Effect of hot isostatic pressing on the microstructure and mechanical properties of porous Ti-6Al-4V alloy manufactured by laser powder bed fusion

Abstract

Laser powder bed fusion (LPBF) enables the production of Ti-6Al-4V alloys with tailored porous structures, which are beneficial for biomedical applications due to their reduced elastic modulus and enhanced bone integration potential. This study examines the effect of hot isostatic pressing (HIP) on the microstructure and mechanical properties of diamond and gyroid porous structures fabricated by LPBF. Solid tensile specimens served as reference materials. HIP significantly reduced porosity, decreased ultimate tensile strength and hardness, but markedly increased ductility (from 6% to 17%). Compressive strengths reached approximately 100 MPa (diamond) and 240 MPa (gyroid), with HIP causing only a slight increase in strain. However, HIP notably improved bending performance, raising the flexural strength of gyroid structures from 280 MPa (as-printed) to 340 MPa (post-HIP). The strength of LPBF-fabricated Ti-6Al-4V porous structures is reduced by HIP, but their ductility and bending performance are enhanced, making them more suitable for biomedical applications.

Keywords

Ti-6Al-4V / Laser powder bed fusion / Hot isostatic pressing / Porous material / Mechanical properties / Lattice structures

Funding

This work was supported by the project “Mechanical Engineering of Biological and Bioinspired Systems” (Project No. CZ.02.01.01/00/22_008/0004634) funded by “Programme Johannes Amos Commenius,” Excellent Research Call. It was also supported by the Ministry of Health of the Czech Republic in cooperation with the Czech Health Research Council (Project No. NW25-08- 00044). The authors also acknowledge the grant of Specific University Research (Grant No. A1_FCHT_2025_011).

Conflict of Interest

The authors declare that they have no competing interests.

References

[1] Pushp P, Dasharath SM, Arati C. Classification and applications of titanium and its alloys. Mater Today Proc. 2022;54(2):537-542. doi: 10.1016/j.matpr.2022.01.008

[2] Elitzer D, Jäger S, Höll C, et al. Development of microstructure and mechanical properties of TiAl6V4 processed by wire and arc additive manufacturing. Adv Eng Mater. 2022;25:2201025. doi: 10.1002/adem.202201025

[3] Carroll BE, Palmer TA, Beese AM. Anisotropic tensile behavior of Ti-6Al-4V components fabricated with directed energy deposition additive manufacturing. Acta Mater. 2015;87:309-320. doi: 10.1016/j.actamat.2014.12.054

[4] Donachie MJ. Titanium: A Technical Guide. United States: ASM International; 2000. p. 369.

[5] Etesami SA, Fotovvati B, Asadi E. Heat treatment of Ti-6Al-4V alloy manufactured by laser-based powder-bed fusion: Process, microstructures, and mechanical properties correlations. J Alloys Compds. 2022;895:162618. doi: 10.1016/j.jallcom.2021.162618

[6] Mohammed MT. Mechanical properties of SLM-titanium materials for biomedical applications: A review. Mater Today Proc. 2018;5(Pt 3):17906-17913. doi: 10.1016/j.matpr.2018.06.119

[7] Gu DD, Shen Y, Popovich VA, Wissenbach K. Laser additive manufacturing of metallic components: Materials, processes and mechanisms. Int Mater Rev. 2012;57(3):133-164. doi: 10.1179/1743280411Y.0000000014

[8] Mueller B. Additive manufacturing technologies-rapid prototyping to direct digital manufacturing. Assembly Automat. 2012;32(2). doi: 10.1108/aa.2012.03332baa.010

[9] Frazier WE. Metal additive manufacturing: A review. J Mater Eng Perform. 2014;23(6):1917-1928. doi: 10.1007/s11665-014-0958-z

[10] Dutta B, Froes FH. Additive manufacturing of titanium alloys. AMP Tech Artic. 2014;172(2):18-23.

