Brown stains were observed forming after the black-oxide coating on the surfaces of grey-cast-iron hot plates made for an electric stove. These stains were metallographically examined using a scanning electron microscope (SEM) equipped with an energy-dispersive x-ray spectrometer (EDXS). For the phase identification we also employed x-ray diffraction (XRD) analyses. The results indicated that the stained surfaces of the hot plates were covered with whiskers of hematite (Fe2O3), while on the surfaces of the non-defective hot plates only magnetite (Fe3O4) was present. The thermodynamic calculations confirmed the possibility of the formation of hematite (Fe2O3) as a result of the oxidation of magnetite (Fe3O4) if the partial pressure of oxygen is increased during the black-oxide-coating process.
COBISS.SI-ID: 1200479
Evaluation of environmental loading which, in principle, depends on a number of factors is problematic due to their different natures and dimensional diversity. Thus, in this area, focus is placed on development and application of multicriterial methods for evaluation of critical parameters of environmental loading. Multicriterial evaluation in environment protection has been in use for a number of years. Depending on the particular goal of investigation, various approaches have been developed and applied. This research presents software for multicriterial evaluation of environmental loading, with special emphasis on the original mathematical model. Beside a detailed description of structure, characteristics and functions of this software, also presented in the research are experimental results from a multicriterial evaluation of environmental loading on six locations.
COBISS.SI-ID: 1161311
In this work, an Al-Mn-Be-Cu alloy was prepared by vacuum induction melting and casting. The alloy was then remelted and gravitationally cast into cylindrical metallic dies with 2 mm, 4 mm and 8 mm diameters in order to obtain the quasicrystalline phase in the aluminium-rich matrix. The samples with height-to-thickness ratio of 3:1 were tested using compression test at room temperature. The deformation rate was 0.001 s - 1. The main objective was to study the behaviour of the alloy during compression tests to obtain information regarding its plastic deformability and fracture. The compression behaviour of 2-mm and 4-mm samples was almost identical. They could be deformed to more than 0.9 true strain without fracture. In the plastic region, true stress of approximately 450 MPa was attained, and almost no hardening was observed. Such behaviour can arise from a microstructure consisting of primary icosahedral quasicrystalline particles and the matrix composed of two-phase eutectic-like structure composed of lamellar icosahedral phase and Al-rich solid solution. The 8-mm sample contained a considerable fraction of crystalline intermetallic compound and much less quasicrystalline phase, fractured at approximately 0.4 true strain, and at the same time, its true strength was approximately lower for 10% than that of 2-mm and 4-mm-samples.
COBISS.SI-ID: 15872278
During secondary refining of high strength steel in ladle furnace aluminium is used for melt deoxidation. Aluminate inclusionsare modified with calcium silicon injection in melt. On the basis of binary diagram CaO-Al2O3 solid and liquid calcium aluminates with different composition and shape are formed after calcium treatment. During calcium silicon injection also manganese sulphide is modified and CaS or (Ca,Mn)S is formed and is wrapped around calcium aluminates. Because of rising of calcium bubbles during calcium silicon injection powerful melt stirring occurs. This enables inclusion coagulation and reaction with slag. Also MgO•Al2O3 spinels formed. Clogging of the tundish nozzle may occur during continuous casting of steel billets. Scull which form on the nozzle inner wall consist of spinel, calcium aluminates with various composition and calcium manganese sulphide.
COBISS.SI-ID: 1211231
The investigation of aluminium alloy die casting die failures was done with the emphasis on thermal cracks. The aim of the study was to prolog the in-service die life by cladding with maraging steels, which would be economically beneficial. A vast analysis of thermal fatigue cracks in aluminium alloy die casting is done. Immersion test apparatus was developed, which enables simulation of conditions during aluminium alloy die casting and enables controlled thermal fatigue testing of materials. Special specimens made of the AISI H13 tool steel were differently heat treated. On the edges of some specimens, the maraging steel is cladded using gas tungsten arc (GTA) welding. These samples are tested in as-welded and in optimally aged condition. After completion of a particular number of cycles, the specimen edge surfaces were examined visually. The specimens were then sectioned and examined with light and scanning electron microscopy (SEM). The energz-dispersive X-ray spectroscopy (EDS) mapping of areas around the cracks was done. The number and length of thermal fatigue cracks were statistically evaluated and a Vickers hardness profiles were measured. The results confirmeda good thermal fatigue resistance of the properly hardened H13 hot work tool steel. The surface cracks growth is accelerated by surface oxidati on.
COBISS.SI-ID: 12133403