Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Single crystal nickel-based superalloys mainly consisting of g and g ' phases are widely used in turbine blades for their excellent mechanical performances, in particular creep resistance at high temperatures. The creep properties of single crystal superalloys are inherently anisotropic. Although commercial single crystal superalloys are all along <001> orientation, it is difficult to ensure the exact orientation during production, and in service the applied centrifugal force on blades unavoidably deviates from <001> orientation, so the study on non-<001> oriented single crystal superalloys is significant on improving the creep theory of superalloys. Compared with the <001> oriented single crystal superalloys, the <011> oriented ones generally display poor creep resistance. Through pre-rafting treatment of g ' phase in <001> oriented single crystal superalloys, the creep resistance of the alloys are expected to be enhanced by changing the deformation mechanism, especially by hindering dislocation movements, but the effect of the treatment on <011> oriented alloys is still not clear. For this reason, by means of pre-compression, creep tests and microstructure observation, the effect of the pre-rafting of g ' phase on creep behavior of a [011] oriented single crystal nickel-based superalloy at 1040 ℃, 137 MPa is studied. Results show that after pre-compression at 1040 ℃, 180 MPa along [100] orientation for 38 h, the g ' phase in the [011] oriented alloy has transformed into P-type rafted structure parallel to the compressive stress axis. Different strain energy density distribution and lattice strain on crystal planes during pre-compression are the main reasons for the rafting behavior of g ' phase. Dislocations slipping in g matrix channels is the main deformation mechanism of the [011] oriented alloy with and without pre-compression. Thereinto, many dislocations-climbing movements occur in the pre-compressed one. The lateral pre-compression remarkably improves the creep strength of the alloy at 1040 ℃, 137 MPa. The elimination of gable channels, relatively narrow roof channels during steady-state creep stage, the formation of micro-bottleneck-like channels and labyrinth-like microstructures due to the lateral growth of g ' rafts, and the more effectively activated slip systems of dislocations are beneficial to impeding dislocation movements and responsible for the better creep resistance of the pre-compressed alloy.
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