The influence of processing, heat-treatment and aging of Cu-(8-9) wt% Al-(7-10) wt% Mn alloy on the kinetics and temperatures of martensitic transformation was investigated by calorimetric measurements. Cu-Al-Mn alloy was prepared by continuous casting, melt-spinner and by melting in the electric arc furnace. Alloys were further heat-treated at 900 oC for 30 min and quenched in water, as well as aged at 300 oC for 1 h. Differential Scanning Calorimetry (DSC) was performed at 3 heating/cooling cycles from 50 to 250 oC. Non-isothermal measurements were determined at five different heating/cooling rates: 5, 10, 15, 20 and 25 oC/min. Activation energy was obtained according to Ozawa and Kissinger kinetic models. Microstructure analysis of investigated systems was performed by scanning electron microscopy (SEM). Results indicate the most intensive formation of martensitic structure in the as-cast state during continuous casting, where the partially formation of needle-like and V-shape martensite was observed. After solution treatment and quenching as well as aging, completely martensitic phase occurred in continuously cast alloy. XRD analysis detected Cu2AlMn, Cu3Al and Al4Cu9 phases in quenched specimens of continuously cast Cu-Al-Mn alloy and ribbon. The highest impact of the solution treatment and aging on the shifting of the martensitic temperatures was observed for Cu-Al-Mn ribbons, while in continuously cast Cu-Al-Mn alloy heat treatment and aging induced formation of different martensitic crystal structures. Kinetic investigations showed increasing start martensitic temperatures, Ms, and wider temperature interval of martensitic transformation with higher cooling rate. The highest values of activation energy of martensitic transformation was obtained for the continuously cast Cu-Al-Mn alloy.
COBISS.SI-ID: 1737055
Catalysts based on the Ni/Al2O3 system are used in a variety of catalytic processes. Catalysts are commonly synthesized through thermochemical routes (impregnation, precipitation, coprecipitation and others). The authors prepared a Ni-Pd/Al2O3 catalyst supported by a ceramic foam, using a novel method, whereby the foam was impregnated with aerosol. This paper evaluates the synthesis methods for the experimentally obtained Ni-Pd/Al2O3 catalyst in comparison with other Ni-based catalysts, using three multi-criteria analysis methods (SAW, TOPSIS and PROMETHEE II). The synthesis methods for Ni-based catalysts were compared with respect to the following parameters: preparation method, addition of the precipitation agent during preparation, forming and mixing precursors, filtration, drying procedure, calcination, reduction, and the presence of NiAl2O4. The final results indicate that the synthesis method for the Ni-Pd/Al2O3 catalyst is the best ranked in comparison with the others.
COBISS.SI-ID: 1681759
This study confirms that the stable icosahedral quasicrystal (iQc) phase Al65Cu20Fe15 (iQc–AlCuFe) can serve as a substrate for the nucleation of the metastable iQc–AlMnSi phase formed in rapidly solidified Al–Mn–Si alloys. The results reveal that a continuous, thin layer of the metastable iQc–AlMnSi phase can be formed on a stable iQc–AlCuFe particle. Electron backscatter diffraction patterns and selected-area electron diffraction patterns confirmed that epitaxy exists between the stable and the metastable iQc phases.
COBISS.SI-ID: 1716063
Sol–gel boehmite coatings were produced on the polished surfaces of hypo-eutectoid C45 carbon steel by dip coating. After the deposition the coatings were heat treated by drying at RT, 150 and 200 °C. It was found that for crack-free coatings, the drying temperature needs to be ?150 °C. Properly heat-treated boehmite coatings then improve the corrosion resistance of steel, while proposed alumina coatings derived from the boehmite coatings during annealing of the steel affect the decarburization. The coated steel samples were annealed at temperatures that are typical for the heat-treatment and thermomechanical process of C45 steel, i.e., (AC1 (tempering, sphereoidization) and )AC3 (austenitization, thermomechanical process). The sol–gel alumina coating decreased the decarburization rate of the quenched steel during the tempering (?600 °C), which meant that the hardness reduction on the steel surface was smaller. Alumina coatings have a smaller effect on the decarburization at higher temperatures; however, the metallographic analyses indicate that the coatings can retard the oxidation rate in comparison to the decarburization rate and thus, somewhat increase the visual level of the decarburization. Under annealing conditions (T = 950 °C, t = 0.5–2 h) at which the oxidation rate is higher than the decarburization rate the decarburization process is not important since the decarburized layer is peeled off the steel surface together with the scale. No visual decarburization is then observed.
