Electron-beam and plasma oxidation-resistant and thermal-barrier coatings deposited on turbine blades using cast and powder Ni (Co)CrAlY(Si) alloys I. Fundamentals of production technology, structure, and phase composition of cast nicraly alloys

Abstract

The process of producing alloys with elements that are uniformly distributed throughout an ingot is described. The structural features of NiCrAlY alloys produced by electron-beam melting, excluding the use of primary vacuum induction melting of the charge, were studied. The MZP6 and MZP7 alloys, differing in aluminum content, were examined. The cast material produced from the MZP7 alloy was characterized by the formation of a g phase, a typical solid solution of chromium and aluminum in nickel. The β-phase of NiAl was found to be the main phase in the MZP6 alloy; chain and globular precipitates characteristic of the g' phase and a small number of chromium-based, α-Cr, compounds of variable composition were identified as well. The g' phase was detected in the NiCrAlY alloys at more than 5 wt.% Al. Typical microstructures of cast ingots produced from the MZP7 and MZP6 alloys showed that the structural elements refined when the aluminum content increased from 4–6 wt.% (MZP7) to 11–14 wt.% (MZP6), the amounts of nickel, chromium, and yttrium being equal. The MZP7 alloy was characterized by a smooth transition from a fine-grained structure in the areas adjacent to the cooled mold surfaces to a coarse-grained one, formed in the central ingot regions. This phenomenon is less pronounced for the MZP6 alloy ingots. The unit cell parameters for the NiCrAlY alloys were determined with the Rietveld refinement of the X-ray diffraction patterns. Maps showing the distribution of elements in the NiCrAlY alloy are provided.