Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
  • C22F1/18—High-melting or refractory metals or alloys based thereon
  • C22F1/183—High-melting or refractory metals or alloys based thereon of titanium or alloys based thereon

Definitions

• This invention relates to processes for making fasteners and other parts from titanium or a titanium alloy, and in particular to a process in which a titanium or titanium alloy part is solution heat treated before being thermomechanically formed.
• the titanium alloy Ti-6A1-4V has been used to make high strength fasteners, such as bolts and screws.
• the alloy is supplied in bar, rod, or wire form depending on the type and size of fastener to be made. Hitherto, the bar, rod, or wire has been supplied to the consumer in the annealed condition.
• the consumer forms the fasteners by such techniques as forging, heading, or extrusion, or a combination of those techniques.
• the fastener blanks are usually formed at an elevated temperature starting from about 649°C, but usually not below about 427°C.
• the fastener blanks are then cleaned by immersion in a molten salt bath, which is followed with acid etching.
• the fastener blanks are next heat treated to achieve a desired strength level.
• the known heat treatment is a two-stage treatment, the first stage, the parts are solution treated, typically in an inert atmosphere, at about 899 to 968 °C for about 1 hour and then water quenched.
• the parts are precipitation hardened by an aging treatment at about 427 to 566° C for 2 to 8 hours and then cooled in an inert gas or in a vacuum. Hitherto, the aging step has been performed directly after the solution-treating step.
• the solution treatment is the most problematic step in the heat treatment cycle because during solution treatment contamination of the fasteners must be prevented. Titanium and its alloys are very reactive, especially at elevated temperatures such as those typically used for solution treatment. Any foreign material which comes into contact with the titanium or titanium alloy during solution heat treatment will result in contamination of the material. Common sources of foreign material in the solution treating process are contaminants in the furnace atmosphere or residual processing materials such as lubricants on the surfaces of the titanium blanks, order to avoid the problems associated with the presence of such contaminants, special furnace atmospheres must be maintained and the fasteners must be thoroughly cleaned before they are placed in the heat treating furnace. Cleaning of the fasteners presents another problem because it involves the use of aggressive chemicals which pose environmental hazards and disposal concerns. Additionally, the cleaning operation can change the chemistry of the fasteners, such as by adding hydrogen, and can alter the dimensions of the fastener by dissolving metal from the blank. These problems make the cleaning step unreliable, time consuming, and costly. ⁇
• Beta titanium alloys such as Ti 3-8-6-4-4 and others, are supplied in the solution treated condition for forming into fasteners. The fasteners are then aged to achieve the desired properties.
• the beta alloys are supplied in the solution treated condition for forming into fasteners. The fasteners are then aged to achieve the desired properties.
• there are significant metallurgical differences between the beta alloys and the other known titanium alloys such as alpha, near-alpha, an alpha-beta alloys.
• a process of making parts from titanium and titanium alloy wire, rod, or bar is provided.
• titanium means unalloyed titanium as well as alpha, near-alpha, and alpha-beta titanium alloys.
• the process includes the step of preparing an intermediate form of titanium.
• the intermediate form is solution treated under conditions of temperature and time that are sufficient to produce a desired level of strength when the alloy is subsequently age hardened.
• the solution treated material is then formed into a desired part or component, such as a fastener or a preform for a fastener.
• the forming step is conducted with the alloy at an elevated temperature and the as- formed part is rapidly cooled from the finish temperature. Subsequent to the forming step, the part is age hardened to achieve the desired level of strength and hardness.
• an intermediate form of a titanium alloy preferably Ti-6A1-4V
• Preferred intermediate forms include wire, rod, and bar.
• the Ti-6A1-4V alloy is a known titanium alloy that contains about 6 weight percent (%) aluminum, about 4 % vanadium, and the balance is titanium and usual impurities.
• the impurities present in the alloy are restricted such that the alloy contains not more than about 0.10% carbon, not more than about 0.05% nitrogen, not more than about 0.0125% hydrogen, and not more than about 0.20% oxygen.
• the oxygen is preferably limited to about 0.14-0.17%.
• the method by which the intermediate form is made is not critical and any of the known methods for making titanium alloy wire, rod, or bar may be used.
• the intermediate form of the titanium alloy is then solution treated at about 899-968 °C for a time of at least about 1 minute up to about 2 hours, and then water quenched.
• the intermediate form is heated at the solution temperature for about 1 hour.
• the intermediate form may be coated with a lubricant.
• the preferred lubricant is a dry film lubricant, which consists of graphite and molybdenum disulfide. Other lubricants that are known to those skilled in the art for similar purposes may also be suitable.
• the lubricated wire, rod, or bar is then subjected to thermomechanical working to form the desired part.
• the preferred forming operation is forging, and heading is particularly preferred for making small parts from wire or rod.
• extruding techniques can be used in connection with the preparation of parts by this process.
• the intermediate form Prior to forming, the intermediate form is cut to a starting size, heated to an elevated starting temperature, and then mechanically worked to the desired size and shape.
• the elevated starting temperature for the thermomechanical forming is selected to be as close to the solution treating temperature as practicable.
• a lower forming temperature can be used for applications where adequate lubrication, extended die life, or dimensional control of the part or preform is important.
• the parts are formed from a starting temperature of about 871 °C, but preferably not below about 704 °C or 649 °C. Lower finishing temperatures may be used under appropriate circumstances. However, it is expected that the finishing temperature would, in any event, not be below about 427 °C.
• the as-formed parts are rapidly cooled from the finishing temperature, preferably by water quenching.
• the as-formed parts are then age hardened, preferably in a vacuum heat treating furnace.
• the parts may also be aged in an inert atmosphere such as argon or helium. It is also expected that the parts can be aged in air.

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• Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Physics & Mathematics (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Forging (AREA)
• Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)

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• 2004
  • 2004-08-04 WO PCT/US2004/025192 patent/WO2005017225A1/en active IP Right Grant
  • 2004-08-04 CA CA2535038A patent/CA2535038C/en not_active Expired - Fee Related
  • 2004-08-04 US US10/910,971 patent/US20050028905A1/en not_active Abandoned
  • 2004-08-04 DE DE602004010138T patent/DE602004010138T2/de active Active
  • 2004-08-04 EP EP04780090A patent/EP1654393B1/en not_active Not-in-force
  • 2004-08-04 AT AT04780090T patent/ATE378436T1/de active
  • 2004-08-04 JP JP2006522698A patent/JP2007501327A/ja active Pending
  • 2004-08-04 RU RU2006106723/02A patent/RU2368696C2/ru not_active IP Right Cessation

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