September 21-24, 2008
CAESARS PALACE
Titanium2008
International Titanium Association
LAS VEGAS, NEVADA USA
Recent Advances of Titanium Alloy Powder Production by Ceramic-free Inert
Gas Atomization
Henrik Franz1, Laurenz Plöchl1, Dr.Frank-Peter Schimansky2
ALD Vacuum Technologies GmbH, Wilhelm-Rohn-Str.35, D-63450 Hanau, Germany
2
GKSS Research Center, Max-Planck-Str. 1, D-21502 Geestacht, Germany
1
ABSTRACT
CP-Ti and γ-TiAl barsticks have been atomized
by the ceramic-free Electrode Induction-melt
Inert Gas Atomization (EIGA) technique. To
date, the EIGA technique had been limited to
relatively small feedstock dimensions (ca. Ø5060mm) and relatively low melt flow rates (ca. 550 kg/h). In this work, the feedstock dimensions
and melt flow rates were significantly increased
(ca. triplicated). Steady-state process conditions
have been achieved at melt flow rates of up to
90 kg/h with feedstock dimensions of up to
Ø140mm. These achievements enable to utilize
titanium alloy VAR electrodes as feedstock for
the EIGA and to atomize titanium powder at
significantly lower specific gas consumption.
INTRODUCTION
Clean, spherical titanium alloy powder is used
for various novel powder metallurgical
processing routes such as Metal Injection
Molding (MIM), rapid prototyping by laser
sintering [1,2] as well as Hot Isostatic Pressing
(HIP) and subsequent hot forming in the medical
[3,4] and aerospace industries [5,6,7]. Typical
alloy grades are CP-Ti, TiAl6V4 and also
intermetallic γ-TiAl. Due to the reactivity and high
melting point of these alloys, only cold crucible
or
crucible-free
melting
techniques
in
combination with argon atomization can be
applied.
One technique capable of delivering the required
powder quality, fine powder yield and cost
efficiency is Electrode Induction-melt Inert Gas
Atomization (EIGA) [8]. Melt flow rates of up to
50 kg/h with electrode diameters up to 60mm
have been demonstrated with titanium [9]. The
present work aimed at further and significant
increase of the melt flow rate and electrode
diameter with the ultimate objective of making
the EIGA technique suitable for the utilization of
commercially available titanium alloy VAR
(Vacuum Arc Remelting) electrode feedstock,
which is available at significantly lower cost than
hot-forged titanium rods but only in diameters ≥
150mm (6 in.). Furthermore, the increase of the
melt-flow rate will lead to a proportional
decrease of the specific inert gas consumption
during atomization.
DESCRIPTION OF EIGA TECHNIQUE
Electrode Induction-melt Inert Gas Atomization
(EIGA) is a technique for powder manufacturing
by gas atomization. The process can be
conducted ceramic-free and is therefore
especially suited for reactive and refractory
metals/alloys (e.g. TiAl6V4, γ-TiAl).
The EIGA technique [8] is schematically shown
in fig. 1. The prealloyed electrode is immersed
into a conical induction coil. By induction of a
high-frequency electro-magnetic field into the
electrode tip, the latter is heated up to melting
temperature. The liquid metal flows downward
along the surface of the heated cone and falls
into a gas nozzle, were it is atomized using Ar
gas.
The melt droplets solidify during free fall in the
atomization tower, are separated from the Ar
gas in the downstream cyclone and collected
under Ar atmosphere in a vacuum-tight powder
can.
The
self-consuming
electrode
is
continuously fed downwards into the induction
coil by an electric drive system. Recent
developments [10,11] allow the utilization of a
bare, non-insulated copper coil without the
occurrence of spark discharge between the coil
and the electrode, thus providing a ceramic-free
atomization
technique
resulting
in
contamination-free powder.
