ELECTRON-BEAM AND PLASMA OXIDATION-RESISTANT AND THERMAL-BARRIER COATINGS DEPOSITED ON TURBINE BLADES USING CAST AND POWDER Ni(Co)CrAlY(Sі) ALLOYS PRODUCED BY ELECTRON BEAM MELTING
ІІ. STRUCTURE AND CHEMICAL AND PHASE COMPOSITION OF CAST CoCrAlY ALLOYS

Abstract

The structure and chemical and phase composition of heat-resistant CoCrAlY alloys produced by electron-beam melting used in aircraft construction, in particular, in the development of thermal barrier coatings on 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 height of the alloy ingots using scanning electron microscopy with quantitative micro-X-ray phase analysis. The analysis showed qualitatively similar distribution of components in the main alloy phases in the lower and middle parts of the ingot. Cobalt, chromium, and aluminum were evenly 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 b-phase based on the CoAl solution, in which dispersed chain and globular inclusions of the g-phase based on the CoCr solid solution depleted in aluminum were dispersed. The highest concentration of yttrium (12–13 wt.%)) was observed in small globular inclusions with the minimum content of aluminum and chromium. Increase in the chromium content to 20–26 wt.% at a relatively constant content of aluminum (5 wt.%) led to decrease in yttrium in the cobalt-based g-solid solution. Increase in the yttrium content of the ingot above 0.4 wt.% was not reasonable because yttrium content of the coating did not exceed 0.1-0.15 wt.%.