PSI has twenty years general experience in the design and construction of thermal/vacuum systems including those with plasma capabilities and, specifically, from its collaboration with QinetiQ in the development of an electron beam evaporation system for the production of bulk aluminium alloy plate by PVD. PSI Ltd under contract from Cranfield University, has manufactured an innovative EB-PVD system for a key aerospace research application. This PSI – Cranfield partnership provided a unique U.K. capability for the design and manufacture of this coater.
The EB-PVD coater facility, incorporates differentially-pumped Pierce electron beam guns, multiple ingot feeds, substrate rotation, substrate
preheat and substrate bias with multiple gas feeds, and has been designed to co-evaporate zirconia, and other ceramic forms, from multiple ingots onto rotating aircraft engine high pressure turbine blades, to provide the next generation of thermal barrier coatings (TBC).
The system is designed to operate with a single Pierce gun with the facility to add on a second gun. Two individually controlled ceramic rod feeds (with provision to add a third) are mounted in the base of the vacuum chamber and pass through a water-cooled copper hearth. To enable the optimum coating uniformity, the turbine blade targets are both rotated and translated through the precipitating ceramic vapours within the temperature-controlled hot zone of the shielded furnace. A novel
Directed Vapour Deposition (DVD) system ensures high material utilisation efficiency by directing the vapour to the target turbines and minimising extraneous coating of the chamber surfaces.
To develop the optimum coating properties, the deposition environment can vary from vacuum to a partial pressure of multiple gases each controlled by mass flow controllers. The PSI system facilitates the production of a plasma on the target which, it is reported, increases density, hardness and other properties of the coatings.
The combined ability multiple ingot evaporation coupled with substrate bias permits functionally gradient TBCs to be produced with lower thermal conductivities and self diagnostic capability.