3:2:1 etchant - Nickel superalloys

3:2:1 etchant - Nickel superalloys

Material Name: Nickel superallloys
Recipe No.: 12070
Primary Chemical Element in Material: Ni
Sample Type: Bulk
Uses: Macrostructure
Etchant Name: 3:2:1 etchant
Type (Macro/Micro): Macro
Etching Method: Chemical
Etchant (Electrolyte) Composition: 3 parts H2O, 2 parts conc. HCl, 1 part H2O2 (35 wt.%)
Procedure (Condition): Preheat the sample in hot water. Immerse slice in etchant. Take from bath when bath reaction stops. (Re-expose if response is incomplete.) Wipe surface, rinse and dry.
Note: The etch responses of its squares were the least definitive of all, though roughly comparable to those for the "Ferric Chloride" etch. Under some conditions, such as the etching of an annealed alloy 718 slice, "3:2:1" will produce a non-adhering dark film. As long as the film does remain on the surface, though, it highlights the dark and white spots and tree ring segregations similarly to the way Canada's does. The samples had not been annealed for either of these experiments. As a result, no such film was observed on any of the samples described here. This unpredictability of etch response gives the user of "3:2:1" no confidence that there will be any discernable definition of any segregation type. Under some conditions, such as the etching of an annealed alloy 718 slice, "3:2:1" will produce a non-adhering dark film. As long as the film does remain on the surface, though, it highlights the dark and white spots and tree ring segregations similarly to the way Canada's does. The samples had not been annealed for either of these experiments. As a result, no such film was observed on any of the samples described here. This unpredictability of etch response gives the user of "3:2:1" no confidence that there will be any discernable definition of any segregation type.
Reference: T. Le Roux and D.A. Wells, AN ASSESSMENT AND COMPARISON OF TEE SENSITIVITY OF VARIOUS MACROETCHES FOR ALLOY 718, Superalloy 718-Metallurgy and Applications, Edited by E.A. Loria, The Minerals, Metals & Materials Society, 1989, pp. 109-118.