Mechanical alloying of Al-C system

A method of mechanical alloying process is described. Carbon transformation to Al4C3 is characterised within the different heat treatment schedules and nine commercial carbon powders are tested. The micromechanism of carbon incorporation into the metallic powder, and its compacting are described. The influence of dispersed carbides on mechanical properties is evaluated together with the influence of deformation on microstructure and properties. It was proved that the transformation efficiency of carbon to Al4C3 by heat treatment of aluminium with the porous furnace black and electrographite is higher than that of the hard cracked graphite. Microstructure changes consisted of fracture processes and welding of the particles with incorporation of C phase and forming of final granules. The dispersed phase Al4C3 particle size was measured on 200 to 300 thin foil structures, and it was constant and as small as 30 nm. The particle size was influenced neither by the carbon type nor by the heat treatment applied. Subgrain size measured in the range of 100 grains in thin foils depended on the carbon type, as well. It ranged from 0.3 to 0.7 µm. Using a depth sensing indentation (DSI) technique, the Martens hardness, indentation modulus E and deformation work W for Al matrix and Al4C3 particles have been measured. It has been shown that the hardness of particles is 5–7 times higher than the hardness of the matrix. The temperature dependence of ductility, and reduction of area in the temperature range of 350 –450°C and strain rate of 10-1 s-1, indicated a considerable increase of these properties. In a case when the volume fraction of Al4C3 changes from lower to higher, the grain rotation mechanism dominates instead of the grain boundary sliding

QUANTITATIVE MICROSTRUCTURE ANALYSIS OF DISPERSION STRENGTHENED Al-Al 4 C 3 MATERIAL BY EBSD TECHNIQUE

Abstract The main aim of the present work was described quantitative analysis of microstructure of by electron backscatter diffraction (EBSD) technique of dispersion strengthened Al-Al 4 C 3 material. It is a technique by which SEM can be used to evaluate the microstructure by crystallographic analysis based on the acquisition of diffraction patterns from bulk samples. Mechanical properties of dispersion strengthened materials depend on microstructural and substructural parameters, their changes at elevated temperatures and also on grain and subgrain matrix structures. From this point of view the most important microstructural parameters of matrix are size, shape, and misorientation of grains and subgrains and their annealing behaviour. Realized microstructure analyses of Al-Al 4 C 3 material were evaluated from two experimental specimens annealed at different temperatures and times. Obtained microstructures were evaluated and compared. Annealing process has influenced the grain size, shape and orientation of experimental material. Grains size and angle grain boundaries were evaluated from acquired crystal orientation maps

Superplastična deformacija Al-Al4C3 kompozita

Deformation of the Al-Al4C3 composites with different volume fraction of Al-Al4C3 phase was investigated at different temperatures (293 - 723 K) and different strain rates (2,5 * 10-5 s-1 do 1,0 * 10-1 s-1). At temperatures 673 - 723 K and at the highest strain rate of 1,0 * 10-1 s-1, a significant ductility increase was observed. TEM analysis suggests the onset of superplasticity may be the result of dynamic grain polygonization, grain slip and rotation, partial recrystallization and dislocation creep in the tested system, which is known as strain induced dynamic recovery. Increase of the volume fraction of secondary phase in the studied composite resulted in a shift from slip on grain boundaries controlled mechanism to the grain rotation controlled deformation mechanism.Istraživana je deformacija Al-Al4C3 kompozita različitog volumnog udjela Al-Al4C3 faze kod različitih temperatura (od 293 do 723 K) i brzina deformacije (od 2,5 * 10-5 s-1 do 1,0 * 10-1 s-1). Kod temperatura od 673 do 723 K i najviše brzine deformacije od 1,0 * 10-1 s-1 zapaženo je značajno povećanje kovkosti. TEM analiza ukazuje da početak superplastičnosti može biti rezultat dinamičke poligonizacije zrna, klizanja i rotacije zrna, djelomične rekristalizacije i puzanja dislokacija u istraživanom sustavu, što je poznato kao deformacijom inducirano dinamičko oporavljanje. Porast volumnog udjela sekundarne faze u istraživanom kompozitu rezultirao je promjenom kontrolnog mehanizma deformacije od klizanja po granicama zrna do rotacije zrna

Stvaranje ultrafino zrnate (UFZ) strukture i mehanička svojstva sa intenzivnom plastičnom deformacijom (IPD)

Commercial pure cooper (99,9% Cu) was deformed by equal channel angular pressing (ECAP) using up to 10 passes, route C. The evolution of microstructure and fracture character were observed by OM, SEM and TEM. The mean grain size decreased with increasing deformation, after 10 passes to 100 – 300 nm. TEM analysis suggested the possible nanostructure formation mechanism by the formation of cellular structure in grains, forming of subgrains and then forming of high angle nanograins with random orientation. Fractures of ECAP Cu material after 10 passes had transcrystalline ductile character with dimple morphology.Trgovački čisti bakar (99,9%) deformiran je kanalnim kutnim prešanjem (KKP) do 10 provlaka-putanje. C. Razvitak mikrostrukture i karakter loma praćeno je sa OM, SEM i TEM. Veličina zrna se smanjuje povećanjem deformacije poslije 10 provlaka na 100-300 nm. TEM analiza ukazuje mogućnost nastajanja mehanizma nanostrukture stvaranjem celularne strukture u zrnima, nastanak subzrna i zatim obrazovanje nanozrna pod visokim kutem sa slučajnom orjentacijom. Lomovi KKP Cu materijala poslije 10 provlaka imali su transkristalni duktilni karakter sa jamičastom morfologijom

Rapid, energy-efficient synthesis of the layered carbide, Al₄C₃

The phase-pure binary aluminium carbide, Al4C3 can be synthesised in vacuo from the elements in 30 minutes via microwave heating in a multimode cavity reactor. The success of the reaction is dependent on the use of finely divided aluminium and graphite starting materials, both of which couple effectively to the microwave field. The yellow-brown powder product was characterised by powder X-ray diffraction, scanning electron microscopy/energy dispersive X-ray spectroscopy thermogravimetric-differential thermal analysis and Raman spectroscopy. Powders were composed of hexagonal single crystallites tens of microns in diameter (rhombohedral space group R[3 with combining macron]m; Z = 3; a = 3.33813(5) Å, c = 25.0021(4) Å) and were stable to 1000 °C in air, argon and nitrogen. Equivalent microwave reactions of the elements in air led to the formation of the oxycarbide phases Al2OC and Al4O4C