JP2007335118A - Cavity of large crystal grain from pure niobium ingot - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a niobium cavity in which a relatively large and uniform crystal grain size characteristics are formed. <P>SOLUTION: The niobium cavity is manufactured by a deep drawing of a slice or tube of cast niobium ingot rather than by a cold rolling sheet. Compared with the manufacture from the cold rolling sheet, crystal grain size characteristics are improved, and manufacturing cost can be reduced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to the fabrication of niobium cavities for use in grain accelerators and similar devices, and more particularly fabrication of such cavities from pure niobium ingot slices or tubes rather than niobium sheet material. Regarding the method.

  In the prior art, niobium cavities used in the operation of well-known types of grain accelerators and similar devices are made by deep drawing niobium sheets produced by cold working and annealing of ingot production materials. It was. Although such materials have proven satisfactory for use in niobium cavities, the materials thus produced exhibit several drawbacks primarily related to grain size and grain size distribution. For example, cold rolled sheet material exhibits a relatively fine grain structure, and thus a large number of grain boundaries affect its performance in cavity operation. Cold rolled sheets also show considerable variation in grain size along the direction through and along the length of the sheet material, which also affects its performance in the cavity. On the other hand, cast ingot niobium exhibits a large grain size and a relatively uniform grain size distribution throughout the material body. The presence of large grains results in a reduction in the number of grain boundaries and thus results in improved performance in the final cavity structure. Thus, if the relatively large and uniform grain size characteristics of “as-cast” or ingot niobium are stored in the formed cavities, performance will undoubtedly be improved.

  In addition to the disadvantages associated with the above grain size of conventional sheet material based cavities, there are other significant disadvantages associated with the use of cold rolled sheet material in the manufacture of niobium cavities. They include: 1) the relatively high cost associated with cold rolling and annealing of niobium to produce sheets; 2) heated due to the relatively small grain size exhibited by cold rolled sheet material If their strength is unacceptably reduced; and 3) cold rolled sheets exhibit “memory” or “springback” characteristics, which are formed after deep drawing to ensure accurate dimensional characteristics May require a large and costly finish of the formed cavity. Such springback is due to the presence of bands in the cold rolled sheet or the lack of uniformity in grain size. All of these drawbacks can be positively affected by the use of “as-cast” ingot-based niobium starting materials that have a large and relatively uniform grain size distribution.

  Accordingly, it is an object of the present invention to provide a method for fabricating niobium cavities having large grains and uniform grain distribution.

  Another object of the present invention is to provide a method for producing niobium cavities at a significantly reduced cost compared to the production of such structures from cold rolled sheets.

  According to the present invention, niobium cavities are made by deep drawing an as-cast ingot slice or tube made from a large grain ingot. This method results in the production of niobium cavities with minimal grain boundaries at a significantly reduced cost compared to the production of such structures from cold rolled sheets.

  As described above, in the prior art, the niobium cavity has been manufactured by deep drawing of a cold-rolled niobium sheet. While such fabrication methods produce satisfactory cavities, most result in cavities that exhibit optimal operating characteristics due to the relatively small grain size and relatively wide grain size distribution exhibited by such cold rolled niobium materials. There wasn't.

  In order to improve the performance of such cavities, methods have been explored to have relatively large grain sizes (or single grains), while simultaneously reducing the number of grain boundaries, and also relatively uniform crystals. Fabrication techniques have been found that provide cavities with a particle size distribution.

  It has now been discovered that fabrication of cavities in a conventional manner, but using starting materials that include ingot sheet thickness slices or tubes, produces cavities that exhibit desirable grain size and grain size distribution characteristics. . Quite surprisingly, cavities manufactured as described herein exhibit excellent thermal conductivity for thermal stability or RRR, as mentioned in the relevant prior art.

  Thus, according to the method of the present invention, pure niobium is cast or rolled into an ingot, typically a round ingot up to about 17 inches in diameter and up to 6 feet in length or more, and the ingot Cut in the transverse direction as described below to a thickness of about 1/16 inch to 1/4 inch, or the cold rolled sheet thickness previously used to fabricate such a structure in the prior art. Slices or tubes. The slice is preferably about 1/8 inch thick. The slices thus obtained are then used in a conventional deep drawing process to produce the desired plurality of cell halves and the thus produced plurality of cell halves are converted to conventional methods. Assemble into cavity by machining and welding. Accordingly, the niobium cavities of the present invention include niobium having an essentially “as-cast” grain structure, provided that the “as-cast” grain structure is a deep drawing process used to form half of the cavity. It can be changed by the cold working provided therein. The goal in developing the method described herein is to minimize the number of niobium grains present in every cavity half. Using the process described herein, it is possible to produce a cavity half that contains only one niobium grain or crystal. However, most of the cavity halves produced as described in this application will contain two or more grains and possibly hundreds of grains, but as described in the prior art, they are made from rolled sheets. Will surely contain fewer grains than the visually unlimited number of grains of the size of about 50 microns present in the cavity half.

