Browsing by Subject "stopy odlewnicze"

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Mikrostruktura połączeń FSW stopów odlewniczych magnez - aluminium
(Data obrony: 2021-01-27) Maciasz, Jakub
Wydział Inżynierii Metali i Informatyki Przemysłowej
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Rola mikrododatków w poprawie żaroodporności staliwa odlewanego odśrodkowo
(Data obrony: 2008-11) Zapała, Renata
Wydział Odlewnictwa
The aim of the submitted doctor's thesis was to indicate the factors that can affect the quality of the centrifugally cast reforming tubes and to examine the relationships that are believed to exist between the oxidation rate and macro/microstructure. To achieve these goals and prove the theses of the study, the research materials, i.e. the centrifugally cast tubes, were subjected to extensive macro- and microstructural examinations (optical, scanning and transmission microscopes combined with X-ray absorption spectroscopy). Using X-ray techniques, the phase composition of the investigated cast steels was examined. Additionally, stereological methods were used to determine the grain size and volume fraction of carbides. To evaluate the corrosion resistance behaviour at high temperatures, the kinetics of oxidation was measured, and the scale formed on alloys was examined. The investigations of the scale included scanning analysis, testing of adherence, measurements of roughness and surface topography as well as phase analysis by Bragg-Brentano geometry diffraction with constant angle of incidence. An important output of the investigations was proving that, besides niobium carbides of the $NbC$ type, the presence of the $Nb_{2}C$ type carbides was also identified in the alloy structure. Additionally, in alloys modified with $Ti$ and $Zr$, the presence of complex carbides of the $(Ti, Zr, Nb)C$ type was reported. In centrifugal steel castings, cerium was observed to be located within the area of equiaxial crystals rather than within the area of columnar grains, and it was not related to the oxide phase. The conducted investigations of the oxidation kinetics were not capable of proving any distinct effect of modification on the values of the parabolic constant rates of the cast steel oxidation. It has been proved, however, that with increasing temperature some discontinuities and spallings start appearing in the scale. Moreover, it has been reported that the introduced microadditives affect the adherence to the substrate of the scale formed on alloy during oxidizing at a temperature of 1093K.