Wyniki wyszukiwania - Biblioteka Nauki

1

Effect of Sc Addition on the Microstructure and Mechanical Properties of Melt-Spun Al-10Ni Alloys

100%

Kilicaslan M. F. , Karakose E.

Archives of Metallurgy and Materials

|

2018

|

tom Vol. 63, iss. 2

575--579

EN

In the present work, rapidly solidified Al-10Ni-XSc (X = 0, 1 and 2) alloys were fabricated by melt spinning under Ar atmosphere. The Effects of Sc on the microstructural and thermal properties and microhardness values were investigated by scanning electron microscopy (SEM), X-ray diffractometer (XRD) and a Vickers microhardness tester. Experimental results revealed that the addition of 2 wt. % Sc to melt-spun Al-10Ni alloys changed their brittle nature and hindered formation of cracks. The addition of Sc to melt-spun Al-10Ni alloys also changed the morphology of Al3 Ni intermetallics from an acicular/needle – like to a rounded particle-like structure and led to reduction in their size. Formation of the metastable Al9 Ni2 phase was observed due to the higher constitutional undercooling caused by Sc addition. A considerable improvement in microhardness value (from 95. 9 to 230. 1 HV) was observed with the addition of Sc.

2

Preparation of Melt Spun Electroconductive Fine Fibres Containing Carbon Nanotubes

75%

Mirjalili M. , Karimi L.

|

2015

|

tom Vol. 15, no. 2

87--92

EN

Preparation of electroconductive fine fibres containing carbon nanotubes (CNTs) by melt spinning was the main goal of the present study. In this regard, the influence of the main operating parameters such as type of polymer used (polyester, polypropylene and polyamide), type and concentration of the CNTs on conductivity, and mechanical and thermal properties of the melt spun fibres was studied. The conductivity of melt spun fibres was measured based on the method developed by Morton and Hearl. The morphologies of the CNTs–polymer composite fibres were studied by scanning electron microscopy. Thermal behaviours and mechanical properties of the CNTs–polymer composite fibres were investigated using differential scanning calorimetry and tearing tester, respectively. The results reveal that using CNTs had tangible effect on electrical, thermal and mechanical properties of the melt spun fibres. Also, polyamide had a better dispersion of CNTs and correspondingly lower surface resistivity.

3

Strengthening of aluminium based composites with amorphous metallic or Al2O3 particles

63%

Kukuła-Kurzyniec A. , Dutkiewicz J. , Bobrowski P. , Wajda W. , Góral A. , Ochin P. , Perriere L.

|

tom R. 13, nr 2

141--146

EN

Aluminium alloy based composites were prepared by hot pressing in a vacuum in order to study the strengthening effect of an amorphous phase addition in the form of ball milled powder from melt spun ribbons of the Al73Si5Ni7Cu8Zr7 (at.%) alloy. For comparison, a composite with a strengthening ceramic Al2O3 phase was hot pressed under the same conditions. DSC measurements allowed the authors to determine the start of the crystallization process of the amorphous ribbons at 240°C. The presence of the majority of the amorphous phase in the melt spun ribbons was additionally confirmed by the X/ray diffraction technique which also revealed the presence of an α/Al solid solution and some peaks of intermetallic phases. SEM studies showed homogenous distribution of the strengthening particles in both kinds of composites and confirmed the existence of α /Al and some intermetallic crystallites inside the metallic amorphous particles. The hardness of all the prepared composites was comparable and amounted to approximately 50 HV1 for those with the Al matrix and 120 HV1 for the ones with the 2618A alloy matrix. The composites have shown a higher yield stress than the hot pressed aluminium or 2618A alloy. SEM studies of the cracks after compression tests revealed that the interfaces between the strengthening phase and matrix in metallic amorphous powder/Al /2618A alloy composites show a different character of the interface between the ceramic particles and the Al matrix. Therefore in the composite with the Al2O3particles, cracks have the tendency to propagate at the interfaces with the matrix more often than in amorphous/Al composites.

