Properties of γ-Ni-γ' composite coatings transformed from Ni+Al electrodeposits
Marek Konieczny, Bartłomiej Szwed, Igor Kardynał
Quarterly No. 1, 2014 pages 33-37
DOI:
keywords: γ-Ni+γ’ composite coating, oxidation resistance, wear behaviour
abstract Composite γ-Ni+γ’ coatings on an iron substrate were developed by the conversion of Ni+Al electrodeposits with dispersed Al particles in an Ni matrix. The conversion was made by vacuum annealing at 900°C for 3 h under a uniaxial pressure of 1 MPa and full-density composite coatings were obtained. A nickel interlayer was successfully employed to block the mutual diffusion between the iron substrate and aluminium and therefore hard and brittle Fe-Al intermetallics were not formed. The oxidation resistance of as-plated Ni and γ-Ni+γ’ composite coatings at 1000°C was compared. After 100 hours at 1000°C, a mass gain of oxides for the γ-Ni+γ’ coating was about 7 times less than for the nickel coating. The γ-Ni+γ’ coating follows parabolic oxidation kinetics, which implies that oxidation is bulk-diffusion controlled. SEM/EDS and XRD characterisation showed that during oxidation, a thin continuous Al2O3 layer is formed below the matrix of an NiAl2O4 spinel. The wear mass loss of the γ-Ni+γ’ coatings was found to be about 3 times smaller than the as-plated Ni and Ni+Al coatings. Moreover, the γ-Ni+γ’ coatings oxidised for 20 h, containing very hard and wear-resistant Al2O3 particles, show the smallest wear mass loss of all the tested materials.