Buffered Oxide Etch: A Safer, More Effective Etchant for Additively Manufactured Ti-Alloys

Abstract

Kroll’s reagent is effective for the metallographic etching of traditional Ti-alloys but struggles with the intricate, refined microstructures of newer Ti-alloy compositions like Ti-Cu and Ti-Mo alloys, which are created through additive manufacturing. The presence of fine intermetallic compounds in these alloys results in limited contrast between grains and phases when using Kroll’s reagent, highlighting the need for an alternative etchant. This study systematically investigates the use of buffered oxide etch, a common etchant for micro-electronics, on a range of additively manufactured Ti-alloys. The results show that buffered oxide etch provides superior etching outcomes compared to Kroll’s reagent and ammonium bifluoride, with a clear colour contrast between grains and fine phases. Furthermore, ammonium bifluoride with an F− ion concentration similar to 40% buffered oxide etch (5.60 mmol/ml) is found to reveal microstructural details effectively. These findings suggest that the buffered oxide etch is a reliable tint etchant for additively manufactured Ti-alloys, and could potentially be used to etch other additively manufactured alloy systems for metallographic studies. Both these etchants supply F− ions without the low pH, significantly improving safety by removing the need for HF in the etching process.