Silver–Nickel
Contact Materials is a very popular type of contact material used
worldwide, and especially in Europe.
Many
customers of LML metal choose this type of contact material.
These
are powder metallurgical contact
materials
since silver and nickel have virtually no mutual solubility. This
makes them
somewhat
analogous to tungsten–silver except the nickel is used in much
lower percentages
similar
in volume percentage to the oxide level in silver metal oxides. The
sintering
is
done in the solid state and the process options for making these
materials are similar to
those
used for powder metallurgical silver metal oxides. The conductivity
varies with the
volume
percentage of silver since there is no decrease in the silver
conductivity from alloying.
Like
powder metallurgical silver metal oxides silver–nickel contacts can
be made by
pressing,
sintering, and coining individual parts or by wrought powder methods
involving
sintering
a billet followed by extrusion or alternative forming methods. The
wrought
method
produces fully dense materials, free of porosity. The particle size
distribution of
silver–nickel
contacts can be varied greatly by the powder metallurgical processes
used
for
making the powders and blending the powders. The nickel particle
shape can also be
varied
for these materials by variances in starting powder combined with
different wire
and
strip forming techniques.
A
study of the particle size and shape effect on electrical erosion was
done by Behrens
et al.
[130]. They tested materials which varied in particle size from
submicron to over
100
μm). They also had materials which had nickel fibers perpendicular
to the contact face
and
parallel to the face. The tests were conducted for break only at 115
A and 220 V ac AC-4
testing.
The results showed no correlation for erosion with particle size. The
orientation also
only
made a difference for the initial part of the testing until an
equilibrium layer of silver
nickel
melt material had been established on the contact face. They
concluded that silver–
nickel
is a unique material since it establishes a nickel particle
distribution on the surface
as a
result of nickel melting and dissolving in the silver to a small
extent during arcing and
then
re-
precipitating
on the surface. Therefore, regardless of the starting microstructure
the
surface
melt layer microstructure is similar for a given arcing condition. It
must be kept in
mind
that this study was limited to break erosion only and since the make
erosion process
is
different these conclusions cannot be extrapolated to make and break
results.
Balme
et al. compared three silver nickel materials and both fine silver
and silver metal
oxide
materials [131]. The testing was done in an automotive relay with
relatively high contact
force,
2 N, for lamp loads with over 100 A inrush current on closing. The
results were
reported
in terms of contact resistance after endurance welding, and sticking
that occurred
during
testing. For welding resistance all three silver nickel grades,
10–40% nickel, showed
make
welding resistance slightly better than fine silver but significantly
inferior to the silver
metal
oxide grades. With regard to contact resistance, the 90/10 Ag/Ni
material was
just a
little higher than fine silver but the 30% and 40% nickel grades were
significantly
higher
and similar to the silver metal oxide materials. Leung and Lee tested
silver–nickel in
automotive
relays and compared a 90/10 material to silver–tin oxide and
silver–copper contacts.
They
found that the silver–nickel was intermediate for contact
resistance with silver–copper
and
silver–tin oxide, but showed a higher amount of material transfer
than either of
the
other two materials [58]. One of the reasons silver–nickel is very
popular is that it can be
directly
welded onto copper substrates from wire. This lowers the contact
assembly costs.
This
same advantage for fabrication is a disadvantage for limiting
applications where the
high
currents cause contact welding in a device. Depending on the device
and type of load
silver–nickel materials work best in devices not exceeding currents of 50–100 A.
Consists of silver–nickel contacts see below:
