Electropolishing of CP Titanium and Its Alloys in an Alcoholic Solution-based Electrolyte

Abstract

A newly developed electropolishing system, equipped with an original agitation function for an electrolyte and using a safe electrolyte composed of an alcoholic solution, was applied for wrought and cast CP titanium and its alloys. Surface roughness and morphology of the polished surfaces were then examined. Under an electrolytic condition of 70-75 V, 2.0 kA/m 2 , and 30℃, wrought CP Ti and Ti-6Al-4V alloy achieved an apparent mirror-like finishing with an average surface roughness (Ra) of 0.03 and 0.12 μm respectively. Under the same condition, on the other hand, cast CP Ti and Ti-6Al-7Nb alloy produced rougher polished surfaces with average Ra values of 0.67-0.80 μm, and the finishing was apparently shiny, but not mirror-like. SEM observation of the polished surfaces showed that wrought CP Ti was even and completely featureless, while wrought Ti-6Al-4V alloy was pitted. For cast CP Ti, a needle-like phase containing traces of iron was observed on the polished surface.

The electropolishing of electron beam melting, additively manufactured TI6AL4V titanium : relevance, process parameters and surface finish.

“…This agrees with literature indicating that under similar circumstances, current/voltage combinations, there is no immediately apparent current limiting plateau for Titanium. Nevertheless, polishing had been performed successfully on Titanium above 50 Volts, so this was the region of focus during this work (Tajima et al, 2008).…”

“…Where machining is not possible on AM parts, EP can be performed on Ti-6Al-4V, albeit traditionally using very hazardous electrolytes, some containing hydrofluoric acid (HF). However, currently a substantially less hazardous, likewise more easily implementable, non-HF, anhydrous, alcohol based Ti-6Al-4V compatible EP electrolyte now exists and shows promise (Tajima et al, 2008, Taylor et al, 2013). …”

“…In the Flow Design factors experiments, the temperature factor levels were set at 85F and 100F and the voltage factor levels were set to 60V and 80V given that these ranges corresponded to existing values within literature (Tajima et al, 2008).…”

“…The electrolyte mixture used was a non-aqueous, alcohol-based electrolyte found in literature known to polish Ti6Al4V (Tajima et al, 2008) The use of an alcohol-based electrolyte greatly widens the applicability of EP to AM Ti6Al4V. To begin with, using typical strong acids to perform EP would only further complicate the design process, as much more stringent safety guidelines would be required.…”

“…A high concentration of alcohol in the final rinse ensured that the interior of the loop was able to be made very dry by the compressed air drying given the good evaporation of the alcohol. This method of alcohol cleaning and drying is recommended in literature (Tajima et al, 2008). Maintenance other than cleaning included periodic sanding of metal components holding samples and cathode strips.…”