Volume 17 Preprint 36
Mechanical properties of electroless nickel coated ABS M30 plastics prepared by rapid prototyping process
K. Raja, C.D. Naiju, S. Narayanan
Keywords: Electroless nickel, ABS M30, corrosion resistance, tensile, SEM
Electroless nickel coating on rapid prototyped ABS M30 plastics was successfully developed. Micro hardness studies indicated that the coatings are enhancing the strength of plastics. The corrosion resistance of coated surface was evaluated in sea water medium using electrochemical techniques. The EN surfaces improved the ultimate tensile strength in comparison with ABS M30 plastics. The appearances of spherical particles of Ni-P are visible in FE-SEM images. The results are presented and discussed.
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Mechanical properties of electroless nickel coated ABS M30 plastics prepared by
rapid prototyping process
K. Raja*1, C.D. Naiju1, S. Narayanan1
of Mechanical & Building Sciences, VIT University, Vellore-632 014, India.
*Corresponding author (firstname.lastname@example.org)
Electroless nickel coating on rapid prototyped ABS M30 plastics was successfully
developed. Micro hardness studies indicated that the coatings are enhancing the
strength of plastics. The corrosion resistance of coated surface was evaluated in sea
water medium using electrochemical techniques. The EN surfaces improved the
ultimate tensile strength in comparison with ABS M30 plastics. The appearances of
spherical particles of Ni-P are visible in FE-SEM images. The results are presented
Keywords Electroless nickel, ABS M30, corrosion resistance, tensile, SEM
Electroless nickel–phosphorus deposition is an established industrial practice as a
protective and decorative coating in various industries due to its superior corrosion
and wear resistance, excellent uniformity, wide range of thickness as well as
mechanical and physical properties. Extensive research has been carried out on the
characterization of the electroless nickel deposition process. Corrosion properties of
electroless Ni–P deposition depend mainly on phosphorus content and the
corresponding structural and mechanical state. Micro porosity, roughness and
inhomogenites due to internal stress within the Ni–P deposited layer are affected by
the substrate pretreatment method.
Brenner and Riddell first developed autocatalytic nickel deposition using a sodium
hypophosphite bath . There are numerous parameters affecting the electroless
concentration, the loading in the bath and agitation affect the nickel deposition
rate[2-3]. Electroless nickel deposition bath is known to have a major problem of
sudden bath decomposition, which results in an increase in the operating cost of
the process and the generation of environmentally hazardous waste . Electroless
Ni-Co-P electrolyte solution containing sodium citrate and lactic acid as complexing
agents in order to obtain a relatively high deposition rate . The coatings can be
tailored for desired properties by selecting the composition of the coating alloy,
composite and metallic to suitable specific requirements . Another serious
consequence of phosphite presence in the EN solution is its effect on the internal
stress of Ni-P deposit. As the phosphite concentration increases, the internal stress
becomes more tensile . The tensile stress is harmful to many applications such as
corrosion and memory disk. However, metallization of ABS plastics prepared
through RP process is still at entry level. The presence of honey comb structure of
ABS obtained by RP method is claiming that metallization on it will improve the
mechanical properties considerably better than the injection molded plastics.
The developed coatings are expected to increase hardness and tensile strength. The
performance of coatings is to be screened by weight gain studies, Vickers hardness
test, Tensile strength, corrosion resistant measurement by tafel polarization and AC
impedance methods. The uniformity of the surface is a desirable factor for
ABS M30 which will be determined by micro structural analysis using FE-SEM
The bath developed in the present study had the following ingredients.
NiSO4.6H2O = 35 g/l
NaH2PO2 = 27 g/l
Tri Potasium Citrate = 50 g/l
Dextrin = 2 g/l
NaNO3 = 1 g/l
pH = 5.83
Temperature = 85±2o C
Plating time = 2 hours (25 microns per hour)
Coating thickness = 50-54 microns
Evaluation of Electroless nickel coatings on ABS M30 through various measurement
ABS M30 plastics prepared by RP process with size 20 x 50 x 2 mm3 were employed
in the EN plating bath. They were mechanically polished with fine grit paper, washed
with distilled water and then degreased by acetone. It is again washed and etched in
2% HCl and 1% H2O2 solution. Then the plastics were sensitized and activated by
adopting the procedure as reported earlier. The initial weight of ABS M30 plastic
was measured using electronic weighing machine. Then the plastics were subjected
to EN plating. The rate of deposition was calculated using the following formula:
W – Weight gain of the deposit (g)
D – density of Ni-P in the coating (g/cm3)
T – plating time (h)
A – Surface area of the ABS M30 (cm2)
Micro hardness measurements
Micro hardness measurements for all the as metalized ABS M30 (20 x 50 x 2 mm3)
were determined adapting ASTM E-384 procedure by Vicker’s harness tester with a
load of 100 g. A diamond shaped indentation was made on each EN coated ABS M30
plastics at eight different points and the average of hardness was measured as given
V.H.N = (1854 x load) / d2
where d = diagonal of the indentor
Corrosion resistance measurements
The potentiodynamic polarization and impedance studies were carried out on
metalized ABS M30 plastics with the electroless nickel coated area of 1 cm2 exposed
surface (test electrode) in sea water medium, 5 cm2 of platinum electrode (counter
electrode) and saturated calomel as reference electrode in three electrode cell setup.
