Microstructural Evolution and Mechanical Properties of Post-Processed IN 625 Fabricated by Laser Powder Bed Fusion

Abstract

Laser powder bed fusion (LPBF) is widely used for manufacturing nickel-based superalloy components with complex geometries; however, the process produces non-equilibrium microstructures characterized by directional grain growth, cellular substructures, and compositional segregation, which can lead to anisotropic mechanical behavior. In this study, the influence of multiple post-processing heat-treatment routes on the microstructural evolution and mechanical properties of LPBF-fabricated Inconel 625 (IN625) was systematically investigated by combining stress relief, hot isostatic pressing (HIP), and solution annealing. Microstructural characterization was performed using optical microscopy and scanning electron microscopy, while tensile properties were evaluated from room temperature to 700 °C. The HT3 condition resulted in a fully recrystallized, equiaxed grain structure with reduced segregation and minimal Nb-rich Laves phase, leading to nearly isotropic mechanical properties, with an ultimate tensile strength of approximately 880 MPa and an elongation exceeding 50%. Elevated-temperature testing demonstrated stable mechanical performance, with a localized strengthening effect near 600 °C attributed to dynamic strain aging. These results demonstrate that appropriate post-processing can effectively homogenize LPBF IN625 and improve its mechanical reliability.

Keywords

Inconel 625 / Laser powder bed fusion / Additive manufacturing / Heat treatment / Microstructure / Mechanical properties

Acknowledgments

The author would like to acknowledge the Additive Manufacturing team at Edison Welding Institute (EWI) for their valuable contributions to this work. Their support in specimen fabrication, process execution, and technical discussions was essential to the successful completion of this study

Statement of the Use of Generative AI and AI-Assisted Technologies in the Writing Process

During the preparation of this work, the authors used Grammarly Pro in order to improve readability and language. After using this tool/service, the author reviewed and edited the content as needed and took full responsibility for the publication’s content.

Ethics Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request. Certain data may be subject to confidentiality or proprietary restrictions due to the nature of the research and associated project agreements.

Funding

This research received no external funding.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References

[1] Zhang D, Feng Z, Wang C, Wang W, Liu Z, Niu W . Comparison of microstructures and mechanical properties of Inconel 718 alloy processed by selective laser melting and casting. Mater. Sci. Eng. A 2018, 724, 357-367. DOI: 10.1016/j.msea.2018.03.073

[2] Chlebus E, Gruber K, Kuznicka B, Kurzac J, Kurzynowski T . Effect of heat treatment on the microstructure and mechanical properties of Inconel 718 processed by selective laser melting. Mater. Sci. Eng. A 2015, 639, 647-655. DOI: 10.1016/j.msea.2015.05.035

[3] Zhang D, Niu W, Cao X, Liu Z . Effect of standard heat treatment on the microstructure and mechanical properties of selective laser melting manufactured Inconel 718 superalloy. Mater. Sci. Eng. A 2015, 644, 32-40. DOI: 10.1016/j.msea.2015.06.021

[4] Popovich VA, Borisov EV, Popovich AA, Sufiiarov VS, Masaylo DV, Alzina L . Impact of heat treatment on the mechanical behavior of Inconel 718 processed with tailored microstructure by selective laser melting. Mater. Des. 2017, 131, 12-22. DOI: 10.1016/j.matdes.2017.05.065

[5] Barros R, Silva FJG, Gouveia RM, Saboori A, Marchese G, Biamino S, et al. Laser powder bed fusion of Inconel 718: Residual stress analysis before and after heat treatment. Metals 2019, 9, 1290. DOI: 10.3390/met9121290

[6] Zhang YC, Jiang W, Tu ST, Zhang XC, Ye YJ, Wang RZ . Experimental Investigation and Numerical Prediction on Creep Crack Growth Behaviour of the Solution Treated Inconel 625 Superalloy. Eng. Fract. Mech. 2018, 199, 327-342. DOI: 10.1016/j.engfracmech.2018.05.048

[7] Xu X, Mi G, Xiong L, Jiang P, Shao X, Wang C . Morphologies, Microstructures and Properties of TiC Particle Reinforced Inconel 625 Coatings Obtained by Laser Cladding with Wire. J. Alloys Compd. 2018, 740, 16-27. DOI: 10.1016/j.jallcom.2017.12.298

