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» Influence of casting parameters on thermal properties of bulk metallic glass Cu48Zr36Ag11Ti5
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Piotr Błyskun  Jerzy Latuch TADEUSZ KULIK
Bulk metallic glasses take their structure straight from the liquid. In
opposition to the crystal metallic alloys they possess neither a crystalline
structure nor its defects, such as vacancies, dislocations or
grain boundaries [1]. This causes an extraordinary properties of this
group of materials. As regards to their properties, metallic glasses
differ significantly among each other, because of their sensitivity
to even the slightest change of chemical composition. However, it
is possible to describe same general features. Bulk metallic glasses
exhibit high compressive strength (from 2 to 5 GPa) [2, 3] and relatively
low Young’s modulus (70÷90 GPa) [4], what gives rise to an
ability of accumulating a large amount of elastic energy. Moreover,
they have very high wear resistance [5] that comes not only from
the hardness [6], but also from very high surface smoothness [7].
These materials also exhibit very attractive formability. A characteristic
temperature area of very high viscosity appears during
heating before crystallization of the amorphous structure. This area
is defined as ΔTx and is called a supercooled liquid region. It appears
between the onset temperature of crystallization - Tx and the
glass transition temperature - Tg: ΔTx = Tx - Tg. In this temperature
region metallic glass is very susceptible for plastic deformation
(that may reach 106%) and many little parts can be put together to
produce one complex detail [5]. What is important, the amorphous
structure is not lost after heating for short time [8÷10]. In addition,
the parameter ΔTx is often being used to describe glass forming
ability of a bulk glassy alloy. It means that alloys with higher value
of ΔTx exhibit better glass forming ability. For this reason, the research
effort is focused to find optimal manufacturing parameters of
the glass with the widest supercooled liquid region.
A lack of long range ordering (characteristic for amo[...]
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INŻYNIERIA MATERIAŁOWA 2010/3
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» Effect of selected parameters of the melt-spinning process on the thickness and magnetic properties of Nd-Fe-Al ribbons
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Waldemar Kaszuwara Bartosz Michalski Jerzy Latuch Janusz Rębiś
The Nd-Fe-Al alloys, first described by Inoue [1] in 1996, are inferior
to Nd-Fe-B magnets as far as the magnetic properties are concerned,
but their great advantage is that they do not need additional
annealing (performed after melt-spinning) to achieve their possibly
good magnetic properties. These properties depend on the cooling
rate of the melted material, and the best values achieve at the
quenching rates at which the ribbons have a thickness of the order
of tenths of millimeter. Magnets of this size could be used directly,
without further treatment, in electromechanical micro-devices or
in the MEMS technique [2]. In the application range so defined,
the melt-spinning processed Nd-Fe-Al alloys can compete with
Nd-Fe-B alloys, since the basic technology of Nd-Fe-B magnets
does not permit producing easily components with a thickness of
the order of tenths of millimeter.
The thickness and properties of the Ne-Fe-Al ribbons can be
modified by controlling the melt-spinning process parameters, such
as the rotational speed of the wheel, the shape and size of the crucible
opening, the temperature of the melted material, and the pressure
of the ejecting gas [3].
It has been demonstrated thus far that rapid cooling (at a wheel
rotational speed of 20÷30 m/s) promotes an increase of the share of
an amorphous phase and gives ribbons with poor magnetic properties.
When cooled at lower rates, the material contains a greater proportion
of crystalline phases and has substantially better magnetic
properties [3, 4].
The microstructure of the Nd-Fe-Al alloys has been described
in many publications [5, 6], but there is no consistency in the interpretation
of the results. At present, we can say that the Nd-Fe-Al
alloys with the best properties contain very small amounts of the
amorphous phase and that their structure is multi-phase and built on
a nanometric level [7].
The aim of the present study was to examine the possibility of
producing [...]
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INŻYNIERIA MATERIAŁOWA 2010/3
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» The microstructure of rapidly quenched Fe-Cu-based alloy with a liquid miscibility gap
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Tomasz Kozieł Zb igniew Kędzierski Anna Zielińska-Lipiec Jerzy Latuch
Although superior properties of metallic glasses such as high
strength and high elastic limit, its application is very limited due
to highly localized shear banding [1, 2] and thus very low ductility.
Ductility of metallic glasses could be improved by formation
of composite materials consisting of crystalline phases dispersed
in the amorphous matrix. Such composites might be produced by
in-situ formation of the crystalline phase.
In 2004 Kündig et al. [3] for the first time showed two-phase
amorphous structure in metallic system. The system he studied included
one pair of elements with high positive heat of mixing (La-
Zr) while negative heat of mixing of the other elements (Al, Cu,
Ni) to both, La and Zr. Positive heat of mixing between two major
elements forced liquid phase separation into La-rich and Zr-rich
melts during cooling of the homogeneous melt below critical temperature
required for decomposition. Negative heat of mixing of
the other alloying elements to La and Zr, increased glass forming
ability of both separated melts. Rapid cooling enabled formation
of two glassy structures, La-rich and Zr-rich, with surface fractal
microstructure [3]. This work initiated research of systems based
on elements with positive heat of mixing and thus possible formation
of two amorphous phases. Several two-phase metallic glasses
were reported up to date including Y-Ti-Al-Co [4], Ni-Nb-Y [5],
Ag-Cu-Zr [6], Cu-Zr-Al-Y [7] and Nd-Zr-Al-Co [8].
Since two-phase amorphous structure was obtained, one can
expect different thermal stability of both glassy phases. Thus formation
of amorphous-crystalline composites with nanocrystalline
structure is possible by partial devitrification of one of the amorphous
phases.
This work deals with another system based on two elements,
namely Fe and Cu, with positive heat of mixing as high as
+13 kJ/mol [9]. Although the Fe-Cu phase diagram does not contain
a liquid miscibility gap, Turchanin et al. [10] p[...]
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INŻYNIERIA MATERIAŁOWA 2010/3
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