A wide range of Metal Additive Manufacturing (MAM) technologies are becoming available. One of the challenges in using new technologies for aerospace systems is demonstrating that the process and system has the ability to manufacture components that meet the high quality requirements on a statistically significant basis. The widest-used system for small to medium sized components is the ARCAM system manufactured in Gothenburg, Sweden. This system features a 4kW electron-beam gun, and has a chamber volume of 250mm long x 250mm wide x 250mm to 400mm tall. This paper will describe the basis for the quality and consistency requirements, the experimental and evaluation procedures used for the evaluation, and an analysis of the results for Ti-6Al-4V

Gilley, Scott

Good, James

McLemore, Carole

Slattery, Kevin

Slaughter, Blake

Speorl, Emily

NASA Technical Reports Server

2nd SAlAS Symposium, 14-16 September 2008, Stellenbosch, South Africa
EVALUATION OF ARCAM DEPOSITED TI-6AL-4V
Kevin Slattery!, Blake Slaughter2, Emily Speore, James Good4, Scott Gilley5and Carole
McLemore6
1 Boeing - Phantom Works
Saint Louis, MO, USA
kevin.t.slattery@boeing.com
2 Boeing - Phantom Works
Saint Louis, MO, USAz
blake.slaughter@boeing.com
3 Boeing - Phantom Works
Saint Louis, MO, USA
emily.j.speorl@boeing.com
4 Teledyne Brown Engineering - Marshall Space Flight Center
Huntsville, AL, USA
Jim.Good@tbe.com
5 Tecmasters - Marshall Space Flight Center
Huntsville, AL, USA
sgilley@techmasters.com
6 NASA - Marshall Space Flight Center
Huntsville, AL, USA
Carole.A.McLemore@nasa.gov
ABSTRACT
A wide range of Metal Additive Manufacturing (MAM) technologies are becoming available.
One of the challenges in using new technologies for aerospace systems is demonstrating that
the process and system has the ability to manufacture components that meet the high quality
requirements on a statistically significant basis.
The widest-used system for small to medium sized components is the ARCAM system
manufactured in Gothenburg, Sweden. This system features a 4kW electron-beam gun, and
has a chamber volume of 250mm long x 250mm wide x 250mm to 400mm tall.
This paper will describe the basis for the quality and consistency requirements, the
experimental and evaluation procedures used for the evaluation, and an analysis of the results
for Ti-6AI-4V.
https://ntrs.nasa.gov/search.jsp?R=20090007714 2019-08-30T06:16:54+00:00Z
I2nd SAlAS Symposium, 14-16 September 2008, Stellenbosch, South Africa
1 INTRODUCTION AND BACKGROUND
While its high strength, low density, and outstanding corrosion resistance make titanium is the
material of choice for a wide variety of applications, especially in aerospace; the high cost of
mill products and machining are obstacles in providing lower-cost aircraft. While many parts
are machined from solid mill products, others are made from closed die forgings. The long
lead times needed for die design and fabrication makes it difficult to optimize design and
build the components on time.
Metal Additive Manufacturing processes have the potential to reduce both the material usage,
cost, and lead time needed to make metallic components. These processes consists of using
software to guide an energy beam to build a net or near-net component in a layerwise fashion,
as shown in Figure 1. Over 20 of these processes have been developed or proposed
throughout the world. Some processes inject powder into a molten puddle, others use a
powder bed, and still others feed a wire into the molten puddle. The majority of the work
performed to date has been on Ti-6AI-4V because of its high cost, and wide application in
aerospace.
Adjacent Passes
Previous Layer
of Passes
Figure 1: Metal Additive Manufacturing
While the Laser Additive Manufacturing (LAM) process was successfully implemented by
Boeing on several aircraft, the company commercializing it in the United States, AeroMet,
was shut down by its parent company. One thing that was gained out of the development and
implementation of the LAM process, however, was an extensive material property database
and product quality standards. The result is that a material specification with chemistry, heat
