An Assessment and Comparison of Tee Sensitivity of Various Macroetches

Companion laboratory-scale studies were conducted on specimens of ESR alloy 718 in order to determine responsiveness of this material to several of the macroetching techniques used in the industry. The work developed from initial efforts to define the relative sensitivity to Alloy 718 segregation of the macroetchants in standard use at the respective locations of Into Alloys International: one an electrolytic etch using a 50% solution of concentrated HCl in water, followed by an electrolytic stain performed in"a 4% H SO solution; the other an immersion etchant using a water solution of Hz0 'and concentrated HCl. Other etchants included in the resulting study'w&-e Canada's, Heppenstall, and one containing ferric chloride. These studies showed that the HCl electrolytic etch technique possesses the greatest sensitivity to variations in segregation, and that the water/HCl/Peroxide immersion technique showed the least sensitivity. The others were found to fall between these two poles. Aside from immediate implications for the Into Alloys International locations involved, there appear to be larger questions for the industry as a whole concerning relative etch responses and standards for assessment of material etched by the various techniques. There are potentially stronger implications for VAR material because of its greater vulnerability to white spot, a key feature which was not observed in the ESR samples studied here. Superalloy 718-Metallurgy and Applications Edited by E.A. Loria The Minerals, Metals & Materials Society, 1989