EIGA process parameters which determine the
powder cost are:
page 1 of 4
September 21-24, 2008
CAESARS PALACE
fig.1 EIGA schematic, showing
conical induction coil, inert
gas nozzle, atomization
tower and powder
collection system
Titanium2008
International Titanium Association
LAS VEGAS, NEVADA USA
As a result of the present work, not only the
atomization conversion cost is further reduced
by further, significant increase of the melt flow
rate, but also the titanium feedstock cost itself is
addressed.
ATOMIZATION EXPERIMENTS
For up-scaling atomization experiments were
carried out with CP-Ti and γ-TiAl feedstock,
ranging between 60 and 150mm in diameter.
For each barstick diameter a dedicated, conical,
non-insulated copper induction coil was
manufactured. Fig.2 illustrates well the size-step
taken in the present work, showing the induction
coils for 40 and 120mm diameter, respectively.
fig.2
¾ cost of the feedstock material;
¾ melt flow rate [kg/h], [lb/min];
¾ specific Ar gas consumption (gas flow per
mass unit powder [Sm3/kg], [scf/lb]);
¾ powder yield of the useful fraction;
¾ amount of satellite formation (in most cases
well expressed by the powder tap density)
Since the Ar gas flow itself cannot be reduced
below a technical limit which is determined by
the adjustment of the gas nozzle gap and the
required gas nozzle aspiration pressure, recent
work [9] has focused on the increase of the melt
flow rate by design optimization of the
resonance circuit and induction coil, leading to a
directly proportional decrease of the specific gas
consumption without significant change of the
powder particle size distribution.
Conical induction coil for 40mm (left) and
150mm (right) electrode feedstock. Large coil
has non-insulated windings.
The LC-oscillating circuit of the EIGA equipment
was tuned to a frequency in the range of 150250 kHz and in such a way as to run the trials
just below the maximum admissible voltage of
the capacitor bank.
After switching on the HF-power, the melt
started to drop off the electrode tip usually within
1-2 min. For compensation of alignment
tolerances between the electrode and the coil as
well as of manufacturing tolerances of the coil
itself, the electrode was rotated at a slow speed
(ca. 5 rpm).
In order to achieve a continuous, steady-state
melt-flow, the vertical feed rate of the electrode
was gradually increased such as to keep the
immersion of the electrode tip into the coil
constant.
page 2 of 4
September 21-24, 2008
CAESARS PALACE
In all trials, the atomization gas pressure was
adjusted to 25 bar. Argon was used as
atomization gas. For each electrode a quantity
of 1500-2500g powder was atomized and
representative powder samples of 100-120g
were obtained by a sample divider. The powder
samples were characterized by sieve analysis
and the fine powder fraction (<45µm) was
determined.
RESULTS
Titanium2008
International Titanium Association
LAS VEGAS, NEVADA USA
The larger annular slit diameter for trials no.48 was chosen in order to provide the
alignment tolerances for the larger induction
coil diameter.
¾ Atomization of γ-TiAl electrodes resulted in a
better fine powder yield.
¾ In trial no.8, steady-state melt-flow was not
achieved due to EIGA equipment power
limits.
Table1 provides a summary of the atomization
trial conditions and results.
trial
no.
alloygrade
electrode
diameter [mm]
steady-state melt
flow rate [kg/h]
1
CP-Ti
60
80
2
CP-Ti
80
80
3
γ-TiAl
80
80
4
CP-Ti
100
80
5
CP-Ti
100
90
6
CP-Ti
120
80
7
γ-TiAl
140
60
8
CP-Ti
150
(60)
trial
no.
annular
slit dia.
[mm]
fine powder
yield <45µm
[wt%]
1
20
21.7
2
20
25.3
3
20
33.5
4
30
18.2
5
30
17.1
6
30
12.8
7
30
18.7
8
30
--
remark
fig.3 CP-Ti EIGA powder
A SEM image of the fine powder fraction of CPTi is shown in fig.3.
