technical trends
A breakthrough in
high-conductivity
PM copper
In his ongoing review of papers presented at PowderMet
2013, MPR consulting editor Joe Capus takes a look at
advancements in powder metallurgy copper and the
implications for electrical applications.
R
ichard Phillips, president of
Engineered Pressed Materials
(EPM), St Marys, PA, is
a modern-day inventorentrepreneur and well known for his
expertise in high density PM developments. At the Chicago PowderMet 2013
conference he gave details of his latest
success in achieving ultra-high sintered
densities with pure copper powder in
components intended for use where high
electrical conductivity was essential for
the application [1]. Using proprietary
processing steps he is able to reach sintered densities above 98% of theoretical, with strength and electrical conductivity competitive with wrought copper.
While much of the current drive
towards full density in the PM industry
has been focused on ferrous materials
and automotive applications, Phillips
has, in addition, turned his attention to
a relatively neglected sector – high-conductivity pure copper, with the potential
to replace wrought and cast components in electrical applications. The
excellent electrical conductivity of pure
copper explains its widespread use for
cables and electrical contacts. Copper’s
high thermal conductivity also finds
application in many areas such as home
heating systems, solar panels, photovoltaic cells, etc. To meet the requirements of such applications and compete
with wrought or cast copper, PM components need to be processed to at least
95% of the theoretical density (8.96 g/
cm³) This level is extremely difficult
to reach with conventional press-andsinter PM, requiring expensive multiple
steps. Phillips referred to traditional
press, pre-sinter, re-press, sinter, followed by coining as yielding densities
only in the 91-93% range, while hightonnage pressing can produce laminations on ejection and other problems
in de-lubrication. In EPM’s process,
Phillips uses conventional water-atomised, minus 100 mesh copper powder
and coats the surfaces of the particles
by dry-blending with proprietary additives that provide lubrication and
sintering activation. After room temperature compaction followed by sintering
in hydrogen or vacuum, the densities
obtained are ­typically above 96% of
theoretical, and in most cases meeting a
minimum of 97.5%.
A comparison of the mechanical and
electrical conductivity properties of EPM
pressed-and-sintered PM copper with
those of wrought and cast components
is given in Table 1. Results show that
Phillips’ PM route can achieve comparable strength and identical electrical conductivity. Microstructural examination
showed the PM samples to have very
fine uniform porosity and non-directional grain structures compared with the
casting (more porosity and larger grains)
and wrought bus bar (directional grain
orientation and properties due to the
processing method). The PM density fell
between those of the wrought and the
cast components. Figure 1 shows EPM
copper parts before and after sintering
and after ­re-pressing. The large shrinkage during sintering allows the parts to
Table 1. Mechanical Properties and Electrical Conductivity of EPM Sintered Copper Samples Compared with Wrought and
Cast Copper (After Phillips)
Property
As sintered PM
Re-pressed PM
Sand casting
Annealed wrought Bus bar wrought
UTS, MPa
214
297
172
220
283
YS, MPa
62
248
62
69
241
El., %
48
14
40
45
14
Hardness, HRF
18
81
24
40
84
Density, % theoretical
98.7
99.0
97.7
99.6
99.2
Elect. Cond., % IACS
100
101
97
101
99
16
MPR November/December 2013
0026-0657/13 ©2013 Elsevier Ltd. All rights reserved
Figure 1. EPM copper parts: As compacted; as sintered; and as repressed. (After Phillips)
be replaced in the compacting tools for
re-pressing. Figure 2 shows silver-plated
EPM copper parts for high-voltage antiarcing contactors.
In conversation subsequent to his
presentation, Phillips mentioned that
high density copper PM parts are
already in production at Engineered
Sintered Materials, and that others were
in the process of field testing. EPM is
actively quoting for new items in the
80,000-150,000 unit volume range,
Project1_Layout 1 1/16/2013 11:57 AM Page 1
while three other PM companies were
said to be interested in licencing arrangements. Phillips indicated that there were
Figure 2. EPM copper parts: Silver-plated copper high-voltage
­anti-arcing contactors. (After Phillips)
a large number of copper components
in the electrical and thermal conductivity application sectors that are not easily processed by extrusion, casting, or
from rolled stock that would make good
candidates for EPM’s PM process. The
PM process also minimises the need for
machining and its inherent difficulties
in the case of pure copper, such as galling. Besides the electrical sector, Phillips
sees applications in chemical processing,
environmental developments, as well as
in heating and cooling. “New interest
is [also] appearing in the medical field
for bacterial resistant items”. All in all,
Phillips and his company appear to have
chalked up another breakthrough in
advanced PM technology and breathed
new life into a relatively neglected sector
of the PM industry.
References
1. Richard R. Phillips, “Powder
Metallurgical Copper Technology
for Thermal and Electrical
Conductivity”, Advances in
Powder Metallurgy and Particulate
Materials—2013, Part 10, pp.14-23,
MPIF/APMI, Princeton, NJ, USA.
Metal Powder Report
Wants Your Technical Papers!
Among the topics/areas to be explored in 2013:
• Alloys
• Metal Injection Moulding
• Refractory/Hardmetals
• Ferrous & Non-Ferrous Powders
• Pressing
• Sintering
• End-User Case Studies
Please submit abstracts or
deadline inquiries to
Reginald Tucker, editor, at
[email protected]
metal-powder.net
November/December 2013 MPR
17