US3666580A - Chemical milling method and bath - Google Patents

Chemical milling method and bath Download PDF

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Publication number
US3666580A
US3666580A US809027A US3666580DA US3666580A US 3666580 A US3666580 A US 3666580A US 809027 A US809027 A US 809027A US 3666580D A US3666580D A US 3666580DA US 3666580 A US3666580 A US 3666580A
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US
United States
Prior art keywords
titanium
bath
metal
hydrofluoric acid
volume
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Expired - Lifetime
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US809027A
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English (en)
Inventor
John F Kreml
John M Leibel
George C Pierpont
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BALTIMORE SPECIALTY STEELS Corp A CORP OF DE
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Armco Inc
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Assigned to ARMCO ADVANCED MATERIALS CORPORATION reassignment ARMCO ADVANCED MATERIALS CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: ARMCO, INC.
Assigned to BALTIMORE SPECIALTY STEELS CORPORATION, A CORP. OF DE. reassignment BALTIMORE SPECIALTY STEELS CORPORATION, A CORP. OF DE. ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: ARMCO ADVANCED MATERIALS CORPORATION
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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
    • C23F1/26—Acidic compositions for etching refractory metals

Definitions

  • our invention generally is concerned with titanium and titanium alloy products.
  • One of the objects of our invention is the provision of a comparatively inexpensive method for chemically removing metal from the surface of titanium and the titanium alloys.
  • Another object is the provision of a method for removing metal from the surface of titanium and titanium alloys in the form of bar and billet, sheet, strip and plate, wire, tubes, special extruded shapes, and the like, to eliminate seams, fissures or other surface discontinuities or to so modify the same as to permit correction by subsequent mechanical processing.
  • Another object is the provision of a bath of removing metal from the surface of titanium and titanium alloys, all with maximum life of bath, and minimum cost.
  • the invention accordingly, consists in the combination of the ingredients forming the bath, in the several operational steps in which the bath is employed, and in the relation of each of these steps to one or more of the others, all as more fully described herein, the scope of the application of which is set out in the claims at the end of this specification.
  • titanium and the titanium alloys are coming into rather widespread use where a savings in weight justifies an increase in cost over other metals.
  • the unalloyed titanium is suited to many applications where ductility and formability are required, along with resistance to corrosion and heat, particularly where light weight is critically important.
  • the unalloyed titanium is particularly suited to ducting, shrouds, stifieners, firewalls and fasteners.
  • the metal also is suited to marine applications. And it commonly is used as weld rod material for the welding of titanium and its alloys.
  • alpha titanium alloys typically is identified as containing about 5% aluminum, 2.5% tin, and remainder titanium. This alloy is strong, ductible and enjoysgood creep-resistance up to about 900 It is'readily welded;
  • a further alloy contains about 8% aluminum, 1% molybdenum, 1% vanadium, and remainder titanium, with mechanical properties slightly improved over the 5% aluminum-2.5% tin alloy.
  • alpha-beta titanium alloys which are most favored in the art, for they respond to heat-treatment.
  • One of the more popular alloys contains about 6% aluminum, 4% vanadium, and remainder titanium, Along with good corrosion-resistance, it is characterized by elevatedtemperature strength and stability, as well as good machinability. It is made available in the form of bars, sheet, strip, wire, extruded shapes, and tubing. It well lends itself to the production of a variety of forgings.
  • a further alpha-beta alloy contains about 6% aluminum, 2% tin, 4% zirconium, 2% molybdenum, and remainder titanium. This alloy when hardened by aging treatment enjoys even higher tensile strength.
  • Another alloy is a titanium alloy containing about 6% aluminum, 6% vanadium, and 2% tin.
  • the titanium alloy having a best combination of mechanical properties, which through age-hardening develops a tensile strength in excess of 210,000 p.s.i., is the beta alloy containing about 13% vanadium, 11% chromium, 3 aluminum, and remainder titanium. This alloy is weldable and is available in the form of bars, wire, sheet and strip.
  • the Beta III alloy may be employed, this containing about 11.5% molybdenum, 6% zirconium, 4.5% tin, and remainder titanium.
  • titanium and titanium alloys enjoy a combination of highly desirable characteristics, including a high ratio of strength-to-weight, weldability, formability, corrosion-resistance and heat-resistance, they are inclined to oxidize at hot-working temperatures. Moreover, they are extremely sensitive to hydrogen embrittlement.
  • an acid pickling bath for example, one comprising a major portion of nitric acid, a minor portion of hydrofluoric acid, and remainderwater.
  • the electrolytic bath typically consisting of a major amount of sulphuric acid, with minor amounts of nitric and hydrofluoric acids.
  • scale is removed and the surface finished by way of mechanical methods, i.e., grinding, grit blasting, sanding, and the like. But these processes not only are time-consuming, but the results had are by no means uniform.
  • the unalloyed titanium as well as its various wellknown alloys, that is, the alpha alloy, the beta alloy, and the alpha-beta alloy, in common converted forms of bar, rod, wire, plate, sheet, strip, tubing and extrusions, as well as forgings, frequently contain minute surface discontinuities in the form of seams, cracks, hairlines and microfissures, which directly and adversely affect further processing.
