| dc.description.abstract | A Fe-based bulk amorphous steel (BAS), Fe41Cr15Mo14C12B9Co7Y2, was successfully fabricated by suction casting and confirmed its amorphous state by X-ray diffraction and differential scanning calorimetry analysis. The Tg, Tx, γ, γm and ΔT are 832 K, 906 K, 0.4, 0.69, and 74 K, respectively. The thermoplastic deformation during supercooled liquid region was firstly investigated by thermal mechanical analysis (TMA).
TMA results reveal that the viscosity decreases with increasing temperature under the same strain rate and no specimen is deformable under the strain rate of 5x10-2 s-1 or higher. Based on the TMA results, the lowest viscosity is about 5x1010 Pa‧s. The thermoplastic deformation behavior of Fe-based BAS was investigated at different temperatures within the supercooled temperature region (namely 873 K, 883 K, 893 K, 903 K) with different strain rate (5x10-2 s-1~1x10-3s-1). The Fe-based BAS only exhibits Newtonian flow at lower strain rate (less than 5x10-3 s-1 at 873 K~883 K, and less than 7.5x10-3 s-1 at 893 K~903 K). Moreover, the Fe-based BAS was fractured during thermoplastic forming process at strain rate higher than 5x10-2 s-1. TEM analysis were carry out for further investigating the amorphous state of the as cast sample and the sample after thermoplastic forming. The Fe-based BAS sample after thermoplastic forming at 903 K with 2.5x10-3 s-1 strain rate was found to have some nano-size crystalline particles embedded locally in amorphous matrix. | en_US |