Morphology, microstructure, and residual stress in EBPVD erbia coatings

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.