CONCLUSION / OUTLOOK
better fine powder
yield with TiAl
¾ Melt flow rates of up to 90 kg/h have been
demonstrated with the EIGA technique, using
electrode diameters up to 150mm of CP-Ti
and γ-TiAl.
¾ A continuous, steady-state melt flow was
achieved.
better fine powder
yield with TiAl
steady-state not
reached
table 1 atomization trial results
¾ A continuous melt flow at the electrode tip
could be established in all trials, also with
larger electrode diameters.
¾ This represents approximately a tripling of the
melt flow rate and corresponding cutting in
three of the specific Ar consumption
compared to the previous status.
¾ With the other atomization parameters being
the same, better fine powder yields could be
obtained with γ-TiAl compared to CP-Ti. This
is probably caused by different physical
properties of both alloy melts (such as melting
point, surface tension, melt viscosity).
¾ The fine powder yield is generally lower for
the larger electrode diameters ≥100 mm
because of the utilization of a larger gas
nozzle annular slit diameter.
page 3 of 4
September 21-24, 2008
CAESARS PALACE
¾ The utilization of 140-150mm electrode
diameter
represents
a
qualitative
breakthrough, allowing for the first time to use
titanium alloy VAR electrode feedstock
directly (instead of hot-forged rod material),
which is available more readily and at lower
cost.
REFERENCES
[1]
N. Calder, M. Hedges, “Near Net Shape
Rapid Manufacture and Repair by LENS”,
AVT-139 Specialists Meeting on Cost
Effective Manufacturing via Net-Shape
Processing, Amsterdam, The Netherlands,
15-17 May 2006
[2]
M. Hedges, R.Grylls, Euro-uRapid 2007
Conference Proceedings
[3]
W. Limberg, E. Aust, T. Ebel, R. Gerling
and B. Oger, Euro PM 2004 Conference
Proceedings, Eds. H. Danninger, R. Ratzi,
EPMA, Shrewsbury, UK, 2004, Vol. 4, p.
457.
[4]
C. Over, W. Meiners, K. Wissenbach and
R. Poprawe, Ti – 2003, Science and
Technology, Eds. G. Lütjering and J.
Albrecht,WILEY- VCH, Weinheim 2004,
Vol. I, p. 525.
[5]
D. Furrer and R. Boyer, Ti – 2003, Science
and Technology, Eds. G. Lütjering and J.
Albrecht,WILEY- VCH, Weinheim 2004,
Vol. I, p. 549.
[6]
R. Gerling, A. Bartels, H. Clemens, H.
Kestler, F. P. Schimansky, Intermetallics,
Vol. 12 (2004), p. 275.
[7]
S. Bystrzanowski, A. Bartels, H. Clemens,
R. Gerling, F.P. Schimansky, G. Dehm, M.
Weller and H. Kestler, Intermetallics Vol.
13 (2005), p. 515.
[8]
M. Hohmann and N. Ludwig, German
Patent DE 4102 101 A1,1991.
[9]
R. Gerling, M. Hohmann, F. P.
Schimansky, Thermec 2006, Materials
Science Forum Vols 539-543 (2007)
pp.2693-2698
Titanium2008
International Titanium Association
LAS VEGAS, NEVADA USA
[11] R. Gerling and F. P. Schimansky, Euro PM
2004 Conference Proceedings, Eds. H.
Danninger, R. Ratzi, EPMA, Shrewsbury,
UK, 2004, Vol. 1, p. 77.
[12] G.
Wegmann,
R.
Gerling,
F.P.
Schimansky, Acta Materialia, Vol.51
(2003),pp. 741-752
CONTACT
Henrik Franz
ALD Vacuum Technologies GmbH
Wilhelm-Rohn-Str.35
D-63450 Hanau / Germany
Tel.+49 (6181) 307 – 3419
[email protected]
http://web.ald-vt.de/cms/
Laurenz Plöchl
ALD Vacuum Technologies GmbH
Wilhelm-Rohn-Str.35
D-63450 Hanau
Tel.+49 (6181) 307 – 3282
[email protected]
http://web.ald-vt.de/cms/
Dr.Frank-Peter Schimansky
GKSS Research Center
Max-Planck-Str. 1
D-21502 Geestacht / Germany
Tel. +49 (4152) 87 – 2513
[email protected]
[10] S. Pleier, M. Hohmann, W. Goy and B.
