Kroll's reagent is most suitable for etching of Ti alloys. Kroll's reagent composition is (2-3ml Hydrofluoric acid, 2-6ml Nitric acid and 100ml water). optimum time for immersion in the reagent is 1-1.5 min to properly reveal the grain and grain boundaries in the microstructure.

HF will be okay

Thank you very much for the answer

Kroll's reagent, prepared by mixing 2 ml of 50% concentrated HF and 4-6 ml of nitric acid in 100 ml of deionized (DI) water, is commonly used for etching. After applying the etchant, it is crucial to immediately rinse the sample thoroughly with DI water, followed by additional cleaning with DI water to remove any residue. Typically, an etching duration of 15-30 seconds is recommended. For best results, etching for 15 seconds initially, with an additional 5-10 seconds if necessary, is advised. More detailed guidelines for etching specific alloys can be found in ASTM E407. Alternatively, electroetching is also an option for certain applications.