  • These various surface imperfections may be attributed to a combination of surface hydrogen contamination and working stresses encountered in conversion, that is, ingot to billet, to bar and plate, and to wire, sheet and strip.
  • the hydrogen contamination very well may derive from decomposition of atmospheric water vapor during some prior processing, or from a reducing atmosphere encountered in the fuel-fired furnaces of some prior heating operation.
  • the surface imperfections also may come from minute mechanical defects in the surface of the rolling equipment.
  • the required amount of surface metal is removed by way of what we call a chem-milling process, employing a combination of hydrofluoric and hydrochloric acids in aqueous solution.
  • the hydrofluoric acid-content ranges from some 2% to 7% by volume, with the hydrochloric acid content ranging from about 1% to 10% especially about 3% to 10%, or for best results from about 3% to 7%, or even 5% to 10%.
  • the remainder, of course, is water.
  • hydrofluoric acid content is critical. We find that where the hydrofluoric acid content is as high as 1 there is had undesired hydrogen contamination of the surface of the metal. And where the hydrofluoric acid content is less than 2%, the bath is ineffective. For a best combination of effective metal removal and yet an assured freedom from objec-v tionable hydrogen contamination we employ hydrofluoric acid in the amount of about 2% to 7% by volume, and more especially about by volume.
  • the hydrochloric acid content ranges between about 3% and 1 0%, a best com, bination of results being had with the hydrochloric acid in the amount of about 5% to 7 v
  • the bath is maintained at a temperature of some 65 to 140 F.; for best results the bath temperature is on the order of some 130 to 140 F. With the bath temperature lower than 65 F., little action is bad. And where the temperature exceeds 140 F., the action is too aggressive, and uneven and irregular attack results, giving a non-uniform surface. Moreover, at the higher temperatures there is a loss of the hydrofluoric acid content.
  • the time of treatment ranges from about 5 minutes to about 25 minutes, depending upon bath temperature; as
  • the metal is washed with water under pressure and set aside for drying and subsequent processing or forming operations.
  • the surface is characterized by a dull, satinlike appearance. This is particularly important for hot-rolled Wire destined for colddrawing, Where leading, soaping or other surface lubricating operation commonly is required.
  • Hydrogen analysis of a number of coils shows that the chem-milling operation results in negligible hydrogen contamination. Actual test reveals that with an initial surface hydrogen content on the order of some 34 to 49 ppm. prior to treatment, the hydrogen content subsequent to the chem-milling operation amounts only to some 37 to 54 p.p.m., a pick-up on the order of 5 ppm.
  • hot-rolled unalloyed titanium in the form of a round mill product and found to have some minor surface discontinuity was immersed in a hydrofluoric acidhydrochloric acid solution for about minutes, the solution being at a temperature of some 90 to 100 F.
  • the hydrofluoric acid content of the solution amounted to about 5% by volume and the hydrochloric acid content also 5% by volume.
  • the remainder was water.
  • Examination of the metal following treatment revealed substantial freedom from seam, fissure or other surface discontinuity. The amount of metal removed was on the order of some 0.012 011? the diameter, that is, 0.006" off one surface.
  • a hot-rolled titanium product prior to treatment in the hydrofluoric acid-hydrochloric acid bath first may be subjected to treatment in a molten salt bath, this principally comprising sodium hydroxide with additions of oxidizing salts.
  • the molten salt bath treatment is applied only where the nature of the surface demands it, that is, where an objectionable oxide film is present as a result of some prior mill treatment.
  • Beta 111 titanium alloy when treated in the 5% hydrofluoric acid-5% hydrochloric acid solution for 10 minutes at 100 F, is effectively milled, as in the case of the unalloyed titanium and the 6% aluminum-4% vanadium-titanium alloy. Here some 0.010" is taken off the diameter, this giving an excellent surface, free of crack, seam or blemish. And so, too, the alloy containing 6% aluminum, 2% tin, 4% zirconium, 2% molybdenum, and remainder titanium, when similarly treated for 10 minutes at 100 F., suffers a loss of some 0.006" off the diameter, giving a smooth surface suited to subsequent processing.
  • the art of treating titanium and titanium alloyed products which comprises removing scale from the surface of the products by immersing the same in a molten salt bath principally comprising sodium hydroxide, wash ing the same, immersing said products in an aqueous solution containing about 2% to 7% hydrofluoric acid by volume and 5% to 7% hydrochloric acid for a period of some 2 to '10 minutes while maintaining the bath at a temperature of some 100 to 140 F. whereby surface metal is removed and discontinuities minimized, and then treating the products in a 5% to 20% nitric acid-2% to 5% hydrofluoric acid solution for some minute to 2 minutes to remove any smut or other discoloration on the surface of the metal.
  • the method which comprises treating said products in an aqueous solution of at least 2% but less than 10% by volume hydrofluoric acid and about 3% to 10% hydrochloric acid maintained at 65 to 140 F. for some 2 to 20 minutes to minimize discontinuities and give a surface of dull satin finish; and then treating the products in a 5% to 20% nitric acid2% to 5% hydrofluoric acid solution for some 4 minute to 2 minutes to remove any smut or other discoloration on the surface of the metal, but without polishing the surface.