[11] Hollander DA, Perez MC, Brinkmann M, et al. Structural, mechanical and in vitro characterization of individually structured Ti-6Al-4V produced by direct laser forming. Biomaterials. 2006;27(7):955-963. doi: 10.1016/j.biomaterials.2005.07.041

[12] Leuders S, Thone M, Riemer A, et al. On the mechanical behavior of titanium alloy TiAl6V4 manufactured by selective laser melting: Fatigue resistance and crack growth performance. Int J Fatigue. 2013;48:300-307. doi: 10.1016/j.ijfatigue.2012.11.011

[13] Das S, Zhang GD, Li H, et al. Processing of titanium net shapes by SLS/HIP. Mater Design. 1999;20(2):115-121.

[14] Vilaro T, Colin C, Bartout JD. As-fabricated and heat-treated microstructures of the Ti-6Al-4V alloy processed by selective laser melting. Metall Mater Trans A. 2011;42(10):3190-3199. doi: 10.1007/s11661-011-0731-y

[15] Bai L, Chen Y, Cheng N, et al. Effects of heat treatment and hot isostatic pressing on microstructure and fatigue improvements in Ti-6Al-4V alloy fabricated by selective laser melting. Mater Lett. 2024;367:136641. doi: 10.1016/j.matlet.2024.136641

[16] Yadav BN, Lin DW, Lin MC, et al. Implemented in-situ heat treatment process for controlling the residual thermal stresses during the fabrication of Ti-6Al-4V titanium alloy through additive manufacturing. Mater Lett. 2024;356:135580. doi: 10.1016/j.matlet.2023.135580

[17] Huang G, Gu D, Liu H, Lin K, Wang R, Sun H. The role of graded layers in interfacial characteristics and mechanical properties of Ti6Al4V/AlMgScZr-graded multi-material parts fabricated using laser powder bed fusion. Mater SciAddit Manuf. 2024;3(2):3088. doi: 10.36922/msam.3088

[18] Strakosova A, Kubásek J, Michalcová A, Průša F, Vojtěch D, Dvorský D. High strength X3NiCoMoTi 18-9-5 maraging steel prepared by selective laser melting from atomized powder. Materials (Basel). 2019;12:4174. doi: 10.3390/ma12244174

[19] Herzog D, Seyda V, Wycisk E, Emmelmann C. Additive manufacturing of metals. Acta Mater. 2016;117:371-392. doi: 10.1016/j.actamat.2016.07.019

[20] Shi J, Liang H, Jiang J, Tang W, Yang J. Design and performance evaluation of porous titanium alloy structures for bone implantation. Math Problems Eng. 2019;2019:5268280. doi: 10.1155/2019/5268280

[21] Yue X, Tang H, Lu S, et al. Impact behavior of AlSi10Mg porous structures with varying single-unit cell rotation angles fabricated via laser powder bed fusion. MSAM. 2025;4(2):025130019. doi: 10.36922/MSAM025130019

[22] Fousová M, Vojtěch D, Kubásek J, Jablonská E, Fojt F. Promising characteristics of gradient porosity Ti-6Al-4V alloy prepared by SLM process. J Mech Behav Biomed Mater. 2017;69:368-376. doi: 10.1016/j.jmbbm.2017.01.043

[23] Wang B, Luo M, Shi Z, et al. Porous titanium alloys for medical application: Progress in preparation process and surface modification research. MSAM. 2024;3(1):2753. doi: 10.36922/msam.2753

[24] Gao X, Zhao Y, Wang M, Liu Z, Liu C. Parametric design of hip implant with gradient porous structure. Front Bioeng Biotechnol. 2022;10:850184. doi: 10.3389/fbioe.2022.850184

[25] Verma R, Kumar J, Singh N, et al. Low elastic modulus and highly porous triply periodic minimal surfaces architectured implant for orthopedic applications. Proc Instit Mech Eng E J Process Mech Eng. 2022;239(4):1553-1561. doi: 10.1177/09544089221111258

