Precipitation hardening of laser powder bed fusion Ti-6Al-4V

Published

November 20, 2024

Author(s)

Nicholas Derimow, Jake Benzing, Jacob Garcia, Zachary Levin, Ping Lu, Newell Moser, Chad Beamer, Frank DelRio, Nikolas Hrabe

Abstract

The laser powder bed fusion (PBF-L) additive manufacturing (AM) community has dedicated significant efforts into process optimization and control for defect-free Ti-6Al-4V. As defects become less of an issue for PBF-L Ti-6Al-4V, the processing-structure-properties (PSP) relationships between AM microstructures can now be explored to optimize mechanical properties. Lower temperature aging treatments around 550 °C in wrought Ti-6A-4V have been historically understood to precipitation harden the α phase with an ordered, hexagonal close packed (HCP) α2 phase. The presence of the α2 phase is that of nanoscale Ti3Al precipitates that are coherent with the parent α phase. The aim of the present investigation was to implement a historical vacuum heat treatment of 545 °C for 100 hours after an initial hot isostatic pressure (HIP) treatment that is commonly used in PBF Ti-6Al-4V to decompose the martensitic as-built microstructure. The vacuum aging did not result in pore regrowth over the detection resolution of 8.5 µm voxel edge length, and successfully produced nanoscale precipitates of α2 phase within α-laths, confirmed via atom probe tomography (APT). Microstructural-length scale and quasi-static mechanical properties were investigated by nanoindentation and uniaxial tensile tests of miniaturized test specimens. Given the sensitivity of Ti-6Al-4V mechanical properties to small changes in chemistry, all test specimens originated from the same build. The α2 precipitation resulted in significantly harder α-laths, as well as a relative yield and ultimate strength increase of 60 MPa and 38 MPa, respectively. Analysis of Variance (ANOVA) of the datasets revealed no statistical differences in total elongation between the HIPed and HIPed + aged specimens, indicative of the aging treatment producing a net benefit of strength with no loss in ductility.

Citation

Materials Science and Engineering A

Pub Type

Journals

Download Paper

https://doi.org/10.1016/j.msea.2024.147549

Local Download

Keywords

Additive Manufacturing, Ti-6Al-4V, Precipitation hardening, heat treatment, laser powder bed fusion

Citation

Derimow, N. , Benzing, J. , Garcia, J. , Levin, Z. , Lu, P. , Moser, N. , Beamer, C. , DelRio, F. and Hrabe, N. (2024), Precipitation hardening of laser powder bed fusion Ti-6Al-4V, Materials Science and Engineering A, [online], https://doi.org/10.1016/j.msea.2024.147549 , https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=958447 (Accessed December 4, 2024)