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 II. Structure and Chemical and Phase Composition of Cast CoCrAlY Alloys

The structure and chemical and phase composition of oxidation-resistant CoCrAlY alloys produced by electron-beam melting and used in aircraft engineering, in particular, in the development of thermal-barrier coatings for aircraft engine blades, were studied. As the CoCrAlY alloy consists of components with significantly different vapor elasticity and density, the main attention was paid to changes in the chemical and phase composition along the alloy ingots studied by scanning electron microscopy with quantitative X-ray microanalysis. The analysis showed qualitatively similar distribution of components in the main alloy phases in the lower and middle ingot parts. Cobalt, chromium, and aluminum were uniformly distributed throughout the material. Harmful impurities, such as iron, carbon, or oxygen, were not found in the alloy. The alloy mainly consisted of the intermetallic β-CoAl solid solution phase that contained dispersed chain and globular inclusions of the γ-CoCr solid solution phase depleted in aluminum. The highest content of yttrium (12–13 wt.%)) was observed in small globular inclusions with the minimum amount of aluminum and chromium. Increase in the chromium content to 20–26 wt.% at a relatively constant amount of aluminum (5 wt.%) led to decrease in yttrium in the γ-Co-based solid solution. Increase in the yttrium content of the ingot above 0.4 wt.% would be unreasonable because yttrium amount in the coating did not exceed 0.1-0.15 wt.%.