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1.
Microstructure of Al-Mn-Be melt-spun ribbons
Franc Zupanič, Tonica Bončina, Borivoj Šuštaršič, Ivan Anžel, Boštjan Markoli, 2008, izvirni znanstveni članek

Opis: Microstructures of two alloys with the nominal compositions of Al92Mn3Be5 and Al89Mn6Be5 were characterized in the initial as-cast condition (after vacuum induction melting and casting) and after melt spinning. In the initial conditions, both alloys consisted of an aluminum-rich solid solution and two metastable intermetallic phases: Be4AlMn and Al10Mn3(Be). Both alloys melted over a rather large temperature range (between 230 °C and 310 °C). This was the main reason for the presence of unmelted particles in the melt-spun ribbons. Nonetheless, with the use of optimized melt-spinning parameters a microstructure composed of the Al-rich solid solution and finely dispersed quasicrystalline particles in ribbons with thicknesses ranging from 30-200 m was achieved. The dispersion of quasicrystalline particles was finest on the wheel side of the thinnest ribbons, attaining microhardness values between 250HV and 300 HV.
Objavljeno: 01.06.2012; Ogledov: 1245; Prenosov: 76
URL Povezava na celotno besedilo

2.
Assessment of the load-bearing capacity of a primary pipeline
Nenad Gubeljak, Jelena Vojvodič-Tuma, Borivoj Šuštaršič, Jožef Predan, Maks Oblak, 2007, izvirni znanstveni članek

Opis: High-alloyed Cr-Ni-based two-phase stainless steel (SS) cast alloys are commonly used in nuclear power plants. The mechanical equipment in these facilities can contribute to a reduction in its resistance to stable crack growth as a result of extended operating times and high temperatures. The toughness of these materials strongly depends on their delta (▫$/delta$▫) ferrite content, which spinodally decomposes into two phases with different ratios of Cr and Ni at a relatively low (slightly above 300 °C) temperature. This temperature is similar to the operating temperature of the vital parts, for example, the coolant system. The formation of two phases with the same crystalstructure but different lattice parameters causes internal elastic stresses that result in a hardness increase and an impact-toughness decrease. The result is an increased risk of crack formation in the stress-concentration zones such as the critical regions of different welded joints (e.g. "L, T, K and X" shapes). The values of the critical stress intensity factor change according to its position along the crack contour. Therefore, the aim of our study was to assess the influence of the materials' changes on the crack extension and the decrease of the primary pipeline's bearing capacity by taking account of the increased temperature and time of operation for the given loading conditions. The SINTAP (European Structural Integrity Assessment Procedure) was used for this assessment.
Ključne besede: welding, welded joints, pipelines, fracture toughness testing, structure integrity assessment procedure
Objavljeno: 01.06.2012; Ogledov: 1162; Prenosov: 60
URL Povezava na celotno besedilo

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DSC/TG of Al-based alloyed powders for p/m applications
Borivoj Šuštaršič, Jože Medved, Srečko Glodež, Marko Šori, Albert Korošec, 2014, izvirni znanstveni članek

Opis: Al-based alloyed powders, appropriate for the sintering procedure (powder metallurgy, P/M) contain the alloying elements with a high solid solubility in Al, enabling reaction and liquid-phase sintering. They are surface oxidised because of a high affinity of Al to oxygen. Besides, this type of powders contains a polymeric lubricant (wax), which reduces the friction on die walls during automatic die compaction into the final compact shape of a product. This lubricant has to be removed slowly during the first stage of sintering in order to prevent deformations and cracking of the product. Consequently, its sintering is very complex. Generally, these powders are sintered in pure nitrogen with a low dew point. The optimum sintering conditions are generally determined on the basis of light and scanning electron microscopy. The investigation can also be completed very successively with differential scanning calorimetry and thermo gravimetry. The first one allows an insight into the endo- and exothermic reactions, taking place during the heating and cooling of a compacted metal powder, and the second one allows an insight into the processes, connected with the mass loss (a reduction, a lubricant removal, etc.) or mass increase (an oxidation). The DSC/TG of three commercial Al-based alloyed powders was performed in the frame of our investigations. The results were compared with the theoretical thermodynamic-based calculations and the optimum sintering conditions were proposed.
Ključne besede: aluminium powders, sintering, differential scanning calorimetry and thermo gravimetry
Objavljeno: 15.03.2017; Ogledov: 454; Prenosov: 49
.pdf Celotno besedilo (319,52 KB)
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5.
Fatigue properties of sintered DIN SINT-D30 powder metal before and after heat treatment
Marko Šori, Borivoj Šuštaršič, Srečko Glodež, 2014, izvirni znanstveni članek

