Giant grains or single crystals of chromium and process for prod

Details Giant grains or single crystals of chromium and process for prod Giant grains or single crystals of chromium and process for prod

1991-05-24

1992-10-13

Kunemund, Robert

Adhesive bonding and miscellaneous chemical manufacture

Delaminating processes adapted for specified product

Delaminating in preparation for post processing recycling step

148DIG41, 156605, 156DIG73, 264 25, 423 53, C30B 3300

Patent

active

051547961

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to giant grains or single crystals of chromium and a process for producing the same.


BACKGROUND TECHNIQUE

Chromium, though excellent in corrosion resistance and heat resistance, is limited in its application to use chiefly as an additive to alloys, and use of chromium as a single substance has not been put into practical use except as a target material for sputtering.
The main reason for this resides in chromium's brittleness which itself is attributed to brittleness of grain boundaries, and plastic processing of chromium is therefore very difficult.
Hence, production of practical chromium moldings cannot but rely on processes having poor yields, such as discharge processing and wire cutting, and it has been virtually impossible to obtain, chromium moldings of complicated shape.
Problems due to the brittleness of grain boundaries of metals such as chromium can be fundamentally solved by obtaining single crystals having no boundaries.
As a method for forming single crystals of metals, for example, molybdenum, there is proposed a recrystallization method as described in JP-A-59-141498. This method is concerned with a method of addition of an additive called a pinning element to a single crystal component as an essential condition for the single crystal formation, and strict quantitative control of the addition (CaO, MgO) is required.
A currently widespread method for obtaining chromium single crystals is a floating zone method. This method, however, involves problems such as limited productivity per unit time, limitation of the products in shape to a bar of relatively small diameter, and need of a very complicated apparatus. It has thus been extremely difficult to obtain a chromium single crystal having a large size or a complicated shape.
If a large-sized, optionally shaped chromium single crystal can be obtained easily, the problem of poor yields in working by the conventional processing techniques would be eliminated, and application to electronic parts in which moldings having a relatively complicated shape are required could be expected, thus greatly broadening the application of chromium.


DISCLOSURE OF THE INVENTION

The present inventors have conducted extensive studies on preparation of chromium single crystals, paying attention to the behavior of impurities present in a chromium component, e.g., Ti, Al, Si, and Ca, in single crystal formation of chromium by secondary recrystallization. As a result, they have noted that these impurities exert a favorable influence on single crystal formation of chromium and found that it is possible to achieve single crystal formation of chromium by first sintering chromium containing at least one of these impurities as an unavoidable component, chromium to which at least one element selected from Ti, Al, Ca, and Si has been added in an amount of a certain range, or chromium to which these have been added and which further contains Co, and then subjecting the sintered material to heat treatment under a relatively mild condition, i.e., secondary recrystallization, leading to accomplishment of the present invention.
That is, the present invention relates to a process for producing giant grains or single crystals of chromium, which comprises heat treating a chromium molding to which at least one element selected from the group consisting of Ti, Al, Ca, and Si has been added, or a chromium molding which contains Co and to which at least one element selected from the group consisting of Ti, Al, Ca, and Si has been added, or a chromium molding which contains at least one of these elements, each chromium molding having a strain imparted thereto by sintering; and giant grains or single crystals of chromium to which at least one element selected from the group consisting of Ti, Al, Ca, and Si has been added in an amount of from 0.0002 wt % as a lower limit to 0.1 wt % as an upper limit calculated as an oxide thereof, or of chromium which contains from 0.01 to 3 wt % of Co and to which at least one element selected from the g

REFERENCES:
"Growth of Large-Diameter Crystals by HEM for Optical and Laser Application", Khattak et al. (1984) vol. 505, pp. 4-8.
"Thermal Expansion of Chromium Single Crystals At The Neal Temperature"; Masumoto et aL.; J. Phys. Soc. Jap. vol. 27 (3) p. 786.

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