Plastic deformation mechanisms of NiCuCrMoTiAlNb Ni-based alloys at cryogenic temperature

Three kinds of Ni-based alloys with a nominal chemical composition of Ni57−xCu20Cr15Mo5Ti2Al1Nbx (wt%), where x stood for 1, 3 and 5, respectively, were fabricated in order to be used for cryogenic environments. The microstructures of three as-cast Ni-based alloys are characterized by dendrite structure, where the matrix belongs to γ-Ni solid solution phase. The emphasis was laid on plastic deformation mechanisms of three as-cast Ni-based alloys under cryogenic environments. Nb element was found to play a significant role in strengthening the Ni-based alloys, where the strength of Ni-based alloys increased with the increase in the content of Nb element. With the increase in the content of Nb element, in particular, nanocrystallization becomes more and more predominant. It would be proposed that geometrically necessary dislocations play a more dominant role in nanocrystallization of Ni-based alloy with high Nb content. At cryogenic temperature, with the increase in the plastic strain and the resultant dislocation density, dislocation slip along with deformation twinning became dominant in the plastic deformation mechanisms. Based on dislocation slip and deformation twinning, the microstructures of Ni-based alloy were able to be refined so consecutively that nanocrystalline grains appeared in the matrix.