Study the effect of adding zirconia particles to nickel–phosphorus electroless coatings as product innovation on stainless steel substrate

Khalid Mutashar Abed; Nabaa S. Radhi; Ahlam Hamid Jasim; Zainab S. Al-Khafaji; Sabaa Radhi; Safa A. Hussien

doi:10.1515/eng-2022-0364

Article Open Access

Study the effect of adding zirconia particles to nickel–phosphorus electroless coatings as product innovation on stainless steel substrate

Khalid Mutashar Abed , Nabaa S. Radhi , Ahlam Hamid Jasim , Zainab S. Al-Khafaji , Sabaa Radhi and Safa A. Hussien

Published/Copyright: December 31, 2022

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From the journal Open Engineering Volume 12 Issue 1

Abstract

Scholars have spent much time studying metal deposition procedures involving the deposition of electroless nickel, alloy, and composite coatings on various surfaces; the most current uses were feasible advantages of the coatings’ many good properties for achieving the final product innovation. Lately, these coatings have demonstrated intriguing wear and corrosion resistance features, resulting in several innovative macro-level developments. The notion of composite coating by co-deposition coating has been presented in this article. The characteristics of Ni–Pb alloy coatings were examined by inserting ZrO 2 particles into the electroless deposited solution. The stainless steel (SS) specimens have been electroless coated with Ni–Pb and ZrO 2 nanoparticles (size = 30–70 nm) at 0, 10, and 20 g/L amounts. The materials have been examined using scanning electron microscope and atomic force microscope, followed by wear-resistant and microhardness testing. According to the investigation findings, including inert particles improved the hardness magnitude and wearing resistance considerably. The base metal exhibited the highest wear rate at 10 N, while the wear rate decreased in the Ni–Pb– ZrO 2 -coated SS316L by 34%. The Vickers hardness magnitudes of the Ni–Pb– ZrO 2 -coated samples at different ZrO 2 contents (0, 10, and 20 g/L) were 19, 50, and 81%, respectively.

Keywords: composite coating; electroless nickel–phosphorus; product innovation; stainless-steel; zirconia; wear-resistant; micro-hardness test

1 Introduction

Electroplating is commonly considered the traditional electrolytic plating process. It is achieved when metal ions are first reduced to their respective metallic states before deposition at the cathode under an external electrical source [1]. Electroless plating can be likened to a chemical reduction process in many aspects, even though they differ significantly. It includes the catalytic decrease of metallic ions in a reducing agent-containing aqueous solution, followed by the subsequent deposition of the metal without any external energy source [2,3,4, 5,6,7].

Electroless Ni–P/Ni–B coatings offer a wide range of applications in sectors that demand high hardness and anti-corrosion rates. The reason for such a thin layer of deposition is that the activated surface seems to be no longer in touch with the electroless solution after the metal is deposited. Because the deposited metal is in touch with the bath, no additional reaction can occur. As a result, at such a thin deposition thickness, it is critical to keep the surface roughness to a minimum, as this characteristic of the coating is linked to other characteristics, including wear and friction that also decrease coating life by subjecting the substrate to increased wear and corrosion, thereby increasing the price.

The chemical nickel reductions result in the formation of the electroless nickel deposit; however, this process depends on the reducing agent utilized. For instance, nickel-phosphorus coatings are produced when hypophosphite is utilized as the reducing agent [8]. Hence, the reaction must be controlled to ensure the reduction only on the substrate without affecting the equipment utilized. This mechanism can be controlled by adding additives to the reaction baths; such additives may include complexing agents, stabilizers, and pH regulators. Stabilizers are commonly utilized additives when working under stable and adequate conditions for long periods [9,10]. Electroless composite coatings are used to co-deposit composite substrates utilizing electroless coatings. Resistance against wear composites may be created by the co-depositions of small particulate substrates; studies have documented the co-depositions of hard particles like diamond and silicon carbide as well as solid lubricants such as polytetrafluoroethylene (PTFE) particles [11,12, 13,14]. Nevertheless, the increased surface area loading of the bath caused by the dispersion of the small particles – which was around 700–800 times more than the standard bath – led to the failure of early efforts at electroless composite coatings and frequently to bath disintegration. However, it has been possible to prepare electroless nickel composite coating using the appropriate stabilizers. Electroless coating permits accurate surface regeneration and prevents subsequent mechanical finishing [15,16].

