Abstract
Soft ferromagnetic Fe-based bulk metallic glass key-shaped specimens with a maximum and minimum width of 25.4 and 5 mm, respectively, were successfully produced using a high pressure die casting (HPDC) method, The influence of die material, alloy temperature and flow rate on the microstructure, thermal stability and soft ferromagnetic properties has been studied. The results suggest that a steel die in which the molten metal flows at low rate and high temperature can be used to produce completely glassy samples. This can be attributed to the laminar filling of the mold and to a lower heat transfer coefficient, which avoids the skin effect in the steel mold. In addition, magnetic measurements reveal that the amorphous structure of the material is maintained throughout the key-shaped samples. Although it is difficult to control the flow and cooling rate of the molten metal in the corners of the key due to different cross sections, this can be overcome by proper tool geometry. The present results confirm that HPDC is a suitable method for the casting of Fe-based bulk glassy alloys even with complex geometries for a broad range of applications.
Highlights
The keys cast at higher temperatures (1573 K) clearly show three distinct crystallization peaks (Tp1, Tp2 and Tp3), whereas for the keys cast at lower temperatures (1353 and 1393 K) the first (Tp1) and third (Tp3) crystallization peaks are not clearly visible
The key samples cast at 1573 K exhibit almost the same first and second crystallization enthalpy values (−15.6 J/g and −3 8.8 J/g, respectively) as that of the sample prepared in lab condition
The other keys cast at the same temperature using the copper die and the specimens cast at lower temperatures using both copper and steel dies show relatively low enthalpy values, indicating the presence of a small amount of crystals in the cast parts
Summary
Other emerging additive manufacturing techniques, like selective laser melting (SLM), have been used to produce BMG parts with refined microstructure and excellent properties[37,38,39] This method requires uniformly-sized glass-forming alloy powders, which is very expensive and highly complicated to produce. In our present work we designed a high pressure die casting tool (key-shaped) for casting Fe-based BMG and optimized the casting parameters for a Fe74Mo4P10C7.5B2.5Si2 alloy This particular Fe-based composition was chosen because of its relatively low melting point of 1283 K, good glass-forming ability (GFA) and good soft magnetic properties[42]. This alloy can be produced from industrial grade elements, which makes it cheap and a realistic candidate for applications. The accuracy of the measured data lies within ±2.5 K in the case of DSC measurements, ±0.1 A/m for coercivity and ±80 A/m (~1 Oe) for the VSM measurements
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