Fe-based metallic glass composites, consisting of dispersed nanocrystallites within an amorphous metallic glass matrix, are used as low-loss soft-magnetic components in energy conversion devices. The nanocrystallites are formed by partial devitrification of the amorphous alloy and the properties of the composite depend on the alloy composition and the devitrification process. Understanding the rate-dependent crystallisation kinetics is therefore essential for tailoring the properties of metallic glass composites. In this study, we monitor the devitrification process in situ during rapid heating of metallic glasses with composition (Fe0.75Co0.25)95−xNb5Bx, x = 15 − 20 at.%, by using high-energy wide angle X-ray scattering. The results are compared to samples devitrified at low heating rates, analysed using differential scanning calorimetry, X-ray diffraction, and magnetometry. Additionally, we present a model describing the crystallisation kinetics based on classical nucleation and growth theory coupled to thermodynamic data for a generalised Fe-B system. The model successfully captures the onset of devitrification as a function of time, temperature, and B-concentration, providing valuable insights for the design of Fe-based soft-magnetic materials.

Metallic glasses exhibit unique mechanical properties. For metallic glass composites (MGC), composed of dispersed nanocrystalline phases in an amorphous matrix, these properties can be enhanced or deteriorated depending on the volume fraction and size distribution of the crystalline phases. Understanding the evolution of crystalline phases during devitrification of bulk metallic glasses upon heating is key to realizing the production of these composites. Here, results are presented from a combination of in situ small- and wide-angle X-ray scattering (SAXS and WAXS) measurements during heating of Zr-based metallic glass samples at rates ranging from 10² to 10⁴ Ks⁻¹ with a time resolution of 4ms. By combining a detailed analysis of scattering experiments with numerical simulations, for the first time, it is shown how the amount of oxygen impurities in the samples influences the early stages of devitrification and changes the dominant nucleation mechanism from homogeneous to heterogeneous. During melting, the oxygen rich phase becomes the dominant crystalline phase whereas the main phases dissolve. The approach used in this study is well suited for investigation of rapid phase evolution during devitrification, which is important for the development of MGC.

Additive manufacturing makes the production of bulk metallic glasses possible in thicknesses exceeding the critical casting thickness. However, a crucial challenge is the build-up of thermally induced stress, often resulting in printed parts suffering from cracking. In this study, the process parameters are optimised for printing soft-magnetic metallic glass samples of an Fe-based alloy (Fe_73.8P_10.6Mo_4.2B_2.3Si_2.3C_6.7), using laser beam powder bed fusion. In addition, the structural and magnetic properties of as-received and heat-treated powder are investigated and compared to those of the printed samples. Kerr microscopy is used for imaging the magnetic domains on single track cross-sections produced on top of a polished printed sample. This reveals the shape of the melt pool of a single laser track, as well as the magnetic domains around it and in other regions of the printed sample. The shape and size of the magnetic domains reflect the residual stress in the sample through the effect of magneto-elastic coupling. This magnetic contrast could be used to get further insights into how to control the development of stress during the printing process.

Additive manufacturing of Fe-based metallic glass alloys can be used to fabricate customised soft-magnetic components with an unprecedented geometrical freedom. In this work, we present an efficient parameter development process for PBF-LB processing of the Fe-based metallic glass alloy Kuamet 6B2. The development is focused on combining che-querboard and double exposure printing to achieve high relative density, high amorphous content, low coercivity, and low enough residual stress so that large parts can be manufactured. As single track study was used to increase the efficiency of the process development; images of single track melt pools produced using different process parameters were used to make informed decisions about which parameters to proceed with for the second exposure. The produced samples were investigated using XRD, magnetometry, magneto-optical imaging, and EBSD. The developed parameters were used to produce large ring-shaped cores with radii of 5 cm, used for measuring the relative permeability.