Residual stress-assisted static globularization in electron beam powder bed
fusion Ti-6Al-4V from powder recovery and hot isostatic pressing
Nicholas Derimow
1∗
, Thomas A. Berfield
2
, Keenan Hanson
3
, Jake T. Benzing
1
, Nik Hrabe
1
1
Applied Chemicals and Materials Division, NIST, 325 Broadway, Boulder, CO 80305, USA
2
Department of Mechanical Engineering, University of Louisville, Louisville, KY 40292, USA
3
Stryker, Mahwah, NJ, 07430, USA
Abstract
The residual stresses from controlled powder recovery blasting on electron beam powder bed fusion (PBF-
EB) Ti-6Al-4V were investigated via hole drilling, profilometry, and microscopy. After hot isostatic pressing,
the near-surface lamellar α + β microstructure underwent a static α globularization resulting from residual
stresses imparted by plastic deformation during powder recovery. Surface residual stresses were measured to
be consistent with shot peening. The results have implications for systematic control of PBF-EB Ti-6Al-4V
through modification of standard practices.
Keywords: Ti-6Al-4V, PBF-EB, Residual stress, Powder reuse, Additive manufacturing
1. Introduction
There is need to outperform wrought metals that leverage the geometrical freedom of additive manufactur-
ing (AM). However, this is challenging in alloys with plastic anisotropy due to preferred slip systems, like
Ti-6Al-4V [1–3]. The microstructure of AM Ti-6Al-4V is composed of lamellar α encapsulating β, referred
to as α + β Widmanstätten or lamellar microstructure [4] and are controlled via heat treatments [5]. How-
ever, lamellar morphology remains unless deformed during hot working [6], which results in equiaxed, or
globular microstructure from α boundary splitting and termination migration [7]. The globular morphology
is desired for fatigue applications, as globular α reduces the mean free path for slip, as lamellar α colonies are
∗
Corresponding author
Email address: nicholas.derimow@nist.gov (Nicholas Derimow
1
)
