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Reduced Glass-Transition Temperature versus Glass-Forming Ability in FeCoB-Based Amorphous Alloys

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Nabiałek M.

Archives of Metallurgy and Materials

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2016

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tom Vol. 61, iss. 4

1957--1962

EN

This work presents studies concerning the relationship between reduction of glass transition temperature Trg and the glass-forming ability of FeCoB-based alloys. On the basis of theoretical considerations, Turnbull [1] determined the reduced glass transition temperature (Tg/Tl) as being 2/3 of the Vogel–Fulcher–Tammann (VFT) temperature; since then, continuous research has been carried out, aiming to calculate the Trg parameter and describe its relationship with glass-forming ability. In the majority of research papers, the reduced glass transition temperature is calculated from the relationship Tg/Tm, proposed by Uhlmann and Davies [2, 3]. On the basis of differential scanning calorimetry (DSC) studies, undertaken in this current work, the values of the following temperatures have been found: Tg, Tx, Tm and Tl, in addition to the temperature ranges: ΔTx, ΔTm and ΔTl. The correlation between: Tg/Tm, Tg/Tl and the glass-forming ability also has been discussed. Finally, for the investigated alloys, it has been found that the relationship proposed by Turnbull is reliable over a wide range of ΔTm.

2

Viscous flow features of amorphous Zr65(Ni,Pd)35 alloy

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Spassov T. , Stefanov G. , Gyurov S.

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tom Vol. 57, no. 4

327--331

EN

Viscous flow behavior of amorphous Zr65(Ni,Pd)35 alloy has been studied at a heating rate of 20 K/min. The viscosity experimental results are interpreted on the basis of the free volume model. The values of the model parameters obtained are used for estimation of glass forming ability in terms of the Angell parameter, and the fracture strength of the alloys based on its correlation with the glass transition temperature. The glass transition temperature is 663 K. The alloy Zr65(Ni,Pd)35 possesses excellent fracture strength of about 2.28 GPa, comparable to that of stainless steels. The relatively good thermal and excellent mechanical properties make this alloy promising for preparing bulk amorphous samples.

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Preparation and glass-forming ability of Mg-based bulk amorphous alloys

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Babilas R. , Zajączkowski A. , Głuchowski W. , Nowosielski R.

Archives of Materials Science and Engineering

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2013

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tom Vol. 62, nr 2

78--86

EN

Purpose: The work presents preparation methods, structure characterization and glass-forming analysis of Mg-based bulk metallic glasses in as-cast state. Design/methodology/approach: The studies were performed on Mg60Cu30Y10 and Mg60Cu29Y10Si1 glassy alloys in the form of plates and rods. The amorphous structure of tested samples was examined by X-ray diffraction (XRD). The thermal properties associated with solidus and liquidus temperature of master alloys were measured using the differential thermal analysis (DTA). The crystallization behavior of the studied plates and rods was also examined by differential scanning calorimetry (DSC). The fracture morphology of the rods in as-cast state was analyzed using the scanning electron microscopy (SEM). Findings: The X-ray diffraction investigations revealed that the tested samples with different thickness and shape were amorphous. The single exothermic peaks describing crystallization process of studied alloys were observed for all examined samples with different thickness. The endothermic and exothermic peaks observed on DTA curves of master alloys allowed to determine the solidus and liquidus temperatures. The characteristics of the fractured surfaces showed different zones, which might correspond with different amorphous structures. The changes of glass transition and crystallization temperatures as a function of sample thickness were stated. Practical implications: The pressure die casting method are useful technique to fabricate bulk amorphous materials in the form of plates and rods. Proposed casting technology could open new possibilities to easier preparation of Mg-based nanostructured materials and forming their properties that is essential for further applications. Originality/value: The Mg-based bulk amorphous alloys are regarded as promising engineering materials with high strength, low density and good corrosion resistance in contrast to the crystalline alloys, due to their different atomic configurations

4

Glass-forming ability analysis of selected Fe-based bulk amorphous alloys

63%

Nowosielski R. , Babilas R.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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tom Vol. 42, nr 1-2

66-72

EN

Purpose: The paper mainly aims to present the structure and thermal stability of selected Fe-based bulk metallic glasses: Fe72B20Si4Nb4 and Fe43Co14Ni14B20Si5Nb4. Design/methodology/approach: The investigated samples were cast in form of the rods by the pressure die casting method. The structure analysis of the studied materials in as-cast state was carried out using XRD and TEM methods. The thermal stability associated with glass transition temperature (Tg), onset (Tx) and peak (Tp) crystallization temperature was examined by differential scanning calorimetry (DSC). Several parameters have been used to determine the glass-forming ability of studied alloys. The parameters of GFA included reduced glass transition temperature (Trg), supercooled liquid region (deltaTx), the stability (S) and (Kgl) parameter. Findings: The XRD and TEM investigations revealed that the studied as-cast metallic glasses were fully amorphous. Changes of the onset and peak crystallization temperature and the glass transition temperature as a function of glassy samples thickness were stated. The good glass-forming ability (GFA) enabled casting of the Fe72B20Si4Nb4 and Fe43Co14Ni14B20Si5Nb4 glassy rods. Practical implications: The obtained examination results confirm the utility of applied investigation methods in the thermal stability analysis of examined bulk amorphous alloys. It is evident that parameters Trg, deltaTx, Kgl, S could be used to determine glass-forming ability of studied bulk metallic glasses. Originality/value: The success of fabrication of studied Fe-based bulk metallic glasses in form of rods with diameter up to 3 mm is important for the future progress in research of this group of materials.

5

Structure and properties of Fe-Cr-Mo-C bulk metallic glasses obtained by die casting method

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Pilarczyk W. , Nowosielski R. , Januszka A.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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tom Vol. 42, nr 1-2

80-87

EN

Purpose: The goal of this work is to investigate structure and properties of Fe54Cr16Mo12C18 alloy rods with different diameters obtained by the pressure die casting method. Design/methodology/approach: Master alloy ingot with compositions of Fe54Cr16Mo12C18 was prepared by induction melting of pure Fe, Cr, Mo, C elements in argon atmosphere. The investigated material were cast in form of rods with different diameters. Glassy and crystalline structures were examined by X-ray diffraction. The microscopic observation of the fracture morphology was carried out by the SEM with different magnification. The thermal properties of the studied alloy were examined by DTA and DSC method. Findings: These materials exhibit high glass-forming ability, excellent mechanical properties and corrosion resistance. Research limitations/implications: It is difficult to obtain a metallic glass of Fe54Cr16Mo12C18 alloy. The investigations carried out on the different samples of Fe54Cr16Mo12C18 bulk metallic alloy allowed to state that the studied ribbon was amorphous whereas rods were amorphous – crystalline. Originality/value: The formation and investigation of the casted Fe-Cr-Mo-C bulk materials and the study of glass-forming ability of this alloy.