Electrochemical etching of titanium alloy castings

Abstract

We used an electrochemical method to etch cast binary titanium alloys in an attempt to show their dendritic structures.Studies showed that when an alloy could be activated in either sulphuric, oxalic or fluosilicic acid, its anodic polarization curve had the same general shape and passivation potential for all alloys independent of alloying element or concentration. Consequently, in acid solutions, electrochemical etching was conducted at a constant potential slightly less noble than the passivation potential where the anodic current density was near the maximum. Of the alloys examined, only Ti-15%Cr was etchable in a concentrated caustic solution and etching occurred only in the transpassive potential region. Under our conditions we were able to show the dendritic structure in alloys containing 15%Cr, Ta, or Mo; at lower concentrations, or in the case of the 15%Nb alloy, the dissolution rates of the dendritic and interdendritic materials were too similar to differentiate between them on the etched surface.