Opis: The main focus of this study was to determine how heat treatment affects the dynamic properties of sintered steel. All the specimens were made of the DIN SINT-D30 metal powder, but only half of them were additionally heat treated. Flat specimens were cold pressed and sintered. The second set was additionally heat treated to increase the strength. After the static mechanical properties were determined, the fatigue strength was investigated in a pulsating machine with a load ratio of R = 0. Wöhler curves were plotted and the parameters for determining the fatigue life (of' and b) were calculated.
Ključne besede: powder metallurgy, fatigue, S-N curve
Objavljeno: 16.03.2017; Ogledov: 404; Prenosov: 69
.pdf Celotno besedilo (157,94 KB)
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6.
Fracture toughness of a high-strength low-alloy steel weldment
Jelena Vojvodič-Tuma, Nenad Gubeljak, Borivoj Šuštaršič, Borut Bundara, 2006, izvirni znanstveni članek

Opis: The use of high-strength low-alloy steels for high-performance structures, e.g., pressure vessels and pipelines, requires often high-strength consumables to produce an overmatched welded joint. This globally overmatched welded joint contains local mis-matched regions, which can affect the unstable fracture behaviour of the welded joint and the welded structure itself. If local mis-matched regions are present in the vicinity of a crack tip, then the fracture toughness of the weld metal can be significantly lower than that of the base metal. In this paper, the influence of the weld-metal microstructure on the fracture behaviour is estimated enabling an evaluation of the resistance to stable crack growth through different microstructures. The lower bound of the fracture toughness for different microstructures was evaluated using a modified Weibull distribution. The results, obtained using specimens with a through thickness crack front, indicated a low fracture toughness, caused by the strength mis-matching interaction along the crack front. In the case of through-the-thickness specimens, at least one local brittle zone (LBZ) or a local soft region is incorporated into the process zone in the vicinity of the crack tip. Hence, an unstable fracture occurred with small stable crack propagation, or without it. Despite the fact that the differences between the impact toughness of the weld metal and the base metal can be insignificant, the fracture toughness of a weld metal can be significantly lower.
Ključne besede: fracture mechanics, welded joint, crack-tip opening displacement, resistance curves
Objavljeno: 16.03.2017; Ogledov: 481; Prenosov: 53
.pdf Celotno besedilo (502,10 KB)
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7.
Morphological and microstructural features of Al-based alloyed powders for powder-metallurgy applications
Borivoj Šuštaršič, Irena Paulin, Matjaž Godec, Srečko Glodež, Marko Šori, Jože Flašker, Albert Korošec, Stanislav Kores, Goran Abramović, 2014, strokovni članek

Opis: Besides advanced nano steels, polymers and ceramics, recently also light metals, i.e., Al, Mg and Ti based materials, have been recognized as future materials for different kinds of advanced applications. Al and its alloys have an acceptable price, excellent corrosive resistance, good mechanical and other physical properties. Therefore, they are also used in the powder-metallurgy (P/M) field. The P/M technology of Al materials is very demanding and has its own specifics compared to the sintering technology of iron and steel. A relatively large quantity of Al-based alloy powder is formed during the sand blasting of slugs and discs in the Talum Al factory, Kidričevo, Slovenia. Therefore, we analysed and investigated its practical usability for a production of advanced products using P/M technology. The formed Al-based powder was compared with the commercially available Al-based powders that are generally used for conventional sintering technology. In the first part of this paper we explain which types of Al-based powders are used for the production of sintered parts, what the required parameters are and why we considered them. Then, the results of theoretical thermodynamic analyses and investigations of the morphological and microstructural characteristics of the selected commercial Al-based powders are given, as well as their comparison with the Al powder formed during the sand blasting and its potential for P/M applications.
Ključne besede: Al-based alloy powders, morphology, microstructure, LM characterisation, SEM/EDS characterisation
Objavljeno: 17.03.2017; Ogledov: 646; Prenosov: 66
.pdf Celotno besedilo (4,85 MB)
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8.
The influence of the morphology of iron powder particles on their compaction in an automatic die
Borivoj Šuštaršič, Matjaž Godec, Črtomir Donik, Irena Paulin, Srečko Glodež, Marko Šori, Milan Ratej, Nada Javornik, 2015, strokovni članek

