Dr. Rajarshi Banerjee is a University Presidential Professor and Regents Professor in the department of materials science and engineering at the University of North Texas (UNT). He is also the Director of the Materials Research Facility at UNT. His primary research focus is on identifying the underlying mechanisms and phase transformations governing microstructural evolution and microstructure-property relationships in complex multi-phase, multi-component materials systems, such as high entropy alloys (HEAs), titanium base alloys, nickel (and cobalt) base superalloys, and magnetic alloys. He works extensively on additive manufacturing (AM) technologies such as directed energy deposition (DED) and laser powder bed fusion (LPBF), as well as conventional thermo-mechanical processing. He has pioneered efforts on AM of functionally/compositionally graded alloys using DED for the past twenty years. The use of advanced characterization techniques, spanning over a range of length scales, including scanning and transmission electron microscopy and atom probe tomography (APT), constitute a common thread tying his multiple research activities. These techniques are used to identify the underlying mechanisms and phase transformations governing microstructural evolution and microstructure-property relationships in these complex multi-phase, multi-component materials systems. Dr. Banerjee also holds appointments as an adjunct/visiting professor in materials science and engineering at the Ohio State University, U.S.A., Nanyang Technological University, Singapore, Indian Institute of Technology Bombay, and Monash University, Australia. He has over 350 publications in peer-reviewed journals, total citations exceeding 25,000, and an H-index of 88.

While additive manufacturing (AM) of titanium alloys has attracted a lot of worldwide attention in the past few decades, there is often a lack of detailed understanding of the microstructural evolution in these 3D printed alloys, as impacted by the unconventional thermo-kinetics experienced by these alloys. Typically the focus has been on maturing this technology for fabricating components of well-established alloys, such as Ti-6Al-4V (wt%), which have traditionally been processed via conventional manufacturing. While these efforts are extremely important, in case of titanium alloys, there exists a tremendous potential of novel microstructural engineering using AM based processing, exploiting the numerous structural and compositional metastablities inherent in these alloys. Therefore it becomes necessary to investigate the microstructure over a range of length scales down to the nanometer and atomic scales to reveal the unique phenomena associated with the rapid cooling rates and thermal cycling experienced during AM processing. The present talk will focus on such detailed investigations of the phase evolution in candidate AM processed Ti alloys, carried out by coupling transmission electron microscopy (TEM) with atom probe tomography (APT). These candidate alloys include the most commonly used Ti-6Al-4V (or Ti-64) the strain-transformable Ti-10V-2Fe-3Al (or Ti-10-2-3), and the high strength Ti-1Al-8V-5Fe (or Ti-1-8-5) (all in wt%) alloys. The focus is on the influence of the non-conventional thermo-kinetics of these AM processes on microstructural evolution, including compositional clustering and second phase precipitation (both omega and alpha) in these alloys, and the consequent influence on mechanical behaviour.

This will be illustrated with three examples:

1. Influence of thermo-kinetics on fine scale isothermal omega precipitation and strain transformability in Ti-10V-2Fe-3Al processed using laser powder bed fusion (LPBF).
2. Influence of thermo-kinetics on vanadium clustering within alpha prime martensitic plates/laths in LPBF processed Ti-6Al-4V.
3. Depending on the process parameter dictated energy density in DED processed Ti-1Al-8V-5Fe, a homogeneous distribution of fine scale omega or alpha precipitates form within the beta grains, strongly influencing the mechanical behaviour.

These representative examples will highlight the power of combining TEM with APT analysis for developing a better understanding of AM processed Ti alloys, essential for achieving an excellent balance of mechanical properties in 3D printed components.

References

• S.A. Mantri, M.S.K.K.Y. Nartu, S. Dasari, A. Sharma, P. Agrawal, R. Salloom, F. Sun, E. Ivanov, K. Cho, B. McWilliams, S.G. Srinivasan, N.B. Dahotre, F. Prima, R. Banerjee, Additive Manufacturing vol. 48 (2021) 102406. https://doi.org/10.1016/J.ADDMA.2021.102406
• M.V. Pantawane, S. Dasari, S.A. Mantri, R. Banerjee, N.B. Dahotre, "Rapid thermokinetics driven nanoscale Vanadium clustering within martensite laths in laser powder bed fused additively manufactured Ti6Al4V", Materials Research Letters 8 (2020): 383-389.
• Nartu, M. S. K. K. Y., S. Dasari, A. Sharma, S. A. Mantri, Shashank Sharma, Mangesh V. Pantawane, B. McWilliams, K. Cho, Narendra B. Dahotre, and R. Banerjee, Materials Science and Engineering: A 821 (2021): 141627.