Comparing High-Temperature Mechanical Behavior of Novel CoNi-Based Superalloys and Conventional Ni-Based Superalloys Exhibiting Local Phase Transformation

Abstract Superalloys are renowned for their exceptional high-temperature strength and are essential in gas turbine engines. Much research has focused on solute partitioning to defects, leading to local phase transformations (LPT) that impact mechanical properties. This study investigates five single-crystalline CoNi-based alloys derived from polycrystalline CoWAlloy1, with variations in Nb, Re, Ta, Ti, and W. Their performance is compared with established Ni-based alloys (NA1, NA6, ME3, RRHT5) using constant strain rate (CSR) compression and compression creep tests. Deformation mechanisms were investigated utilizing transmission electron microscopy (TEM) and atomic resolution X-ray energy dispersive spectroscopy (EDS). Thermodynamic calculations were also employed to rationalize alloy behavior in the context of LPT. Results showed CSR testing at 850 °C ( $$\dot{\varepsilon }=1{0}^{-4}\,{\text{s}}^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mover> <mml:mi>ε</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> <mml:mo>=</mml:mo> <mml:mn>1</mml:mn> <mml:msup> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> </mml:msup> <mml:mspace/> <mml:msup> <mml:mrow> <mml:mtext>s</mml:mtext> </mml:mrow> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> ) parallels creep testing in predicting alloy performance within deformation regimes dominated by γ ′ shearing via planar defects. Nb and Ta were highlighted as critical in enhancing LPT by increasing η and χ ordering, unlike Ti, which showed significantly less influence. Although theoretical models suggested Re and W would enhance LPT, they exhibited poor behavior in creep tests due to low diffusivity. These findings validated using η -ordering tendency to estimate high-temperature performance and establish the groundwork for computationally driven LPT design in CoNi-based superalloys for disk applications.