Ni-B coatings with low, increasing amount of Boron have been produced using a Ni sulfamate plating bath with the addition of dimethylaminborane. Coatings’ characterization revealed that it is possible to produce crack-free coatings with a B content up to 0.12 wt%, with a thickness of about 40–50 μm. The introduction of an increasing amount of B changes progressively the coatings microstructure from columnar, to fine fibrous and then to lamellar. The presence of B as interstitial atom in the Ni elementary cell caused an increase of the residual stress, as measured by FIB-DIC method, which change from compressive to tensile as a function of B concentration. The microstructure refinement and the increase of the residual stresses caused a noticeable increase of the microhardness. On the other hand, the resistance to localized corrosion decreased by increasing the B content maybe due to the formation of micro-defects or micro-cracks on the Ni passive layer due to the residual stresses. To confirm this hypothesis, the Ni-B coatings have been annealed at 400 °C to achieve a complete stress relaxation. The stress relaxation caused a decrease of the hardness and a noticeable increase of the corrosion resistance.

Ni-B electrodeposits with low B content: Effect of DMAB concentration on the internal stresses and the electrochemical behaviour

Lekka M.
;
Offoiach R.;Lanzutti A.;Fedrizzi L.
2018-01-01

Abstract

Ni-B coatings with low, increasing amount of Boron have been produced using a Ni sulfamate plating bath with the addition of dimethylaminborane. Coatings’ characterization revealed that it is possible to produce crack-free coatings with a B content up to 0.12 wt%, with a thickness of about 40–50 μm. The introduction of an increasing amount of B changes progressively the coatings microstructure from columnar, to fine fibrous and then to lamellar. The presence of B as interstitial atom in the Ni elementary cell caused an increase of the residual stress, as measured by FIB-DIC method, which change from compressive to tensile as a function of B concentration. The microstructure refinement and the increase of the residual stresses caused a noticeable increase of the microhardness. On the other hand, the resistance to localized corrosion decreased by increasing the B content maybe due to the formation of micro-defects or micro-cracks on the Ni passive layer due to the residual stresses. To confirm this hypothesis, the Ni-B coatings have been annealed at 400 °C to achieve a complete stress relaxation. The stress relaxation caused a decrease of the hardness and a noticeable increase of the corrosion resistance.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11390/1144954
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