Kovinsko-keramični material z infiltrirano magnezijevo zlitino : doktorska disertacija

slovenian

doktorska dela

2013

Univerza v Mariboru, Fakulteta za strojništvo

This work presents the development of a metal-ceramic material with an infiltrated magnesium alloy (interpenetrating phase composite; IPC). The IPC was manufactured by gravity permanent mould casting, characterized by optical microscopy, scanning and transmission electron microscopy, energy dispersive spectroscopy, energy dispersive X-ray analysis, and it was mechanically tested. The matrix, an AE44 magnesium alloy that contained 4.94 wt. % Al and 4.42 wt. % rare-earth elements (RE) was composed of Ž-Mg primary crystals of amulti-component solid solution, Al11RE3, Al2RE, and Al10RE2Mn7 intermetallic phases. The reinforcement, ceramic foam was composed of Ž-Al2O3, Ž-SiC, Ž-SiC, and SiO2. The ceramic foam had open primary and mostly closed secondaryporosity. Upon casting, the melt infiltrated into the primary pore and it partly infiltrated and partly penetrated through the struts of ceramic foam into the secondary pore. Strong reaction appeared at the interfaces between the AE44 alloy and the ceramic foam and influenced the microstructure of the IPC. Therefore, the majority of work was oriented towards defining the mechanisms and kinetics of chemical reactions at the interfaces. Experimental castings using different parameters, model experiments of interactions also with compact ceramics, and a theoretical study of the thermodynamic reactions were made for this purpose. The main reaction products at the AE44 - ceramic foam interfaces and in the penetrated struts of ceramic foam were MgO, AlSiRE,and AlMgSiRE. MgO was formed first with a reduction of SiO2 and Al2O3 by magnesium. Then AlSiRE was formed on the MgO. Later AlMgSiRE was epitaxially crystallized on AlSiRE and its content was increased by increasingthe reaction times. Their chemical composition was defined using microchemical analysis and it was established that the phases had tetragonal crystal structures with clear mutual crystallographic orientation. It was discovered that AlSiRE and AlMgSiRE did not correspond to any known phase. TheIPC had, for all the investigated states, a higher yield stress and Young'smodulus and a lower bending and compression strength in comparison to the AE44 alloy. The AlMgSiRE phase had a lower hardness and Young's modulus than the AlSiRE phase.

08.08.2023