Effect of the Interfacial Strain Anisotropy on the Raft Structure of Ni-Base Single Crystal Superalloys and Novel Alloy Design Approach by Controlling the Lattice Misfit and the Elastic Misfit

Enhancing the aspect ratio of the γ′ precipitatesPrecipitates in the raft structureRaft structure of Ni-base single crystal superalloysNi-based single crystal superalloy for high-pressure turbine bladesTurbine blades is a fundamental approach to improve the creep resistanceCreep resistance at higher temperature and lower stress conditions. To obtain a larger aspect ratio, the alloy designAlloy design strategy to enlarge the lattice misfitLattice misfit between γ and γ′ phases towards the negatively larger side has been applied. However, the fundamental driving force for the raft structureRaft structure formation, “interfacial strain anisotropyAnisotropy”, has been ignored for the alloy designAlloy design. Here, interfacial strain anisotropyAnisotropy is a difference of the interfacial strain between horizontal and vertical γ/γ′ interface, and this is caused by the interaction of loading stress with the elastic misfitElastic misfit between γ and γ′ phases. In this study, model alloysModel alloy imply that the aspect ratio is modulated by kinetic factor caused by Re with a presence of interfacial strain anisotropyAnisotropy. The lattice misfitLattice misfit and the elastic misfitElastic misfit can be used as new alloy designAlloy design parameters. Regression analysis using database of creepCreep ruptured lives indicates that negatively larger lattice misfitLattice misfit and the positively larger elastic misfitElastic misfit can enhance the creepCreep rupture lives although the relationship between the lattice misfitLattice misfit and the elastic misfitElastic misfit was basically trade-off. However, additional regression analysis of the lattice and the elastic misfitElastic misfit indicates that the addition of Re, moreover, co-addition of Mo and W, Ti, or Ta could intentionally realize both negatively larger lattice misfitLattice misfit and positively larger elastic misfitElastic misfit.