Size effect of local single-crystal-layered ultrathin nickel-based superalloy GH4145 strip

Abstract

Austenitic nickel-based superalloys with very few grain layers or even a single-crystal layer in the thickness direction of the ultrathin strips can be achieved by controlling the cold rolling and subsequent annealing process, which leads to mechanical properties and deformation mechanisms that differ from those of macroscopic polycrystalline layered materials as a result of the size effect. In this study, nickel-based superalloy GH4145 with the thickness of 0.2 mm was used as the raw material. By controlling the cold rolling and annealing process, local single-crystal and multi-layer-crystal ultrathin strips with the thicknesses of 70 μm and 100 μm were successfully prepared. The effects of annealing on the microstructural evolution of the ultrathin strips with different grain layers on the deformation mechanism and room-temperature mechanical properties were studied. At annealing temperatures above 1000 °C, the γ′-Ni3 (Al, Ti) phase dissolved, and the main precipitates in the microstructure changed from γ′ and carbide at low-temperature annealing to only carbide. The weakened pinning effect on the grain-boundary effect and abnormal coarse grains owing to secondary recrystallization generated a local single-grain layer in the thickness direction of the strips. Furthermore, because the grain boundary decreases and the proportion of free surface increases, the abnormal decrease in elongation with increasing annealing temperature is called the size effect, which critically influences the mechanical properties of the strips. The ultrathin strips, which have a partially deformed microstructure and a large number of fine recrystallized grains, show better comprehensive mechanical performance.