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

Definitions

• the present invention relates to the fabrication of niobium cavities for use in particle accelerators and the like apparatus and more particularly to a process of fabricating such cavities from slices or tubing of pure niobium ingot rather than niobium sheet material.
• niobium cavities of the type well known and used in the operation of particle accelerators and the like apparatus have been fabricated by deep drawing of niobium sheet produced by cold rolling and annealing ingot produced material. While such material has proven satisfactory for use in niobium cavities, the material thus produced exhibits several shortcomings principally related to grain size and grain size distribution.
• Cold roll sheet material for example, exhibits a relatively fine grain structure and thus a plurality of grain boundaries that can affect its performance in cavity operation.
• Cold rolled sheet also exhibits significant variation in grain size through and along the length of the sheet material which also affects its performance in cavities.
• Cast ingot niobium on the other hand exhibits large grain size and relatively uniform grain size distribution through the body of the material.
• niobium cavities are fabricated by the deep drawing of as cast ingot slices or tubing made from large grain ingots. This method results in the production of niobium cavities having a minimum of grain boundaries at a significantly reduced cost as compared to the production of such structures from cold rolled sheet.
• niobium cavities have been fabricated by the deep drawing of cold rolled niobium sheet. Such a fabrication approach, while producing satisfactory cavities did not result in cavities that exhibited optimum operating characteristics, due in large part to the relatively small grain size and the relatively wide grain size distribution exhibited by such cold rolled niobium materials.
• pure niobium is cast or milled into an ingot, generally a round ingot of up to about 17 inches in diameter and up to or beyond 6 feet in length, and the ingot cut transversely, as described below, into slices between about 1/16 and 1 ⁇ 4 inch thick or about the thickness of the cold rolled sheet previously used in the prior art to fabricate such structures or into_tubing.
• the slices are preferably about 1/8 inch in thickness.
• the slices thus obtained are then used in the conventional deep drawing process to produce the desired half cells and the half cells thus produced further fabricated by machining and welding into cavities in the conventional fashion.
• the niobium cavities of the present invention comprise niobium having an essentially "as-cast” grain structure except as such "as-cast” grain structure may have been modified by cold work imparted thereto during the deep drawing process used to form the cavity halves.
• An objective in the development of the process described herein is to minimize the number of grains of niobium present in any single cavity half.
• cavity halves comprising as few as one grain or crystal of niobium is possible, although most of the cavity halves produced as described herein will comprise upwards of two grains to perhaps as many as several hundred grains, but certainly fewer grains than the virtually unlimited number of grains of an about 50 micron size that are present in cavity halves fabricated from rolled sheet as described in the prior art.
• niobium ingot is well known in the art and hence, no further description of this process is presented herein.
• conventionally cast pure niobium ingot is used.
• the ingot is sliced or cut transversely to yield a thin and round piece of niobium of the general size and shape of the cold rolled sheet commonly used for the production of cavities in the prior art or it is cast into tubing.
• the "as cast" structure of the material from which the niobium cavities of the present invention are fabricated includes no grain structure imparted by hot or cold working of the metal (e.g. by hot or cold rolling) other than that which may be incidental to the cold work imparted to the metal during the deep drawing process to form the cavity halves.
• the grain structure is essentially that which was present in the "as cast” ingot from which the ingot slice that is converted into the cavity half by deep drawing was cut.
• Transverse slicing or cutting of the niobium ingot into sheet or tubing_ may be performed in any of a number of conventional fashions including e.g. EDM (electric discharge machining) or even conventional sawing with, for example, a band saw. Whatever method of cutting is used however, care must be taken to assure that the sliced or cut surfaces exhibit satisfactory smoothness for the subsequent drawing and ironing operation.
• EDM sliced material the surfaces are relatively smooth, but in the case of conventional sawing the surfaces will be relatively rough and may require subsequent treatment either, for example by chemical etching, electro-polishing or some other suitable method.
• chemical etching can be accomplished through treatment of the surfaces with a mixture of hydrofluoric, nitric and phosphoric acids.

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• Chemical & Material Sciences (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacture And Refinement Of Metals (AREA)

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Citations (1)

• 2006
  • 2006-06-09 EP EP06252987A patent/EP1865087A1/de not_active Withdrawn

Patent Citations (1)

Non-Patent Citations (4)

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