SELECTIVE CHEMICAL MILLING OF RECAST SURFACES

摘要

Disclosed is a process for machining nickel-base superalloys wherein a thermal effect process, such as laser or electric discharge machining, is first used to remove material but leaves a recast layer. Next a chemical milling process is used wherein the etchant only attacks and removes the recast layer. The etchant is comprised by volume percent of 40-60 HNO3, 5-20 HC1, and balance H2O, with which is included 0.008-0.025 moles/liter FeC13 and at least 0.016 moles/liter CuSO4. The FeC13 improves removal rate but tends to cause unwanted pitting and intergranular attack. These tendencies are inhibited by the addition of CuSO4, preferably the molar ratio of CuSO4 to FeC13 is 2:1. The beneficial combination of FeC13 and CuSO4 is usable in other etchants.