The development of electroless coatings relies on the settling and effect of particles on the workpiece surface, followed by the deposition of Ni–P matrix, which will surround these particles. No molecular bonding exists between the introduced fine particles and the metal matrix. Guglielmi [17] has suggested a mathematical model for composite coating electrodeposition. The outcome of the experiments agreed with the proposed mechanism by ref. [17]. Furthermore, Grosjean et al. [18] reported an experimental set-up for electroless Ni-SiC composite coatings production; the study relied on the agitation induced by the circulating fluid. The bath circulation (top to bottom) generated a laminar fluid flow on the sample surface; this type of cell provided the agitation, and one of its advantages is that the particles are kept in suspension within the solution.

Another study by Apachitei et al. [19] demonstrated that Al 2 O 3 particles (spherical shaped) exhibited better incorporation compared to irregularly shaped ones; the shape of the particle also determines the kind of deposit’s finish. Large angular and small rounded particles normally give rough and smooth surfaces, respectively. Many authors have investigated particles such as SiC, CrC, ZrO 2 , Al 2 O 3 , PTFE, and graphite [20,21,22].

Nanosized diamond particles (0.52–2.21 wt%) have exhibited a surface change from bright and smooth to foggy and rough appearance with the nodular surface in the electroless Ni–Pb matrix [23]. Another study reported obtaining Ni–Pb composite coatings via the introduction of SiC and Si 3 N 4 to investigate their influence on the coating properties and the co-deposition process. The study noted modifications in the mechanism of growth of the metallic matrix by the nanosized particles compared to the nanosized ones [24].

In this work, the aim is to investigate the impact of the introduced ZrO 2 particles with nano-size on the structural and mechanical characteristics of the product in comparison to stainless steel (SS) 316L substrate.

2 Experimental work

2.1 Electroless procedures

Table 1 demonstrates the chemical analysis of the SS316L sample utilized in this study. The sample was chemically analyzed utilizing a device of spectroscopy for metal materials.

Table 1

Chemical analysis of the specimen utilized

Elements	C	Si	Mn	P	Cr	Mo	Ni	Al	Cu	Fe
Percentage × 1 0 − 2 %	1.9	44.2	85.4	4.6	1,671	209	1,007	0.12	35.6	Rem

All the samples for the experiments were cylindrical, while the final samples were disc-shaped, with thickness = 3 mm, diameter = 12 mm, and surface area = 3.391.

The preparation of the surface of the sample was done by:

First pulverizing the sample surface with Grit silicon carbide papers of different grades (220, 240, 400, 600, 800, 1,000, and 1,200), followed by surface cleaning with brine and acid; the cleaning process was done in preparation for the electroless process based on the required period per sample.
Then the surface was then pretreated for substrate deposition; the substrates were first cleaned with NaOH (10%) for 10–20 min at 60– 8 0 ∘ C to clean off grease, then it was rinsed with water and dipped in HCl (5%) for 30 s for surface activation before rinsing in deionized water before electroless [25].
Table 2 presents the chemical composition and operating conditions of the plating baths. The deposition process was conducted in a 150 mL bath maintained at 90 ± 1 ∘ C for 80 min. NaOH was utilized to regulate the pH of the solution to 5. The particles have been prevented from sedimentation by utilizing a magnetic stirrer at 300 rpm as a rotation rate. The samples after the coating process are shown in Figure 1.

Table 2

Components of an electroless solution [25]

Solution	Chemical composition for 150 mL	Condition of deposition
Ni–Pb solution	Nickel sulfate = 30 g/L	pH = 5
	Sodium hypophosphite = 25 g/L
	Sodium citrate = 20 g/L	Temperature = 90 ± 1 ∘ C
	Thiourea = 2 mg/L	Coating time = 80 min
	ZrO 2 = 0 , 10, and 20 g/L	bath stirring rate 300 rpm
	Nanoscale, d (30–70) nm

Figure 1

The samples after the coating process.

The schematic diagram and the electroless set-up utilized in this work are demonstrated in Figure 2. A thermometer has been placed into the electroless plating bath to monitor the temperature of the plating bath. After cleaning and activation, the substrate was immersed in the electroless bath using an inert rod or thread. The substrates have been immersed in the plating bath for a set amount of time to achieve a coating thickness of 30 nm or more. The needed plating time was maintained depending on the plating rate to guarantee the correct plating thickness was reached. The coatings have been rinsed in deionized water and dried in the air after plating. The same procedure was performed for all electroless Ni–Pb and Ni–Pb– ZrO 2 (10 and 20 g/L) alloy coatings to guarantee homogeneous substrate coatings.

