High Temperature Coatings by Pulsed Electron Beam Ablation
Abstract
The objective of this program was to investigate the deposition and properties of new high temperature coatings using pulsed-electron-beam ablation (PEBA) and to characterize the corrosion of those compounds in relevant environments. The PEBA technique has potential advantages for depositing compounds that are known to be difficult to deposit by conventional electron-beam evaporation. The use of ablation rather than melting and evaporation avoids changes in composition associated with differing evaporation rates of constituents in a molten target. The use of electrons rather than eximer laser radiation (as in conventional laser ablation methods) enables ablation of materials that do not couple well to the laser because they are partly transparent at the laser wavelength or reflective. Using a chamber with stationary and rotating heated substrates, coatings of both lanthanum phosphate and lanthanum silicate were successfully deposited. Rare-earth phosphates are of interest for thermal barrier coatings, while rare-earth silicates are of interest for environmental barrier coatings. The coatings deposited at high temperature were crystalline. However, when stoichiometric targets were used, the coating stoichiometry was always deficient in the lighter elements, phosphorous and silicon. A model experiment was designed to map out the stoichiometry of the gas phase as a function of distance from the center of the plume. The results showed that the non-stoichiometry was the result of a faster diffusion rate of the lighter elements away from the center of the plume, likely due to collisions with the heavier rare-earth element. In the case of LaPO4, the loss of phosphorous could be compensated for by using a phosphorous-rich target, thus leading to deposition of stoichiometric monazite LaPO4 as the major phase on the substrate.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 2005
- Accession Number
- ADA441277
Entities
People
- David B. Marshall
- Olivier Sudre
- Sergio Lucato