Saurabh Mangal, M Noushad Bin Jamal, V B Brahmadathan, Ashish Pandey, C Lakshmana Rao, P. Chellapandi
Nickel-based superalloys, essential for gas turbine aero-engines, are vulnerable to creep under high temperatures and sustained mechanical loading. Their creep behavior is governed by the degradation of the γ/γ′ microstructure through diffusion and dislocation-driven mechanisms. This work develops a micromechanics-based constitutive model for creep in polycrystalline nickel-based superalloys within the Unified Mechanics Theory (UMT) framework. Material degradation is represented by the thermodynamic state index (TSI), derived from entropy generation, thereby avoiding reliance on empirical damage laws. The model incorporates dislocation generation, annihilation, and trapping kinetics, with a newly proposed annihilation-rate expression for the alloy. The resulting creep rate formulation is implemented in a three-dimensional ABAQUS user-defined CREEP subroutine. Validation against ASTM E139-11 creep tests on GH4169 alloy at 600 °C and stress levels of 860–900 MPa shows strong agreement with experimental data. The proposed physics-based model successfully captures the linear secondary regime, the transition to tertiary creep, and the nonlinear tertiary regime. Compared with traditional phenomenological models, it provides a physically grounded tool for simulating creep and predicting service life of nickel-based superalloys in high-temperature applications. • First-of-its-kind constitutive creep model for nickel-based superalloys derived from Unified Mechanics Theory (UMT ). • Thermodynamic State Index as a degradation parameter, quantitatively linking microstructure deterioration and entropy generation with macroscopic creep and rupture • Captures major creep regimes : secondary creep plateau, transition, nonlinear tertiary creep, and rupture. • Provides a physics-based , computationally efficient framework for predicting creep and service life of GH4169 and other nickel-based superalloys in gas turbine engines.