United Technologies Corporation

Henry Lada

Robert E Fishter

Brian A Manty

Victoria M Putnam

Herbert R Liss

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.

Method and composition for removing nickel aluminide coatings from

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.

Selective chemical milling of recast surfaces

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.

Chemical milling of high tungsten content superalloys

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.

Method and composition for removing aluminide coatings from nickel

The adherence and wear resistance of chromium alloy electroplates on titanium is improved by pretreating the substrate to form a chromium conversion coating, and post-treating the substrate at a temperature at about 700-820.degree. C. (1300-1500.degree. F.) for about 1-300 hours. The pretreatment is comprised of the formation of a chromium conversion coating from an acid chromate solution; a preferred solution is comprised of hydrofluoric acid, sodium chromate, and water. The post treatment causes diffusion sufficient to obtain a bond but avoids completely interdiffusing the chromium alloy electroplate, to preserve the wear resistance of the electroplate surface.

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Lake Park, FL, United States of America

Henry Lada