[8] Cinoglu IS, Charbal A, Vermaak N . Towards Exploiting Inelastic Design for Inconel 625 under Short—Term Cyclic Loading at 600 °C. Mech. Mater. 2020, 140, 103219. DOI: 10.1016/j.mechmat.2019.103219

[9] Huebner J, Kata D, Kusiński J, Rutkowski P, Lis J . Microstructure of Laser Cladded Carbide Reinforced Inconel 625 Alloy for Turbine Blade Application. Ceram. Int. 2017, 43, 8677-8684. DOI: 10.1016/j.ceramint.2017.03.194

[10] Zhang HY, Zhang SH, Cheng M, Li ZX . Deformation characteristics of δ phase in the delta—processed Inconel 718 alloy. Mater. Charact. 2010, 61, 49-53. DOI: 10.1016/j.matchar.2009.10.003

[11] Liu FC, Lin X, Yang GL, Song MH, Chen J, Huang W . Microstructure and residual stress of laser rapid formed Inconel 718 nickel—base superalloy. Opt. Laser Technol. 2011, 43, 208-213. DOI: 10.1016/j.optlastec.2010.06.015

[12] Rai SK, Kumar A, Shankar V, Jayakumar T, Rao KBS, Raj B . Characterization of Microstructures in Inconel 625 using X—ray Diffraction Peak Broadening and Lattice Parameter Measurements. Scripta Mater. 2004, 51, 59-63. DOI: 10.1016/j.scriptamat.2004.03.017

[13] Evans ND, Maziasz PJ, Shingledecker JP, Yamamoto Y . Microstructure Evolution of Alloy 625 Foil and Sheet during Creep at 750 °C. Mater. Sci. Eng. A 2008, 498, 412-420. DOI: 10.1016/j.msea.2008.08.017

[14] Rodriguez R, Hayes RW, Berbon PB, Lavernia EJ . Tensile and Creep Behaviour of Cryomilled Inco 625. Acta Mater. 2003, 51, 911-929. DOI: 10.1016/S1359—6454(02)00494—9

[15] Mathew MD, Rao KBS, Mannan SL . Creep Properties of Service—Exposed Alloy 625 after Re—solution Annealing Treatment. Mater. Sci. Eng. A 2004, 372, 327-333. DOI: 10.1016/j.msea.2004.01.042

[16] Bean E, McLouth TD, Witkin DB, Sitzman SD, Adams PM, Zaldivar PMRJ . Build orientation effects on texture and mechanical properties of selective laser melting Inconel 718. J. Mater. Eng. Perform. 2019, 28, 1942-1949. DOI: 10.1007/s11665—019—03980—w

[17] Cabrini M, Lorenzi S, Testa C, Brevi F, Biamino S, Fino P, et al. Microstructure and Selective Corrosion of Alloy 625 Obtained by Means of Laser Powder Bed Fusion. Materials 2019, 12, 1742. DOI: 10.3390/ma12111742

[18] Shi R, Khairallah SA, Roehling TT, Heo TW, McKeown JT, Matthews MJ . Microstructural control in metal laser powder bed fusion additive manufacturing using laser beam shaping strategy. Acta Mater. 2020, 184, 284-305. DOI: 10.1016/j.actamat.2019.11.053

[19] Raghavan N, Simunovic S, Dehoff R, Plotkowski A, Turner J, Kirka M, et al. Localized melt—scan strategy for site—specific control of grain size and primary dendrite arm spacing in electron beam additive manufacturing. Acta Mater. 2017, 140, 375-387. DOI: 10.1016/j.actamat.2017.08.038

[20] Roehling TT, Wu SSQ, Khairallah SA, Roehling JD, Soezeri SS, Crumb MF, et al. Modulating laser intensity profile ellipticity for microstructural control during metal additive manufacturing. Acta Mater. 2017, 128, 197-206. DOI: 10.1016/j.actamat.2017.02.025

[21] Luna V, Trujillo L, Gamon A, Arrieta E, Murr LE, Wicker RB, et al. Comprehensive and comparative heat treatment of additively manufactured Inconel 625 alloy and corresponding microstructures and mechanical properties. Manuf. Mater. Process. 2022, 6, 107-124. DOI: 10.3390/jmmp6050107

[22] Gamon A, Arrieta E, Gradl PR, Katsarelis C, Murr LE, Wicker RB, et al. Microstructure and hardness comparison of as—built Inconel 625 alloy following various additive manufacturing processes. Results Mater. 2021, 12, 100239. DOI: 10.1016/j.rinma.2021.100239

[23] Vilaro T, Colin C, Bartout JD, Nazé L, Sennour M . Microstructural and mechanical approaches of the selective laser melting process applied to a nickel—base superalloy. Mater. Sci. Eng. A 2012, 534, 446-451. DOI: 10.1016/j.msea.2011.11.092

[24] AMS666K; Nickel Alloy, Corrosion and Heat—Resistant, Bars, Forgings, Extrusions, and Rings 62Ni—21.5Cr—9.0Mo—3.65 (Cb [Nb]+Ta) Annealed . SAE International: Warrendale, PA, USA, 2022.

