Tailoring electroless Ni-W-P polyalloy coatings: Unveiling the synergistic impact of cerium addition and annealing on surface functional properties

Abstract

Electroless deposition of Ni-based coatings is a cost-effective solution to augment the surface mechanical and electrochemical properties of engineering components. This work explores the influence of addition of rare-earth element Ce on the characteristics of Ni-W-P coatings. The concentration of Ce salt in the deposition bath was varied in the range 0–14 mg/L, and the highest deposition rate was for the solution with 8 mg/L Ce. A homogeneous distribution of Ce over the coated surfaces was observed, and the share of Ce in the composition of the deposition varied monotonically with the Ce concentration in solution. Further, the coating surface compositions also depended on the Ce-content. Coating obtained using 8 mg/L Ce was found to have significantly improved scratch hardness (8.49 GPa), fracture toughness (7.05 MPa.m1/2), specific wear rate (3.1 × 10−6 mm3/N.m) and corrosion protection efficiency (94.16 %) as compared to the coating without Ce (3.87 GPa, 3.39 MPa.m1/2, 9.03 × 10−6 mm3/N.m, and 45.44 %, respectively). Interestingly, the ability of the coating to inhibit biofilm formation on the surface initially increased with increasing Ce content, but this effect also diminished above 8 mg/L Ce. Additionally, annealing the coatings caused further alterations in the microstructures, resulting in improvement in the microhardness, scratch, wear, and biocorrosion resistance, but at the cost of compromised corrosion resistance. Properties of such annealed coatings also depended on the annealing temperature. Therefore, this study indicates that a wide spectrum of combinations of surface physical, mechanical, and electrochemical properties can be achieved by controlling only two processing conditions, i.e., the Ce concentration, and the annealing temperature.