Effects of Si Addition on the Microstructure and Properties of Cr-Al alloy for High Temperature Coating

Cr-Al alloys are attracting attention as oxidation resistant coating materials for high temperature metallic materials due to their excellent high temperature stability. However, the mechanical properties and oxidation resistance of Cr-Al alloys can be further enhanced, and such attempts are made in this study. To improve the properties of Cr-Al alloys, Si is added up to 5 wt%/o. Casting specimens with different amounts of Si content are prepared by a vacuum arc remelting method and isothermally heated under steam conditions at 1,100 degrees C for 1 hour. The as-cast microstructure of low Si alloys is mainly composed of only a Cr phase, while AlsCr(5) and Cr3Si phases are also observed in the 5 % Si alloy. In the high Si alloy, only Cr and Cr3Si phases remain after the isothermal heating at 1,100 degrees C. It is found that Si additions slightly decrease the oxidation resistance of the Cr-Al alloy. However, the microhardness of the Cr-Al alloy is observed to increase with an increasing Si content.