The effect of phosphorus content on the microstructure and corrosion resistance of electrodeposited Ni-Co-Fe-P coatings.

Ni-Co-Fe-P quaternary alloy coatings were electrodeposited and the dependence of microstructure and erosion-resistance against corrosion with different P content was investigated. By adding H3PO3 from 0 to 40 g L-1 to the electrolyte bath, the phosphorus content in Ni-Co-Fe-P quaternary alloy coating increased to 12.92% by weight. Along with the increase of phosphorus content, the microstructure changed from a crystalline and amorphous composite structure to a pure amorphous structure and then to another composite structure, while the grain size was gradually refined and the micro hardness clearly increased from about 510 to 1150 HV. Found. Corrosion rate and synergism between erosion and corrosion increased first and then decreased with increasing amount of phosphorus. The polarization curves were detected in the slurry flow with an impact speed of 4.19 m/s, showing a tendency to passivity for all deposited coatings. Ni-Co-Fe-12.92P coating deposited from H3PO3 concentration of 40 g/L has the best erosion-corrosion resistance due to the highest hardness and lowest corrosion current density. Large amounts of lip cracking along the micro-plow grooves can be observed on the worn surface morphology of the deposited coatings, and the dominant wear mechanism is micro-mechanical cutting of the Ni-Co-Fe-P coatings during placement. Erosion - Corrosion in the slurry flow. 1. Introduction Corrosion-erosion is a common destruction of materials applied in two-phase fluid, especially oil sand slurry or salt sand [1-2]. In order to improve the erosion resistance of fiber-reinforced plastics, electro-deposited protective metal layers have been considered [3]. And electrolytic deposition of a Ni-Co based coating on carbon steel can significantly increase the hardness and resistance to wear and corrosion of steel in oil sand slurry [1]. Previously, Makar also showed a possible way to improve the corrosion-erosion resistance of steel with electrodeposited coatings [4]. Based on nickel plating, co-deposition of cobalt with nickel is widely used to improve mechanical bonds and Corrosion resistance was studied [5]. In recent years, ternary Ni-Co-Fe alloys have been intensively studied because these ternary alloys show a higher saturation inductance and a lower coercive field than binary magnetic alloys [6]. In fact, the coating of Ni-Co-Fe alloy is also absorbed as an important intermediary metal alloy to highlight its physical and chemical properties [7]. Its hardness, corrosion resistance and surface luster close to the hard chrome steel deposit may to a certain degree replace the real hard chrome coating [8]. Since it is accepted that the hardness, wear and corrosion resistance of Ni-P coatings Clearly influenced by the composition of Russian phosphorus [9-10], different phosphorus contents were investigated. In order to understand the effect of composition on the mechanical properties of nickel-P electrodeposits [11]. Based on this, the microstructure of amorphous, nanocrystalline and their composites was obtained with different phosphorus contents [9-11]. In addition, the addition of 0.45 M sodium hypophosphite to the chloride base electrolyte can also improve the corrosion resistance of electrodeposited coatings [12]. Therefore, the addition of phosphorus was supposed to improve the hardness, wear and corrosion resistance of Ni coatings. - Improve Co-Fe. However, the articles about the Ni-Co-Fe-P quaternary alloy coatings were very limited. By adding H3PO3 to the electrolyte bath, the Ni-Co-Fe-P coating was created and deposited and has a higher hardness and a lower friction coefficient and a lower wear rate. Compared with ternary Ni-Co-Fe electrodeposited alloy coating [13]. However, it is still unclear about the effect of phosphorus content on physical or chemical properties. Therefore, in this work, the dependence of microstructure and erosion-corrosion is. 2. Experimental work 2.1. Electrodeposition of Ni-Co-Fe-P alloy coatings Ni-Co-Fe-P alloy coatings with a thickness of about 30 to 40 micrometers galvanostatically from an electrolyte consisting of NiSO4·6H2O 120 grams L-1 NiCl2·6H2O 40 grams L-1, FeSO4 7H2O 20 g L-1, CoCl2 7H2O 10 g L-1 