Metallographic characterization and indentation of two commercial cobalt-based superalloys synthesized with a fine microstructure

Author(s): Adrien Frigério, Pierre-Yves Girardin, Patrice Berthod

Two commercial chromium-rich cobalt-based cast superalloys belonging to the ones often considered for the hottest pieces of aero-engines were reproduced in laboratory scale by melting of pure elements under inert atmosphere and solidification of ingots of several tens grams. The as-cast microstructures were examined and specified using electron microscopy and energy dispersion spectrometry while the room temperature hardness wasmeasured byVickers indentation. The microstructures of the two alloys are especially fine and rich in carbides of several types: chromiumcarbides and MC-carbides, thanks to rather high carbon contents. Chromium, and eventually tungsten,was found in some of the coarse carbideswhile tantalum and tungsten obviously belonged to the elongated MC carbides. Titanium and zirconium, the two other MC-former elements were essentially found, in addition to Ta and W, in the blocky MC carbides existing besides the elongated ones. The Vickers macro-hardness at ambient temperature of the two alloys are all slightly higher than 400 HV.

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