2910 Harvard Avenue, Cleveland, OH 44106-3010,
Telephone216 441-4900, Fax 216 441-1377
Glenn 0. Mallory
ElectrolessTechnologiesCorporation
LosAngeles, California 90008
Dr. Gary W. Loar and Dale G. Block
McGean-Rohco, Inc.
Cleveland, Ohio 44105
INTRODUCTION
Electroless Nickel (EN) plating is used in many applications where wearability is necessary. In November
of 1995, an EN bath which deposited a nickel-phosphorus alloy with excellent as-plated hardness and
wearability was presented’. This deposit (Deposit I-I) in some cases could be used as a replacement for
chromium plating because of its excellent wearability. Prior art required that an EN deposit be heat
treated to achieve high hardness and wearability where typical heat treatments are performed at 400 0C
for 1 hour. As a result of this new deposit, heat treatment to achieve the desired hardness and/or
wearability may not be necessary. If greater hardness is required then Deposit H can be heat treated to
increase the hardness of the deposit to 1000 + 50 HV1OO. This paper discusses further studies of this new
EN system and the early results of trials in production.
DESCRIPTION OF DEPOSIT H
The most important property which we are trying to achieve with Deposit H is wear resistance. In many
cases, hardness can be used as a guide to the wear resistance but hardness alone should not be used as the
sole factor when determining wearability. The data in this section are mostly hardness data which are
used for trend identification as related to bath properties. The trends found in this section are then used to
investigate wearability in the next section.
Bath Operation
The deposit H bath operates under fairly normal EN plating conditions. The optimum operating
conditions as well as the range of variables are given in Table 1.
Table I. Operating Parameters for Deposit H EN Bath
Nickel Concentration g/l
Additive H Concentration %
PH
Temperature 0F
Bath Loading ft2/gal
Metal Turn Overs (MTO)
Agitation
Filtration
Appearance
4.8 - 5.2
100
6.5 - 7.5
185 - 195
0.3 - 1.0
0-6
Air or Solution Movement
Continuous through 0.5 pm or less filter
Semi-bright
3.0 - 8.0
0 - 200
5.0 - 9.0
170 - 200
0.15 - 1.0
0 - 10
While this bath is operated under fairly normal conditions, a special hardening agent, that is referred to
here as Additive H, is included in the formulation and is the most important factor in the deposition of the
very hard deposit. Figure 1 gives the microhardness data when Additive H is varied from 0 to 200% of
its optimum concentration. It can be stated that when the concentration of additive H >2 50% of its
optimum value there are no significant effects on the microhardness or the operation of the bath.
The microhardness is directly dependent on the concentration of the additive up to about 50 % of the
optimum value. However, in order to account for consumption it was necessary to establish the optimum
at twice the 50% concentration of Figure 1.
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Effect of Metal Turnovers
Regardless of any outstanding results that may be obtained from an EN plating bath upon its initial makeup and operation, equivalent results must be obtained over repeated application of the system through as
many metal turnovers (MTO) as possible. In many critical engineering applications the number of
MTO’s is limited to 5 or less. This is due to changes in plating bath chemistry which in turn affects the
quality of deposit obtained from the regenerated plating solution. As is well known, the changes in
plating bath chemistry and hence performance are due to the accumulation of by-products of the EN
deposition reaction. The microhardness of deposit H when the EN bath is regenerated several times are
graphed in Figure 2.
Heat Treatment
Differential Scanning Calorimetry (DSC) has shown that the phase transition temperature for the
formation of the Ni3P phase of deposit H occurs at about 400 0C. Since nickel phosphide formation is the
accepted mechanism for hardening of EN deposits, panels from 0 - 10 MT0 were heat-treated at 400 0C
for 1 hour. The resulting heat-treat data are given in Table 2.
Table 2. Microhardness for Deposit H after Heat Treatment
None
0
400 C for 1 hour
0
3
6
882
863
824
10
845
0
3
6
10
948
973
1071
1097
Physical Properties of Deposit H
The physical properties as determined for deposit H are shown in Table 3.
Composition of deposit H
The composition of deposit H was determined at each MTO. The results are given in Table 4.
Table 4. Phosphorus Content and Bath Aging
2.62
3.02
3.94
4.8
0
3
6
10
Thus this is a low phosphorus Ni-P deposit that increases in phosphorus as bath aging occurs.
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Mechanical Properties of Deposit H
The mechanical properties of deposit H are listed in Table 5.
Table 5. Mechanical Properties of Deposit H
Tensile Strength, ksi
Modulus of Elasticity, msi
Elongation, %
Hardness (as plated), HV100
Hardness (heat-treated1), HV100
Internal Stress, ksi
1
134.3
18.98
0.71
800 - 890
900 - 1100
- 2.6 (compressive)
4000C for 1 hour
Deposit H is seen to be a very hard (as-plated), relatively strong Ni-P deposit. An unexpected result was
derived from the tensile tests; i.e. the tensile strength range for deposit H compares favorably with values
reported for high phosphorus deposits*. Deposit H, a low phosphorus alloy, is considerably stronger than
many Ni-P deposits where the phosphorus content </- 7 per cent.