[26] Roudnicka M, Mertova K, Vojtech D. Influence of hot isostatic pressing on mechanical response of as-built SLM titanium alloy. IOP Conf Ser Mater Sci Eng. 2019;629(1):012034. doi: 10.1088/1757-899X/629/1/012034

[27] Alcisto J, Enriquez A, Garcia H, et al. Tensile properties and microstructures of laser-formed Ti-6Al-4V. J Mater Eng Perform. 2011;20:203-212. doi: 10.1007/s11665-010-9670-9

[28] Amsterdam E, Kool G. High cycle fatigue of laser beam deposited Ti-6Al-4V and Inconel 718. In: Proceedings of the 25^th Symposium of the International Committee on Aeronautical Fatigue (ICAF). Rotterdam, The Netherlands: Springer; 2009.

[29] Alegre JM, Díaz A, García R, Peral LB, Cuesta II. Effect of HIP post-processing at 850 °C/200 MPa in the fatigue behavior of Ti-6Al-4V alloy fabricated by selective laser melting. Int J Fatigue. 2022;163:107097. doi: 10.1016/j.ijfatigue.2022.107097

[30] Ma HY, Wang JC, Qin P, et al. Advances in additively manufactured titanium alloys by powder bed fusion and directed energy deposition: Microstructure, defects, and mechanical behavior. J Mater Sci Technol. 2024;183:32-62. doi: 10.1016/j.jmst.2023.11.003

[31] Wang Y, Liu X, Zhang X, et al. Cell-size graded sandwich enhances additive manufacturing fidelity and energy absorption. Int J Mech Sci. 2021;211:106798. doi: 10.1016/j.ijmecsci.2021.106798

[32] Wu MW, Lai PH. The positive effect of hot isostatic pressing on improving the anisotropies of bending and impact properties in selective laser melted Ti-6Al-4V alloy. Mater Sci Eng A. 2016;658:429-438. doi: 10.1016/j.msea.2016.02.023

[33] Wu MW, Chen JK, Lin BH, Chiang PH. Improved fatigue endurance ratio of additive manufactured Ti-6Al-4V lattice by hot isostatic pressing. Mater Design. 2017;134:163-170. doi: 10.1016/j.matdes.2017.08.048

[34] Lee J, Ha H, Seol JB, et al. Reverse effect of hot isostatic pressing on high-speed selective laser melted Ti-6Al-4V alloy. Mater Sci Eng A. 2021;807:140880. doi: 10.1016/j.msea.2021.140880

[35] Lv Z, Li H, Che L, et al. Effects of HIP process parameters on microstructure and mechanical properties of Ti-6Al-4V fabricated by SLM. Metals. 2023;13:991. doi: 10.3390/met13050991

[36] Yan X, Yue S, Ge J, Chen C, Lupoi R, Yin S. Microstructural and mechanical optimization of selective laser melted Ti6Al4V lattices: Effect of hot isostatic pressing. J Manuf Process. 2022;77:151-162. doi: 10.1016/j.jmapro.2022.02.024

[37] Xu Q, Chen B, Bai Q, et al. Effects of hot isostatic pressing temperature on casting shrinkage densification and microstructure of Ti6Al4V alloy. China Foundry. 2017;14(5):429-434. doi: 10.1007/s41230-017-7178-8

[38] Alketan O, Abu Al-Rub RK. MSLattice: A free software for generating uniform and graded lattices based on triply periodic minimal surfaces. Mater Design Process Commun. 2020;3:e205.

[39] Školáková A, Pinc J, Kubik R, et al. The effect of pulsed laser on the surface state of 3D-printed triply periodic structures in TiAl6V4 alloy. Prog Addit Manuf. 2025. doi: 10.1007/s40964-025-01254-7

[40] Technologies Canada Inc. DragonflyComet. Montreal, Canada: Technologies Canada Inc.; 2022.