Tafel polarization studies
A constant quantity of 250 ml of sea water(3.5% NaCl) solution was accurately
measured and used as electrolyte for this study. The working electrode, reference
electrode and the auxiliary electrode were arranged in the electro chemical
workstation (Sinsil Model 604E, USA) and the readings were measured by changing
values ± 300 mV from open circuit potential at a sweep rate 1
mV.second-1 for the metalized ABS M30 rapid prototypes.
The corrosion kinetic parameters such as Ecorr and Icorr, were determined. The
decremental values of Ecorr and Icorr confirmed that the coatings are protecting the
etching of plastics from the attack of aggressive chloride ions[9-13].
AC impedance was performed using Nyquist plots in the frequency range of 10 kHz
to 0.01 Hz under potentiostatic conditions using sea water as electrolyte for EN. The
impedance measurements were carried out on test surface at room temperature.
The Randell’s electrochemical equivalent circuit was adopted which is highly
suitable system for corrosion resistance surfaces as reported by Raja et.al.
Charge transfer resistance
Double layer capacitance
The circuit composed of real impedance (Z’) and imaginary impedance (Z’’). A plot
of real impedance (Z’) Vs imaginary impedance (Z’’) showed a uncompleted
semicircle which is the characteristics of EN coatings as reported earlier. The
formation of Warburg impedance equivalence were arrived by analyzing the plots to
identify the best fit for corrosion resistant surfaces. A capacitance is created
between EN coatings and electrolyte which is measured as double layer capacitance
at coating/solution interface.
The higher value of frequency was used to calculate Cdl using the following relation
Tensile strength measurements
This experiment was carried out using Instron 8801 as per ASTM D638 at a strain
rate of 2 mm/min.
Scanning electron microscopic studies (SEM)
The cross-sectional micro structural images of EN coated ABS M30 plastics were
examined using FE-SEM analyzer. The EN coated test electrodes were prepared for
size 1 cm2 and placed firmly on test plate pre-coated with Au to make a conducting
surfaces on ABS M30 rapid prototypes.
Results and Discussions
Weight gain studies
The results of electroless nickel coatings on ABS M30 plastics obtained by weight
gain method and eddy current tests are placed in Table 1. It has been noticed that
the incorporation improves the micro hardness values. The addition nickel coatings
on fiber matrix enhanced the tensile strength because of its higher anti-galling
effect than uncoated plastics. The rate of deposition for EN was calculated as 50µm
at the plating duration of 2 hours.
Micro hardness measurements
The hardness of the electroless nickel coated ABS M30 plastics was measured by
Vicker’s hardness tester is given in Table 2. The higher hardness is due to the
presence of non-metallic phosphorus in Ni matrix.
Corrosion resistance studies
Tafel polarization studies
The corrosion resistance experiments were carried out for EN coatings on ABS
M30 plastics has been done by employing current-voltage measurements using
polarization studies. The shift of Potential to less negative direction by coating
indicated the corrosion protection nature of the surface. Also Icorr values have
reduced to a greater extent by EN coatings and the results are presented in table 3.
Electrochemical Impedance Spectroscopy (EIS) studies
The calculated impedance values of EN coated ABS M30 plastics in 3.5% sea water
medium are indicated in the table 4. It is cleared that Rt values are increased at the
expense of double layer capacitance. The reduction in Cdl values have been
accounted for the system following Warburg’s impedance. It is evident that EN
coatings on ABS M30 plastics prepared by FDM RP method can be useful for
electronic circuits as this coatings exhibit EMI shielding effect due to the presence
of phosphorus in Ni matrix.
Tensile strength measurements
The table 5 indicates that at strain rate of 2.48 in the case uncoated plastics
resulted maximum stress at 27.78 MPa. For EN coated plastics, the rate of strain
started at 2.48% and at 2.51%, the ultimate tensile strength of 28.94 Mpa was
achieved due to presence of Ni-P coatings on ABS M30 Rapid prototypes. Hence it is
understood that EN coated surfaces can be used as intermittent layers for
developing surface finishing for automobile components.
Scanning Electron Microscopic studies
Figure 1 indicates the cross-sectional SEM images of EN coatings obtained from
citrate based bath. The appearance of layered structures with hanging of spherical
particles aggregation indicating that the presence of Ni-P in the coatings. This
entire coatings micro structures seem to be a caterpillar resting on a leaf. The black
images are the conductive gold coatings on ABS M30 plastics. The top layer in the
image is the indicative of reflected X-rays in SEM instrument and not on the coating
The authors of the paper are thankful to Centre for Advanced Materials Processing &
Testing, VIT University, Vellore funded by DST-FIST project for using Instron facility
to carry out tensile test.
An attempt has been made successfully to develop non magnetic coatings based on
EN on ABS M30 plastics. The EN coatings improved hardness, corrosion resistance
and tensile strength of ABS plastics. SEM images confirmed the existence of Ni-P in
ABS polymer matrix. This investigation was found useful to develop an EMI shielding
coatings for and PCB.
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Table 1 The results of weight gain studies and eddy current test obtained for
EN coated ABS M30 plastics
Thickness ( µm)
Uniform coating thickness
Table 2 Micro hardness values for EN coatings on ABS M30 plastics
EN coated ABS M30
Table 3 Current-Potential results for the rapid prototyped ABS M30 in sea water
Corrosion kinetic factors
Table 4 Impedance values of EN coatings ABS M30 plastics
Nature of deposit
EN coatings on ABS
Table 5 The results of tensile test obtained for EN coated ABS M30 plastics
Legends for figure
1. FE-SEM image of EN coated rapid prototyped ABS M30