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Magneto-Thermo-Gravimetric technique to investigate the structural and magnetic properties of Fe-B-Nb-Y Bulk Metallic Glass
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.ORCID iD: 0000-0003-2170-0076
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2009 (English)In: 13TH INTERNATIONAL CONFERENCE ON RAPIDLY QUENCHED AND METASTABLE MATERIALS, 2009, 012074- p.Conference paper (Refereed)
Abstract [en]

Magneto-thermo-gravimetric (MTG) technique is highly informative about the changes in the magnetic state, as well as structural changes in a system, which cannot be often noticed in calorimetric measurements. We demonstrate the versatility of this technique in determining the magnetic transition temperature, and the subsequent crystallization process in a (Fe(0.72)B(0.24)Nb(0.04))(95.5)Y(4.5) Bulk Metallic Glass (BMG). MTG and DSC analyses were carried out at the heating rate of 0.67 K/s from RT similar to 1170 K. As a result of the repeated MTG measurements, a magnetic 2(nd) amorphous phase was observed in the BMG sample, which could be the first measurement for the Magnetic Short Range Ordering (MSRO). Consequently, the MTG measurement is proved as the most convenient method for determining the various structural and magnetic transitions in a glassy material.

Place, publisher, year, edition, pages
2009. 012074- p.
, Journal of Physics Conference Series, ISSN 1742-6588 ; 144
National Category
Metallurgy and Metallic Materials
URN: urn:nbn:se:kth:diva-101991DOI: 10.1088/1742-6596/144/1/012074ISI: 000271827100074ScopusID: 2-s2.0-80052821307OAI: diva2:550225
13th International Conference on Rapidly Quenched and Metastable Materials, AUG 24-29, 2008, Dresden, GERMANY

QC 20120906

Available from: 2012-09-06 Created: 2012-09-06 Last updated: 2012-09-06Bibliographically approved
In thesis
1. Functional Metallic Glasses
Open this publication in new window or tab >>Functional Metallic Glasses
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

For decades, Metallic Glass, with its isotropic featureless structure while exhibiting outstanding mechanical properties was possible only at a high rate of quenching and with at least one dimension in the submicron regime.  This limitation was overcome with the discovery of Bulk Metallic glasses, BMGs, containing three or more elements following the additional two empirical rules of optimum geometric size differences and negative energy of mixing among the constituent elements. Since then thousands of Fe-, Ni-, Al-, Mg-, Ti- based BMGs have been discovered and comprehensively investigated mainly by groups in Japan and USA. Yet the discovery of new combinations of elements for BMGs is alchemy. We do not know with certainty which element when added will make possible a transition from being a ribbon to a bulk rod.

   In this thesis we report a discovery of castable BMGs rods on substitution of Fe by nickel in an alloy of FeBNb which could otherwise have been only melt-spun into ribbons.  For example, we find that substitution of just 6 at.% of Fe raises the glass forming range, GFA, to as much as ∆Tx =40K while the other parameters for GFA like Trg, γ, and δ reach enhanced values 0.57, 0.38, and 1.40 respectively.  Furthermore, the electrical conductivity is found to increase by almost a factor of two.  Magnetically it becomes softer with coercivity 260mOe which further reduces to much lower values on stress relaxation.  Ni does not seem to carry a magnetic moment while it enhances the magnetic transition temperature linearly with Ni concentration. We have investigated the role of Ni in another more stable BMGs based FeBNbY system in which case ∆Tx becomes as large as 94K with comparable enhancement in the other GFA parameters. Due to the exceptional soft magnetic properties, Fe-based bulk metallic glasses are considered potential candidate for their use in energy transferring devices. Thus the effect of Ni substitution on bulk forming ability, magnetic and electrical transport properties have been studied for FeBNb and FeBNbY alloy systems. The role of Ni in these systems is densification of the atomic structure and its consequence.

We have exploited the superior mechanical properties of BMGs by fabricating structures that are thin and sustainable.  We have therefore investigated studies on the thin films of these materials retaining their excellent mechanical properties. Magnetic properties of FeBNb alloy were investigated in thin films form (~200-400nm) in the temperature range of 5-300K. These Pulsed Laser deposited amorphous films exhibit soft magnetism at room temperature, a characteristic of amorphous metals, while they reveal a shift in hysteresis loop (exchange anisotropy, HEB=18-25Oe), at liquid helium temperature. When thickness of films is reduced to few nanometers (~8-11nm), they exhibit high transparency (>60%) in optical spectrum and show appreciably high saturation Faraday rotation (12o/μm, λ= 611nm). Thin films (~200-400nm) of Ni substituted alloy (FeNiBNb) reveal spontaneous perpendicular magnetization at room temperature. Spin-reorientation transition was observed as a function of film thickness (25-400nm) and temperature (200-300K), and correlated to the order/disorder of ferromagnetic amorphous matrix as a function of temperature. These two phase films exhibits increased value of coercivity, magnetic hardening, below 25K and attributed to the spin glass state of the system.

   Using the bulk and thin films we have developed prototypes of sensors, current meters and such simple devices although not discussed in this Thesis.                                     

   Ti-based bulk metallic glasses have been attracting significant attention due to their lower density and high specific strength from structural application point of view. High mechanical strength, lower values of young’s modulus, high yield strength along with excellent chemical behaviors of toxic free (Ni, Al, Be) Ti-based glassy metals make them attractive for biomedical applications. In the present work, toxic free Ti-Zr-Cu-Pd-Sn alloys were studied to optimize their bulk forming ability and we successfully developed glassy rods of at least 14mm diameter by Cu-mold casting. Along with high glass forming ability, as-casted BMGs exhibit excellent plasticity. One of the studied alloy (Ti41.5Zr10Cu35Pd11Sn2.5) exhibits distinct plasticity under uniaxial compression tests (12.63%) with strain hardening before failure which is not commonly seen in monolithic bulk metallic glasses.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xiv, 60 p.
Bulk Metallic glasses, glass forming ability, soft magnetism, thin films, magnetic properties, magnetic hardening, plasticity, biocompatibility
National Category
Engineering and Technology
urn:nbn:se:kth:diva-101901 (URN)978-91-7501-476-0 (ISBN)
Public defence
2012-09-21, V2, Teknikringen 76, 2tr, Stockholm, 14:00 (English)

QC 20120906

Available from: 2012-09-06 Created: 2012-09-05 Last updated: 2012-09-19Bibliographically approved

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