[41] Su C, Yu H, Wang Z, Yang J, Zeng X. Controlling the tensile and fatigue properties of selective laser melted Ti-6Al-4V alloy by post treatment. J Alloys Compds. 2021;857:157552. doi: 10.1016/j.jallcom.2020.157552

[42] Kuang DM, Long ZL, Ogwu I, Kuang FL, Yang LM. DEM study on the effect of pore characteristic on single particle crushing behavior of porous particles. Comput Geotechnics. 2024;165:105919. doi: 10.1016/j.compgeo.2023.105919

[43] Pilliar RM, Filiaggi MJ, Wells JD, Grynpas MD, Kandel RA. Porous calcium polyphosphate scaffolds for bone substitute applications -- in vitro characterization. Biomaterials. 2001;22(9):963-972. doi: 10.1016/s0142-9612(00)00261-1

[44] Ji R, Zhang H, Chen L, Cheng L, Luo H, Mao J. Improving the strength and maintaining good ductility of as-forged Ti6Al4V alloy by regulating the microstructural defects. Mater Sci Eng A. 2024;911:146913. doi: 10.1016/j.msea.2024.146913

[45] Li J, Liu X, Luo X, et al. Overcoming the strength-ductility trade-off and anisotropy of mechanical properties of Ti6Al4V with electron beam powder bed fusion. Mater Sci Eng A. 2023;879:145301. doi: 10.1016/j.msea.2023.145301

[46] Liu J, Sun Q, Zhou C, et al. Achieving Ti6Al4V alloys with both high strength and ductility via selective laser melting. Mater Sci Eng A. 2019;766:138319. doi: 10.1016/j.msea.2019.138319

[47] Vrancken B, Thijs L, Kruth JP, Van Humbeeck J. Heat treatment of Ti6Al4V produced by selective laser melting: Microstructure and mechanical properties. J Alloys Compds. 2012;541:177-185. doi: 10.1016/j.jallcom.2012.07.022

[48] Gain AK, Cui Y, Zhang L. Pore-gradient Ti6Al4V alloy mimicking the properties of human cortical bones: The design of TPMS structures by selective laser melting. Mater Sci Eng A. 2024;915:147220. doi: 10.1016/j.msea.2024.147220

[49] Barui S, Chatterjee S, Mandal S, Kumar A, Basu B. Microstructure and compression properties of 3D powder printed Ti-6Al-4V scaffolds with designed porosity: Experimental and computational analysis. Mater Sci Eng C Mater Biol Appl. 2017;70:812-823. doi: 10.1016/j.msec.2016.09.040

[50] Li X, Wang CT, Zhang WG, Li YC. Properties of a porous Ti-6Al-4V implant with a low stiffness for biomedical application. Proc Inst Mech Eng H. 2009;223(2):173-178. doi: 10.1243/09544119JEIM466

[51] Suresh S, Sun CN, Tekumalla S, Rosa V, Ling Nai SM, Wong RC. Mechanical properties and in vitro cytocompatibility of dense and porous Ti-6Al-4V ELI manufactured by selective laser melting technology for biomedical applications. J Mech Behav Biomed Mater. 2021;123:104712. doi: 10.1016/j.jmbbm.2021.104712

[52] Timercan A, Sheremetyev V, Brailovski V. Mechanical properties and fluid permeability of gyroid and diamond lattice structures for intervertebral devices: Functional requirements and comparative analysis. Sci Technol Adv Mater. 2021;22:285-300. doi: 10.1080/14686996.2021.1907222

[53] Anatolie, T.; Sheremetyev, V.; Brailovski, V.; Mechanical properties and fluid permeability of gyroid and diamond lattice structures for intervertebral devices: Functional requirements and comparative analysis. Science and Technology of Advanced Materials 2021, 22.

[54] Naghavi, S. A.; Tamaddon, M.; Garcia-Souto, P.; Moazen, M.; Taylor, S.; Hua, J.; Liu, C., A novel hybrid design and modelling of a customised graded Ti-6Al-4V porous hip implant to reduce stress-shielding: An experimental and numerical analysis. Front Bioeng Biotechnol 2023, 11, 1092361.