treat, and quality assurance provisions has been drafted. This draft specification, known as
AMS 4999A, not only contains the usual part minimum tensile property requirements, but
also the mechanical property requirements for process and supplier qualification, and process
parameter qualification. This enables use of multiple processes and feedstocks, and enables
suppliers to perform one set of tests to be approved by multiple Original Equipment
Manufacturers.
One of the best selling Metal Additive Manufacturing machines is made by Arcam in
Sweden. In excess of 20 of these machines have been sold worldwide. The purpose of this
work was to see if the ARCAM system was capable of making parts that meet the
requirements for qualification to the draft revision to AMS 4999. This work was performed
jointly by Boeing and NASA-Huntsville.
2nd SAlAS Symposium, 14-16 September 2008, Stellenbosch, South Africa
2 DESCRIPTION OF ARCAM SYSTEM
The Arcam process is a powder-bed based layered - or additive - manufacturing process. The
process uniquely utilizes an electron beam as an energy source. A wide variety of materials
have been processed on the Arcam system. The nature and efficiency of the electron beam's
interaction enables the processing of many difficult materials from aluminum to tungsten.
Vaporization of lower melt point alloying elements is often more of a concern than the ability
to melt the base material, due to the vacuum environment. The environment also provides
some advantages in eliminating residual stress, because of the temperature and dwell time of
builds.
Arcam's first offering, the S12, featured basic functions, and is a good representation of the
technology. Recently, the company has begun offering the A2. The A2 offers a taller build
chamber, improved process monitoring, and process stabilization techniques. The A2 process
improvements - available to some extent as an upgrade for the S12 - should be a welcome
improvement for those focusing on production applications.
3 TEST PROCEDURE AND MATRIX
The test program involved fabrication of eight bulk specimens on each of two separate but
identical design EBM systems per Table 1. One system was located at the NASA Marshall
Space Flight Center in Huntsville, AL and the other at Boeing Phantom Works in St. Louis,
MO. Specimens in the as-built condition directly from the systems were compared to those
post-treated by the Hot Isostatic Press (HIP) process as shown in the first two rows of Table 1.
The lower part of the table shows that the test plan included four different powder feedstock
lots to investigate multiple lot effects. The powder lots were first utilized in the Boeing
sample builds and then transferred to the NASA system for fabrication of the same geometries
with identical process settings. .
Table 1- Bulk S eelmen Test Matrix
Bulk Specimen Treatment Condition
A - As-Built, H - HIP Post-Processed
S32 S4 S413
NfDD!!;~~f~~~aiiiiiiiiliiiiiiiiiiiiii H
J~e~"""D¥.i~~~JJJ~JJtcJ~;;";D;"D;DfJWJW~~
System,
Powder,
Lot IDt
Boein Powder .. 87·:
I. All powder lots were Plasma Rotating Electrode Processed (PREP) per AMS 4999.
2. S3 comprised two mirrored features in the same build. Prior to NASA S3 coupon extractions, one half was HIPed and the
other was as-built.
3. Specimen S4I was a grouping of individual coupons arranged in the same build orientation as that for the S4 bulk
specimen.
HIP treatment was performed on the indicated bulk specimens in Table 1 prior to coupon
extraction. This was carried out under pressure greater than 100 MPa at a temperature range
of 899°C to 954°C for 2 to 4 hours, and cooled under inert atmosphere to below 427°C.
Subsequent stress relief was not performed for the test results presented herein.
The test plan involved extraction of over 300 individual test coupons out of the bulk
specimens via machining in the three main axis directions X, Y and Z. The test coupons
included tensile, strain-life, fatigue crack growth, and short bar fracture toughness as shown in
Table 2. Note that two sets of all the tests shown were performed since each fabrication
f2nd SAlAS Symposium, 14-16 September 2008, Stellenbosch, South Africa
