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<p>This study investigates the effects of temperature and stress ratio on the short fatigue crack (SFC) growth behavior of a laser coaxial powder-fed (LCPF) Ni-based superalloy K477. Microstructural analysis revealed a heterogeneous multiphase structure comprising TiC carbides and γ/γ′ (Ni<sub>2</sub>Al) phases, which induces local stress concentration and governs crack initiation behavior. Quasi-static tensile tests conducted over 298-1023 K demonstrated excellent strength retention, with the yield strength decreasing from 858 MPa to 732 MPa and elongation increasing from 15.1 to 19.6%, indicating enhanced ductility at elevated temperatures. In situ SEM fatigue experiments at 573 K, 923 K, and 1023 K were employed to monitor real-time SFC initiation and propagation. The results show that both elevated temperature and higher stress ratio accelerate crack growth. At intermediate temperatures, crack propagation is dominated by transgranular slip along crystallographic planes with high Schmid factors (≈0.45-0.47), while at higher temperatures, fracture modes transition from stable transgranular to brittle intergranular cracking, attributed to the combined effects of grain boundary sliding and oxidation-assisted damage. These observations provide detailed mechanistic insight into the temperature and stress ratio-dependent SFC behavior of additively manufactured K477, which is critical for assessing its high-temperature fatigue performance.</p>

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Effects of Temperature and Microstructure on Short Crack Growth of Laser Coaxial Powder-Fed Ni-based Superalloy

  • 期刊论文

  • 发表日期：

    2026年4月9日

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  • Yatong Wang,
  • Shiqiang Yu,
  • Lutsenko Vladyslav,
  • Wenfei Hu

摘要

This study investigates the effects of temperature and stress ratio on the short fatigue crack (SFC) growth behavior of a laser coaxial powder-fed (LCPF) Ni-based superalloy K477. Microstructural analysis revealed a heterogeneous multiphase structure comprising TiC carbides and γ/γ′ (Ni2Al) phases, which induces local stress concentration and governs crack initiation behavior. Quasi-static tensile tests conducted over 298-1023 K demonstrated excellent strength retention, with the yield strength decreasing from 858 MPa to 732 MPa and elongation increasing from 15.1 to 19.6%, indicating enhanced ductility at elevated temperatures. In situ SEM fatigue experiments at 573 K, 923 K, and 1023 K were employed to monitor real-time SFC initiation and propagation. The results show that both elevated temperature and higher stress ratio accelerate crack growth. At intermediate temperatures, crack propagation is dominated by transgranular slip along crystallographic planes with high Schmid factors (≈0.45-0.47), while at higher temperatures, fracture modes transition from stable transgranular to brittle intergranular cracking, attributed to the combined effects of grain boundary sliding and oxidation-assisted damage. These observations provide detailed mechanistic insight into the temperature and stress ratio-dependent SFC behavior of additively manufactured K477, which is critical for assessing its high-temperature fatigue performance.