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<p>This study examines the morphological evolution of γ′ precipitates in cast CMSX-4 single-crystal Ni-based superalloy subjected to prestraining at either 982&#xa0;°C or room temperature, followed by long-term high-temperature exposure (up to 1185 h at 982&#xa0;°C and 1088 h at 1150&#xa0;°C). Four initial conditions were evaluated: (1) unstrained specimens; (2) specimens prestrained to 2.6% by interrupted creep at 982&#xa0;°C and 250 MPa; and (3–4) specimens prestrained to 0.5% and 1.0% by interrupted tensile testing. In dendrite cores, unstrained and 0.5% prestrained samples exhibited subtle rafting after exposure at 982&#xa0;°C for up to 1185 h. By contrast, 2.6% and 1.0% prestrained specimens developed spontaneous rafting after just 150&#xa0;h. At 1150&#xa0;°C, all conditions showed partial γ′ dissolution. In the 1.0% prestrained sample, subtle rafting appeared after 203&#xa0;h but degraded with further exposure due to γ′ coarsening, while the 0.5% condition displayed only γ′ dissolution and coarsening. These results demonstrate that, in cast CMSX-4, both the degree and mode of prestraining, together with exposure temperature and duration, promote instability in the aged γ–γ′ microstructure and strongly influence the early onset of spontaneous rafting. Although mechanical performance was not assessed in this study, spontaneous rafting is known to contribute to the degradation of mechanical properties under high-temperature service. Overall, the findings show that rafting at 982&#xa0;°C is primarily driven by elastic energy minimisation, whereas at 1150&#xa0;°C interfacial energy becomes dominant, leading to more extensive isotropic γ′ coarsening.</p>

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Effect of Prestraining and Prolonged High-Temperature Exposure on γ′ Precipitate Morphology in Cast CMSX-4 Superalloy

  • 期刊论文

  • 发表日期：

    2025年10月14日

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  • G. P. Souza,
  • L. B. Fantin,
  • M. F. Moreira,
  • C. R. F. Azevedo

摘要

This study examines the morphological evolution of γ′ precipitates in cast CMSX-4 single-crystal Ni-based superalloy subjected to prestraining at either 982 °C or room temperature, followed by long-term high-temperature exposure (up to 1185 h at 982 °C and 1088 h at 1150 °C). Four initial conditions were evaluated: (1) unstrained specimens; (2) specimens prestrained to 2.6% by interrupted creep at 982 °C and 250 MPa; and (3–4) specimens prestrained to 0.5% and 1.0% by interrupted tensile testing. In dendrite cores, unstrained and 0.5% prestrained samples exhibited subtle rafting after exposure at 982 °C for up to 1185 h. By contrast, 2.6% and 1.0% prestrained specimens developed spontaneous rafting after just 150 h. At 1150 °C, all conditions showed partial γ′ dissolution. In the 1.0% prestrained sample, subtle rafting appeared after 203 h but degraded with further exposure due to γ′ coarsening, while the 0.5% condition displayed only γ′ dissolution and coarsening. These results demonstrate that, in cast CMSX-4, both the degree and mode of prestraining, together with exposure temperature and duration, promote instability in the aged γ–γ′ microstructure and strongly influence the early onset of spontaneous rafting. Although mechanical performance was not assessed in this study, spontaneous rafting is known to contribute to the degradation of mechanical properties under high-temperature service. Overall, the findings show that rafting at 982 °C is primarily driven by elastic energy minimisation, whereas at 1150 °C interfacial energy becomes dominant, leading to more extensive isotropic γ′ coarsening.