Mechanical Properties of an Ultrahard In Situ Amorphous Steel Matrix Composite

We report compression tests on micropillars manufactured from bulk specimens of partially devitrified SAM2×5 (Fe_49.7Cr_17.7Mn_1.9Mo_7.4W_1.6B_15.2C_3.8Si_2.4). Yield strength values of ≈6 GPa are obtained. Such a high strength can be attributed to the higher glass transition temperature (883 K) of this material, which impedes the multiplication of shear bands under loading, and to the presence of hard crystalline domains that result from devitrification of the amorphous powders during powder consolidation. The Vickers hardness of the specimens is found to be strongly correlated to the processing temperature and, hence to the volume of crystalline phases present in the specimens. As the processing temperature is increased, there is a reduction in free volume from the structural relaxation process in the amorphous alloy, leading to the eventual nucleation of crystalline phases of BCC Fe, Cr₂B, Cr_21.30Fe_1.7C₆, or Fe₂₃B₂C₄, during the densification process. These results shed light on the relationship between nanocrystalline domains and the mechanical behavior of Fe-based amorphous/crystalline composites.