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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)
  • Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
US809027A 1969-03-20 1969-03-20 Chemical milling method and bath Expired - Lifetime US3666580A (en)

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US80902769A 1969-03-20 1969-03-20

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US (1) US3666580A (enrdf_load_stackoverflow)
JP (1) JPS4843251B1 (enrdf_load_stackoverflow)
DE (1) DE2013149A1 (enrdf_load_stackoverflow)
FR (1) FR2039062A5 (enrdf_load_stackoverflow)
GB (1) GB1304043A (enrdf_load_stackoverflow)
SE (1) SE364078B (enrdf_load_stackoverflow)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4002489A (en) * 1973-06-21 1977-01-11 Nyby Bruk Ab Method of pickling metallic material
US4540465A (en) * 1984-06-11 1985-09-10 Mcdonnell Douglas Corporation Process for continuous recovery of nitric acid/hydrofluoric acid titanium etchant
US4900398A (en) * 1989-06-19 1990-02-13 General Motors Corporation Chemical milling of titanium
US4943419A (en) * 1988-05-24 1990-07-24 Megy Joseph A Process for recovering alkali metal titanium fluoride salts from titanium pickle acid baths
US5100500A (en) * 1991-02-08 1992-03-31 Aluminum Company Of America Milling solution and method
US5248386A (en) * 1991-02-08 1993-09-28 Aluminum Company Of America Milling solution and method
US5462640A (en) * 1991-04-24 1995-10-31 Kernforschungszentrum Karlsruhe Gmbh Etching solution
US20080169270A1 (en) * 2007-01-17 2008-07-17 United Technologies Corporation Method of removing a case layer from a metal alloy
EP2662475A1 (en) * 2012-05-09 2013-11-13 Mitsubishi Heavy Industries, Ltd. Method of removing work-affected layer formed on the surface of a TiAl -based alloy by machining work
US20210293694A1 (en) * 2018-07-17 2021-09-23 Nippon Telegraph And Telephone Corporation Hydrogen Analysis System

