Comparative Study on Intermediate-Temperature Deformation Mechanisms of Inconel 718 Alloys Fabricated by Additive...

Area of Science:

• Materials Science
• Metallurgy
• Additive Manufacturing

Background:

• Additively manufactured (AM) Inconel 718 (IN718) displays distinct solidification behavior compared to conventionally forged IN718.
• This leads to unique microstructural and precipitation responses, affecting heat treatment and intermediate-temperature deformation.
• Understanding these differences is crucial for optimizing AM IN718 performance.

Purpose of the Study:

• To systematically compare the intermediate-temperature (450-750 °C) deformation mechanisms of laser powder bed fusion (LPBF)-fabricated and forged IN718 alloys.
• To investigate the influence of various heat-treatment conditions on these mechanisms.
• To elucidate the role of the delta (δ) phase and niobium (Nb) segregation in LPBF IN718.

Main Methods:

• Comparative analysis of LPBF-fabricated and forged IN718 alloys.
• Application of different heat treatments: solution treatment and solution + aging (STA).
• Microstructural characterization and mechanical property evaluation under intermediate-temperature deformation.

Main Results:

• Solution-treated LPBF IN718 showed fine columnar grains, high dislocation density, and retained δ phase at grain boundaries.
• Forged IN718 exhibited coarse equiaxed grains without δ phase after solution treatment.
• STA treatment: δ phase in LPBF IN718 pinned grain boundaries, enhancing flow stress; forged IN718 strengthening dominated by γ″/γ' precipitation.
• LPBF IN718 had fewer γ″/γ' precipitates and slightly lower strength post-STA due to Nb consumption by δ phase.

Conclusions:

• The inherent δ phase retention and Nb segregation in LPBF-built IN718 critically influence its precipitation behavior and deformation resistance.
• These factors distinguish LPBF IN718 from conventionally processed alloys.
• Provides valuable insights for microstructure design in AM-built high-temperature superalloys.