Opis: Fe- and steel-based powder metallurgy (P/M) products, such as steel gears, spurs, locking mechanisms, porous filters, sliding bearings and bushes, as well as other machine parts and structural elements, are mainly produced with the so-called conventional sintering technology. It is the most efficient technology for the mass production of small, complex, functional and structural parts. Therefore, it is the most convenient and popular among all of the P/M technologies. The most important end-user of sintered parts is the automotive industry. However, small, complex, sintered parts can also be frequently used in the furniture and household industries, precise mechanics, articles for recreation and sports. A fine, iron-based powder mixture or prealloyed powder is first automatically uniaxial-die compacted (ADC) into the final shape of the product with a mechanical or hydraulic press and then sintered in a protective atmosphere at approximately 1100 °C. The metal powder mixture must have the appropriate engineering properties given by the chemistry and particle morphology, enabling a fast and reliable die-compaction process. The most important are a high tap density, a good powder flowability and a low compressibility. All this gives the green compacts an appropriate final shape with a smooth surface, a relatively high and uniform green density, as well as a green strength without internal flaws and cracks. In the case of very small two-or-more-heights products, for example, spur gears with a low module, it is very difficult to obtain a uniform green density at acceptable compaction pressures. Often small cracks are formed at height crossings and big differences in the green density appear in smaller or thinner regions. In the frame of our investigation we analysed the influence of the selected prealloyed commercial iron powder’s morphology and its technological properties on automatic die compaction, as well as the sintering process in the case of small two-level sintered gear dimensions of 5/40–7/10×7mm with module m = 0.5. The original iron powder was sieved and the finest powder particle fraction (< 45 µm) was compared with the original powder mixture considering ADC and sintering process. It was found that the selection of the finer powder mixture could not contribute to the improvement in the overall ADC process, as well as a better green compact. In the present paper the results of our investigations are presented and the reasons why a finer powder mixture cannot contribute much to an improvement of the conventional sintering process.
Ključne besede: Fe-based alloy powders, particles, morphology, microstructure, automatic die compaction, sintering
Objavljeno: 27.03.2017; Ogledov: 509; Prenosov: 239
.pdf Celotno besedilo (1,18 MB)
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9.
The introduction of fine SiC particles into a molten Al alloy matrix
Varužan Kevorkijan, Borivoj Šuštaršič, 1995, objavljeni znanstveni prispevek na konferenci

Opis: The immersion of fine SiC particulates into a Al is one of the major factors hampering the commercial development of particle reinforced composites prepared by liquid metallurgy techniques. Smaller particles are generally more difficult to wet and disperse than larger particles because of their inherently greater surface area. On the other hand, smaller particles generally give MMCs with superior mechanical properties. The challenge is to control the reaction between the matrix and reinforcement particles to achieveimproved wetting so that good distribution and interfacial bonding are obtained. This paper will review the actual technological challenge of fine particulate reinforced MMC fabrication, and will describe the most promissing new processes.
Ključne besede: kompozitni materiali, livarstvo, omakanje, keramični delci
Objavljeno: 10.07.2015; Ogledov: 512; Prenosov: 24
URL Povezava na celotno besedilo

10.
Mikrostruktura hitro strjenih trakov zlitine Cu-Zr
Ivan Anžel, Alojz Križman, Tonica Bončina, Franc Zupanič, Gorazd Lojen, L. Kosec, Borivoj Šuštaršič, 1995, izvirni znanstveni članek

Opis: Hitro strjene trakove zlitin Cu -0,5% Zr in Cu - 1% Zr smo izdelali s postopkom litja taline na hitro se vrteči boben pri različnih procesnih parametrih. Mikrostrukturo trakov smo raziskali v odvisnosti od debeline oziroma povprečne ohlajevalne hitrosti in od sestave zlitin. V prečnem prerezuje mikrostruktura tankih trakov (50-55▫$mu$▫m) sestavljena iz cone transkristalnih zrn, ki sega do zgornje proste površine in v kateri ločimo tri področja z različno substrukturo: področje brez mikrosegregacij, področje trakaste substrukture in področje s celično/dendritno substrukturo. Trakovi z debelino 85-90▫$mu$▫m vsebujejo v prečnem prerezu poleg transkristalne cone še cono globularnih zrn z dendritno morfologijo. Velikost posamezne cone ter substrukturnih področij znotraj transkristalne cone je pri isti debelini trakov odvisna od kemijske sestave zlitin.
Ključne besede: hitro strjevanje, mikrostruktura, trakovi, Cu - Zr zlitina
Objavljeno: 10.07.2015; Ogledov: 675; Prenosov: 32
URL Povezava na celotno besedilo

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