Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

Summary

Here, we present a protocol to describe ex situ and in situ investigations of structural transformations in metallic glasses. We employed nuclear-based analytical methods which inspect hyperfine interactions. We demonstrate the applicability of Mössbauer spectrometry and nuclear forward scattering of synchrotron radiation during temperature-driven experiments.

Abstract

We demonstrate the use of two nuclear-based analytical methods that can follow the modifications of microstructural arrangement of iron-based metallic glasses (MGs). Despite their amorphous nature, the identification of hyperfine interactions unveils faint structural modifications. For this purpose, we have employed two techniques that utilize nuclear resonance among nuclear levels of a stable ⁵⁷Fe isotope, namely Mössbauer spectrometry and nuclear forward scattering (NFS) of synchrotron radiation. The effects of heat treatment upon (Fe_2.85Co₁)₇₇Mo₈Cu₁B₁₄ MG are discussed using the results of ex situ and in situ experiments, respectively. As both methods are sensitive to hyperfine interactions, information on structural arrangement as well as on magnetic microstructure is readily available. Mössbauer spectrometry performed ex situ describes how the structural arrangement and magnetic microstructure appears at room temperature after the annealing under certain conditions (temperature, time), and thus this technique inspects steady states. On the other hand, NFS data are recorded in situ during dynamically changing temperature and NFS examines transient states. The use of both techniques provides complementary information. In general, they can be applied to any suitable system in which it is important to know its steady state but also transient states.

Introduction

Iron-based MGs prepared by rapid quenching of a melt represent industrially attractive materials with numerous practical applications¹. Especially since their magnetic properties are often superior to conventional (poly)crystalline alloys^2,3. To better benefit from their advantageous parameters, their response to elevated temperatures should be known. With increasing temperature, the amorphous structure relaxes and, finally, the crystallization starts. In some types of MGs, this can lead to the deterioration of their magnetic parameters and, consequently, poorer performance. There are, ....

Protocol

1. Preparation of a MG

NOTE: To demonstrate a broad range of diagnostic capabilities of NFS in combination with Mössbauer spectrometry, an appropriate MG composition was designed, namely (Fe₃Co₁)₇₆Mo₈Cu₁B₁₅ (at.%). This system shows the magnetic transition from the ferromagnetic to paramagnetic state below the onset of crystallization. Moreover, crystallites that emerge during the first crystallization step form bcc-Fe,Co phase. Because cobalt replaces iron in some atomic positions of the bcc lattice, deviations in the respective hyperfine interactions occur.

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Results

The XRD pattern in Figure 2 exhibits broad featureless diffraction peaks. The observed reflections demonstrate that the produced ribbon of the (Fe_2.85Co₁)₇₇Mo₈Cu₁B₁₄ MG is XRD amorphous.

Due to its sensitivity, XRD has some limitations in unveiling surface crystallization. The presence of crystallites amounting to less than about 2-3%.......

Discussion

Ex situ Mössbauer effect experiments describe a steady situation which is encountered in the investigated MG after the applied heat treatment. Each spectrum was collected for a duration of several hours at room temperature. Thus, the evolution of the originally amorphous structure was followed as a function of annealing conditions. Because Mössbauer spectrometry is sensitive to hyperfine interactions acting upon the resonant nuclei, faint details of structural and/or magnetic modifications induced by e.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
stable isotope, 57Fe	Isoflex USA	iron-57	metallic form
standard eletrolytic Fe, 99.95 %	Sigma Aldrich (Merck)	1.03819	fine powder
electrolytic Co, 99.85 %	Sigma Aldrich (Merck)	1.12211	fine powder
electrolytic Cu, 99.8 %	Sigma Aldrich (Merck)	1.02703	fine powder
electrolytic Mo, 99.95 %	Sigma Aldrich (Merck)	1.12254	fine powder
crystalline B, 99.95 %	Sigma Aldrich (Merck)	266620	crystalline
calibration foil for Mössbauer spectrometry, bcc-Fe	GoodFellow	564-385-23	foil 0.0125 mm, purity 99.85 %
HNO3 acid, ANALPURE Ultra	Analytika Praha, Czech Republic	UAc0061a	concentration 67 %, volume 500 mL
spectrometer for atomic absorption spectrometry	Perkin Elmer 1100, Germany
spectrometer for optical emmission spectrometry with inductively coupled plasma	Jobin Yvon 70 Plus, France
X-ray diffractometer	Bruker D8 Advance, USA
differential scanning calorimeter	Perkin Elmer DSC 7, Germany