Rate and Composition Control for Plasma-assisted EB-PVD Processes by Optical Emission Spectroscopy

Increasing performance requirements of coatings on components and tools drive new approaches and developments, e.g.,in the field of thermal (TBC) and environmental (EBC) barriercoatings 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 EBPVD 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 paper, another beneficial effect of the plasma assist shall be discussed: Due toexcitation of vapor and gas species, the discharge also stimulates element-specific light emission. Hence, optical emissionspectroscopy (OES) can be utilized to monitor and control thePVD process in-line, which has been done in electron beam(EB) co-evaporation of several metal ingots in inert vacuum aswell as of yttria-stabilized zirconia (YSZ) in oxygen atmosphere, both activated by an HAD plasma. In both examples, OES was utilized to create an automatic control loop tuningthe 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. Thecombination of EB (co)evaporation, plasma activation and OES-based control demonstrated great potential to become aversatile tool for the development of complex coating systems and their reliable deposition in future production processes.