Electrodeposition of composite Ni+FeAl gradient coatings
Bożena Łosiewicz, Antoni Budniok, Karol Stępień, Marian Kupka Silesian University, Institute of Materials Science, 12 Bankowa, 40-007 Katowice, Poland
Quarterly No. 1, 2005 pages 84-98
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abstract An electrolytic co-deposition technique has been successfully used to prepare the composite Ni+FeAl gradient coatings with a continuous compositional gradient. Production of this functional gradient material (FGM) was carried out by simultaneous electrodeposition of nickel with FeAl powder on a copper substrate from a bath in which iron aluminide particles concentration was increased gradually and suspended by mechanical stirring (Fig. 1). Electroplating of the Ni+FeAl FGMs was conducted under constant current conditions at room temperature (Tab. 1). The microstructure, distribution and percentage volume fraction of FeAl powder in the deposit, were analyzed and determined by metallographic microscope. Surface morphology was carried out using a scanning electron microscope (SEM). Structural investigations were conducted by XRD. The microhardness (μHV) of the deposit was determined with a Vickers diamond testing machine. The percentage volume fraction of iron aluminide for composite Ni+FeAl gradient coatings plated under proposed conditions indicated that the FeAl particle content in the deposit increased gradually in the direction of the deposit growth from 0 to 39.3 vol.% (Fig. 2). The microstructure of a cross-section (Fig. 3) and SEM observations of the deposit surface morphology (Fig. 4) revealed that FeAl particles were uniformly distributed in the Ni matrix and their content increased gradually throughout the thickness. Microstructural transition with composition of the FeAl FGM including a nickel matrix, a dispersive structure, a network structure, and an alternative dispersive structure, have been discussed. The phase composition investigations of the Ni+FeAl FGM exhibited a diphase composite structure with a polycrystalline nickel matrix into which the solid crystalline FeAl particles with the B2 structure were embedded (Fig. 5). The Vickers microhardness as a function of the thickness of the gradient deposit has been also determined (Fig. 6). It increased with a gradual increase in the thickness from 196.9 for pure nickel up to 453.1 μHV for the top layer of the deposit. It was found that embedding of FeAl particles with high intensity and hardness in the Ni matrix, started to harden and strengthen the deposit. Key words: electrodeposition, FGM, composite coatings, Ni+FeAl