Molds for the glass industry can be made from special copper alloys that have excellent thermal conductivity and resistance to thermal fatigue. Nickel plates are welded or nickel inserts are engulfed by a molten alloy at the most structurally critical points of the molds. At the end of their service life, the used molds are recycled together with the nickel plates and inserts.
The aim of the master’s thesis was to characterize the microstructure of five samples of the special copper alloy OMX containing 15-16,5 wt. % Ni, 9,5-10 wt. % Al, 7,5-9 wt. % Zn and up to 1,25 wt. % Fe, focusing on impurities. The microstructure of nickel plate and nickel insert and their joints with a special copper alloy were also investigated to further explain the source of impurities in OMX alloys. Characterization methods used in this work include optical microscopy (LE), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD).
The microstructure of the OMX special copper alloy samples consists of equiaxed dendrites of primary phase β-AlNi and eutectic (αCu + β-AlNi). The samples also contained several impurities, especially chromium and iron rich borides, while complex oxides and lead were also found very frequently. The amount of iron in the borides was found to significantly affect their shape. The chemical composition and microstructure of the nickel plate and nickel insert are quite different. It was also found that borides form at the weld between the nickel plate and the special copper alloy, while aluminum-based oxides form most frequently near the joint between the insert and the special copper alloy.
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