[25] AMS5599J; Nickel Alloy, Corrosion and Heat—Resistant, Sheet, Strip, and Plate 62Ni—21.5Cr—9.0Mo—3.7 Cb (Nb) Solution Heat Treated . SAE International: Warrendale, PA, USA, 2022.

[26] Leary M. Chapter 11—Powder Bed Fusion ; Elsevier: Amsterdam, The Netherlands, 2020. DOI: 10.1016/B978—0—12—816721—2.00011—7

[27] Fang ZC, Wu ZL, Huang CG, Wu CW . Review on residual stress in selective laser melting additive manufacturing of alloy parts. Opt. Laser Technol. 2020, 129, 106283. DOI: 10.1016/j.optlastec.2020.106283

[28] Blakey—Milner B, Gradl P, Snedden G, Brooks M, Pitot J, Lopez E, et al. Metal additive manufacturing in aerospace—A review. Mater. Des. 2021, 209, 110008. DOI: 10.1016/j.matdes.2021.110008

[29] Marchese G, Lorusso M, Parizia S, Bassini E, Lee J, Calignano F, et al. Influence of heat treatments on microstructure evolution and mechanical properties of Inconel 625 processed by laser powder bed fusion. Mater. Sci. Eng. A 2018, 729, 64-75. DOI: 10.1016/j.msea.2018.05.044

[30] Li C, White R, Fang XY, Weaver M, Guo YB . Microstructure evolution characteristics of Inconel 625 alloy from selective laser melting to heat treatment. Mater. Sci. Eng. A 2017, 705, 20-31. DOI: 10.1016/j.msea.2017.08.058

[31] Roy TD, Wei HL, Zuback JS, Mukherjee T, Elmer JW, Milewski JO, et al. Additive manufacturing of metallic components—Process, structure and properties. Prog. Mater. Sci. 2018, 92, 112-224. DOI: 10.1016/j.pmatsci.2017.10.001

[32] ASTM F3056; Standard Specification for Additive Manufacturing Nickel Alloy (UNS N06625) with Powder Bed Fusion . ASTM International: West Conshohocken, PA, USA, 2014.

[33] Liu J, Yang HY, Zhong XM, Dong BY, Li ZY, Chen JB, et al. Microstructure manipulation and high—temperature service performance enhancement of nickel—based superalloys, J. Mater. Res. Tech. 2026, 40, 2930-2961. DOI: 10.1016/j.jmrt.2025.12.205

[34] Degnah A, Tabbakh T, Kurdi A, Basak AK . Role of precipitation and solute segregation on micro—scale deformation of additively manufactured Inconel 718. Mater. Sci. Eng. A 2023, 887, 145762. DOI: 10.1016/j.msea.2023.145762

[35] Devaux A, Naze L, Molins R, Pineau A, Organista A, Guedou JY, et al. Gamma double prime precipitation kinetic in Alloy 718. Mater. Sci. Eng. 2008, 486, 117-122. DOI: 10.1016/j.msea.2007.08.046

[36] Smith GD, Patel SJ . The Role of Niobium in Wrought Precipitation Hardened Nickel Base Alloys ; Sixth International Symposium on Superalloys 718, 625, 706 and Derivatives 2005; Loria EA, Ed.; TMS (The Minerals, Metals & Materials Society): Pittsburgh, PA, USA, 2005; pp. 135-154.

