Recommendations for the metallographic preparation of crack-like defects in PBF-LB/M additively manufactured alloy 625 builds

Abstact Crack-like defects were found in powder bed fusion-laser beam/metal additive manufacturing built gas turbine burner components. This was somewhat surprising, since the subject material, Alloy 625, is readily weldable. The original equipment manufacturer responsible for the print job had a good track record and excellent experience with this particular alloy. From the findings obtained in the metallographic investigation that is the subject of this contribution it can be concluded that i) the crack-like defects may not be liquation or solidification cracks as initially thought (both hot cracking phenomena), but possibly lack of fusion defects, ii) after a first preparation step, the defects were not detectable with light optical microscopy, even after etching with Kalling’s II reagent, iii) only after re-polishing using oxide particle suspension, or, alternatively, after reverse electrolytic etch with the anode and cathode swapped, using Kalling’s II reagent as electrolyte (Kalling’s II modified, a.k.a. Ätzen von Alloy 625 – Ätzlösung nach Boromir – Boromir’s etch ), defects became detectable, and iv) only observation in the scanning electron microscope allowed characterization of the defects as lack of fusion rather than hot cracking.