Kinetic analysis of the non-isothermal crystallization process, magnetic and mechanical properties of FeCoBSiNb and FeCoBSiNbCu bulk metallic glasses

Abstract

The crystallization kinetics of [(Fe 0.5 Co 0.5) 0.75 B 0.2 Si 0.05 ] 96 Nb 4 and {[(Fe 0.5 Co 0.5) 0.75 B 0.2 Si 0.05 ] 0.96 Nb 0.04 } 99.5 Cu 0.5 bulk metallic glasses were evaluated using differential scanning calorimetry under non-isothermal condition. The fully glassy rods with diameters up to 2 mm were obtained by copper mold injection casting. Both glasses show good thermal stability, but the addition of only 0.5% Cu completely changes the crystallization behavior. The average activation energy required for crystallization decreases from 645 kJ/mol to 425 kJ/mol after Cu addition. Upon heating, the Cu-free alloy forms only the metastable Fe 23 B 6 phase. In contrast, two well-separated exothermic events are observed for the Cu-added bulk glassy samples. First, the (Fe,Co) phase nucleates and then (Fe,Co) 2 B and/or (Fe,Co) 3 B crystallize from the remaining glassy matrix. The Cu-added alloy exhibits a lower coercivity and a higher magnetic saturation than the base alloy, both in as-cast as well as in annealed condition. Besides, the Cu-added glassy sample with 2 mm diameter exhibits a maximum compressive fracture strength of 3913 MPa together with a plastic strain of 0.6%, which is highest plastic strain ever reported for 2 mm diameter ferromagnetic bulk metallic glass sample. Although Cu addition improves the magnetic and mechanical properties of the glass, it affects the glass-forming ability of the base alloy.

Effect of Ge Addition on Magnetic Properties and Crystallization Mechanism of FeSiBPNbCu Nanocrystalline Alloy with High Fe Content

“…where a, b, and p are the nucleation index, growth dimension index, and growth index, respectively. Different values of a, b, and p reflect the different nucleation and growth mechanisms of the crystallization process [30,32]. It can see in Figure 7b that the value of the n of the first crystallization reaction of the Ge0, Ge1 and Ge2 alloys is essentially within the range of n < 1.…”

“…where n is the Avrami index, t 0 is the induction time, and k(T) is the kinetic coefficient as a function of temperature. Equation ( 3) can be written as [30]:…”

Crystallization Mechanism in Spark Plasma Sintered Bulk Metallic Glass Analyzed using Small Angle Neutron Scattering

“…The Avrami exponent n was estimated, by linear fit to the plots, to be 0.25 ± 0.01 and 0.39 ± 0.01 at 700 °C and 725 °C respectively. www.nature.com/scientificreports www.nature.com/scientificreports/ The Avrami exponent is representative of the nucleation behavior prevalent during the progress of crystallization in metallic glass 57 . In particular, a value of n less than 1.5, as in the present case, shows that the evolution of (Fe,Cr) 23 C 6 crystals within the iron based metallic glass during isothermal annealing both at 700 °C as well as 725 °C occurs by diffusional transformation from pre-existing nuclei 58,59 .…”

Evaluation of the Effect of Minor Additions in the Crystallization Path of [(Fe0.5Co0.5)0.75B0.2Si0.05]100-xMx Metallic Glasses by Means of Mössbauer Spectroscopy

“…In 2004, Shen and co-workers presented a new family of Fe-based glassy alloys, FeCoSiBNb, which could be cast in bulk form and have excellent functional properties and high strength [19,20]. Their thermal stability, microstructural evolution and crystallization kinetics, as well as functional properties, have been a matter of an extensive number of studies [21][22][23][24][25][26]. The large GFA in these alloys arises from the presence of a transition metal like Nb that stabilizes the supercooled liquid region and inhibits the crystallization [27].…”

“…Other transition metals like Mo and Y [29] also have a similar effect while Cr leave GFA unaffected but has a beneficial effect on the corrosion resistance and plasticity. Alloying of rare earths is a matter of discussion: Gd has been reported to deteriorate GFA [24,29] whereas Tb and Dy have a positive effect if not exceeding an optimal amount [30][31][32]. In these cases, to understand the effect of the minor additions on the stability of the amorphous structure and its crystallization route is fundamental for developing new alloys.…”