High-strength glass-ceramics in the system MgO/Al2O3/SiO2/ZrO2/Y2O3 – microstructure and properties

Abstract

Glasses with the composition 51.9SiO₂·21.2MgO·21.2Al₂O₃·5.7ZrO₂ (in mol%) were crystallized in different annealing steps at 950 °C and 1060 °C. Using X-ray diffractometry and high resolution (scanning) transmission electron microscopy with energy-dispersive X-ray spectroscopy, it is found that the annealing-induced devitrification results in glass-ceramics with α-quartz solid solution as the main crystal phase, with a few additional ZrO₂ and MgAl₂O₄ crystals as secondary crystal phases. If 2.5 mol% Y₂O₃ are added to the base glass, however, an identical heat treatment leads to glass-ceramics with dendritic ZrO₂ crystals as the main crystal phase, and subsequently grown MgAl₂O₄ as the secondary crystal phase. The quartz solid solution was found to be absent in those Y₂O₃-bearing samples, as Y₂O₃ is incorporated in the residual glass matrix, thus stabilizing it. It was observed that the bending strength was comparable for both sample sets, thus indicating that the existence of α-quartz is not necessarily an important prerequisite for excellent mechanical properties of glass-ceramic materials based on the MgO/Al₂O₃/SiO₂ system. Strengthening mechanisms for both Y₂O₃-bearing and Y₂O₃-free glass-ceramics are discussed.