SIPS 2018

DETAILLED PROGRAM OVERVIEW

Rare Earth-containing Multi-component Metallic Glasses
Jean-marie Dubois¹; Luka Kelhar¹; Saso Sturm¹; Spomenka Kobe¹;
¹JOSEF STEFAN INSTITUTE, Ljubljana, Slovenia;
PAPER: 143/SISAM/Invited (Oral)
SCHEDULED: 14:50/Tue./Copacabana A (150/1st)

ABSTRACT:
Metallic glasses belong to the class of advanced materials, which exhibit mechanical properties, corrosion resistance, and magnetic properties far superior to that of crystalline materials of similar compositions. Rare earth (RE) containing metallic glasses, which hold some extraordinary properties (such as a very low glass transition temperature), however, have not been extensively studied in the past. Due to the complex electronic and magnetic structure induced by the RE elements, their alloys are expected to possess some excellent fundamental properties. The subject of this paper addresses Ce- and Gd-based metallic glasses, which differ upon their magnetic moments and electronic configurations. At room temperature (RT), cerium reveals paramagnetic behavior with a low magnetic moment of 0.6 μB, while gadolinium, on the other hand, shows the transition into the ferromagnetic state just below RT and possesses one of the highest magnetic moments among REs, with 7.5 μB. Electronic structure of cerium has an unusual 4f electron configuration, which fluctuates up to 4 outer electrons depending on its neibourhood, thus giving Ce and its alloys some unexpected physical properties, such as significant volume change or the emergence of a Kondo state. The fundamental differences between Ce and Gd based metallic alloys originate in different electronic and magnetic structure and the goals of the proposed doctoral dissertation are focused to the experimental analysis of structure, thermal analysis, microstructure and magnetic properties of the multicomponent alloys. Coupling of the fundamental physical and magnetic properties of Ce and Gd, with elements of Al, Fe, and Cu (which by the way are respectively immiscible in each other) is to date unknown. The subject of the proposed talk is to provide fundamental answers and to show a connection between the composition and structure of the alloy and corresponding properties. The purpose here is to investigate the influence of Ce and Gd rare earth (RE) with greatly differing magnetic moments, on the structure, thermal properties, microstructure and magnetic properties of multicomponent Al-RE-Fe-Cu alloys. Formation and stability of glasses can be traced via differential thermal analysis (DTA) and calorimetry (DSC), which also enable the characterization of transformation kinetics. Via pulsed electric current sintering (PECS), powdered samples can be formed into bulk metallic glasses through the process of thermoplastic consolidation in the vicinity of the glass transition temperature (Tg). Magnetic properties of the glasses are analyzed as a function of temperature and time, via controlled crystallization at a temperature 5°C higher than the crystallization temperature (Tx) and time-varying from several minutes to hours. Detailed structural and microstructural characterization is performed via X-ray diffraction (XRD) and electron microscopy, which encompasses scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The field of RE-based metallic glasses has not yet been thoroughly investigated concerning the influence of low and high magnetization RE elements on the structure and magnetic properties. It is of fundamental significance to connect the observed magnetic behavior of glasses with their structural features. In this view, particularly interesting is the coupling between the crystalline lattice and magnetic properties since the behavior of short-range ordered amorphous materials is different from long-range ordered crystalline matter. Another parameter that plays a role is the interlinking effect of the Gibbs free energy and transformation kinetics, in the metastable region of the highly viscous glass when Tg<T<Tx. The hypothesis is based on the fact that the electronic structure and magnetic moments of Ce and Gd are significantly different. It is expected that consequently the difference will also be reflected in the magnetic behaviour of the corresponding alloys. Due to the metastable nature of the glassy materials, heating above Tx will trigger crystallization. However, since some of these alloys possess a well marked Tg that is lower than Tx, we are offered with a temperature gap, which facilitates the study of the transition from viscous glassy state (at Tg) to the crystalline state commencing at Tx. Experimental parameters are varied through the selection of different annealing temperatures and annealing times. Differences in structure, microstructure, and magnetic properties are anticipated with different amounts of crystallites; however, detailed experimental work is essential to provide acute answers.

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