and other additives. During electrodeposition, the concentration of H3PO3 (10 to 40 g/L) was adjusted to produce Ni-Co Fe-P alloy coatings with different P contents. All chemical reagents were graded and dissolved in distilled water. The pH value of Boudroi solution was adjusted to 1.8. A pure nickel sheet and an AISI 1045 cylindrical rod with a diameter of 4 mm and a length of 40 mm were used as anode and cathode, respectively. The current density of 2 A dm-2 and the temperature of 65 °C were maintained in all plating steps. And the plating time was controlled in 3 hours. After electrodeposition, the samples were washed in running water and ethanol, in hot dry air and then kept for coal generation and erosion-corrosion test. 2.2. The material characteristics of the coatings were determined by X-ray diffraction (XRD) analysis. To determine the surface morphology structure and chemical composition position, S3400 scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS) was obtained. The microhardness was determined by using a HXD-1000TC digital microhardness device according to the GB4342-84 standard and measured at 5 random positions located on the electrodeposited surface for each sample. A constant load of 0.98 N was applied for 15 seconds to indent the sediments. The average of 5 readings was taken as the hardness value for each sample. Electrochemical measurements were performed by a PS-268A system (Beijing, China) with a platinum counter electrode and a saturated calamel electrode (SCE) reference electrode in 3.5% NaCl aqueous solution for static corrosion and in sand containing slurry for dynamic corrosion before performing the electrochemical tests. were kept in 3.5 wt% sodium chloride solution at room temperature and the open circuit potential (OCP) was measured and recorded until no further changes were observed (b10 mV h-1). All corrosion tests were carried out in a standard three-electrode cell, where the deposited steel rod was placed. As the working electrode (WE), a saturated calomel electrode (SCE) was used. Auxiliary electrode title. At least two tests were performed for each sample in order to confirm the reproducibility of the results. 2.3. Erosion-Corrosion Test Corrosion-erosion tests with slurry pot erosion are carried out by an intensifier (MSH type erosion-corrosion system, China) equipped with an electrochemical detector system. It mainly consists of a rotating device and the schematic diagram of the erosion tester is shown in Figure 1, which is also described by Rajharam et al. [14]. The samples were mounted on a 20 mm diameter rotary disk edge holder and the sample motor rotates in the slurry at a rotation speed of 400 rpm. Impact velocity means the velocity of the particle as it impacts the sample and it can be considered as the difference in velocity between rotation and flow. Therefore, the actual impact speed is lower than the rotation speed because the rotation speed is easy to identify and useful for comparing the erosion-corrosion with the impact speed. The rotation disk line speed was used to indicate the impact location (Vi). It can be calculated from the diameter (D) and rotation speed (Vr) using this equation Vi = πDVr. Therefore, the nominal impact location ve is 4.19 m s-1 at a rotation speed of 400 rpm in this study. In our erosion, silica sands with an average size of 250 to 550 micrometers were used. Corrosion tests. Each corrosion erosion test was performed for 3 hours. The slurry pot was filled with a 10-liter aqueous solution containing 10% by weight of sand particles and 3.5% NaCl. The old slurry was replaced with fresh slurry. For all three tests in this present study, the mass loss due to net erosion (Ma) was assumed to be equal to the mass loss in distilled water containing 10% by weight of sand particles without adding NaCl. Mass reduction due to net corrosion (Wc), the test was carried out in 3.5% NaCl solution without sand particles. Synergy between erosion and corrosion (Ws) Expressed as the difference between the total mass loss (Wt) and the sum of We and Wc. Three repetitions of the wear test were performed to minimize data scatter. All samples were first ground by SiC paper in #800 grit and degreased with ace dye, then cleaned in an ultrasonic bath with ethanol and air-dried in a desicator before gravimetric measurement of mass loss. The measurement was done using a precision scale with an accuracy of ±0.1 mg. Measurements were repeated six times, maximum and minimum values ​​obtained for each sample were discarded. The remaining 4 readings were averaged to obtain the mean age mass loss for each test sample. All electrochemical measurements and corrosion erosion tests were performed at ambient temperature. 