  Since niobium ingot casting is well known in the art, no further description of this process is presented here. For the purposes of the present invention, a conventional cast pure niobium ingot is used. After casting, the ingot is sliced or cut transversely to obtain thin and round niobium pieces of the general size and shape of cold rolled sheets commonly used in the prior art for the manufacture of cavities, or into tubes Cast. The “as-cast” structure of the material from which the niobium cavities of the present invention are made is distinct from the grain structure that can occur accidentally in the cold work imparted to the metal during the deep drawing process to form the cavity half. As described above, a crystal grain structure imparted by hot or cold working (for example, hot or cold rolling) of a metal is not included. Thus, in the final cavity, the grain structure is essentially the grain structure present in the “as-cast” ingot that is cut into ingot slices that are converted into cavity halves by deep drawing.

Many conventional methods including slicing or cutting niobium ingots into sheets or tubes into a sheet or tube, including, for example, EDM (Electric Discharge Machining), or even conventional sawing using, for example, a band saw It can be done with either. However, whatever cutting method is used, care must be taken to ensure that the sliced or cut surface exhibits satisfactory smoothness for subsequent drawing or ironing operations. In the case of EDM slice material, the surface is relatively smooth, but in the case of conventional sawing, the surface is relatively rough and, for example, by chemical etching, electropolishing or some other suitable method Subsequent processing may be required. As is well known in the art, chemical etching can be performed by treating the surface with a mixture of hydrofluoric acid, nitric acid and phosphoric acid.

  Once a sufficiently smooth “sheet” produced by slicing or cutting an ingot and the surface smoothing just described is obtained, it is processed according to conventional well known deep drawing, machining and welding processes. To produce a finished cavity exhibiting the improved properties previously described.

  Thus, a method for producing a large grain cavity from a pure niobium ingot, in which the pure niobium ingot is cast, and the ingot is sliced in the transverse direction to obtain an approximate thickness of the cold-rolled niobium sheet. A method has been described which comprises making the improved niobium cavities of the present invention by slicing or slicing the tube and then deep drawing, machining and welding according to conventional processing techniques.

  As described in the present invention, the invention may be modified in many ways without departing from the intended spirit and scope of the invention, and any or all of such modifications are within the scope of the appended claims. It will be apparent to those skilled in the art that it is intended to be included in

Claims (10)

Niobium cavity manufacturing method including:
a) forming a pure cast niobium ingot;
b) slicing the cast niobium ingot to form a cast niobium ingot slice or tube;
c) Deep drawing a slice or tube of a cast niobium ingot into cell halves; and d) welding a plurality of cell halves to form a cavity.   The method of claim 1, wherein the cast niobium ingot slice is produced by cutting the cast niobium ingot in a transverse direction.   3. The method of claim 2, wherein the cast niobium ingot slice is about 1/16 inch to 1/4 inch thick.   The method of claim 1, wherein the slice of cast niobium ingot has a surface and the surface is smoothed before deep drawing.   The production method according to claim 4, wherein the smoothing is performed by chemical etching or electropolishing. Niobium cavities produced by a method comprising:
a) casting a pure niobium ingot to form a cast niobium ingot;
b) slicing the cast niobium ingot to form a slice of the cast niobium ingot;
c) Deep drawing a slice of cast niobium ingot into cell halves; and d) welding a plurality of cell halves to form a cavity.   The niobium cavity according to claim 6, wherein the slice of cast niobium ingot is produced by cutting the cast niobium ingot transversely.   A half of the niobium cavity containing niobium having an essentially as-cast grain structure.   9. Niobium cavity half as claimed in claim 8 wherein the essentially as-cast grain structure is altered only by cold working provided during deep drawing to form the cavity half. The niobium cavity half of claim 8 comprising from about 1 to about several hundred grains having a diameter greater than about 50 microns.