Electron-Beam and Plasma Oxidation-Resistant and Thermal-Barrier Coatings Deposited on Turbine Blades Using Cast and Powder Ni(Co)CrAlY(Si) Alloys Produced by Electron Beam Melting IV. Chemical and Phase Composition and Structure of Cocralysi Powder Alloys and Their Use

A new technique for producing powders from the electron-beam CoCrAlYSi alloy (MZP-11 grade) is proposed. The method includes step-by-step grinding of the alloy employing a press and a two-roll vertical mill. The energy consumed to produce these powders is almost one-seventh the energy consumed in conventional methods (crushers, mills) and within one-twentieth that in spraying methods. The chemical and phase composition and structure of the CoCrAlYSi powders were studied. The proposed grinding method allowed the production of powders that corresponded to the starting alloy in terms of chemical composition and structure. The powder particles had polyhedral shape, being close to round, were quite uniform in size, and almost completely preserved the microstructure of the starting CoCrAlYSi alloy. Grinding the alloy led to a slight increase in the content of some impurities in the 40–100 μm powders; in particular, the amount of oxygen increased from 0.05 to 0.08–0.09 wt.% and that of carbon from 0.06 to 0.08–0.1 wt.%. According to the chemical composition and technical characteristics, the powders comply with technical specifications for plasma deposition of two-layer thermal-barrier metal/ceramic coatings. The outer ceramic topcoat is formed with the participation of yttria-stabilized zirconia of at least 99.5 wt.% purity. The coating thickness is controlled by technical documents and is 135–225 μm for the metal layer and 80–120 μm for the ceramic layer. The developed metal powders are used to deposit thermal-barrier coatings on various types of gas turbine blades. The structure and composition of a two-layer thermal-barrier coating produced by plasma spraying of the CoCrAlYSi alloy and ZrO₂– Y₂O₃ ceramic powders were studied.