Figure 2

The apparatus of the electroless coating process.

2.2 Tests

For evaluating the performance of the coating layers in this research, the following tests were carried out.

2.2.1 Thickness test

The thickness of the Ni–Pb, Ni–Pb– 10 ZrO 2 , and Ni–Pb– 20 ZrO 2 layer was measured using a thickness measuring device.

2.2.2 Scanning electron microscope (SEM)

Some grain boundary characteristics have been measured by identifying and measuring the phases, shape, and grain size. Moreover, each of these parameters has a specific characteristic. The Ni–Pb, Ni–Pb– 10 ZrO 2 , and Ni–Pb– 20 ZrO 2 layers’ microstructure were evaluated using contact mode SEM at 2.50k × magnification.

2.2.3 Atomic force microscope

The morphology (films’ depth morphology and roughness) of Ni–Pb, Ni–Pb– 10 ZrO 2 , and Ni–Pb– 20 ZrO 2 layers was observed using atomic force microscopy (AFM, contacting phase, spm AA3000 Angstrom advance Inc., America).

2.2.4 Hardness test

The hardness of the Ni–Pb, Ni–Pb– 10 ZrO 2 , and Ni–Pb– 20 ZrO 2 layers was measured using TH-717 Digital Micro Vickers Hardness Tester at 200 N load and 20 s holding time.

2.2.5 Wear resistance test

The SS, Ni–Pb, Ni–Pb– 10 ZrO 2 , and Ni–Pb– 20 ZrO 2 samples have been prepared with a diameter of 12 mm and a thickness of 3 mm following ASTM (G99-04) guidelines [26]. A sensitive electric balancing model with + 0.1 × 1 0 − 4 accuracy has been utilized to calculate the weight of the specimens. The pin-on-disk idea has been employed to examine dry wear on the wear tester gadget. The specimens have been pressed vs. a standard rotating steel disk with a hardness of 850 HV (in which normal force on the pin ( F ) = 10 N, pin diameter ( d ) = 1 cm, disk diameter ( d ) = 3 cm, wear track radius ( R ) = 0.5 cm, and disk rotation speed ( ω ) = 300 rpm). The animals’ reduced weight was calculated by weighing them after 5, 10, 15, and 20 min. The following formula has been utilized to transform weight loss into volume loss:

(1) Volume loss ( mm 3 ) = Weight loss ( g ) Density g mm 3 ,

where loss in weight = weighting before the test – weighting after the test.

3 Results and discussion

3.1 Thickness results

The observed loss in weight has been converted to loss in volume using the next relation: The thickness of the coating specimens was 30.7 nm for Ni–Pb, 34.5 nm for Ni–Pb- 10 ZrO 2 , and 37.9 nm for Ni–Pb- 20 ZrO 2 , demonstrating that the last coating layers’ rates of deposit were great. The reason for this observation could be the ZrO 2 -induced high diffusivity of the specimens, as the rate of thickness was found to improve with increases in the particle size and amount of the ZrO 2 layer (Table 3).

Table 3

The thickness of layer coating

Samples	Thickness (nm)
Ni–Pb	30.7
Ni–Pb–10 ZrO 2	34.5
Ni–Pb–20 ZrO 2	37.9

3.2 SEM

The SEM micrographs of the specimens at various zirconia contents are demonstrated in Figure 3. The figure also demonstrated the influence of the ZrO 2 content on the coatings’ thickness. ZrO 2 particles were deposited in clusters resembling an aggregated base metal composition.

$Figure 3 SEM morphology topographic for coating layers at magnification (2,500 × \times ): (a) SS, (b) Ni–Pb, (c) Ni–Pb– 10 ZrO 2 10{{\rm{ZrO}}}_{2} , (d) Ni–Pb– 20 ZrO 2 20{{\rm{ZrO}}}_{2} .$

Figure 3

SEM morphology topographic for coating layers at magnification (2,500 × ): (a) SS, (b) Ni–Pb, (c) Ni–Pb– 10 ZrO 2 , (d) Ni–Pb– 20 ZrO 2 .

3.3 AFM

The topography of the coating thickness layer for the samples was determined using the AFM, as demonstrated in Figure 4a–c. The figures demonstrated the smooth morphology of the zirconia layer at 0 g/L (Figure 4a); however, the morphology was less smooth for Ni–Pb upon adding 10 and 20 g/L of nano- ZrO 2 (Figure 4b and c).

