Abstract
The formation of liquation cracking in a simulated heat affected zone of René108 is reported. The stress controlled thermo-mechanical experiments were carried out on a Gleeble®3800 testing system. The base alloy was lost-wax cast and then solution treated and aged. Light and scanning electron microscopy of this material revealed high volume fraction of γ' precipitates in the dendrite arms and residual eutectic γ/γ' islands in the interdendritic areas. As a result of short-term exposure to high homologous temperature, the volume fraction of γ' phase was significantly decreased due to the dissolution of precipitates in the surrounding matrix. The thin non-equilibrium liquid film, formed locally along grain boundaries, was a key-factor favoring initiation of cracks and their spreading during the Gleeble testing. The liquid appeared as a result of constitutional liquation, mainly of the γ' precipitates.
Highlights
The combination of high mechanical properties and resistance to hot corrosion make cast Ni-based superalloys one of the most important materials in the construction of jet engine components
The necessary condition for the occurrence of constitutional liquation in Ni-based superalloys is the presence of intermetallic phases, carbides, or topologically closed packed phases at a temperatures equal to or exceeding the eutectic temperature during heating above the solvus line [8]
Despite the similar content of γ'formers in the various nickel superalloys, the contribution of eutectic islands in the microstructure can vary within a wide range, which can be exemplified by René 108 and for example IN713C [2]
Summary
The combination of high mechanical properties and resistance to hot corrosion make cast Ni-based superalloys one of the most important materials in the construction of jet engine components. Their mechanical properties of alloys are mainly dependent on the morphology, size, distribution and volume fraction of γ’ precipitates. The intermetallic Ni3Al phase has good crystallographic matching with the γ matrix; lattice misfit is generally below one percent [1]. This is connected with a low coarsening rate of precipitates during service. The necessary condition for the occurrence of constitutional liquation in Ni-based superalloys is the presence of intermetallic phases, carbides, or topologically closed packed phases at a temperatures equal to or exceeding the eutectic temperature during heating above the solvus line [8]
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