The new approach of the production technique of discontinuous Cu-C composite

The samples of the Cu-C composite were produced by two different techniques (i) the sintering of powders, and (ii) the internal carbonization of rapidly solidified pure copper. The aim of the present research was to produce a discontinuous Cu-C composite with the submicron dispersion of graphite particles. The results of our microstructural investigation show that the use of the mechanical alloying and sintering of consolidated powders is an inappropriate way to achieve a submicron dispersion of the graphite particles. On the other hand, the combination of rapid solidification and internal carbonization was found to be an efficient technique to obtain the requested microstructure

Multilayered nano-foils for low-temperature metal-ceramic joining

Over almost two decades metal-ceramic fusing has been the essential step in obtaining materials which benefit from both ceramic and metal materials, i.e. where the combined properties of the metal and ceramic layers are desirable. Soldering and active metal brazing are the most effective when considering fusing methods. This paper presents a low-temperature process for soldering and brazing ceramics to metals, which is based on the use of reactive multilayer foils as a local heat source. The reactive foils range in thickness from 40 μm to less than 100 μm and contain many nanoscale layers and/or domains that alternate between materials with high mixing heat.

Karakterizacija hitrostrjenih trakov zlitine Cu-Al-Ni z uporabo fokusiranega ionskega curka

This work investigates the possibilities for applying a focussed ion beam (FIB) for the metallographic preparation and characterization of Cu-Al-Ni melt-spun ribbons. Two alloys were selected for this reason: CuAl13Ni4 and CuAl15Ni4. The microstructure of the first alloy was fully martensitic and the microstructure of the second consisted of two phases: martensite and ▫$gamma_2$▫. It was discovered that with FIB-etching the microstructures of both alloys can be clearly revealed on polished cross-sections of the melt-spun ribbons, as well as on their wheel-side and air-side surfaces. However, better results were obtained when the etched surface was smoother, and finer details were visible when using smaller ion currents. In addition, a study was made into the influence of platinum deposition on the quality of 3D-cross sections. It was found that Pt-deposition is necessary when the edge of the trench should be straight and sharp, and the surface of the 3D cross-section smooth. However, in this case, the microstructure of the ribbons free surface cannot be seen.V tem delu smo raziskali mo.nosti uporabe fokusiranega ionskega curka (FIB) pri metalografski pripravi in karakterizaciji hitro strjenih zlitin Cu-Al- Ni. Izbrali smo dve zlitini: CuAl13Ni4 in CuAl15Ni4. Mikrostruktura prve zlitine je bila v celoti martenzitna, medtem ko je bila mikrostruktura druge zlitine sestavljena iz dveh faz: martenzita in ▫$gamma_2$▫. Ugotovljeno je bilo, da lahko pri jedkanju z ionskim curkom odkrijemo mikrostrukturo tako na poliranih prečnih prerezih trakov, kot tudi na obeh prostih površinah hitrostrjenih trakov. Mikrostruktura se je boljše odkrila, če je bila raziskana površina bolj gladka, medtem ko smo lahko razločili drobnejše mikrostrukturne sestavine pri uporabi manjših ionskih tokov. Poleg tega smo študirali tudi vpliv nanosa platine na kakovost 3D-prečnih prerezov. Ugotovili smo, da je nanos platine smiselno uporabiti, če želimo zelo ravne in ostre robove reza ter gladko površino prečnega reza, vendar pa v tem primeru ne moremo videti mikrostrukture proste površine

Investigation of mechanical and biomedical properties of new dental alloy with high content of Au

