Phase Equilibrium Evolution in Single-Crystal Ni-Based Superalloys

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 experimental 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 amplitudes of % . %, % . %, % . %, and % % for 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 direction were separated by γ + γ′ -eutectic pools. The length of newly formed dendrites depends on cumulative strainstress 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 singlecrystal superalloy during testing.

Effect of Ru on Deformation Mechanism and Microstructure Evolution of Single-Crystal Superalloys under Medium-Temperature and High-Stress Creep

“…The second and third generations contain 2–6% Re, while the fourth generation contains Ru at different weight percentages. It is widely known that Co, Cr, Ir, Mo, Re, and Ru dissolve into the γ matrix phase of the alloy while Al, Ti, Ta, Nb, Pt, and Hf partition into the γ′ phase, which serves as the precipitated phase in the γ-phase matrix [ 6 , 7 ].…”