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Abstract: The aim of this research was to analyse the inhibition of internal passivation by changing the chemical composition of silver alloys and to estimate the concentration boundaries of the selected microalloying element at which the passivation is still inhibited. Since, the ability of inocculationor modification is mostly based on the large free energy of formation of oxides of microalloying elements and their crystallographic similarity, Mg in the quantities of 0.001 to 0.5 mass% was chosen as a microalloying element for Ag-based alloys in addition to the main alloying element (Yn). For the Ag-5.8%Yn alloy, the boundary conditions of the inhibition of passivation were established. For concentrations of MgO below 0.005 vol.% not enough nuclei are formed. For too high concentration of MgO (above 1.2 vol.%) defect microstructures are formed which are characteristic for MgO precipitation. This produces a local or general passivation. By changing the composition of microalloying the internal passivation of Ag-5.8%Yn alloy could not only be inhibited but increased. Thus under some microalloying conditions much bigger depths of internal oxidation were reached.
Keywords: internal oxidation, chemical composition, silver alloys
Published in RUP: 15.10.2013; Views: 3725; Downloads: 25
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