Wear behavior of graded nickel-phosphorus coatings with a medium phosphorus top layer: An experimental and molecular dynamics simulation study

Nickel-phosphorus electroless plating is widely used to improve surface properties. Despite various applications in industry, mismatch properties at the interface between the Nickel-Phosphorus layer and the substrate can cause stress concentration that could fail of the interface and consequently reduce the wear resistance of the deposit. Recent studies confirmed that the graded Nickel-Phosphorus electroless plating coatings could be considered an effective approach to reducing the stress at the interface. Therefore, in this study, the graded nickel-phosphorus coatings with various phosphorus content in the form of multilayer structures were investigated. The phosphorus content in the nickel-low phosphorus layer (Ni-LP), nickel-medium phosphorus layer (Ni-MP), and nickel-high phosphorus layer (Ni-HP) were 4.88 wt%, 8.99 wt%, and 13.88 wt%, respectively. In the Ni-LP/Ni-MP double layer, the wear resistance was 1.5 times compared to the Ni-MP single layer. Using the molecular dynamics simulation, it is shown that during the wear process, the inhibition of propagation of cracks has occurred for graded structure. The experimental results showed that the higher hardness of the Ni-MP upper layer, compact surface morphology, and the crystallinty graded structure were important parameters in improving the wear resistance of the Ni-LP/Ni-MP coating. The direct relationship between the experimental parameters and the wear simulated results of the Ni-LP/Ni-MP coating also confirmed each other completely.