Effects of Ti Content and Annealing on Fracture Toughness and Scratch Resistance of Electroless Ni-P-Ti Coatings
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JMEPEG https://doi.org/10.1007/s11665-020-05101-4
Effects of Ti Content and Annealing on Fracture Toughness and Scratch Resistance of Electroless Ni-P-Ti Coatings Zhi Li and Zoheir Farhat (Submitted March 28, 2020; in revised form July 20, 2020) Ni-P coatings exhibit good corrosion resistance; however, they have not been used in applications where high toughness and wear resistance are required. Therefore, to enhance the toughness and wear resistance of Ni-P coatings, superelastic NiTi particles were incorporated within the Ni-P coatings. However, due to the high cost of the superelastic NiTi compared to Ti powder, Ti was co-deposited with Ni-P and subsequently annealed to produce Ni-P-NiTi coating. The fracture toughness and scratch resistance of the coatings were measured by scratch tests. The effects of Ti content and annealing on coatingsÕ microstructure were investigated using XRD and laser confocal microscope. The relationship between the microstructure and the fracture toughness and scratch resistance was also studied. It is found that the formation of superelastic NiTi particles within the annealed Ni-P-Ti coating significantly improves the coatingÕs fracture toughness and scratch resistance. The average grain sizes of Ni and Ni3P decrease with an increase in Ti content and decrease in annealing temperature and time. The reduction in grain size improves both fracture toughness and hardness (or strength), which gives rise to promoted scratch resistance. Keywords
fracture toughness, grain size effect, Ni-P-Ti composite coating, scratch resistance, superelastic NiTi
1. Introduction Due to excellent corrosion resistance, high hardness, and superior adhesion, electroless Ni-P coatings have been extensively employed as protective surface coatings (Ref 1-3). However, Ni-P coatings have been reported to have low toughness, which are readily to crack and fracture during dent and scratch events (Ref 4-7). During installation or maintenance, scratch resistance of protective surface coatings is critical (Ref 8-10). Cracking and fracture during scratch may reduce the lifetime of brittle coatings (Ref 10). Additionally, failure or delamination of coatings with low scratch resistance may expose the more susceptible substrate to an aggressive environment (Ref 11). In order to improve the toughness of NiP coatings, the addition of ductile particles in Ni-P matrix has been reported (Ref 4, 7, 12). It was found that the toughness of Ni-P-Ti composite coatings improves by incorporation of ductile Ti particles into Ni-P matrix (Ref 12). It was also observed that the first crack load (the load required to initiate the first crack) increases with an increase in Ti content during scratch (Ref 4). Furthermore, Maclean et al. reported that the addition of superelastic NiTi particles into the brittle Ni-P matrix significantly improves the toughness through crack Zhi Li and Zoheir Farhat, Department of Mechanical Engineering, Dalhousie University, Halifax, NS B3J 2X4, Canada. Contact e-mail: [email protected].
Journal of Materials Engineer
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