The basis for developing a new dental alloy with high Au content is appropriate chemical composition and manufacturing technology. The demands which have to be met when developing a new dental alloy are linked with fulfilling the necessary requirements for making the alloy suitable for use in metal-ceramic restorations. Due to the stress generated by masticatory forces, alloys for dental restorations must have corresponding mechanical properties (yield strength, tensile strength, and elongation), hardness, the coefficient of thermal expansion (CTE), and biocompatibility. Namely dental alloy placed in an oral cavity reacts with the environment and deteriorates. New dental alloy with high Au content is based on the ternary system of Au-Pt-Zn with a nominal composition of 86.9Au-9.9Pt-1.5Zn, and about 1,5 wt.% micro-alloying elements (In, Ir, Rh). The dental alloy was melted and cast in a vacuum-induction melting furnace in Zlatarna Celje. The results analyses of different heat-treated states showed that the optimal mechanical properties and hardness of an Au-Pt-Zn alloy can be reached with combinations of heat treatment for 20 minutes at 723 K and then slowly cooling, if the alloy was annealed at 1223 K for 30 minutes and the water quenched. Research results confirmed that the microstructure of the Au-Pt-Zn alloy consists of two phases: a1-phase rich in Au (main phase) and a2-phase rich in Pt (minor phase). During XRD analysis and use of the Rietveld method, it was found that the a1-phase content is about 98,5 wt.% while the content of a2- phase is 1,5 wt.%. STA analyses show that the Au-Pt-Zn alloy has a solids temperature of about 1292 K and a liquids temperature of about 1412 K. The optical properties of Au-dental alloy were investigated by means of spectrophotometric colourimetry. Spectral reflectance data from the mirror-polished flat samples of initial Au dental alloy were collected under the CIE standard illuminant D65. Finally the test of cytotoxicity of new Au based dental alloys using standard in vitro assays for testing the biocompatibility with establishing new, more sensitive, in vitro tests on cell lines was done. According to the results of our research we can conclude that new dental alloy from Zlatarna Celje satisfied all requested standards regarding mechanical properties, hardness and CTE: Rp0.=550 [N/mm2], Rm =610 [N/mm2], A= 9%, 180 HV and CTE (25-600°C) about 14,45×10-6K-1. This new Au dental alloy has a yellow tinge in comparison to conventional Au-Pt-Zn alloys and did not show cytotoxicity when using standard short-term in-vitro assays on an L929 cell.

Notranja oksidacija Cu-C in Ag-C kompozitov

The internal oxidation in copper-carbon and silver-carbon composites occurs when they are exposed to air or oxygen at high temperature. Solubility of carbon in copper or in silver is very low. The kinetics of oxidation at high temperature and activation energy were determined and the mechanism of internal oxidation was analysed. The kinetics of internal oxidation was determined for both cases and it is depended from the diffusion of oxygen following parabolic time dependence according to Wagner\u27s theory. The activation energy for Cu-C composite is 70.5 kJ/mol, and for Ag-C composite is 50.1 kJ/mol, what is in both cases close to the activation energy for the volume diffusion of oxygen in copper or in silver. In both cases gas products are formed during the internal oxidation of composites. In the internal oxidation zone pores, bubbles occur. The carbon oxidates directly with the oxygen from solid solution as long there is a contact, which breaks down with the presence of gas products. Then the oxidation occurs over the gas mixture of CO and CO2.Pri visokih temperaturah kompoziti bakra in srebra z ogljikom na zraku ali v kisiku reagirajo po mehanizmu notranje oksidacije. Topnost ogljika v trdnem bakru in trdnem srebru je zelo majhna. Analizirali smo kinetiko oksidacije kompozitov, določili aktivacijsko energijo in mehanizem notranje oksidacije. Kinetika oksidacije je pri obeh skupinah materialov odvisna od difuzije kisika in sledi parabolični odvisnosti od časa v skladu z Wagnerjevo teorijo. Aktivacijska energija procesa je za kompozit Cu-C enaka 70,5 kJ/mol, za kompozit Ag-C pa 50,1 kJ/mol, kar je blizu aktivacijski energiji za volumsko difuzijo kisika v trdnem bakru oziroma srebru. Pri oksidaciji kompozita nastajajo plinski produkti. Oksidacija ogljika poteka neposredno s kisikom iz trdne raztopine, ko pa se zaradi nastanka plinske faze stik prekine, pa preko plinske zmesi CO in CO2

Liquid metal/ceramic interfaces in dental practice and jewellery manufacturing

Metal-ceramic fusing has been the essential step in obtaining materials that benefit from both ceramic and metal constituents. i e where the combined properties of metal and ceramic layers are desirable When considering fusing methods. soldering and active metal brazing are the most effective These processes involve braze melting and flowing between the two pieces of material In the first part the phenomena occurring on the boundary between the ceramics and the active filler metal during the metal-ceramics joining are discussed Three interconnected sub-processes are considered (1) wetting of the ceramic surface. (2) chemical reactions at the Interlace and (3) diffusion with a moving interface Then, the appearances at the grain boundary grooves of the ceramic surface are presented as phenomena on the catalytic surface In the second pan, examples from dental practice and jewellery manufacturing are used for comparative analysis Finally we discuss the composition and properties of the soldering and brazing alloys used for dental practice and jewellery manufacturin

