Devitrification of Fe-Based Amorphous Metal SAM 1651: A Structural and Compositional Study

The effect of heat treatment on the chemistry and structure of an Fe-based bulk metallic glass (BMG) Fe(48)Cr(15)Mo(14)C(15)B(6)y(2) (SAM 1651) was examined experimentally. Chemical segregation was found in the as-received material, with islands 10 to 200 nm in diameter enriched in Y, Mo, and C and depleted in Fe and Cr, with respect to the surrounding matrix. Heat treatment in the range of 600 degrees C to 800 degrees C caused partial devitrification of the BMG with the formation of nanocrystalline (Fe, Cr)(23)C(6) and (Fe, Cr)(7)C(3) carbides in a matrix of the remaining amorphous phase. The devitrification process followed a primary crystallization route. Amorphous particle-free zones (PFZs) in the devitrified material were found, corresponding to the Y-Mo-rich islands in the fully amorphous SAM 1651. The formation of Cr-rich carbide during devitrification caused the formation of nanometer-sized Cr-depleted zones surrounding the carbide particles, which is detrimental to the corrosion performance of the alloy after thermal exposure.