Evolution of structure and local magnetic fields during crystallization of HITPERM glassy alloys studied by in situ diffraction and nuclear forward scattering of synchrotron radiation

Abstract

Evolution of structure and local magnetic fields in (Fe1-xCox)76Mo8Cu1B15 (HITPERM) metallic glass ribbons with various amounts of Co (x = 0, 0.25, 0.5) were studied in situ using diffraction and nuclear forward scattering of synchrotron radiation. It was found that crystallization for all three glasses proceeds in two stages. In the first stage, bcc (Fe,Co) nanocrystals are formed, while in the second stage additional crystalline phases evolve. For all three glasses, the crystallization temperatures at the wheel side were found to be lower than at the air side of the ribbon. The crystallization temperatures were found to decrease with increasing Co content. The lattice parameters of the bcc nanocrystals decrease up to about 550 °C and then increase pointing to squeezing Mo atoms out of the nanograins or to interface effects between the nanocrystals and the glassy matrix. Nuclear forward scattering enabled separate evaluation of the contributions that stem from structurally different regions within the investigated samples including the newly formed nanocrystals and the residual amorphous matrix. Even minor Co content (x = 0.25) has a substantial effect not only upon the magnetic behaviour of the alloy but also upon its structure. Making use of hyperfine magnetic fields, it was possible to unveil structurally diverse positions of Fe atoms that reside in a nanocrystalline lattice with different number of Co nearest neighbours.

On the Formation of Nanocrystalline Grains in Metallic Glasses by Means of In-Situ Nuclear Forward Scattering of Synchrotron Radiation

“…The sample remains paramagnetic up to the final annealing temperature. However, as demonstrated by the results of diffraction of synchrotron radiation, this system starts to crystallise at the temperature of ∼450 ∘C [14]. So, even though the bcc-Fe nanocrystals are formed, their presence cannot be confirmed via corresponding hyperfine magnetic fields, which are rather weak, and consequently, the NFS patterns do not show any remarkable changes in their shapes.…”

“…Well-established methods comprising X-ray diffraction and differential scanning calorimetry provide information that is averaged over the entire sample and are related exclusively to structural characterization. Recently, the method of NFS, which also scans the magnetic order of the studied systems via their hyperfine interactions, was applied to in-situ investigations of crystallization processes in Fe-Co-Mo-B-Cu MGs [14]. The influence of external magnetic field on the crystallization of FeZrB under isothermal conditions [15] and in FeCuMoB exposed to dynamical temperature increase [16] was studied too.…”

Identification of spatial magnetic inhomogeneities by nuclear forward scattering of synchrotron radiation

“…Nuclear forward scattering (NFS), which can be used for the investigation of hyperfine interactions within solid-state samples, is currently one of the most rapidly developing synchrotron methods. It has successfully been applied to investigating diffusion, magnetic ordering or structural/phase transformation kinetics (Vogl & Sepiol, 1999;Miglierini et al, 2012Miglierini et al, , 2015Machala et al, 2015).…”

Nanocrystallization of Metallic Glasses Followed by in situ Nuclear Forward Scattering of Synchrotron Radiation

“…Due to extremely high brilliance of the latest synchrotron sources, studies can be performed in dynamic in situ regimes. Rapid recording of experimental data allows for direct observation of dynamical processes that are taking place during heat treatment [18][19][20][21][22].…”