This study investigates the impact of heat treatment (HT) and hot isostatic pressing (HIP) parameters on the microstructural evolution, texture, and hardness distribution in laser powder bed fusion (L-PBF) Alloy 718. The findings highlight key factors influencing uniform microstructure development and isotropic mechanical property enhancement. The varying grain evolution processes likely stem from distinct recrystallization mechanisms triggered by the different thermo-mechanical histories in each post-process treatment. Higher HIP pressures (200 MPa) enhanced the recrystallization fraction and grain refinement compared to 103 MPa, as shown by increased low-grain orientation spread (GOS) area fractions and grain number density. The reduction in <InlineEquation ID="IEq1"> <EquationSource Format="TEX">$\langle {1}00\rangle$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">⟨</mo> <mn>100</mn> <mo stretchy="false">⟩</mo> </mrow> </math></EquationSource> </InlineEquation>//BD texture for both HIP and HT samples was linked to recrystallization and orientation broadening via recovery, even without direct recrystallization evidence. The twin-assisted recrystallization texture, driven by FCC annealing twins, amplified <InlineEquation ID="IEq2"> <EquationSource Format="TEX">$\langle 212\rangle$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">⟨</mo> <mn>212</mn> <mo stretchy="false">⟩</mo> </mrow> </math></EquationSource> </InlineEquation>//BD texture components in HIP-treated samples. Microhardness mapping revealed significant heterogeneity in as-built samples, with an average of 296 ± 19 HV0.5 and a range of 250–400 HV0.5. Post-processing significantly reduced variability. HT-90-WQ (heat treatment at 1120 °C for 1.5 h + water quenching) achieved 222 ± 16 HV0.5, while HT-240-WQ (HIP process at 103 MPa at 1120 °C for 4 h + rapid cooling in Ar gas) homogenized hardness further to 208 ± 8 HV0.5. HIP at 103 MPa and 200 MPa reduced hardness ranges to 214 ± 17 HV0.5 and 206 ± 10 HV0.5, respectively, after 240 min. These improvements were attributed to solutionizing, recrystallization, and equiaxed grain formation. This study emphasizes the critical role of pressure in recrystallization and demonstrates that optimizing HIP and heat treatment parameters is essential for enhancing mechanical property uniformity in L-PBF Alloy 718 components.

Unraveling the impact of pressure and hold time in post-process heat treatments on microstructure and microhardness evolution in laser powder bed fusion Alloy 718

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发表日期：

2025年8月22日

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Mohammadreza Asherloo,
Yonguk Lee,
Chad Beamer,
Victoria Mayne Miller,
Amir Mostafaei

摘要

This study investigates the impact of heat treatment (HT) and hot isostatic pressing (HIP) parameters on the microstructural evolution, texture, and hardness distribution in laser powder bed fusion (L-PBF) Alloy 718. The findings highlight key factors influencing uniform microstructure development and isotropic mechanical property enhancement. The varying grain evolution processes likely stem from distinct recrystallization mechanisms triggered by the different thermo-mechanical histories in each post-process treatment. Higher HIP pressures (200 MPa) enhanced the recrystallization fraction and grain refinement compared to 103 MPa, as shown by increased low-grain orientation spread (GOS) area fractions and grain number density. The reduction in $\langle {1}00\rangle$ $⟨ 100 ⟩$ //BD texture for both HIP and HT samples was linked to recrystallization and orientation broadening via recovery, even without direct recrystallization evidence. The twin-assisted recrystallization texture, driven by FCC annealing twins, amplified $\langle 212\rangle$ $⟨ 212 ⟩$ //BD texture components in HIP-treated samples. Microhardness mapping revealed significant heterogeneity in as-built samples, with an average of 296 ± 19 HV_0.5 and a range of 250–400 HV_0.5. Post-processing significantly reduced variability. HT-90-WQ (heat treatment at 1120 °C for 1.5 h + water quenching) achieved 222 ± 16 HV_0.5, while HT-240-WQ (HIP process at 103 MPa at 1120 °C for 4 h + rapid cooling in Ar gas) homogenized hardness further to 208 ± 8 HV_0.5. HIP at 103 MPa and 200 MPa reduced hardness ranges to 214 ± 17 HV_0.5 and 206 ± 10 HV_0.5, respectively, after 240 min. These improvements were attributed to solutionizing, recrystallization, and equiaxed grain formation. This study emphasizes the critical role of pressure in recrystallization and demonstrates that optimizing HIP and heat treatment parameters is essential for enhancing mechanical property uniformity in L-PBF Alloy 718 components.