Mechanical and optical properties in precipitated regions of alumina‐rich magnesium aluminate spinel |
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| Authors: | Jesse Miller Ivar Reimanis Weiguo Miao Jonathan Salem |
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| Affiliation: | 1. Colorado Center for Advanced Ceramics, Metallurgical and Materials Engineering Department, Colorado School of Mines, Golden, Colorado;2. Corning Incorporated, Corning, New York;3. National Aeronautics and Space Administration, Cleveland, Ohio |
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| Abstract: | The toughening and strengthening of transparent ceramics is challenging because microstructural alterations typically lead to light scattering. Here, controlled precipitation of α‐Al2O3 from nonstoichiometric spinel is explored to demonstrate unique control over the evolution of second phase Al2O3 and how the microstructure might be altered to enhance fracture toughness while minimizing light scatter. Alumina‐rich magnesium aluminate spinel, MgO·nAl2O3, where n=2, was hot pressed and HIPed to produce fully dense, single‐phase material. The material was then heat treated in air at 1573 K for up to 20 hours to create a two‐phase spinel‐Al2O3 composite. The fracture toughness varies from 0.88 to 2.47 MPa√m depending on the microstructure; enhanced toughness at the surface was due to increased crack tortuosity at phase boundaries, but residual tensile stresses were observed in the interior of the material. Precipitation causes local volume contraction and the formation of porosity, decreasing optical transmission, especially for heat treatment times longer than 5 hours. |
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| Keywords: | fracture mechanics/toughness hardness precipitates/precipitation spinels transparent |
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