ARC EVAPORATION OF MULTICOMPONENT MCRALY CATHODES

A major aim in today's development of aircraft and land-based gas turb ines is the higher efficiency of the combustion process. The base mate rial of the components is optimized for its mechanical properties, suc h as its creep strength or low and high cycle fatigue behaviour. There fore, the corrosion and oxidation resistances have to be improved by a n overlay coating. In fact, most Ni-based turbine blades are protected by an MCrAIY overlay. The conventional deposition method for this coa ting is low pressure plasma spraying (LPPS). As a result of new demand on the quality of hot gas corrosion-resistant MCrAIY coatings, proces ses that are alternatives to LPPS are under investigation. Evaporation with a cathodic are is one possibility with technical and economical potential. Are PVD systems are in use for several applications. Most a ctual target materials are only made of one or two elements. Therefore , the study of the behaviour of the are, running on multicomponent tar get materials, such as the MCrAIY compositions with 5-7 elements used, is very important. The paper reports on the basic deposition phenomen as of the cathodic are and presents the coating compositions and struc tures in the ''as-deposited'' and homogenized states. It is shown that the chemical coating composition is different from that of the cathod e material, but the difference is relatively small, so that the compos ition desired in the coating can be reached by proper adjustment of th e cathode material. The morphology of the MCrAIY coating shows the two - or three-phase structure which is typical for this type of hot gas c orrosion-resistant overlay. A sufficient bond strength of the coating was measured, so that the industrial application of this coating is po ssible. The process itself offers new possibilities, such as the depos ition of multilayer structures and the combination of the MCrAIY with a high temperature diffusion barrier, so that new improvements of the coating system can be achieved in one step. Summarizing the evaluation of the results shows that the are technology is competitive with the conventional deposition techniques and offers some new possibilities f or improved complex coating systems.