Schaub, Euro PM 2004 Conference
Proceedings, Eds. H. Danninger, R. Ratzi,
EPMA, Shrewsbury, UK, 2004, Vol. 1, p.
89.
page 4 of 4
Recent Advances of Titanium Alloy Powder
Production by Ceramic
Ceramic--free Inert Gas Atomization
Henrik Franz1,a, Laurenz Plöchl1,b, Dr.FrankDr.Frank-Peter Schimansky2,c
1 ALD Vacuum Technologies GmbH, WilhelmWilhelm-Rohn
Rohn--Str.35, D
D--63450 Hanau, Germany
2 GKSS Research Center, MaxMax-Planck
Planck--Str. 1, D
D--21502 Geestacht, Germany
a [email protected],
henrik franz@ald-vt de, b [email protected],
laurenz ploechl@ald-vt de, c [email protected]
frank-peter schimansky@gkss de
Recent Advances of Titanium Alloy Powder
Production by Ceramic
Ceramic--free Inert Gas Atomization
Presentation Contents
„ Description of EIGA Atomization Process
„ Previous Status and Limits - „Large EIGA“ Development Objectives
„ Atomization Experiments
„ Results
„ Conclusion and Outlook
Recent Advances of Titanium Alloy Powder
Production by Ceramic
Ceramic--free Inert Gas Atomization
„ Description of EIGA Atomization Process
„
„
„
„
„
„
Frequency
Voltage
Current
Rotational Speed
Vertical Feed
Coil Immersion Depth
of Melt Power
of Electrode
HF EM
EM--field (ca.200 kHz)
… to match
„ Physical Properties
„ Drip/Melt Flow Behavior
electrode tip temperature field
of Feedstock Material
(Electrode)
drip melting
electrode tip
Recent Advances of Titanium Alloy Powder
Production by Ceramic
Ceramic--free Inert Gas Atomization
„ Description of EIGA Atomization Process
EIGA: Electrode Induction
nduction--melt Inert Gas Atomization
Recent Advances of Titanium Alloy Powder
Production by Ceramic
Ceramic--free Inert Gas Atomization
„ Description of EIGA Atomization Process
EIGA Characteristics
„ suitable for all metallic materials
„ … and especially for reactive, refractory and
precious
i
metal
t l alloys
ll
(Ti,
(Ti Zr,
Z Hf,
Hf V,
V Cr,
C Nb,
Nb Mo,
M Pt)
„ d50 usually > 60µm (free(free-fall atomizing system)
„ spherical powder
„ super
super--clean powder, no ceramic inclusions from
melting process
„ Batch process with quick electrode changechange-over
(few minutes)
Example Particle Size Distributions of EIGA powder
100
Cum
m. Volume Percen
ntage [%]
90
Ti-Alloy, Ø 60 mm
80
Stainless Steel, Ø 45/65 mm
70
Ti-Alloy, Ø 45 mm
60
Niobium-Alloy, Ø 35 mm
50
40
30
20
10
0
1
10
100
Particle Diameter [μ m]
TiAl6V4 EIGA powder (fraction <45µm)
1000
Recent Advances of Titanium Alloy Powder
Production by Ceramic
Ceramic--free Inert Gas Atomization
Previous Status and Limits
„ atomization rate ≤ 50 kg/h
„ batch (electrode) weight ranging from 5 to 50kg, depending on
alloy mass density
„ specific inert gas consumption approx. 10 Sm3/kg
… „Large“ EIGA Development Objectives
„ Increase significantly the electrode diameter
„ Thereby increase significantly the metal flow rate
„ Thereby significantly decrease the specific inert
gas consumption
due to limited coil size and
electrode diameter
40mm Ti electrode
120mm Ti electrode
Recent Advances of Titanium Alloy Powder
Production by Ceramic
Ceramic--free Inert Gas Atomization
Atomization Experiments
„ Fabrication of large diameter conical induction coils
(non--insulated copper coils Æ ceramic completely eliminated)
(non
„ Set proper process parameters (U, I, electrode tip immersion into coil)
depending on electrode diameter for meltmelt-flow start
start--up
„ Achieve and uphold steadysteady-state meltmelt-flow
(steady-state is characterized by stabilization/constant values of U, I and electrode
(steadytip immersion in dynamic equilibrium with vertical electrode feed rate)
„ Atomization of Ø60, Ø80, Ø100, Ø120, Ø150 mm CP
CP--Ti electrodes
(For each electrode diameter a dedicated conical induction coil was fabricated.)
