Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F1/00—Etching metallic material by chemical means
  • C23F1/10—Etching compositions
  • C23F1/14—Aqueous compositions
  • C23F1/16—Acidic compositions

Definitions

• the invention relates. to etching solutions and more particularly to etching solutions for etching surfaces which are partially masked so as to achieve localised etching.
• One of the problems encountered in the etching of partially-masked surfaces is;the formation of a fillet radius at the boundary between the masked and exposed areas 9f .thesurface.
• the fillet radius extends-under the maskant to a distance approximately equal to the depth of etch.
• Channelling is characterised by an area of increased attack in the immediate vicinity of the fillet radii, thus resulting in localised areas of stress concentration which in turn may affect the fatigue properties of the etched article.
• an etching solution comprises a dispersion of finely divided particles, said particles being'inert to'said etching solution and to the surface'to be'etched.
• etching solution contains from 2 to 40 grams per litre of said finely divided particles.
• aid finelyldivided particles may-be selected from the p ice group comprising silicon, silicates, metal oxides, metal carbides, borides, nitrides and carbon.
• Said etching solution may comprise an acidic solution of metal ions.
• Said etching solution may be based on a mixture of hydrochloric and nitric acids and metal ions present in the following concentrations:
• a method of etching a partially masked surface comprises exposing the surface to an etching solution comprising a dispersion of finely divided particles, said particles being inert to said etching solution and to the surface to be etched.
• Channelling appears to be related to the grain size of the articles to be etched, this being particularly true in the case of articles made of nickel and iron based alloys.
• the grain boundaries of alloys such as these are composed of minor alloy constituents which migrate to the grain boundaries during heat treatment. These minor constituents tend to be more electro-positive the remainder of the alloy. Consequently when these alloys are exposed to acidic solutions, their grain boundaries are preferentially attacked, resulting in the localised evolution of hydrogen.
• grain size varies from alloy to alloy and thus when considering a unit surface area, some alloys possess a larger surface area of grain bound aries than do others.
• the surface area of the grain boundaries is comparatively high and consequently the hydrogen ions from the etching solution are able to easily depolarise and evolve as hydrogen gas.
• the hydrogen ions however, have more difliculty in depolarising on alloys having larger grains due to the reduced area of the grain boundaries. As a result of the decreased rate of hydrogen evolution, large hydrogen bubbles form in the vicinity of the grain boundaries.
• the finely divided particles may be of any material which is inert to the etching solution and the surface to be etched. Suitable materials include silicon, silicates, metal oxides, metal carbides, borides, nitrides and carbon. These examples illustrate the type of materials suitable and do not constitute a complete list of materials capable of producing the desired effect.
• Iron and nickel based alloys are alloys of large grain size which exhibit channelling when partly masked and etched.
• a typical solution for etching partly masked articles made of nickel and iron based alloys without channelling is as follows:
• Example 1 An aqueous etching solution was prepared by dissolving an alloy of iron, chromium and nickel in a mixture of hydrochloric and nitric acids and water to give a solution of the following composition:
• Percent Mo 6 Ti 2 the remainder being nickel plus impurities was partially masked and etched in the aforementioned etching solution fora period of one hour Whilst maintaining the temperature of the solution at 45 C. After removal from the solution the sample was examined and was found to have severe channelling in the region of the maskant/exposed surface interface.
• a further etching solution was prepared as above and to it was added finely divided wood charcoal such that the concentration of the wood charcoal in the etching solution was five grams per litre.
• the wood charcoal comprised particles of the following sizes:
• Example 2 Concentration H+ 4.2 Normal. NO 3.1 Normal. Fe g./l.
• Example 2 A sample of the same nickel based alloy as is mentioned in Example 1 was partly masked and exposed to the afore: mentioned etching solution for a period of one hour whilst maintaining the temperature of the solution at 45 C. After removal from the solution, the sample was examined and found to have severe channelling in the region of the maskant/ exposed surface interface.
• a further etching solution was prepared as above and to it was added finely divided Kaolin such that the concentration of Kaolin in the etching solution was 40 grams per litre.
• Example 3 A partly masked sample of the nickel based alloy described in Example 1 was etched in this solution under the same condition of temperature and time as in Example! with no visible channelling.