The internal intrinsic stress of deposit H is compressive at 0 MTO. The change in stress with bath aging
(MTO) is shown in Figure 3.
Figure 3. Internal Stress of Deposit H vs. MT0
The intrinsic stress is seen to remain compressive up to 6 MTO. Compressively stressed EN deposits are
reported to show superior performance characteristics under extreme conditions when compared to
deposits that are in tensile stress. This fact is especially important in engineering applications which
demand good wear. At 10 MT0 the intrinsic stress of deposit H becomes tensile. Even though the
deposit at 10 MT0 is still considered low phosphorus, other factors come into play and the deposit shows
moderate internal tensile stress.
WEAR RESISTANCE
The physical and mechanical properties of deposit H show it to be a very good candidate for use
in applications where extreme tribological conditions prevail. Since wear is primarily a surface
phenomenon, surface properties are major factors in determining wear behavior. For example, the high
thermal conductivity exhibited by deposit H allows for the frictional heat generated during surface-to
surface contact to be rapidly dissipated. The mechanical properties of deposit H associated with good
wear behavior are: high as-plated hardness, high tensile strength, and excellent adhesive strength.
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Abrasive Wear of Deposit H
Abrasive wear mechanisms are generally considered to occur when a rough, hard surface slides on a softer
surface leaving grooves and wear particles on the softer surface. One technique for determining abrasive
wear is the Taber abraser , which uses standard abrasive wheels to evaluate materials. The Taber Wear
Index (TWI) is the weight loss due to abrasion in milligrams per cycle. Each cycle consists of 1000
revolutions of the test material. The deposit H bath was installed in an electroless nickel shop where
(mostly) automotive parts are plated (production 1). The excellent wearability found in the laboratory was
the reason for the installation of the deposit H bath. After the bath had been operated for about one
month, Taber wear panels were plated with deposit H and TWI’s were obtained. Figure 4 shows the
result from the production 1 bath and is graphed with other EN deposits, chromium, and the laboratory
(Deposit H) results. The production 1 bath results are the average of 6 different Taber tests run through
the course of production and include data points at several MTO’s. The production data varied only from
4.58 mg loss (at 0 MTO) to 4.96 mg loss (at 6 MTO) so only the average (4.72) of all 6 tests is shown in
Figure 4.
18
16
14
12
10
8
6
4
2
0
Figure 4. Taber Wear Index (TWI) for Electroless Nickel Deposits
As can be seen, the production TWI of 4.72 mg/l000 cycles compares very well with the laboratory value
3.9 mg/l000 cycles and is much better than standard high or low phosphorus EN deposits.
A second production site also installed the deposit H bath and had Taber tests performed including a
direct comparison to their low Phosphorus production bath (low Phos Production 2 on chart). The results
are plotted in Figure 5 as TWI vs. the number of cycles. Also included are the laboratory results (Deposit
H 0 MT0 and Deposit H 3 MTO) along with the original laboratory chrome results. As can be seen. in
this study the TWI for deposit H is not as good as in the laboratory study (average of about 10 mg loss per
1000 cycles) but the TWI is still significantly better than the production 2 low Phosphorus deposit.
Deposit H is still showing excellent wear resistance and the unexpected high result for the low Phosphorus
deposit (previous reports estimate the low Phosphorus TWI at about 12 mg/l000 cycles1) leads one to
speculate that had chrome been run under the same conditions that it’s TWI may have been higher.
Figure 5. Taber Wear Index for EN Deposits at Production 2 Site and Laboratory
Ball on Disc Wear/Friction
During sliding or rolling contact between two surfaces friction is encountered. The energy associated with
surface deformation is best illustrated by the results of the Ball on Disc tests, where deposit H is compared
to chromium. Chromium is noted for its ability to provide a low coefficient of friction. relative to EN
deposit, in particular.
Laboratory Ball on Disc results are shown in Table 6. This data show that the loss of material due to wear
is greater for chromium vs. deposit H; i.e. - 33.6 mg (Cr) vs. 6.1 mg (Deposit H). As of yet, no Ball on
Disk tests have been performed on production baths to confirm this result.
SUMMARY
A wear resistant electroless nickel bath has been developed and installed at two production sites. Wear
testing on those deposits have shown significant improvement over typical EN deposits; whether they are
high-, mid-, or low-Phosphorus deposits. Many parts are have been plated in Deposit H and are being
evaluated for a number of applications; including valves, pinion shafts, pistons, heddles, circuit boards,
and almost any application where wear resistance is of importance. This wear resistance is not due
entirely to phosphorus content but is the result of a unique nanocrystalline structure1 that is produced in
the deposit H.
1
G. 0. Mallory, G. W. Loar, and D. G. Block, “Studies and Properties of a Very Hard Electroless Nickel Deposit”;
Conference Proceedings Electroless Nickel ‘9.5, Cincinnati, Ohio.
2
W. H. Safhnek, “The Properties of Electrodeposited Metals and Alloys”, American Elsevier Publishing Company,
1974.
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