X-ray diffraction characterization of electrodeposited Ni–Al composite coatings prepared at different current densities

• Different X-ray diffraction techniques were applied to characterize the Ni–Al composite coatings.
• Al2O3 formed on the coating surface after potentiostatic polarization experiments.
• The relationship between corrosion and the Al content and the texture were also investigated.

Ni–Al composite coatings were prepared at different applied current densities (1–8 A/dm2) from a conventional Watt bath. The influences of current densities on the texture, grain size, microstrain, residual stress of the Ni–Al composite coating were investigated with X-ray diffraction method, which includes texture coefficients (TC) and pole figures, Voigt method, classical sin2 ψ X-ray diffraction method and the Multi-reflection grazing incidence geometry (referred to as MGIXD) method. The morphology, composition, anti-corrosion properties and friction coefficients at 200 °C of the coating were also studied. The results showed that the texture of coating deposited at higher current densities evolved from the (2 0 0) preferred orientation with fiber texture to random orientation with reducing current density. Al particle content increased with reducing current density, grain size decreased with the reducing current density, while the microstrain and the tensile residual stresses increased. The MGIXD result showed stress gradient on the near-surface of the coating. Potentiodynamic polarization results demonstrated that the Ni–Al coating deposited at 2 A/dm2 exhibited the best anti-corrosion which was contributed by the formation of Al2O3 on the surface. The minimum friction coefficient of 0.57 was also observed for coating deposited at 4 A/dm2.