Phase Equilibrium Evolution in Single-Crystal Ni-Based Superalloys

Abstract

Abstract The phase equilibrium evolution resulting from the interdiffusion of atoms in single crystals of nickel-based superalloys was studied with the aid of microstructural, chemical composition, and micromechanical property investigations. The experimen‐ tal observation methods—optical microscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy, microchemical analyses, X-ray diffraction, hard cyclic viscoplastic deformation, and nanoindentation —were combined to obtain new insights into the phases’ chemical composition and micromechanical properties’ characterization that depend on strain-stress levels which are induced by tension-compression cycling in viscoplastic conditions at room temperature. The test samples with differences in the strain-stress parameters were received on the tension-compression stepped sample with four different cross-section areas. The strains with four levels of intensivity were added by using strain ampli‐ tudes of 0%–0.05%, 0%–0.2%, 0%–0.5%, and 0%–1% for 30 cycles, respectively. Microstructural investigations show that dendrite length decreased significantly in samples with minimal cross-section and accordingly at maximal strain-stress amplitudes. The main dendrites of the (001) direction were separated by (γ + γ′)- eutectic pools. The length of newly formed dendrites depends on cumulative strain- stress amplitudes. The chemical composition and micromechanical properties of phases were changed as a result of the atoms’ interdiffusion between different phases. These changes were influenced on the phases’ equilibrium evolution of the single- crystal superalloy during testing. Keywords: