Wyniki 1-10 spośród 12 dla zapytania: authorDesc:"JERZY LATUCH"

Influence of silicon content on the microhardness of Al91-xSixNi7Mm2 rapidly solidified ribbons

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Rapid soldification is well known method to obtain alloys with nanometer grain size. The nanometer grains provide an increase of mechanical properties of the alloys. In the present work Al-Si-Ni-Mm (mischmetal) alloys were produced by melt spinning technique to obtain nanoscale grains embeded in amorphous matrix. The melt spun ribbons were invastigated by X-Ray difraction (XRD) and different[...]

Influence of casting parameters on thermal properties of bulk metallic glass Cu48Zr36Ag11Ti5

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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[...]

Influence of silver on the glass forming ability and mechanical properties in Cu-Zr-Ti-Ag bulk metallic glasses

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Cu-based bulk metallic glasses (BMGs) exhibit promising mechanical properties: high fracture stress, large elastic strain, good fracture toughness and good corrosion resistance [1]. In addition, non-elastic flow has been reported in some new Cu-based systems [1, 2]. These glasses are also less expensive than currently exploited commercially Zr-based BMGs [3]. The unique set of mechanical properties of Cu-based BMGs is the reason for potentially wide application zone of these materials [4, 5]. However, their mechanical properties and glass forming ability (GFA) need to be improved even further before common industry usage. The aim of this work was to investigate the influence of silver addition on the GFA and mechanical properties of the Cu-Zr-Ti alloys. Chemical composition of examined alloys was prepared after following formula: Cu48Zr36Ti16 - xAgx (x = 0, 5, 8, 11, 13 at. %). The GFA was investigated on the basis of the temperature interval of supercooled liquid region (ΔTx). This region appears between the onset temperature of crystallization (Tx) and the glass transition temperature (Tg). In this temperature region bulk metallic glasses are very susceptible for plastic deformation. Moreover, it is possible to join many little parts together. Mechanical properties of the investigated alloys were determined by means of Vickers microhardness and room temperature compression test. EXPERIMENTAL The m[...]

Hard magnetic properties of bulk Nd-Fe-Al glasses

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Rapidly cooled Nd-Fe-Al alloys of, containing about 60at.% of Nd and about 10at.% of Al, are hard magnetic materials. They can be produced in the form of massive large-size samples. When examined by the X-ray methods they seem to be amorphous, but in fact, their phase structure contains both amorphous and ordered regions. The present study is concerned with the effect of the Nd content (from [...]

Właściwości stopu Ti-Ni-Cu wykazującego pamięć kształtu wytworzonego metodą melt-spinning

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Stopy tytanowo-niklowe o składzie chemicznym zbliżonym do równoatomowego pozostają w centrum zainteresowania ze względu na unikalne właściwości związane z występowaniem efektu pamięci kształtu. Efekt ten nierozerwalnie jest połączony z odwracalną przemianą martenzytyczną występującą w relatywnie szerokim zakresie temperatury, który można modyfikować przez zmianę składu chemicznego - wprowadzając trzeci pierwiastek stopowy w miejsce niklu [1]. Pierwiastki stopowe, takie jak aluminium, żelazo, kobalt, powodują obniżenie temperatury charakterystycznej przemiany nawet do -140°C, natomiast dodatek miedzi, hafnu lub cyrkonu powoduje podwyższenie temperatury przemiany [2, 3]. W przypadku hafnu czy cyrkonu możliwe jest uzyskanie wysokotemperaturowych stopów, w których odwracalna przemi[...]

Effect of selected parameters of the melt-spinning process on the thickness and magnetic properties of Nd-Fe-Al ribbons

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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 [...]

The microstructure of rapidly quenched Fe-Cu-based alloy with a liquid miscibility gap

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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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