Abstract
The selection of electroless nickel-phosphorus plating (ENP) has been inclined towards their properties and advantages with complex geometry applications. These properties include coating uniformity, low surface roughness, low wettability, high hardness, lubricity, and corrosion- and wear-resistance. Materials used in geothermal environments are exposed to harsh conditions such as high loads, temperature, and corrosive fluids, causing corrosion, scaling, erosion and wear of components. To improve the corrosion- and wear-resistance and anti-scaling properties of materials for geothermal environment, a ENP duplex coating with PTFE nanoparticles was developed and deposited on mild steel within the H2020 EU Geo-Coat project. ENP thin adhesive layer and ENP+PTFE top functional layer form the duplex structure of the coating. The objective of this study was to test the mechanical and tribological properties of the developed ENP-PTFE coatings with varying PTFE content. The microstructural, mechanical and tribological properties of the as-deposited coating with increasing PTFE content in the top functional layer in the order: ENP1, ENP2 and ENP3 were evaluated. The results showed maximum wear protection of the substrates at the lowest load; however, increasing load and sliding cycles increased the wear rates, and 79% increased lubrication was recorded for the ENP2 duplex coating. The wear performance of ENP3 greatly improved with a wear resistance of 8.3 × 104 m/mm3 compared to 6.9 × 104 m/mm3 for ENP2 and 2.1 × 104 m/mm3 for ENP1. The results are applicable in developing low friction, hydrophobic or wear-resistive surfaces for geothermal application.
Highlights
Electroless nickel plating (ENP) is a conventional deposition method that involves a chemical reduction of Ni2+ from an aqueous solution onto metallic substrates
This study aims to improve adhesion to mild steel and assess the tribological properties as a function of different PTFE content in the top coating layer to establish potential application in geothermal power generation systems
Since the objective was to produce duplex coatings (i.e., nickel-phosphorus alloy (Ni-P) undercoat followed by Ni-P+PTFE top coat), the etched specimens were first transferred into Ni-P bath for producing undercoat
Summary
Electroless nickel plating (ENP) is a conventional deposition method that involves a chemical reduction of Ni2+ from an aqueous solution onto metallic substrates. The low-to-high phosphorous material, which typically ranges from 3 to 14 wt% [1], has a significant effect on the deposited electroless nickel-phosphorous layer properties. ENP offers a broad application spectrum via its inherent high coating uniformity, good adhesion, low roughness, high hardness, and corrosion- and wear-resistant properties. The common co-deposition processes with either or both soft and hard particles developed over time include: SiO2 , Al2 O3 , ZrO2 , TiO2 , Mo, MoS2 , PTFE, Diamond, CNT, SiC, CNT-SiC, Si3 N4 , WC, ZnO, B4 C, BN, TiN [3,5,6,7,8,9,10,11,12]. The addition of hard particles creates a hard and wear-resistant composite coating, whereas soft, solid lubricants result in a film with self-lubricating and excellent anti-stick properties [5]
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