Indentation Size Effect (ISE) of Transparent AlON and MgAl2O4

Report No. ARL-TR-3852
Authors: Parimal J. Patel; Jeffrey J. Swab; Mark Staley; George D. Quinn
Date/Pages: July 2006; 20 pages
Abstract: Hardness is a widely reported mechanical property for materials. Aluminum oxynitride (AlON) and magnesium aluminate spinel (MgAl2O4) are two important materials for some U.S. Army applications since they can be transparent in their polycrystalline form. In many of these military applications, harder materials tend to perform better, hence it is necessary to properly measure and compare hardness values of competing materials. Measuring the hardness of most ceramics is straightforward, but comparing the hardness data for different ceramics can be complicated due to the well-known indentation size effect (ISE). This report describes the determination of the Vickers hardness-load curves for transparent AlON and MgAl2O4 in a load range between 0.98 and 19 N. Both materials exhibited a significant decrease in hardness with increasing load. The critical hardness (the point at which fracture, rather than plastic deformation, is dominant around the indentation) of spinel and AlON was found to be 13.5 and 16.8 GPa, respectively, which differs from other investigations that did not take into account the ISE.
Distribution: Approved for public release
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Last Update / Reviewed: July 1, 2006