Insights into Phase Transformations during Selective Laser Melting of Ti6Al4V: A Numerical Approach

Document Type : Research Paper

Authors
Gasser Abdelal 1
Daniel Higgins 2
Chi-Wai Chan 1
Brian Falzon 3
1 School of Mechanical and Aerospace Engineering, Queen's University Belfast, Northern Ireland, UK
2 THALAS Group, Belfast, Northern Ireland, UK
3 Western Sydney University, Sydney, Australia
10.22055/jacm.2024.47217.4677
Abstract
Selective Laser Melting (SLM) is a transformative additive manufacturing technique that enables the production of complex metallic components with high precision. Understanding the microstructural evolution during the SLM process is crucial for optimising the mechanical properties and performance of the fabricated parts. This study focuses on developing a predictive model for the microstructure evolution of Ti6Al4V alloy during SLM. The model integrates thermal simulations with phase transformation kinetics using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory to predict the formation and dissolution of alpha and martensite phases. The thermal history of the SLM process was simulated using Finite Element Analysis (FEA) in Abaqus, which provided the temperature distribution and cooling rates experienced by the material. These thermal profiles were then used to drive the microstructure evolution model, which predicts the phase fractions and grain structures resulting from the SLM process. The model was validated against experimental data, showing good agreement in predicting phase fractions and microstructural features. Our results highlight the significant impact of processing parameters, such as laser power and scanning speed, on the microstructure of Ti6Al4V. Higher laser powers and slower scanning speeds were found to promote the formation of coarser microstructures, while faster cooling rates led to finer grains and higher martensite fractions. This comprehensive modelling approach provides valuable insights into optimising SLM process parameters to achieve desired microstructural characteristics and improve the mechanical performance of Ti6Al4V parts. The developed model is a robust tool for guiding the design and optimisation of SLM processes, reducing the reliance on trial-and-error methods, and enhancing the efficiency and quality of additive manufacturing for critical applications in aerospace, biomedical, and automotive industries.
Keywords
Selective Laser Melting
Ti6Al4V
Additive Manufacturing
Microstructure Evolution
Phase Transformation
Subjects

Publisher's Note Shahid Chamran University of Ahvaz remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

[1] Khairallah, S.A., et al., Laser powder-bed fusion additive manufacturing: Physics of complex melt flow and formation mechanisms of pores, spatter, and denudation zones, Acta Materialia, 108, 2016, 36–45.
[2] Wang, X.C., et al., Direct selective laser sintering of hard metal powders: experimental study and simulation, The International Journal of Advanced Manufacturing Technology, 19(5), 2002, 351–357.
[3] Yang, Z., et al., Modeling laser beam absorption of metal alloys at high temperatures for selective laser melting, Advanced Engineering Materials, 23(9), 2021, 2100137.
[4] German, R.M., A quantitative theory for supersolidus liquid phase sintering, Powder Metallurgy, 34(2), 1991, 101–107.
[5] Ladani, L., et al., Effective liquid conductivity for improved simulation of thermal transport in laser beam melting powder bed technology, Additive Manufacturing, 14, 2017, 13–23.
[6] Gusarov, A.V., et al., Heat transfer modelling and stability analysis of selective laser melting, Applied Surface Science, 254(4), 2007, 975–979.
[7] Rosenthal, D., Mathematical theory of heat distribution during welding and cutting, Welding Journal, 20, 1941, 220–234.
[8] Nunes, A.C., An extended Rosenthal weld model, Welding Journal, 62(6), 1983, 165s–170s.
[9] Dai, K., Shaw, L., Thermal and mechanical finite element modeling of laser forming from metal and ceramic powders, Acta Materialia, 52(1), 2004, 69–80.
[10] Goldak, J., et al., A new finite element model for welding heat sources, Metallurgical Transactions B, 15(2), 1984, 299–305.
[11] King, W., et al., Overview of modelling and simulation of metal powder bed fusion process at Lawrence Livermore National Laboratory, Materials Science and Technology, 31(8), 2015, 957–968.
[12] Wang, L., Particle scale modelling of powder spreading in powder bed fusion additive manufacturing, PhD Thesis, Monash University, 2020.
[13] Weber, S., et al., Parameters on support structure design for metal additive manufacturing, Proceedings of the Design Society: DESIGN Conference, Vol. 1, Cambridge University Press, 2020.
[14] Sing, S.L., et al., 3D printing of metals in rapid prototyping of biomaterials: Techniques in additive manufacturing, Rapid Prototyping of Biomaterials, Second Edition, Woodhead Publishing Series in Biomaterials, Woodhead Publishing, 2020.
[15] Kruth, J.-P., et al., Binding mechanisms in selective laser sintering and selective laser melting, Rapid Prototyping Journal, 11(1), 2005, 26-36.
[16] Scheil, E., Anlaufzeit der Austenitumwandlung, Archiv fur das Eisenhuttenwesen, 8(12), 1935, 565–567.
[17] Koistinen, D.P., Marburger, R.E., A general equation prescribing the extent of the austenite-martensite transformation in pure iron-carbon alloys and plain carbon steels, Acta Metallurgica, 7(1), 1959, 59–60.
[18] Geijselaers, H.J.M., Numerical simulation of stresses due to solid state transformations: the simulation of laser hardening, PhD Thesis, University of Twente, 2003.
[19] Baykasoglu, C., et al., A process-microstructure finite element simulation framework for predicting phase transformations and microhardness for directed energy deposition of Ti6Al4V, Additive Manufacturing, 35, 2020, 101252.
[20] Sun, W., et al., A simulation and experiment study on phase transformations of Ti-6Al-4V in wire laser additive manufacturing, Materials & Design, 207, 2021, 109843.
[21] Kelly, S.M., Thermal and microstructure modeling of metal deposition processes with application to titanium aluminum vanadium, PhD Thesis, Virginia Polytechnic Institute and State University, 2004.
[22] Higgins, D., Investigating the microstructure evolution of additive manufactured parts using multiscale modelling, PhD Thesis, Queen's University of Belfast, Northern Ireland, UK, 2023.
[23] Malinov, S., et al., Differential scanning calorimetry study and computer modelling of β→α phase transformation in a Ti-6Al-4V alloy, Metallurgical and Materials Transactions A, 32(4), 2001, 879–887.
[24] Malinov, S., et al., Resistivity study and computer modelling of the isothermal transformation kinetics of Ti–6Al–4V and Ti–6Al–2Sn–4Zr–2Mo–0.08 Si alloys, Journal of Alloys and Compounds, 314(1-2), 2001, 181–192.
[25] Babu, S.S., et al., Measurement of Phase Transformation Kinetics During Repeated Thermal Cycling of Ti-6Al-4V Using Time-Resolved X-Ray Diffraction, URL: https://www.osti.gov/biblio/1008995.
[26] Murgau, C.C., Pederson, R., Lindgren, L.E., A model for Ti–6Al–4V microstructure evolution for arbitrary temperature changes, Modelling and Simulation in Materials Science and Engineering, 20(5), 2012, 055006.
Journal of Applied and Computational Mechanics
Volume 11, Issue 2
Spring 2025
Pages 399-415