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5470162U (enrdf_load_stackoverflow) * 1977-10-28 1979-05-18
US4322254A (en) * 1980-09-22 1982-03-30 Uop Inc. Regeneration of electrical conductivity of metallic surfaces
DE19843738A1 (de) * 1998-09-24 2000-03-30 Univ Ilmenau Tech Beizlösung zur Aktivierung der Oberfläche von Titan und Titanlegierungen
JP2012224894A (ja) * 2011-04-18 2012-11-15 Sumitomo Metal Ind Ltd チタン板の脱スケール方法

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4002489A (en) * 1973-06-21 1977-01-11 Nyby Bruk Ab Method of pickling metallic material
US4540465A (en) * 1984-06-11 1985-09-10 Mcdonnell Douglas Corporation Process for continuous recovery of nitric acid/hydrofluoric acid titanium etchant
US4943419A (en) * 1988-05-24 1990-07-24 Megy Joseph A Process for recovering alkali metal titanium fluoride salts from titanium pickle acid baths
US4900398A (en) * 1989-06-19 1990-02-13 General Motors Corporation Chemical milling of titanium
US5100500A (en) * 1991-02-08 1992-03-31 Aluminum Company Of America Milling solution and method
US5248386A (en) * 1991-02-08 1993-09-28 Aluminum Company Of America Milling solution and method
US5462640A (en) * 1991-04-24 1995-10-31 Kernforschungszentrum Karlsruhe Gmbh Etching solution
US20080169270A1 (en) * 2007-01-17 2008-07-17 United Technologies Corporation Method of removing a case layer from a metal alloy
EP1947217A1 (en) * 2007-01-17 2008-07-23 United Technologies Corporation Method of removing an alpha-case titanium layer from a beta-phase titanium alloy
EP2662475A1 (en) * 2012-05-09 2013-11-13 Mitsubishi Heavy Industries, Ltd. Method of removing work-affected layer formed on the surface of a TiAl -based alloy by machining work
US9481934B2 (en) 2012-05-09 2016-11-01 Mitsubishi Heavy Industries Aero Engines, Ltd. Method of removing work-affected layer
US20210293694A1 (en) * 2018-07-17 2021-09-23 Nippon Telegraph And Telephone Corporation Hydrogen Analysis System

Also Published As

Publication number Publication date
GB1304043A (enrdf_load_stackoverflow) 1973-01-24
FR2039062A5 (enrdf_load_stackoverflow) 1971-01-08
SE364078B (enrdf_load_stackoverflow) 1974-02-11
JPS4843251B1 (enrdf_load_stackoverflow) 1973-12-18
DE2013149A1 (de) 1970-10-01

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AS Assignment

Owner name: ARMCO ADVANCED MATERIALS CORPORATION, STANDARD AVE

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST. , EFFECTIVE DEC. 31, 1987.;ASSIGNOR:ARMCO, INC.;REEL/FRAME:004850/0157

Effective date: 19871216

Owner name: ARMCO ADVANCED MATERIALS CORPORATION,PENNSYLVANIA

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:ARMCO, INC.;REEL/FRAME:004850/0157

Effective date: 19871216

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Owner name: BALTIMORE SPECIALTY STEELS CORPORATION, A CORP. OF

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:ARMCO ADVANCED MATERIALS CORPORATION;REEL/FRAME:004923/0686

Effective date: 19880401

Owner name: BALTIMORE SPECIALTY STEELS CORPORATION, 3501 E. BI

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:ARMCO ADVANCED MATERIALS CORPORATION;REEL/FRAME:004923/0686

Effective date: 19880401