Enhanced Corrosion Resistance and Microhardness of Titanium with Electroless Deposition Ni-W-Cr-P Coating

Abstract

In the present study, Ni-W-Cr-P quaternary alloy coatings were prepared on titanium-based alloys by electroless deposition. The morphology, crystal structure, microhardness, and corrosion resistance of samples were studied by scanning electron microscope (SEM), X-ray diffractometer (XRD), microhardness tester, and electrochemical analyzer. The results show that the microstructure of these alloy films changes with the increase of annealing temperature. As-deposited alloy layers belong to nickel-based mischcrystal structure, and its crystallinity was enhanced to 200°C and 300°C, gradually; the new phase Ni₃P began to appear at 400°C, completely crystallized at 600°C; Cr_1.12Ni_2.88 and Ni₃Ti phases were present at 700°C; Ni and Ni₃P phases were totally decomposed at 800°C, and Cr₄Ni₁₅W, Cr₂Ni₃, Ni₁₇W₃, Cr, Cr₃P, and Ni₂P generated. Because of the different structures after annealing, microhardness and corrosion resistance of the alloy coatings possess a relevant change. The Ni–W–Cr–P alloy coatings heated at 600°C exhibit better microhardness and corrosion resistance than those of samples at other annealing temperature. The related mechanisms of those results were also discussed, briefly.

Keywords:

• Corrosion resistance
• Electroless Ni-W-Cr-P coating
• Heat-treatment
• Microhardness
• Microstructure
• Titanium alloy