Journal
MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
Volume 691, Issue -, Pages 203-210Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.msea.2017.03.041
Keywords
Nanoindentation; Mechanical characterization; Ceramics; Phase transformation; Twinning
Categories
Funding
- National Nuclear Security Administration of the U.S. Department of Energy [DE-AC52-06NA25396]
- National Science Foundation (NSF) [DMR-1352499]
- Direct For Mathematical & Physical Scien
- Division Of Materials Research [1352499] Funding Source: National Science Foundation
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Low elastic modulus and hardness, as well as anomalous indentation behavior, have been observed during indentation of xenotime rare-earth orthophosphate ceramics (REPO(4)s) with compositions near the monazite/xenotime phase boundary. Pressure-induced phase transformation has been identified as a potential cause for both observations. This study comprehensively characterizes the mechanical properties and indentation behavior of four elemental REPO4 materials (EuPO4, GdPO4, TbPO4, and DyPO4) that span the monazite/xenotime phase boundary using ex situ nanoindentation for a range of loading rates and indentation depths. In situ nanoindentation within a SEM was used to correlate discrete load-depth behavior to the development of surface features. Anomalous, elbow-type behavior was not restricted to xenotimes, but occurred in all four materials; thus we concluded that the presence of an elbow in the indentation data was not a unique identifier of phase transformation in rare-earth orthophosphates. Furthermore, it was shown that the elastic modulus of each of these compositions approached the value predicted by simulations and hardness was consistently above 5 GPa, provided that the samples were processed to nearly full density.
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