaries on the Fe 2 B (001) basal plane. The DS Fe-B alloy with Fe 2 B vertical to the corrosion interface possessed the best corrosion resistance to liquid zinc owing to the formation of an interface-pinning multilayer induced by the Fe 2 B orientation. The epitaxially grown columnar z-FeZn 13 products were controlled by the geometric constraint of Fe 2 B grain orientation and size, and a mechanism model that explains the interfacial orientation-pinning behavior is discussed in detail. Transmission electron microscopy (TEM) results revealed that the possible orientation relationships of the oriented Fe 2 B and columnar z-FeZn 13 products are (001) Fe2B //(À402) z-FeZn13 and [002] Fe2B //[110] z-FeZn13 . The corrosion damage of the DS Fe-B alloy with Fe 2 B [002] orientation vertical to the corrosion interface in liquid zinc was governed by the competitive mechanisms of Fe 2 B/FeB transformation and microcrack-spallation resistance, which is proposed as being the result of a multiphase synergistic effect in the micro-structures.

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The effects of Fe 2 B-grain orientation on microstructure and properties of bulk Fe 2 B intermetallic fabricated by directional and ordinary solidification techniques have been investigated. The results show that unidirectional solidified Fe 2 B intermetallic possesses a strong (002) texture in the transverse direction owing to the opposite unidirectional heat-squeeze effect while random Fe 2 B grains can be produced under ordinary solidification conditions. The nonoriented Fe 2 B intermetallic has the highest linear expansion coefficient of 13.04 Â 10 À6°CÀ1 while the microhardness and fracture toughness of transverse Fe 2 B intermetallic in the (002) plane are larger than those of Fe 2 B with other grain orientations and their values are ;18.72 GPa and 6.42 MPaÁm 1/2 , respectively. Liquid zinc corrosion results indicate that unidirectional Fe 2 B intermetallic with long axis perpendicular to the direction of liquid zinc corrosion displays the best corrosion resistance to liquid zinc owing to its beneficial barrier effect. The FeB transition phase can naturally form and grow parabolically during liquid zinc corrosion.

The interface characterization and erosion-corrosion behavior of directional Fe-3.5 wt.% B steel in the flowing zinc at 460ºC to 550ºC were investigated. The result indicated that directional Fe-3.5 wt.% B steel possesses better erosion-corrosion resistance to liquid zinc with the [002] orientation of Fe 2 B boride perpendicular to the erosion-corrosion interface. Liquid zinc temperature, Fe 2 B orientation in steel, and micromechanical scour have a significant effect on erosion-corrosion interface structure, which in turn governs the corrosion behavior of the matrix by influencing the dissolution and diffusion process, erosion-enhanced corrosion, the Fe 2 B boride failure mode, and further erosion-corrosion resistance.