PL

W artykule opisano badania dotyczące struktury i właściwości kompozytów na osnowie aluminium i jego stopu / 2618A, wykonanych metodą prasowania na gorąco w próżni. Fazę umacniającą stanowił 10% dodatek proszku o składzie Al73Si5Ni7Cu8Zr7 (% at.), otrzymany w wyniku mielenia kulowego metalicznych taśm amorficznych odlanych na wirujący walec (melt spinning). W celu porównawczym w tych samych warunkach sprasowano również kompozyt o osnowie Al, w którym fazę umacniającą stanowił 10% dodatek cząstek ceramicznych - Al2O3. Metodą mikrokalorymetrii różnicowej (DSC) określono temperaturę początku krystalizacji taśm amorficznych na około 240°C. Techniką dyfrakcji rentgenowskiej (XRD) potwierdzono obecność znacznego udziału struktury szklistej zarówno w odlanych, jak i sproszkowanych taśmach, a także stwierdzono niewielki udział roztworu α/Al oraz faz międzymetalicznych. Badania strukturalne wykonane metodą skaningowej mikroskopii elektronowej (SEM) wykazały równomierne rozmieszczenie cząstek faz umacniających w obu rodzajach kompozytów, a w przypadku cząstek taśm amorficznych potwierdzono obecność w ich wnętrzu krystalitów roztworu α/Al i faz międzymetalicznych. Twardość wszystkich przygotowanych kompozytów była porównywalna i wynosiła około 50 HV1 dla kompozytów o osnowie Al oraz 120 HV1 dla materiałów na bazie stopu 2618A. Obserwacja SEM mikrostruktury próbek kompozytowych po testach ściskania pozwoliła zauważyć inny charakter granicy rozdziału cząstek fazy umacniającej i osnowy w przypadku zastosowania cząstek taśmy Al73Si5Ni7Cu8Zr7, co wpływa na odmienny przebieg drogi propagacji pęknięć niż w przypadku proszku Al2O3, gdzie występuje słabsze połączenie w granicy osnowa/cząstki wzmacniające. W przypadku zastosowania ceramicznej fazy umacniającej kompozyt wykazuje tendencję do propagacji pęknięć po granicach wprowadzonych cząstek.

4

The solidification of CuCr alloys under various cooling rates

63%

Wang Y. , Song X. , Sun Z. , Zhou X. , Guo J.

Materials Science Poland

|

2007

|

tom Vol. 25, No. 1

199--207

EN

The paper focuses on the solidification especially on the liquid phase separation of Cu-35 at. % Cr alloys under various cooling rates. When the solidification temperature is below the liquidus and above the spinodal temperature, solidification runs normally, with the growth of primary Cr-rich dendrites. When the solidification temperature is below the spinodal temperature, liquid phase separation should occur through the solidification process and the primary Cr-rich phase has a special nodular structure under an appropriate cooling rate. Large Cr-rich particles obtained from liquid phase separation can grow by absorbing smaller ones via the transfer of matter. Furthermore, some particles collide with each other, mutually losing surface energy by joining to form a single particle. The size of the Cr-rich particles obtained from liquid phase separation decreases with increasing cooling rate. Using thermodynamic calculations and referring to literature data, the viewpoints on liquid phase separation are systematized and applied to the CuCr system. Liquid phase separation in an undercooled liquid is not advantageous in refining the microstructure of alloys and should be restricted.

5

Electret properties peculiar to fibrous polymer materials

63%

Kravtsov A. , Goldade V. , Zotov S.

|

tom Vol. 40, nr 15

9-15

EN

Some peculiar electret properties of fibrous polymer materials have been studied by complementary methods. The residual polarization has been proved to result from capture of free charge carriers on two main types of defects, namely oxygen-containing groups and the defects formed from violated permolecular structure. A spontaneous electrel charge is generated in the fibrous material at both melt blowing and melt spinning and its value depends on the process parameters. The forced polarization of fibers in an external electric field makes the electret effect more pronounced and adds a specific character to the polarizing charge relaxation.