COBISS.SI-ID: 1720927
The internal oxidation (IO) of Ag - VC composites containing 5 vol.% of carbide was examined at three oxidation temperatures (350, 400, 600 °C). Two mechanisms were observed due to the formation of double oxides with relativelylow melting points. At temperatures below the lowest eutectic point in-situ, or diffusion less IO, was observed with the formation and growth of oxide layers surrounding the initial carbide. At temperatures above the eutectic point IO resulted in the formation of liquid oxide pools, which grew in size and developed into a network of oxides within the metal matrix. The kinetics confirmed the presence of two distinct mechanisms
COBISS.SI-ID: 14376214
An Al–Mn alloy with additions of copper, magnesium, and silicon was prepared and cast into a copper mold. It contains in situ-formed icosahedral quasicrystals (iQCs), as confirmed by electron backscatter diffraction. The aim of this work is to present the mechanical and corrosion properties of this alloy and compare its properties with some conventional commercial materials. The compressive strength and compressive yield strength were 751 MPa and 377 MPa, while the compressive fracture strain was 19%. It was observed that intensive shearing caused the final fracture of the specimens and the fractured iQC dendrites still showed cohesion with the ?-Al matrix. The polarization resistance and corrosion rate of the artificially aged alloy were 7.30 k? and 1.2 µm/year. The evaluated properties are comparable to conventional, discontinuously reinforced aluminum metal-matrix composites and structural wrought aluminum alloys.
COBISS.SI-ID: 1731679
Rapidly solidified ribbons of CuCr alloys with 2.27 and 4.20 at. % of chromium were produced using the meltspinning method. Alloys were analysed by electron microscopy for complete solubility of Cr in copper matrix. To avoid disturbing effects of Cr phase particles, the kinetics and he sequence of microstructural transformations during heating were analysed only the sample with 2.27 at.% of chromium with complete Cr solubility in the copper matrix. We then investigated the precipitation process for this alloy that was subsequently heated at a constant rate. The increased solid solubility obtained allowed the extensive precipitation of a Crrich phase. The kinetics and the sequence of microstructural changes that occurred during the heating were analysed using an in-situ measurement of the electrical resistance. The quenched microstructure was analysed at transition points using scanning and transmission electron microscopy. X-ray photoelectron spectroscopy, as a very surfacesensitive method, was applied to study the changes in thechemical composition of the surface for the Cu–Cr alloy ribbons in the temperature range 400–700 °C during an in-situ heat treatment in an ultrahigh vacuum. The results show a relatively rapid precipitation of chromium to the surface, which starts at 400 °C and is correlated with a change in the microstructure and the electrical resistance. The Cr precipitation is faster at higher temperatures and follows the parabolic law. The resistivity results for the supersaturated binary alloy were analyzed using the Ozawa method to give an activation energy for the precipitation of 196 ± 10 kJ/ mol.
COBISS.SI-ID: 26708263
The article describes the effect of friction stir processing (FSP) on the superplastic behaviour of the Al–4.5 Mg alloy containing Sc and Zr. The results yielded by the FSPed sheet were compared with the superplastic behaviour of the same alloy produced conventionally by cold rolling. The measurements of the superplasticty included the flow stresses and the maximum elongations of the alloy at initial strain rates ranging from 1×10-3 s-1 to 1 s-1, and at testing temperatures from 350 °C to 500 °C. The inclusion of the FSP step considerably enhanced the superplastic behaviour of the alloy in comparison with its rolled counterparts, which was reflected in higher elongations at higher strain rates and lower forming temperatures.
COBISS.SI-ID: 1315679
In this paper the results of microstructure analysis before and after fracture along with mechanical properties and hardness of the CuAlNiMn shape memory alloy was presented. Melting of the alloys was carried out in vacuum induction furnace in protective atmosphere of argon. Alloy was casted into ingot of 15 kg weight. After casting the alloy was forged and rolled into a diameter of approximately 10 mm. Microstructural characterization was performed by optical microscopy (OM) and scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS). Martensitic microstructure of CuAlNiMn alloy before tensile test was observed. A tensile test and hardness measurements were carried out. The fractographic analysis showed some areas with intergranular and mainly transgranular brittle fracture. Tensile test results showed that tensile strength was 401.39 MPa and elongation was 1.64%. The hardness of the CuAlNiMn alloy was 290.7 HV 0.5.
COBISS.SI-ID: 1671775
The non-alloyed hypo-eutectoid steel C45 was annealed in a steady air atmosphere at T ) AC1 using three temperature ranges and annealing times ta = 12, 1 and 2 h. The oxidation and decarburization obeyed the parabolic law of growth with time and increased with higher temperatures and longer annealing times. The maximum visible thickness of the decarburized surface layer for all the temperature ranges can be predicted from the equations for the oxidation of iron and from the Van-Ostrand-Dewey equation (derived from Fick’s 2nd law) for the distribution of carbon. In this relation, the equation that gives the lowest values for the diffusion coefficient of carbon in austenite is appropriate. It was found that the Van-Ostrand-Dewey equation is applicable at T ) AC1, despite thefact that it was derived for the decarburization of austenite at T ) AG. A comparison of the results showed that the depth of the decarburization with a carbon content of 0.91–0.98C0 can be determined with optical metallography and that both the theoretical and measured values are, in general, mutually accurate in the regions of 93% to 98%. In practice, visible decarburization might not be present under some conditions while annealing in a steady air atmosphere. The reason for this is that the process of oxidation is faster than the process of decarburization. Considering the oxidation of steel under these conditions, annealing in a steady air atmosphere can be performed without any protective measures.
COBISS.SI-ID: 1728863