Electrolytic Plasma Polishing of Ti 6Al-4V titanium alloyThursday (07.11.2019) 11:25 - 11:45 Part of:
Electrolytic plasma polishing (EPPo) is a method for the superficial material removal and finishing of metals. Its applications see fast-growing interest, and is particularly attractive for the finishing additive manufactured light alloys pieces. The promises of additive manufacturing include a disruptive impact on manufacturing globally, however suffers to this day from unsatisfactory final surface states. Perhaps the most promising approach to the issue lies in contactless post-treatment, EPPo being one of the best-fitting contenders.
EPPo consists in setting the workpiece as the anode in an electrolytic cell, and apply DC voltages in the hundreds of volts. The energy liberated at the interface through the strong polarization results in a series of physical and chemical phenomena, which ultimately mediate the processes controlling the dissolution of the workpiece. EPPo features electrolyte compositions much more benign to workplace safety and to the environment compared to traditional electropolishing methods, as well as slower material removal. It however retains all the advantages of contactless, geometry-independent polishing, which are particularly well aligned with the characteristics of additive manufacturing.
Titanium and its alloys are of notorious interest to a wide range of industries and as such are an extremely valuable application for EPPo. The electrodissolution of titanium and of some of the elements usually alloyed to it, notably aluminum, is however significantly more difficult to control than is the case for other common metals. The main cause is a strong competition against the formation of insoluble oxides into EPPo-blocking passivation layers. In this work, a range of supporting electrolytes and Ti-complexing agents were used in combination with different electrical and thermodynamical parameters to investigate the interplay between electrodissolution and oxide formation in Ti 6Al-4V. In situ measurements of the electric response from the system and of the glow light emitted by the process were collected and analyzed. Characterization of the treated surface was furthermore performed, in terms of elemental and chemical composition, morphology and topography. The goal of this work is to shed light on the complex interactions at play during EPPo, and in addition to identify the range of surface states that can be produced by the method, both in topological and chemical terms.