Rate and Composition Control for Plasma-assisted EB-PVD Processes by Optical Emission Spectroscopy
(Room Room 104-B)
02 May 19
2:40 PM
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3:00 PM
Tracks:
High-Powered Electron Beam Technology
The increasing need for enhanced fuel efficiency, reduced emissions and extended service life drives new approaches and developments in the field of thermal (TBC) and environmental (EBC) barrier coatings on turbine components, characterized by more complex compositions and a desire for morphology control. Consequently, the corresponding PVD processes become more challenging and call for advanced monitoring and control means. Plasma activation by hollow cathode arc (HAD) or spotless arc (SAD) discharges has been proven in various EB-PVD processes as an enabling tool for achieving enhanced film properties at high deposition rates – facilitated by the energy gain of the condensing particles. In this presentation, another beneficial effect of the plasma assist shall be discussed: Due to excitation of vapor and gas species, the discharge also stimulates element-specific light emission. Hence, optical emission spectroscopy (OES) can be utilized to monitor and control the PVD process in-line. Three examples with particular relevance for TBC/EBC will be presented: (1) EB evaporation of YSZ ingots, activated by an HAD plasma, (2) EB co-evaporation of zirconium and yttrium in oxygen atmosphere, activated by an SAD plasma, and (3) EB co-evaporation of several metal ingots in inert vacuum, activated by an HAD plasma. (1) and (2) were aimed at depositing thick YSZ layers, (3) at forming dense multi-element metal compounds. In all examples, OES was utilized to create an automatic control loop (tuning the beam scan pattern, the beam power and/or the feeding speed of the individual source materials) to maintain the desired deposition rate and stoichiometry of the coatings. The combination of EB (co‑)evaporation, plasma activation and OES-based control demonstrated great potential to become a versatile tool for the development of complex coating systems and their reliable deposition in future production processes.