system produced one set. Chemical analyses were performed on the coupons as well as pre-
build and post-build powder feedstock samples to assess compositions relative to
specification limits. These also assessed oxygen build-up or loss of alloy elements during any
single build and after multiple fabrication runs.
T MI CT bl " Sa e - ample oupon est atr x
Test Type
Bulk Specimen Identification
SI S21 S3 S4 S4I S5 S6 S7_.
... -
-
.. -_.- _.-
-_.__. f-----
--- - -Tensile 24 30 12 21 21 24 15 36
Strain-Life 9 12 0 0 0 3 0 0
da/dN 0 1 1 0 0 0 0 0
Toughness 0 0 3 0 0 0 3 0
Chemical2 3 3 4 3 4 3 4 5
I. Boemg 52 bulk specImen was not completed m tIme for testIng.
2. Boeing powder feedstock was not tested.
Tensile testing was performed per ASTM E8 with strain rate maintained within 0.003 to 0.007
mm/mrn/minute through the yield strength and then increased so as to produce failure in
approximately one additional minute. Strain-life fatigue testing was in accordance with
ASTM E606 with R = -1 and Rmax = 0.005. Fatigue coupons were tested per ASTM E606-04
using a triangular waveform at a frequency of 30 cycles per minute with an R ratio of -1.0
and a maximum strain of 0.5%. Failure was defined as the point where the maximum stress
decreased to 50% of the maximum stress at the 100th cycle. Fracture toughness was assessed
per ASTM E1304 for short fracture bars. Chemical composition analyses were performed on
extracted coupons and powder feedstock in accordance with AMS 4911 L.
4 MICROGRAPHIC TEST RESULTS
The thirteen (13) parts were successfully fabricated, with some of the larger parts taking up to
40 hours to build. One of these parts is shown in Figure 2. Figure 3 shows the columnar
microstructure typical of deposits in the ARCAM system, and many other MAM processes.
Figure 4 shows the fine Widmanstatten structure also typical of these processes, where the
material cools rapidly across the B-transus. Nothing atypical was observed in the
microstructures.
Figure 2: Part S7
(Hole Diameter is 25mm)
Figure 3 - Typical Cross-
Section - 13mm Wide
1OOxt-so ~mJJJN
~ ==~....... ~i~~~~
Figure 4: Typ Microstructure
2nd SAlAS Symposium, 14-16 September 2008, Stellenbosch, South Africa
5 MECHANICAL TEST RESULTS AND ANALYSIS
The mixture of powder heats, heat treatments, and machines used enabled analysis of the
variables in a variety of ways
In this study 335 tensile coupons were harvested from 13 components produced on two
separate Arcam S12 machines. Some of the produced coupons come from hot isostatically
pressed (HIP'ed) material, and the remainder were produced from material in the "as-
deposited" condition. Of the coupons produced, roughly 9% of the coupons were suspected -
and verified - to have lack of fusion conditions. Of these coupons, only one coupon came
from HIP'ed material. These coupons have been excluded from the data analysis, and the
parts will be replaced at a later date for evaluation per AMS 4999.
Table III: Test Result Summa
Hot Isostatically As Deposited Specimens·
Criteria Direction Pressed· All Excluding Those with Draft AMS 4999A
S eclmens Detectable Lack of Fusion
Minimum X 1031 1032 130
Y 931 917 130UTS (MPa) Z 928 968 125
Coefficient X 0.55 0.85 3.3
of Variation Y 0.91 3.3
for UTS (%) Z 2.96 3.3
Minimum X 927 116
YS (MPa) Y 820 116Z 836 110
Coefficient X 1.48 3.1
of Variation Y 1.06 3.1
for YS (%) Z 2.76 2.23 3.1
Minimum X 14 10 6
Elongation Y 13 10 6
(%) Z 16 6 6
With respect to Boeing deposited material which received HIP treatment, the material meets
the requirements of AMS 4999 with the exception of a Coefficient of Variation (CV) for the Z
direction of 3.4% YTS (3.1 % is allowed) and 3.5% UTS (3.3% is allowed). The CV values of
coupons taken from the same component are less than 1%. However, the mean values of YS
and UTS are significantly different for the two components. When the populations are
combined the collective CV grows out of spec. Boeing material which was not HIP
processed, meets the requirements of AMS 4999 in the Y and Z directions for minimum
tensile values. However, the Y oriented coupons have a CV higher than is allowed by the
