Effect of hest treatment on electrochemical properties of the composite Ni+Ti layers in an alkaline solution
Iwona Napłoszek-Bilnik, Antoni Budniok Uniwersytet Śląski, ul. Bankowa 12, 40-007 Katowice
Quarterly No. 4, 2005 pages 20-24
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abstract The composite Ni+(55% at.)Ti and Ni+(25% at.)Al+(25% at.)Ti layers were obtained by electrolytic co-deposition of Ni as well as Ti and Al powder suspended in the Watts bath. The layers were deposited on a steel substrate under galvanostatic conditions. In case of the Ni+Al+Ti layer, aluminium was leached out in 5M KOH solution. The as-received layers were heated at 1100°C in argon and the intermetallic phases (Ni3Ti for the Ni+Ti layer, and Ni3Ti, Ni2Al3, NiTi2 for the Ni+Al+Ti(-Al) layer) were created (Fig. 3). Chemical and physical characteristics of the as-received and heated layers were examineted. Electrochemical characteristics of the layers concerned the investigation of their corrosion resistance in 5M KOH solution. Based on the results obtained using classical electrochemical methods, a corrosion potential, Ecor, and a corrosion current density, jcor, for each layer was determined. As-received Ni+Ti layer was characterized by Ekor = −365 mV, jkor = 5,25 μA cm−2; its good corrosion resitance resulted from passivation of Ti in an alkaline solution (Tab. 1). Heat treatment of the Ni+Ti layers caused an improvement of the corrosion resistance (Ekor = 141 mV, jkor = 1,079 μA cm−2). The reason of that was the formation of stable intermetallic phases. Electrochemical impedance spectroscopy (EIS) was also applied to study the electrochemical properties of the layers. The impedance spectra were registered at the value of Ekor, and then, approximation of experimental EIS data using different electrical equivalent models (CPE1 and POR model) have been done (Fig. 4). Key words: electrolytic composite layers, electrodeposition, titanium