Effect of cooling rate on glass forming ability of novel Fe-Based bulk metallic glass

Abstract

In the present study, the effect of cooling rate on the glass forming ability of Fe41Co7Cr15Mo14Y2C15B6 bulk metallic glass was investigated. For this purpose, three samples with a mentioned nominal composition were prepared with diameters of 2 mm in water-cooled copper, and 2.5 mm and 3 mm in graphite molds. The amorphicity of the samples were confirmed by X-ray diffraction (XRD). Also, thermal behavior of the glassy samples was evaluated with a differential scanning calorimeter (DSC) from ambient to 1200 ◦C. The characteristics temperatures, such as the glass transition temperature (Tg), the onset temperature of crystallization (Tx), solidus (Tm), and liquidus (Tl) temperatures were determined by using DSC curves. The results calculated by using the various criteria (i.e., Trg = Tg/Tl, ω = (Tg/Tx) - (2Tg/ (Tl + Tg)), δ = Tx/ (Tl - Tg), and New β = (Tx ×Tg)/ (Tl - Tx)2) revealed that the thermal stability of this BMG was increased by decreasing the cooling rate. On the other hand, Tang’s isoconversional method was used to determine the activation energy of crystallization in these samples. These results confirmed that activation energy of crystallization process was increased by decreasing the cooling rate, which was in good agreement with that were calculated by various criteria. Finally, an increase in the GFA can be related to the formation of clusters in the amorphous matrix with a decrease in the cooling rate and thus change the chemical composition of the amorphous matrix.