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<p>This study systematically investigates the evolution of δ-phase (Ni<sub>3</sub>Nb) and Laves phase and their impact on mechanical properties in cast IN625 alloy during isothermal aging at 800 °C for 4h to 12h, targeting advanced ultra-supercritical (A-USC) power plant applications. Results reveal that δ-phase morphology follows Ostwald ripening: transitioning from short acicular (4h) → spheroidized (6h) → elongated acicular (8h) → coarse lath-like (12h). Both δ-phase and Laves phase reach peak area fractions at 8h (δ-phase &gt;1.0%), subsequently decreasing due to coarsening/dissolution. Mechanical properties exhibit aging-time dependence: optimal strength-ductility synergy (tensile strength: 572 MPa, elongation: 75 %) is achieved at 8h, attributed to potent strengthening by high-density elongated acicular δ-phase. Spheroidized δ-phase at 6h reduces strengthening but maximizes ductility (78 % elongation). Over-aging at 12h causes severe strength loss and ductility degradation due to coarse lath-like δ-phase embrittling the matrix. Fracture mode shifts from ductile dimple (4h) to brittle cleavage/quasi-cleavage (12h), driven by stress concentration and grain boundary weakening from coarsened hard phases. This work establishes 800 °C/8h as the optimal aging parameter to maximize δ-phase strengthening while avoiding over-aging embrittlement, providing a critical basis for designing high-performance cast IN625 components in A-USC systems.</p>

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Evolution of δ-Phase Morphology and Its Impact on Mechanical Properties in Aged IN625 Superalloy

  • 期刊论文

  • 发表日期：

    2026年5月23日

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  • Pengwei Jiao,
  • Yongxin Li,
  • Xueyang Na,
  • Xiaobiao Mu,
  • Zhourong Feng,
  • Xiaoli Zhang,
  • Guiqun Liu

摘要

This study systematically investigates the evolution of δ-phase (Ni3Nb) and Laves phase and their impact on mechanical properties in cast IN625 alloy during isothermal aging at 800 °C for 4h to 12h, targeting advanced ultra-supercritical (A-USC) power plant applications. Results reveal that δ-phase morphology follows Ostwald ripening: transitioning from short acicular (4h) → spheroidized (6h) → elongated acicular (8h) → coarse lath-like (12h). Both δ-phase and Laves phase reach peak area fractions at 8h (δ-phase >1.0%), subsequently decreasing due to coarsening/dissolution. Mechanical properties exhibit aging-time dependence: optimal strength-ductility synergy (tensile strength: 572 MPa, elongation: 75 %) is achieved at 8h, attributed to potent strengthening by high-density elongated acicular δ-phase. Spheroidized δ-phase at 6h reduces strengthening but maximizes ductility (78 % elongation). Over-aging at 12h causes severe strength loss and ductility degradation due to coarse lath-like δ-phase embrittling the matrix. Fracture mode shifts from ductile dimple (4h) to brittle cleavage/quasi-cleavage (12h), driven by stress concentration and grain boundary weakening from coarsened hard phases. This work establishes 800 °C/8h as the optimal aging parameter to maximize δ-phase strengthening while avoiding over-aging embrittlement, providing a critical basis for designing high-performance cast IN625 components in A-USC systems.