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<p>The combination of strength, corrosion resistance, and weldability make Alloy 718 attractive for additive manufacturing (AM); however, the AM build process generates considerable residual stresses, and large compositional and microstructural heterogeneities that promote variability in the performance. The solution anneal protocol prescribed in the American Petroleum Institute (API)-6ACRA standard is customarily applied to relieve those stresses and homogenize the composition. However, it was designed for wrought material and does not sufficiently alleviate the compositional heterogeneities in the solidification microstructure. As such, AM-processed material fails to meet the specifications prescribed in that standard. An ICME framework combining CALPHAD-based modeling tools and experimental validation was adopted to design a heat treatment specifically for AM-processed Alloy 718 that consistently achieves the API-6ACRA specifications. This evaluation revealed that the remnant microsegregation promoted coarsening of <i>γ</i>′′ precipitates that formed during solidification and networks of second-phase precipitates. The results also demonstrated that 1&#xa0;hour at a temperature between (1125 and 1150)&#xa0;°C completely homogenized the composition and produced a consistent <i>γ</i>′′ morphology after aging. Application of this alternative heat treatment protocol produced material that exhibited mechanical properties that were virtually identical to those of wrought material heat-treated to achieve an 825&#xa0;MPa yield stress.</p>

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Design and Optimization of a Heat Treatment Protocol for Alloy 718 Produced by Laser Powder Bed Fusion for Oil and Gas Applications

  • 期刊论文

  • 发表日期：

    2025年7月25日

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  • M. R. Stoudt,
  • J. S. Zuback,
  • A. D. Iams,
  • C. E. Campbell,
  • S. A. Habib,
  • M. E. Williams,
  • K. W. Moon,
  • M. Yunovich

摘要

The combination of strength, corrosion resistance, and weldability make Alloy 718 attractive for additive manufacturing (AM); however, the AM build process generates considerable residual stresses, and large compositional and microstructural heterogeneities that promote variability in the performance. The solution anneal protocol prescribed in the American Petroleum Institute (API)-6ACRA standard is customarily applied to relieve those stresses and homogenize the composition. However, it was designed for wrought material and does not sufficiently alleviate the compositional heterogeneities in the solidification microstructure. As such, AM-processed material fails to meet the specifications prescribed in that standard. An ICME framework combining CALPHAD-based modeling tools and experimental validation was adopted to design a heat treatment specifically for AM-processed Alloy 718 that consistently achieves the API-6ACRA specifications. This evaluation revealed that the remnant microsegregation promoted coarsening of γ′′ precipitates that formed during solidification and networks of second-phase precipitates. The results also demonstrated that 1 hour at a temperature between (1125 and 1150) °C completely homogenized the composition and produced a consistent γ′′ morphology after aging. Application of this alternative heat treatment protocol produced material that exhibited mechanical properties that were virtually identical to those of wrought material heat-treated to achieve an 825 MPa yield stress.