3. Results and discussion 3.1. Morphology and chemical composition Figure 2 shows the surface morphology of Ni-Co-Fe-P electroalloy deposits with different phosphorus contents. Colony-like morphology of different sizes can be seen in all samples. And each colony can be found to contain several smaller seeds. Surface morphologies similar to the deposited coating were also observed in Ni-Co-W [15] and Ni-P [16] alloys. It is noteworthy that the cracks were deposited on the Ni-Co-Fe-P alloy in the amount of electrolyte containing 10 g L-1 H3PO3, which indicates a high internal tension in the coating deposited in this H3PO3 creating the intensity center. As the concentration of H3PO3 increases, a smaller colony-like structure is obtained. This indicates that the incorporation of phosphorus is useful for refining the grain size of Ni-Co-Fe-P alloy coatings. Typical EDS patterns of Ni-Co-Fe-P alloy coatings deposited from different concentrations of H3PO3 are shown in Figure 3. It can be seen , the content of P in the Ni-Co-Fe-P coating increases with the increase in the concentration of H3PO3 in the plating bath. By increasing the H3PO3 concentration from 10 to 40 g/L, the P content increased from 5.60 to 12.92% by weight. In addition, not only the content of other elements composed of Ni-Co-Fe-P alloy decreased, but their relative content also decreased, the percentage was different with the increase of H3PO3 concentration. 4. Conclusion Ni-Co-Fe-P quaternary alloy coatings were electrodeposited and the phosphorus content of the deposited coating was adjusted by changing it. The H3PO3 concentration of the microstructure and dependence of the resistance to erosion-corrosion of the phosphorus content of Ni-Co-Fe-P coatings were investigated. The results showed that: (1) the surface morphology of the coatings was shown to be like a colony, the structure and increasing the concentration of H3PO3 is useful for refining the grain size of the phosphorus content of Ni-Co-Fe-P coating increased with increasing the concentration of H3PO3 inside the plating bath (2) the microstructure of the structural composed of long and amorphous crystals was transformed into a pure amorphous and then into another. The composite structure increased significantly with increasing P content and the inclined hardness as the deposited coating was about twice (3) the anodic polarization of the deposited coatings at 3.5 wt% NaCl solution shows that the corrosion resistance first decreased with the addition of H3PO3 and then increased further with the addition of H3PO3. The tendency to passivity can be seen from the polarization curves of the deposited coatings and Ni-Co-Fe-12.92P coating, the best resistance to (4) The mass loss rate of the deposited coating in the erosion-corrosion test shows that high phosphorus content is beneficial for improving the erosion-corrosion resistance, while the synergy between erosion and corrosion increases first and then increases with the increase of phosphorus content. is reduced The Ni-Co-Fe-12.92P coating has the best resistance to erosion-corrosion due to the highest hardness and the lowest density of corrosion current (5), the wear mechanism of mechanical micro-cutting is dominant in these types of quaternary alloy coatings exposed to erosion-corrosion in the slurry flow. . References: [1] Y. Yang, Y.F. Cheng, Electrolytic deposition of Ni-Co-SiC nano-coating for erosion-en�hanced corrosion of carbon steel pipes in oilsand slurry, Surf. Coat. Technol. 205 (2011) 3198–3204. [2] X. Ji, J. Zhao, S. Yang, L. Gu, Erosion–corrosion behavior of electrodeposited amor�phous Ni-W-P coating in saline-sand slurry, Corrosion 69 (2013) 593–600. [3] A.H. Whitehead, H. Simunkova, P. Lammel, J. Wosik, N. Zhang, B. Gollas, Rain erosion characteristics of electrodeposited Ni-SiC metal-matrix composite layers, Wear 270 (2011) 695–702. Editor:A.Salemi