[37] Kreitcberg A, Brailovski V, Turenne S . Effect of heat treatment and hot isostatic pressing on the microstructure and mechanical properties of Inconel 625 alloy processed by laser powder bed fusion. Mater. Sci. Eng. A 2017, 689, 1-10. DOI: 10.1016/j.msea.2017.02.038

[38] Murr LE, Martinez E, Gaytan SM, Ramirez DA, Machado BI, Shindo PW, et al. Microstructural architecture, microstructures, and mechanical properties for a Nickel—Base Superalloy fabricated by Electron Beam Melting. Metall. Mater. Trans. A 2011, 42, 3491-3508. DOI: 10.1007/s11661—011—0748—2

[39] Kreitcberg A, Brailovski V, Turenne S . Elevated temperature mechanical behavior of IN625 alloy processed by laser powder—bed fusion. Mater. Sci. Eng. A 2017, 700, 540-553. DOI: 10.1016/j.msea.2017.06.045

[40] Hrutkay K, Kaoumi D . Tensile deformation behavior of a nickel—based superalloy at different temperatures. Mater. Sci. Eng. A 2014, 599, 196-203. DOI: 10.1016/j.msea.2014.01.056

[41] Hale C, Rollings W, Weaver M . Activation energy calculations for discontinuous yielding in Inconel 718SPF. Mater. Sci. Eng. A 2001, 300, 153-164. DOI: 10.1016/S0921—5093(00)01470—2

[42] Rahman MS, Priyadarshan G, Raja KS, Nesbitt C, Misra M . Characterization of high—temperature deformation behavior of IN 617. Mech. Mater. 2009, 41, 261-270. DOI: 10.1016/j.mechmat.2008.10.003

[43] Wright JK, Carroll LJ, Cabet C, Lillo TM, Benz JK, Simpson JA, et al. Characterization of elevated temperature properties of heat exchanger and steam generator alloys. Nucl. Eng. 2012, 251, 252-260. DOI: 10.1016/j.nucengdes.2011.10.034

[44] Fournier L, Delafosse D, Magnin T . Oxidation induced intergranular cracking and Portevin—Le Chatelier effect in nickel—base superalloy 718. Mater. Sci. Eng. A 2001, 316, 166-173. DOI: 10.1016/S0921—5093(01)01224—2

[45] Kaoumi D, Hrutkay K . Tensile deformation behavior and microstructure evolution of Ni—based superalloy 617. J. Nucl. Mater. 2014, 454, 265-273. DOI: 10.1016/j.jnucmat.2014.08.003

[46] Mo K, Lovicu G, Chen X, Tung HM, Hansen JB, Stubbins JF . Mechanism of plastic deformation of a Ni—based superalloy for VHTR applications. J. Nucl. Mater. 2013, 441, 695-703. DOI: 10.1016/j.jnucmat.2013.03.083

[47] Nalawade SA, Sundararaman M, Kishore R, Shah JG . The influence of ageing on the serrated yielding phenomenon in a nickel—base superalloy. Scr. Mater. 2008, 59, 991-994. DOI: 10.1016/j.scriptamat.2008.07.004

[48] Amato KN, Hernandez J, Murr LE, Martinez E, Gaytan SM, Shindo PW . Microstructures and mechanical behavior of Inconel 625 fabricated by selective laser melting. Acta Mater. 2012, 60, 2229-2239. DOI: 10.1016/j.actamat.2011.12.032

[49] Kuo YC, Kakehi K . Effects of heat treatment on microstructure and mechanical properties of selective laser melted Inconel 625 alloy. J. Alloys Compd. 2020, 815, 152404. DOI: 10.1016/j.jallcom.2019.152404

[50] Zhihua T, Chaoqun Z, Dayong W, Daniel W, Yongtao Z, Yingtao T . A Review on laser powder bed fusion of Inconel 625 nickel—based alloy. Appl. Sci. 2020, 10, 81-95. DOI: 10.3390/app10010081

[51] Jie Z, Kai F, Hiroyuki K, Zhuguo L . Effect of heat treatment on the anisotropic mechanical properties and corrosion resistance of laser powder bed fusion fabricated Inconel 625. J. Alloys Compd. 2024, 1001, 175087. DOI: 10.1016/j.jallcom.2024.175087

[52] Ma K, Wang J . Microstructural Characteristics and Mechanical Properties of an Additively Manufactured Nickel—Based Superalloy. Crystals 2022, 12, 1358. DOI: 10.3390/cryst12101358

[53] ASTM E112—13; Standard Test Methods for Determining Average Grain Size . ASTM International: West Conshohocken, PA, USA, 2025.

[54] ASTM E8/E8M—21; Standard Test Methods for Tension Testing of Metallic Materials . ASTM International: West Conshohocken, PA, USA, 2021.

[55] ASTM E21—20; Standard Test Methods for Elevated Temperature Tension Tests of Metallic Materials . ASTM International: West Conshohocken, PA, USA, 2020.