Effect of Powder Reuse Times on Additive Manufacturing of Ti-6Al-4V by Selective Electron Beam Melting
JOM
Effect of Powder Reuse Times on Additive Manufacturing of Ti-6Al-4V by Selective Electron Beam Melting
H.P. TANG 0
M. QIAN 0
N. LIU 0
X.Z. ZHANG 0
G.Y. YANG 0
J. WANG 0
0 1.-State Key Laboratory of Porous Metal Materials, Northwestern Institute for Nonferrous Metal Research , Xi'an 710016 , China. 2.-School of Aerospace, Mechanical and Manufacturing Engineering, Centre for Additive Manufacturing, RMIT University , Melbourne, VIC 3001 , Australia. 3.-School of Materials and Metallurgy, Northeastern University , Shenyang 110819, China. 4.-
An advantage of the powder-bed-based metal additive manufacturing (AM) processes is that the powder can be reused. The powder reuse or recycling times directly affect the affordability of the additively manufactured parts, especially for the AM of titanium parts. This study examines the influence of powder reuse times on the characteristics of Ti-6Al-4V powder, including powder composition, particle size distribution (PSD), apparent density, tap density, flowability, and particle morphology. In addition, tensile samples were manufactured and evaluated with respect to powder reuse times and sample locations in the powder bed. The following findings were made from reusing the same batch of powder 21 times for AM by selective electron beam melting: (i) the oxygen (O) content increased progressively with increasing reuse times but both the Al content and the V content remained generally stable (a small decrease only); (ii) the powder became less spherical with increasing reuse times and some particles showed noticeable distortion and rough surfaces after being reused 16 times; (iii) the PSD became narrower and few satellite particles were observed after 11 times of reuse; (iv) reused powder showed improved flowability; and (v) reused powder showed no measurable undesired influence on the AM process and the samples exhibited highly consistent tensile properties, irrespective of their locations in the powder bed. The implications of these findings were discussed.
INTRODUCTION
Powder-bed-based metal additive manufacturing
(AM) processes build parts from melting and
solidification of metal powder layer by layer following a
digital computer-aided design (CAD) model. They
offer unrivaled advantages over conventional
subtractive manufacturing processes in terms of design
freedom, shape formation or creation, lead time
management, and materials utilization. The feedstock
metal powder materials, including their
characteristics and cost, play a critical role in determining the
quality, mechanical properties, surface finish, and
cost of the additively manufactured components. For
example, the flowability of the powder is expected to
affect the continuity and uniformity of each layer of
the powder spread on the powder bed and metal
(Published online February
5, 2015
)
powders with a higher tap density may favor the
formation of a higher density deposition layer. In an
effort toward standardizing the characteristics of
metal powders used for AM, the recently released
ASTM 3049-14 provides a standard guide for
characterizing metal powders for AM, including their
chemical composition, flow characteristics, size
distribution, morphology, and density.1
The cost affordability of additively manufactured
metal products has been a concern for their wider
acceptance. An advantage of the powder-bed AM
processes is that the powder can be reused. As a
result, the powder reuse times that are permitted
carry a significant influence on the average cost of
the additively manufactured products. In fact,
because of the high cost of the feedstock metal
powders used for AM, especially for the AM of
titanium (Ti) and Ti alloys, much effort has been
made to develop cost-effective or more affordable
metal powder materials suitable for AM.2–7 The
Arcam AM process (Arcam, Mo¨lndal, Sweden),
which has found applications in several sectors,8–10
builds metal parts based on selective electron beam
melting (SEBM) of metal powders layer by layer in a
high-vacuum environment. Unlike other
powderbed-based AM processes, the powder bed used in the
Arcam process can be set up to 1100 C, which is
necessary for the AM of some specialty materials
such as TiAl-based alloys. For the AM of Ti-6Al-4V
(wt.%), which is the most widely studied alloy, the
temperature of the powder bed is usually above
550 C. As a result, in each cycle, the Ti-6Al-4V
powder will be exposed to both preheating (650 C to
750 C) and prolonged thermal holding (above
550 C) in the powder bed in a high-vacuum
environment. This happens to all the powder particles in
the powder bed and more severely to the powder
close to the parts that are being built due to melting
(high temperature) and solidification (release of
latent heat). As powder reuse times increase, many
properties of the powder are expected to change,
including their chemical composition, surface
features (e.g., surface roughness and overall particle
roundness), and physical and thermal pr (...truncated)