Effect of Silicon Content on Microstructures and Properties of Directionally Solidified Fe-B Alloy

Abstract

In order to investigate the effect of Si content on the microstructures and properties of directionally solidified (DS) Fe-B alloy, a scanning electron microscope (SEM) with an energy dispersive spectrum (EDS), and X-ray diffraction have been employed to investigate the as-cast microstructures of DS Fe-B alloy. The results show that Si can strongly refine the columnar microstructures of the DS Fe-B alloy, and the columnar grain thickness of the oriented Fe2B is reduced with the increase of Si addition. In addition, Si is mainly distributed in the ferrite matrix, almost does not dissolve in boride, and seems to segregate in the center of the columnar ferrite to cause a strong solid solution strengthening and refinement effect on the matrix, thus raising the microhardness of the matrix and bulk hardness of the DS Fe-B alloy.

Effects of Boride Orientation and Si Content on High-Temperature Oxidation Resistance of Directionally Solidified Fe–B Alloys

“…Clearly, the microstructures of the DS Fe–B alloys containing various Si addition showed good orientation effects. The columnar gray Fe 2 B were arranged with long rods with a preferred growth orientation of columnar Fe 2 B [002] crystal orientation [ 7 , 34 ]. Furthermore, the gray-white α-Fe matrix was distributed among the lamellar structures of columnar Fe 2 B, exhibiting dual-phase oriented microstructures of the DS Fe–B alloys ( Figure 4 ).…”

“…Obviously, the increasing Si addition resulted in the vanishing peaks of some small diffraction angles and strengthened peaks of large diffraction angles for oriented Fe 2 B, which may be influenced by the various oriented crystal planes of Fe 2 B grain in its lateral grain plane (i.e., prismatic plane of Fe 2 B with strong faceted crystal growth). Meanwhile, with the increase in Si content, there was no new phase in the DS Fe–B alloys, which indicates that Si just dissolves into the matrix and refines the lamellar structures of α-Fe and Fe 2 B [ 34 ].…”

“…Once the alloy had melted at 1450–1480 °C, it was poured into the designed circulating water-cooled mold to solidify directional (DS) microstructures, i.e., obtaining Y-block ingots of the DS Fe–B alloy, as shown in Figure 1 . The directional region near the chilled mold, where the sample with an average solidification rate of approximately 16 °C/s was measured by a thermocouple [ 34 ]. The oxidation samples were prepared for the oxidation direction parallel to the preferential growth direction of Fe 2 B (i.e., defined as Fe 2 B // sample) and the oxidation direction perpendicular to the Fe 2 B preferential growth direction (defined as Fe 2 B ⊥ sample).…”