Abstract: A solution is described for the chemical processing of beta phase-containing titanium alloys. The solution contains HNO.sub.3 and HF, along with a small but effective amount of copper, ruthenium, rhodium, palladium, osmium, iridium, platinum or gold to reduce hydrogen absorption, ammonium formate and citric acid to increase the milling rate, and a surfactant to ensure a satisfactory milled surface.

Abstract: A solution is described for the chemical milling of niobium and niobium-base alloys. The solution contains about 25% HNO.sub.3, about 19% HF, balance H.sub.2 O, with additions of citric acid and ammonium formate to control the reaction rate and provide a smooth surface finish without intergranular attack, and a small amount of a noble metal to control hydrogen absorption. A process for using the solution to mill niobium alloys is also described.

Abstract: Chemical milling of the commercial gamma-gamma prime nickel superalloy IN-100 is carried out by using an aqueous solution comprised of 32.5-85 volume percent HCl, with other ingredients proportioned on the HCl, preferably 40 ml/l nitric acid, 0.0141 M/l metal sulfate ion, 0.0326 M/l metal chloride ion, 0.0168 M/l alkali metal ion and 0.0073 M/l citric acid. The chemical milling is particularly effective in uniformly removing a small amount of surface layer without any deleterious attack. It hereby is useful to improve the effectiveness of surface penetrant inspection, to find small flaws which would otherwise be concealed by a worked surface layer.

Abstract: Disclosed is a method for stripping nickel aluminide coatings of up 10 weight percent aluminum from nickel base alloy substrates at room temperature. The preferred solution contains by volume percent 43-45 nitric acid, 7-12 hydrochloric acid, 0.1-1.5 sulfuric acid, balance water; it also contains 0.008-0.025 moles per liter of ferric chloride, at least 0.016 moles per liter copper sulfate. The ratio between the sulfate and chloride is 2:1 or greater.

Abstract: 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 HNO.sub.3, 5-20 HCl, and balance H.sub.2 O, with which is included 0.008-0.025 moles/liter FeCl.sub.3 and at least 0.016 moles/liter CuSO.sub.4. The FeCl.sub.3 improves removal rate but tends to cause unwanted pitting and intergranular attack. These tendencies are inhibited by the addition of CuSO.sub.4 ; preferably the molar ratio of CuSO.sub.4 to FeCl.sub.3 is 2:1. The beneficial combination of FeCl.sub.3 and CuSO.sub.4 is usable in other etchants.

Abstract: Chemical milling of cast superalloys having high tungsten contents is advantageously accomplished with an etchant which consists by volume percent of 40-60 concentrated HNO.sub.3, 0.6-0.8 concentrated HF, 30-70 H.sub.2 O, with which is included at least 0.008 moles/liter CuSO.sub.4 and 0.0016-0.025 moles/liter FeCl.sub.3. Preferably the molar ratio of CuSO.sub.4 to FeCl.sub.3 is 2:1 and etching is accomplished in the range 50.degree.-80.degree. C.

Abstract: Nickel aluminide and like coatings are stripped from nickel base superalloy substrates using a 60.degree.-71.degree. C. solution consisting essentially by volume percent of 43-48 nitric acid, 7-12 hydrochloric acid, balance water, and containing 0.008-0.025 mole/liter ferric chloride and at least 0.016 mole/liter copper sulfate. Coating removal is rapid while significant attack of the substrate is avoided.

Abstract: An effective cyanide free solution and process for removing gold-nickel braze alloys from superalloy parts are described. The solution contains about 50% nitric acid with intentional additions of materials which ionize to provide chloride ions, sulfate ions, and metal ions in specific concentrations.

Abstract: Chemical milling of cast superalloys having high tungsten contents is advantageously accomplished with an etchant which consists by volume percent of 40-60 concentrated HNO.sub.3, 0.6-0.8 concentrated HF, .[.30.]..Iadd.40.Iaddend.-70 H.sub.2 O, with which is included at least 0.008 moles/liter CuSO.sub.4 and 0.0016-0.025 moles/liter FeCl.sub.3. Preferably the molar ratio of CuSO.sub.4 to FeCl.sub.3 is 2:1 and etching is accomplished in the range 50.degree.-80.degree. C.