Morphology, microstructure, and residual stress in EBPVD erbia coatings
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The electron-beam physical vapor deposition of erbium-oxide coatings onto sapphire wafers is investigated to evaluate processing effects on the residual stress state and microstructure. The erbium-oxide coatings are found to be in a compressive stress state. The crystallographic texture of the erbium-oxide coating is evaluated using X-ray diffraction along with an assessment of forming the cubic erbia phase as a function of substrate temperature. In addition to the cubic erbia phase, an orthorhombic phase is found at the lower deposition temperatures. A transition is found from a two-phase erbium-oxide coating to a single phase at deposition temperatures above 948 K. The variation in morphology with deposition temperature observed in fracture cross-sections is consistent with features of the classic zone growth models for vapor-deposited oxide coatings. For high-temperature applications, a deposition process temperature above 948 K is seen to produce a stoichiometric, fully dense, and equiaxed-polycrystalline coating of cubic erbia.
KeywordsErbia Deposition Temperature Sapphire Substrate Physical Vapor Deposition Orthorhombic Phase
The research was sponsored by the Office of Fusion Energy Sciences, U.S. Department of Energy and by the US-Japan JUPITER-II collaboration with the MHD coating subtask led by Prof. T. Muroga, NIFS (Natl. Institute for Fusion Science). This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.
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