The influence of Mg content and impurities in AA5083 alloy on the properties of flow formed tubes

Microstructure and mechanical properties of flow formed thin-walled tubes of AA5083 alloy from two metallurgical heats are presented. The influence of the chemical composition and applied reduction on the surface features and residual macro stresses were also studied. The residual macro stresses were estimated by ring method. The heat with higher content of alloying elements and impurities (Mg, Mn, Fe, Si) had higher strength of preforms as well as flow formed tubes. These tubes exhibit three times higher residual stresses, lower spinnability, and the large amount of the surface defects (microcracks). This behaviour is attributed to the inhomogeneous material flow during deformation and presence of impurities

Preparation and Characterization of Poly(D,L-Lactide-co-Glycolide) Nanoparticles Containing Ascorbic Acid

This paper is covering new, simplistic method of obtaining the system for controlled delivery of the ascorbic acid. Copolymer poly (D,L-lactide-co-glycolide) (DLPLG) nanoparticles are produced using physical method with solvent/nonsolvent systems where obtained solutions were centrifuged. The encapsulation of the ascorbic acid in the polymer matrix is performed by homogenization of water and organic phases. Particles of the DLPLG with the different content of ascorbic acid have different morphological characteristics, that is, variable degree of uniformity, agglomeration, sizes, and spherical shaping. Mean sizes of nanoparticles, which contain DLPLG/ascorbic acid in the ratio 85/150%, were between 130 to 200 nm depending on which stereological parameters are considered (maximal diameters Dmax, feret X, or feret Y). By introducing up to 15% of ascorbic acid, the spherical shape, size, and uniformity of DLPLG particles are preserved. The samples were characterized by infrared spectroscopy, scanning electron microscopy, stereological analysis, and ultraviolet spectroscopy

Stereological analysis of DLPLG nanoparticles containing ascorbic acid during in vitro degradation process

Poster presented at the 3rd Serbian Congress for Microscopy (3SCM-2007) Belgrade, September 25-28, 200

Effect of electrodeposition current density on the microstructure and magnetic properties of nickel-cobalt-molybdenum alloy powders

Nanostructured nickel-cobalt-molybdenum alloy powders were electrodeposited from an ammonium sulfate bath. The powders mostly consist of an amorphous phase and a very small amount of nanocrystals with an mean size of less than 3 nm. An increase in deposition current density increases the amorphous phase percentage, the density of chaotically distributed dislocations and internal microstrains in the powders, while decreasing the mean nanocrystal size. The temperature range over which the structural relaxation of the powders deposited at higher current densities occurs is shifted towards lower temperatures. A change in relative magnetic permeability during structural relaxation is higher in powders deposited at higher current densities. Powder crystallization takes place at temperatures above 700oC. The formation of the stable crystal structure causes a decrease in relative magnetic permeability

The influence of Mg content and impurities in AA5083 alloy on the properties of flow formed tubes

Microstructure and mechanical properties of flow formed thin-walled tubes of AA5083 alloy from two metallurgical heats are presented. The influence of the chemical composition and applied reduction on the surface features and residual macro stresses were also studied. The residual macro stresses were estimated by ring method. The heat with higher content of alloying elements and impurities (Mg, Mn, Fe, Si) had higher strength of preforms as well as flow formed tubes. These tubes exhibit three times higher residual stresses, lower spinnability, and the large amount of the surface defects (microcracks). This behaviour is attributed to the inhomogeneous material flow during deformation and presence of impurities

Defectoscopy of direct laser sintered metals by low transmission ultrasonic frequencies

This paper focuses on the improvement of ultrasonic defectoscopy used for machine elements produced by direct laser metal sintering. The direct laser metal sintering process introduces the mixed metal powder and performs its subsequent laser consolidation in a single production step. Mechanical elements manufactured by laser sintering often contain many hollow cells due to weight reduction. The popular pulse echo defectoscopy method employing very high frequencies of several GHz is not successful on these samples. The aim of this paper is to present quadraphonic transmission ultrasound defectoscopy which uses low range frequencies of few tens of kHz. Therefore, the advantage of this method is that it enables defectoscopy for honeycombed materials manufactured by direct laser sintering. This paper presents the results of testing performed on AlSi12 sample. [Projekat Ministarstva nauke Republike Srbije, br. OI 172057

PDLLA Microparticles Containing BSA: Effect of Formulation Variables on Size Distribution

Poster presented at the 9th Conference of the Yugoslav Materials Research Society - YUCOMAT 2007, Herceg Novi, Crna Gora, September 10-14, 2007

The Effect of Processing Parameters on Characteristics of Plla Microspheres

Poster presented at the 8th Conference of Yugoslav Materials Research Society – YUCOMAT 2006, Herceg Novi, Montenegro, September 4-8, 2006

Microstructure development during heat treatment of high chromium white cast iron

Even though it has been in use for a very long time, the high chromium white cast iron (HCWCI) still triggers scientists due to its outstanding wear resistance. Besides its well-known as-cast usage, it can be used as a coating material, as well. HCWCI owes this feature due to the presence of carbides in microstructure, which depends on the composition and heat treatment regime. This investigation was conducted on two HCWCI alloys, where in addition to chromium, the second important alloying element is molybdenum (Mo). Apart from other alloying elements, HCWCI_1 is alloyed with 24.48% Cr and 1.32% Mo, while HCWCI_2 contains 14.11% Cr and 2.47% Mo. The comprehensive microstructural characterization was carried out on as-cast samples and samples obtained after quenching (at -196oC) and/or quenching followed by tempering (at 250oC). Important microstructure indicators are: the stability of austenite, the ratio of microconstituents (especially different types of carbides), as well as their arrangement and morphology, so they are revealed and discussed in relation to the influencing mechanical properties

The investigation on the structural transformations of the Cu(1-x)-Al2O3(x) systems during sintering process

U cilju proučavanja strukturnih transformacija, kao i mehanizma i kinetike termički aktiviranih procesa stabilizacije neravnotežne strukture kod hladno sinterovanih uzoraka sistema Cu-Al2O3 sa 5, 10 i 15% disperzoida, izvršeno je ispitivanje izotermske zavisnosti specifičnog električnog otpora od vremena. Merenjem specifičnog električnog otpora u izotermskim uslovima na temperaturama nešto nižim od temperature oporavljanja (450-650K), određeni su kinetički parametri i energija aktivacije procesa oporavljanja uzoraka presovanih pod pritiskom od 100MPa. Pri tome se došlo do zaključka da se proces oporavljanja odvija u dva stadijuma. Pored ovoga, eksperimentalni rezultati pokazuju da sa porastom sadržaja Al2O3 konstanta brzine odgovorna za promenu specifičnog električnog otpora, za oba stadijuma opada, a energija aktivacije odgovarajućih procesa raste. Analiza mikrostrukture sinterovanih uzoraka pokazuje da efekat poroznosti ima značajan uticaj na vrednosti specifičnog električnog otpora, kao mere strukturne stabilizacije sistema. Takođe, analiza mikrostrukture ukazuje na korelaciju promene specifičnog električnog otpora i rasta zrna. Tačnije, rast zrna, usled smanjenja ukupne površine granica, pokazuje smanjenje specifičnog električnog otpora sinterovanih uzoraka