Karakterizacija nove dentalne zlitine z visoko vsebnostjo Au

The basis for developing a new dental alloy with high Au content is appropriate chemical composition and manufacturing technology. This new Au dental alloy is based on the ternary system of Au-Pt-Zn with a nominal composition of 88.5Au-8.7Pt-1.5Zn-0.5In-0.4Ir-0.3Rh. The alloy was melted and cast in a vacuum-induction melting furnace in Zlatarna Celje. Casting was followed with subsequent thermo-mechanical treatment (procedures of profile and polish milling, thermal treatment) and cutting-off strips to form a regular shape. The heat treatments of Au alloy samples were carried out in a tube furnace under different temperatures, and over different times. Testing of the new Au dental alloy included examining the initial cast, and the different heat treated conditions of the Au alloy. The optical properties of Au-dental alloy were investigated by means of spectrophotometric colourimetry. Finally the test of cytotoxicity of new Au based dental alloys using standard in vitro assays for testing the biocompatibility with establishing new, more sensitive, in vitro tests on cell lines was done.Osnovo razvoja nove dentalne zlitine z visoko vsebnostjo Au predstavljata pravilna določitev kemijske sestave in tehnologije izdelave. Nova dentalna zlitina temelji na ternarnem sistemu of Au-Pt-Zn z nominalno kemijsko sestavo 88,5Au-8,7Pt-1,5Zn-0,5In-0,4Ir-0,3Rh. Izdelava dentalne zlitine je potekala s pretaljevanjem zelo čistih komponent v vakuumski indukcijski peči v Zlatarni Celje. Temu je sledilo odlivanje taline v ustrezno formo, postopek termo-mehanske obdelave odlitka in razrez zlitine v ustrezno obliko. Toplotna obdelava je bila izvedena pri različnih temperaturah in za različne čase. Testiranje dentalne zlitine je vključevalo določitev lastnosti začetnega stanja in stanja po različnih toplotnih obdelavah. Optične lastnosti dentalne zlitine so bile raziskane s spektro-fotometrično kolorimetrijo. Na novi Au dentalni zlitini so bili narejeni še testi citotoksičnosti z uporabo standardain vitro analize za testiranje biokompatibilnosti z uvajanjem novih, bolj občutljivih in vitro testov na celični liniji

Mechanical properties and microstructure characterisation of Au-Pt dental alloy

Development of a dental alloy with high Au content is based on the ternary system of Au-Pt-Zn with a nominal composition of 86,9Au-9,9Pt-1,5Zn, and about 1,5 wt.% micro-alloying elements (in, Ir, Rh). The results analyses of different heat-treated states showed that the optimal mechanical properties and hardness of an Au-Pt-Zn alloy can be reached with combinations of heat treatment for 20 minutes at 723 K and then slowly cooling, if the alloy was annealed at 1223 K for 30 minutes and the water quenched. Research results confirmed that the microstructure of the Au-Pt-Zn alloy consists of two phases: alpha(1)-phase rich in Au (main phase) and alpha(2)-phase rich in Pt (minor phase). During XRD analysis and use of the Rietveld method, it was found that the alpha(1)-phase content is about 98,5 wt.% while the content of alpha(2)-phase is 1,5 wt.%. STA analyses show that the Au-Pt-Zn alloy has a solidus temperature of about 1292 K and a liquidus temperature of about 1412 K

Ellipsometric measurements of plastically deformed copper

Chemically pure copper (99.99) prepared in the sample of square cross-section (10 x 10 mm2) and length about 50 mm was extremely plastically deformed with the repeated application of equal channel angular pressing. Equal channel angular pressing was applied as an effective technique for producing bulk nanoscaled structures. It is well known that severe plastic deformation of metallic materials often leads to microstructure with ultrafine grains and cross-sections which remain about equal before and after deformation. Optical properties of the sample were studied using spectroscopic ellipsometry in UV-VIS range. The parameters of the sample like copper oxide and surface roughness overlayer were calculated using two-film model together with the Bruggeman effective medium approximation

Comparison of niti orthodontic archwires and a determination of the characteristic properties

The aim of this paper was to analyse the characteristic properties of six different, commercially available nickel-titanium orthodontic wires with a diameter of 0.305 mm (0.014"). The characteristic properties were determined by using semi-quantitative EDX analyses, DSC analyses for a determination of the phase temperatures, and a tensile test to obtain the mechanical properties of the wires. The investigation of the chemical composition showed an equiatomic NiTi alloy. Analyses of phase temperatures showed that the nickel-titanium orthodontic wires were, in an austenitic microstructure, exhibiting a superelastic effect in the oral environment. The uniaxial tensile stress strain curves showed different values for the beginning and the end of the transformation range during the loading