„ Atomization of Ø80, Ø140 mm γ-TiAl electrodes
„ Production of 15001500-2500g powder per atomization batch
„ Division into representative samples of 100
100--120g
„ Sieve analysis – determination of fine powder fraction <45µm
>> Movie Clip Ø100mm CPCP-Ti
Recent Advances of Titanium Alloy Powder
Production by Ceramic
Ceramic--free Inert Gas Atomization
„ Results
trial
no.
electrode
Ø [mm]
alloy
y
g (Ar)
gas
( )
pressure
[bar]
steady-state
y
melt
flow rate [kg/h]
g nozzle
gas
annular slit
diam. [mm]
fine powder
fraction
<45µm (wt%)
1
60
CP-Ti
25
80
20
21.7
2
80
CP-Ti
25
80
20
25.3
3
80
γ-TiAl
25
80
20
33.5
4
100
CP-Ti
25
80
30
18.2
5
100
CP-Ti
25
90
30
17.1
6
120
CP-Ti
25
80
30
12.8
7
140
γ-TiAl
25
60
30
18.7
better fine powder yield for TiAl
8
150
CP-Ti
25
(60)
30
--
steady-state not reached due to
equipment power limit
remark
better fine powder yield for TiAl
Recent Advances of Titanium Alloy Powder
Production by Ceramic
Ceramic--free Inert Gas Atomization
„ Results
„ A continuous melt flow at the electrode tip could be
established in all trials, also with larger electrode diameters.
„ The fine powder yield is generally lower for the larger
electrode diameters ≥100 mm because of the utilization of a
larger gas nozzle annular slit diameter.
„ The larger annular slit diameter for trials no.4-8 was chosen
in order to provide the alignment tolerances for the larger
induction coil diameter.
„ Atomization of γ-TiAl electrodes resulted in a better fine
powder yield.
„ In trial no.8, steady-state melt-flow was not achieved due to
EIGA equipment power limits.
CP--Ti EIGA powder
CP
Recent Advances of Titanium Alloy Powder
Production by Ceramic
Ceramic--free Inert Gas Atomization
Conclusion and Outlook
„ Melt flow rates of up to 90 kg/h have been demonstrated with the EIGA technique, using electrode
diameters up to 150mm of CP-Ti and γ-TiAl.
„ A continuous, steady-state melt flow was achieved.
„ This represents approximately a tripling of the melt flow rate and corresponding cutting in three of the
specific Ar consumption compared to the previous status.
„ With the other atomization parameters being the same, better fine powder yields could be obtained with
γγ-TiAl compared
p
to CP-Ti. This is p
probably
y caused by
y different p
physical
y
p
properties
p
of both alloy
y melts
(such as melting point, surface tension, melt viscosity).
„ The utilization of 140-150mm electrode diameter represents a qualitative breakthrough, allowing for the
first time to use titanium alloy VAR electrode feedstock directly (instead of hot-forged rod material),
which is available more readily and at lower cost.