• Example 4 An aqueous etching solution was prepared as described in Example 2 and to it was added finely divided aluminium oxide such that the concentrationof aluminiu oxide in the solution was 15 grams per litre.
• Example 1 A partly masked sample of the nickel based alloyzdee scribed in Example 1 was etched in this solution under the same conditions of time and temperature as described in Example 1 with no visible channelling.
• Example 5 An aqueous etching solution was prepared as described in Example 2 and to it was added finely divided wood charcoal such that the concentration of wood charcoal in the solution was 10 grams per litre. The woodcharc'oal was of a similar particle size range asthat'deScribed in Example 1. V j r A partly masked sample of the nickel based alloyldescribed in Example 1 was etched in this solution under the same conditions of time and temperature as in Example l with no visible channelling.
• Example 6 An aqueousetching solution was prepared by dissolving an al,ly 0f;iron, nickel and chrominum in a mixture of nitric acid and hydrochloric acids. The free acid .and nitrate concentrations in the solution were then adjusted to the following levels by further additions of nitric and hydrochloric acids:
• Example 1 A partly masked sample of the nickel based alloy described in Example 1 was etched in the aforementioned solution under the same conditions of time and temperature as in Example 1. After removal from the solution, the sample was examined and found to have severe channelling.
• a further etching solution was prepared as above and to it was added finely divided wood charcoal such that the concentration of the wood charcoal in the etching solution was 10 grams per litre.
• the wood charcoal was of a similar particle size range as that described in Example 1.
• Example 7 An aqueous etching solution was prepared by dissolving ferric chloride and ferric nitrate in a mixture of nitric and hydrochloric acids and water to give a solution of the following composition:
• Example 1 A partly masked sample of the nickel based alloy described in Example 1 was etched in this solution under the same conditions of time and temperature as described in Example 1. Upon removal from the etching solution the sample was examined and found to have severe channelling.”
• a further etching solution was prepared as above and to it was added finely divided particles of aluminium oxide and graphite such that the concentration of the aluminium oxide was grams per litre and the concentration of the graphite was 5 grams per litre in the etching solution.
• Example 1 A partly masked sample of the nickel based alloy described in Example 1 was etched in this solution under the same conditions of temperature and time as in Example 1 with no visible channelling.
• Example 8 An aqueous etching solution was prepared by dissolving a mixture of ferric chloride and ferric nitrate in a mixture of nitric and hydrochloric acids and water to give A partly masked nickel based alloy of the following composition:
• the remainder being nickel plus impurities was etched in this solution under the same conditions of temperature and time as described in Example 1. Upon removal from the etching solution, the sample was examined and found to have severe channelling.
• a further etching solution was prepared as above and to it was added finely divided wood charcoal such that the concentration of the wood charcoal in the etching solution was 15 grams per litre.
• the wood charcoal was of a similar particle size range as that described in Example 1.
• a further partly masked sample of the aforementioned nickel alloy was etched in this solution under the same conditions of time and temperature as in Example 1 with no visible channelling.
• Example 9 Concentration H+ 4 Normal. NO 2 Normal. Fe 150 g./l.
• a further etching solution was prepared as above and to it was added finely divided wood charcoal such that the concentration of wood charcoal in the etching solution was 15 grams per litre.
• the wood charcoal was of a similar particle size range as that described in Example 1.
• a further partly masked nickel based alloy sample was etched in this solution under the same conditions of temperature and time as Example 1 with no visible channelling.
• An etching solution comprising a dispersion of finely divided particles less than p. in diameter and selected from the group consisting of silicon, silicates, metal oxides,

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• ing And Chemical Polishing (AREA)
• Photosensitive Polymer And Photoresist Processing (AREA)

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Cited By (3)

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• 1971
  • 1971-09-21 GB GB4386571A patent/GB1353960A/en not_active Expired
• 1972
  • 1972-09-12 US US00288309A patent/US3836473A/en not_active Expired - Lifetime
  • 1972-09-13 DE DE2244958A patent/DE2244958A1/de active Pending
  • 1972-09-14 IT IT29198/72A patent/IT967463B/it active
  • 1972-09-20 JP JP47094431A patent/JPS4838845A/ja active Pending
  • 1972-09-21 FR FR7233474A patent/FR2153379B1/fr not_active Expired

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