Abstract
In a Co–Al–W base superalloy, two types of topologically close-packed (TCP) phases, μ and Laves phases, were investigated by high-resolution transmission electron microscopy, scanning transmission electron microscopy and energy dispersive X-ray spectroscopy. It is found that an intergrowth structure of Laves within μ phases can be formed and both have a completely coherent interface relationship. With the aid of image simulation, both μ and Laves phases are identified as the quaternary compounds containing Co, Cr, W and Mo. Compared to Co7W6-type μ phase, W1 and W3-sites are the preferred sites of substitution by Mo atoms and Co1-site is a preferred site of substitution by Cr atoms in the quaternary μ phase, leading to the atomic displacement and an alteration of lattice parameter. In contrast to Co2W-type Laves phase, the newly formed quaternary Laves phase can maintain the C14-type Laves structure although Co and W are substituted partially by Cr and Mo respectively.
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