Influence Of Element Re On Creep Properties At Medium Temperature Of Nickel-Base Single Crystal Superalloys

By means of SEM/EDS composition analysis and heat treatment of the single crystal nickel-base superalloys with Re and 4.5%Re, the influence of the element Re and solution temperature on the composition segregation in the interdendrite/dendrite regions of alloys is researched. And the effects of the element Re on the microstructure and creep properties of the single crystal nickel-base superalloys are investigated by means of the measuring creep properties and microstructure observation. And the effect of element Re on deformation mechanisms of the alloy during creep were discussed by means of TEM observation and dislocation configuration analysis.Results show that the element Re may increases the segregation extent of the elements in the interdendrite/dendrite regions, and enhancing the partitioning ratio of the elements Al, Ta in theγ′/γphases, decreasing the partitioning ratio of the elements W, Mo in theγ′/γphases. Compared to the Re-free single crystal superalloy, 4.5%Re superalloy has a better creep resistance. The segregation extent of the elements in the interdendrite/dendrite regions may be decreased, as the solution temperature enhances, to improve the creep properties of alloy. In the ranges of the applied stresses and temperatures, the creep activation energy and stress exponent of Re-free single crystal nickel base superalloy are measured to be Q₁ = 483.6 kJ/mol and n₁ = 10, and the creep activation energy and stress exponent of 4.5% Re superalloy are measured to be Q₂ = 522.6 kJ/mol and n₂ = 15, respectively.During creep at medium temperature/high stress, noγ′phase rafting transformation is detected in two superalloys, thereinto, the cubicalγ′phase in Re-free superalloy has been transformed into the sphere-like structure, but the one in 4.5%Re superalloy still keep the cubical configuration. the deformation mechanism of the alloy during steady state creep is that significant amount of (1/2)<110> dislocation are activated in theγmatrix channel, and the <110> super dislocations shear into the cubicalγ′phase. After the single crystal nickel base superalloys with Re and Re-free are crept up to fracture, the various morphology ofγ′phase is displayed in the different regions of the creep samples, the configuration of theγ′phase remains still the cubic, and arranged regularly in the region far from the fracture, but the twistedγ′phase appears in the region near the fracture, which is attributed to the servere plastic deformation occurred in the region. Thereinto, the <110> super dislocation shearing intoγ′phase may be decomposed to form the configuration of (1/3)<112> partials + stacking faults, which may hinder the cross-slipping of the dislocations to improve the creep resistance of the alloy. The <110> super-dislocations shearing into theγ′phase are firstly activated in the {111} planes, as the creep goes on, the super-dislocation may be cross-slipped to (100) crystal plane from (111) plane to form the K-W dislocation locking with the configuration of the non-plane dislocation core structure, for hindering effective the dislocations slipping on (111) crystal plane, which is the main reason of the alloy having the better creep resistance.