Abstract
The effects of hafnium additions on the microstructure of ALLOY 713-LC have been investigated using electron microscopy and by a radiographic technique which reveals the grain boundary structure. It is shown that the Chinese script MC carbides in ALLOY 713-LC are altered to a particulate morphology in alloy MM-004 (hafnium-modified ALLOY 713-LC). Unlike the script carbides, the discrete MC particles do not provide any easy path for rapid crack propagation and hence, ductility is enhanced. In the hafnium-bearing alloy, the morphology of γ’ phase is also modified. Colonies of ((γ + γ′) with a rosette morphology are formed and individual γ’ platelets exhibit dendritic growth. It is shown that this morphology of γ’ causes grain boundaries to be distorted from planar equilibrium interfaces to a convoluted interlocking configuration. It is suggested that the interlocking boundaries retard grain boundary sliding and separation during creep and result in higher stress-rupture life for hafnium-modified alloys.
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Formerly with Research Institute for Advanced Studies, Baltimore, Md.
Formerly with Research Institute for Advanced Studies.
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Kotval, P.S., Venables, J.D. & Calder, R.W. The role of hafnium in modifying the microstructure of cast nickel-base superalloys. Metall Trans 3, 457–462 (1972). https://doi.org/10.1007/BF02642049
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DOI: https://doi.org/10.1007/BF02642049