Electrochemical determining of penetrating porosity and the chemical and phase composition of pulse plasma deposited Ti–Al and Ni–Al coatings

The electrochemical behavior of Ti–Al and Ni–Al coated iron was compared to that of bulk Ti–Al and Ni–Al-based alloys of defined chemical and phase composition. Bulk pure metals of Al, Ni, Ti, and Fe, intermetallic compounds of Ti3Al, TiAl, TiAl3, Ni3Al, NiAl and several Ti–Al and Ni–Al alloys, as well as pulse-plasma deposited coatings of Ti–Al and Ni–Al on iron were tested in 2 N solutions of HNO3, H2SO4, Na2SO4, H3PO4 and NaOH. The penetrating porosity (permeability) of each coating was determined using an electrolyte in which the electrochemical behavior of Ti–Al and Ni–Al alloys differed from that of the Fe substrate. To estimate the chemical composition of deposits, a relationship between some electrochemical parameters and the Al content established for bulk alloys was used. The phase composition of deposits was estimated by comparing the shape of polarization curves recorded for material coated with aluminides with those for bulk alloys, in the chosen electrolytes. The chemical and phase composition of coatings established by electrochemical methods was in good agreement with the data obtained by EDS and XRD analyses. The electrochemical tests with application of microcell may be used to check the properties of deposited layers and thus, to optimize the process of deposition of alloys and intermetallic compounds.