specification. As with the HIP treated material, CV within components is very minimal, but
the difference in mean values across the components causes the failure. Z orientation coupons
meet requirements of AMS 4999.
NASA material in the HIP'ed condition met all requirements of AMS 4999 in the Y and Z
directions. Because of the selection of components, no X orientation components were
HIP'ed in this study. These coupons met the requirements of AMS 4999 before any lack of
fusion coupons where removed. NASA "as-deposited" material met the requirements of
AMS 4999 in the X, Y, Z directions once coupons with detectable lack-of-fusion were
removed from the population.
2nd SAlAS Symposium, 14-16 September 2008, Stellenbosch, South Africa
Low Cycle Fatigue (LCF) results for the material confirm an expected increase in sensitive to
lack-of-fusion conditions. All coupons which failed to meet AMS 4999 where from material
in the as-deposited condition. If the coupons with detectable levels of lack-of-fusion are
removed from the population, the remaining material meets AMS 4999 with a mean value of
35,653 cycles at failure, well above the criteria If 15,000 cycles.
All Boeing and NASA fracture toughness samples met the requirements of AMS 4999. As a
result no coupons were removed from the population or examined for lack-of-fusion
conditions.
Additional coupon testing is needed to increase statistical significance. However, based on
current available data, material which is HIP processed will meet requirements of AMS 4999.
Material in the as-deposited state - while comfortably above minimum values - suffers from
scatter in some cases. This scatter may be addressable or acceptable. Until process maturity
improves, the use of as-deposited material may be practically and economically infeasible in
most aerospace applications. The presence of lack-of-fusion in as-deposited material places a
great deal of pressure on NDT evaluation to detect unacceptable flaws. The presence of these
defects would also cause high scrap rates for components. It should be pointed out that
processing parameters for individual components can be customized to improve the quality of
as-deposited material on a case-by-case basis.
6 FRACTOGRAPHY
Fractographic methods are often used to determine crack growth behavior and locations of
premature fracture. Using destructive and non destructive testing methods enables the
identification of lack of fusion in the tensile and fatigue coupons. Regions that contain lack of
fusion exhibit gaps of air between the particle spheres, which facilitate crack growth and are
the location of failure during tensile and fatigue testing in the X, Y, and Z coordinates.
Testing of the coupons involved over 300 specimens from Boeing and NASA, with less than
40 containing noticeable lack of fusion that likely led to premature failure. In the majority of
specimens viewed, lack of fusion is very apparent and characterized by the spherical dimples
left in the metallic surface. Lack of fusion would have been determined via x-ray
metallographic techniques for lack of fusion greater than 2% of total thickness or via dye
penetrant testing up to 0.050 mm deep.
Figure 5: V-direction tensile coupon
containing significant lack of fusion
'"Figure 6: Close up of lack of fusion in
fatigue coupon in the X-direction
2nd SAlAS Symposium, 14-16 September 2008, Stellenbosch, South Africa
0.635 mmldiv
Figure 7: Spherical lack of fusion In Y-dlrectlon Figure 8: Z-dlrectlon lack of fusion in tensile
coupon
7 CONCLUSIONS
Ti-6AI-4V components produced on the Arcam system are capable of meeting the
requirements of the proposed Revision A to AMS 4999, when the part receives Hot Isostatic
Pressing.
The lack of fusion that does occur in the Arcam system is of a size that can be detected with
standard aerospace inspection methods.
8 obCl~bkaATflkp
The root cause of the lack of fusion should be investigated and corrected.
Additional parts should be made and tested to replace those containing lack of fusion, and the
results re-compiled.


Evaluation of ARCAM Deposited Ti-6Al-4V

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