$Figure 4 AFM pattern of a sample: (a) SS, (b) Ni–Pb, (c) Ni–Pb- 10 ZrO 2 10{{\rm{ZrO}}}_{2} , (d) Ni–Pb- 20 ZrO 2 20{{\rm{ZrO}}}_{2} .$

Figure 4

AFM pattern of a sample: (a) SS, (b) Ni–Pb, (c) Ni–Pb- 10 ZrO 2 , (d) Ni–Pb- 20 ZrO 2 .

3.4 Hardness results

The effect of Ni–Pb, Ni–Pb- 10 ZrO 2 , and Ni–Pb- 20 ZrO 2 coatings on the hardness magnitude of the base metal was determined using the hardness test. The test also aimed to determine the effect of different ZrO 2 and nickel contents on the hardness magnitudes of the base metal and the coatings. The findings of the hardness test for the base metal and the coatings are presented in Figure 5. The hardness magnitude between the coatings differed due to the different zirconia contents in the layers. The particle size exerted a significant effect on the material hardness, as could be mathematically explicated using the Hall-Petch correlation [27]:

(2) HV = H O + K ∕ d ,

wher HV is the material’s hardness with small granular size; H O is the material’s hardness is multi-size granular (polycrystalline grain size); K is the constant that represents the slope of the Hv hardness once plotted depending on the material type, and 1/ d is the particle’s diameter.

Figure 5

The hardness magnitude for the coated layers.

The Hall-Petch correlation is a theory that describes the reason for the high hardness magnitudes (520 Hv) of ultra-fine microstructures compared to the coarser particles of the same hardened material.

3.5 Wear tests

The loss in weight of each sample has been converted to the respective density, and the outcomes of this test under the same situations earlier mentioned are presented in Figure 6 previously ( F : 10 N); ω : 300 rpm; t : 5, 10, 15, and 20 min.

Figure 6

Wear rate of samples at 10 N loads.

This study’s optimum thickness (37.9 nm) was more than the deposited layer thickness. A layer thickness of < 20 nm is considered non-protective.

Figure 6 demonstrated that the wear rate continued to increase with load magnitudes at a constant velocity due to an increasing rate of sub-surface deformation. This was supported by the results of ref. [28], which found that wear rate increases linearly at a higher sliding distance. The study found that Ni coatings exhibited the most improved properties (in terms of better strength, higher wear, better adhesion, and better corrosion resistance) compared to the properties of the conventional coarse-crystalline coatings.

The results also demonstrated an increase in the volume loss with time due to the increase in particle loss at prolonged friction time. The effect of adding zirconia particles to the electroless-deposition solution on the wear rates was also studied under different conditions. The results demonstrated a significant reduction in volume loss as the zirconia content increases, reaching the minimum magnitude at the zirconia amount of 20 g/L due to the role of ZrO 2 in increasing the hardness of the coated layers, thereby increasing the wear resistance. The thick layers could be due to the defects and loss of adhesion observed in the coated layer with 10 g/L ZrO 2 after 15 min.

4 Conclusion

The following points are concluded from the test results of the research:

All the coatings demonstrated that the Ni–Pb and Ni–Pb– ZrO 2 composite coatings are completely covered by nanoparticles of about 30–70 nm average grain size.
Ni–Pb– ZrO 2 composite layer demonstrated a stable structure with a good level of crystallization and surface mechanical bonding due to the good interaction between ZrO 2 and the Ni–Pb matrix.
The base metal exhibited the highest wear rate at 10 N, while the wear rate decreased in the Ni–Pb– ZrO 2 -coated SS316L by 34%.
The Vickers hardness magnitudes of the Ni–Pb– ZrO 2 coated samples at different ZrO 2 contents (0, 10, and 20 g/L) were 19, 50, and 81%, respectively.

Acknowledgment

The Ministry of Higher Education, University of Babylon, and Al-Mustaqbal University College are gratefully acknowledged. This research was carried out in the laboratory at the University of Babylon.

Conflict of interest: Authors state no conflict of interest.

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Received: 2022-04-19

Revised: 2022-07-28

Accepted: 2022-08-01

Published Online: 2022-12-31

This work is licensed under the Creative Commons Attribution 4.0 International License.

Articles in the same Issue

https://doi.org/10.1515/eng-2022-0364

Keywords for this article

composite coating; electroless nickel–phosphorus; product innovation; stainless-steel; zirconia; wear-resistant; micro-hardness test

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