Development of a process window for a NiCoCrAlY plasma-sprayed coating

Some recent research has shown the importance of the substrate temperature during spraying on the properties of thermal barrier coatings. In the future, applications like small combustor cans for stationary gas turbines will be sprayed at high temperatures. For that purpose, the Metco Sulzer SM-F-100 Connex Gun which can be used at higher temperatures, has been tried at Volvo Aero. In a first step, which is described in this paper, a NiCoCrAlY bondcoat was studied. A LI Taguchi matrix was sprayed to improve the microstructure of the coatings. Varying parameters were current intensity, argon and hydrogen flow rates. The DPV2000 diagnostic system was used to measure the velocity, temperature and diameter of the in-flight particles in order to search for a process-window The microstructures of the coatings, i.e. the number of unmelted particles, the percentage of pores, delaminations and oxides were evaluated and linked both to the spray parameters and to the in-flight properties of the particles. It is shown that the temperatures of particles are directly related to the amount of unmelted particles, oxides and delaminations in the microstructure. Tensile strength measurements also show a clear correlation to the amount of delaminations in the coating and therefore to the in-flight particle temperature. (C) 1998 Elsevier Science S.A. All rights reserved.