ELECTROLYTE FOR NANOCRYSTALLINE Fe-Ni ALLOYS WITH LOW THERMAL EXPANSION
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrolyte and processing conditions, by which Fe-Ni alloy sheets having a coefficient of thermal expansion of not more than 9 μm/m K can be produced using electrodeposition or electroforming.
2. Description of the Related Art
Fe-Ni alloys exhibit various properties according to the Ni content, and low thermal expansion properties are exhibited when the Ni content is in a range of 20% to 50% by weight (see D. R. Rancourt, S. Chehab and G. Lamarche, J. Mag. Mag. Mater. 78 (1989) 129.). Specifically, an alloy consisting of 64% Fe and 36% Ni, which is referred to as an invar alloy, has a coefficient of thermal expansion of about zero. The invar alloy has, since its discovery in 1897 by Guillaume (see C. E. Guillaume, C.R. Acad. Sci. Paris 124 (1897) 176.), been used for various practical applications as a typical low thermal expansion alloy.
A useful example of the invar alloy is a shadow mask, which is an essential component of a cathode ray tube (CRT) for a color monitor of a T or PC, and so on. The shadow mask functions to induce electron beams emitted from an electron gun to collide a fluorescent body through apertures formed therein, during which about two thirds (2/3) of total electron beams collide the shadow mask, so that the temperature of the shadow mask increases. Thus, in order to maintain the accurate size and shape of the aperture even with an increase in the temperature of the shadow mask, it is necessary to use a low thermal expansion material, i.e., an invar alloy, thereby acquiring a resolution adaptable for a color monitor. The use of a shadow mask made of invar alloys is expected to be used not only in CRTs but also in field emission displays (FEDs) for flat monitors, which have recently been developed.
Another useful example of such low thermal expansion Fe-Ni alloys includes a lead frame for mounting integrated circuit (IC) chips. The lead frame is a component for electrically connecting chips to external circuits. A chip material and a lead frame
must have a similar coefficient of thermal expansion in the case where it is desired to reduce thermal stress, thereby ensuring an extended life time of an IC chip. In this case, Fe-Ni alloys having the Ni content varying in a range of 40% to 49% according to the chip material selected are generally used. In addition, such low thermal expansion Fe-Ni alloys can be used for bimetal, glass/metal seal, electric components, internal combustion engine pistons and so on, while varying Ni contents.
Various processes have been employed to produce the Fe-Ni alloy sheets, and cold rolling has been typically used for that purpose. When conducting the cold rolling, vacuum melting, forging, hot rolling, normalizing, primary cold rolling, intermediate annealing, secondary cold rolling, and final annealing under a reduction atmosphere etc. should be performed. In order to produce a thin invar alloy sheet having a thickness of 0.1 mm or less, it is necessary to carry out a multi-stage rolling process, as disclosed in U.S. Patent No. 494834, which is, however, complex, and makes it difficult to obtain homogenous products. Also, this process undesirably requires a high production cost. Furthermore, a coefficient of thermal expansion is undesirably sensitive to impurities involved in the process and to a change in the processing conditions (see Metals Handbook, 9th ed. Vol. 3, ASM (1980) 889.).
To avoid such limitations of the conventional processes, vigorous research into preparation processes of Fe-Ni alloys by electrodeposition (electroforming) has recently been carried out. However, the known processes of producing the Fe-Ni alloys containing 20 to 50 wt% of Ni by electrodeposition (electroforming) have failed to provide favorable products, since the composition of electrolytes and processing conditions are quite a complicated work. The research has not yet proven to be satisfactory. For example, Korean Patent Application No. 10-2001-0019169 discloses an electrolyte and processing conditions, by which a permalloy consisting of 20% Fe and 80% Ni is reproducibly produced. However, in order to produce an invar alloy and a Fe-Ni alloy containing Ni of not more than 50 wt%, the composition of the electrolyte and processing conditions thereof should be fundamentally changed.
SUMMARY OF THE INVENTION
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide an electrolyte and processing
conditions for producing an Fe-Ni alloy having a desired coefficient of thermal expansion by a single-step electroforming process, thereby providing the Fe-Ni alloy with a uniform alloy composition.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic diagram of an electrodeposition (electroforming) apparatus for producing an Fe-Ni alloy sheet according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In accordance with the present invention, there are provided an electrolyte having a desired composition and special processing conditions, thereby acquiring a uniform Fe-Ni alloy composition.
The electrolyte proposed in the present invention is a solution comprising ferrous sulfate (FeSO4 7H2O) or ferrous chloride (FeCl 4H2O); nickel sulfate (NiSO4 6H2O) or nickel chloride (NiCli 6H2O) or nickel sulfamate (Ni(NH2SO3)2); and boric acid (H3BO3); sodium saccharin (C H NO3SNa); sodium lauryl sulfate (Cι2H25O4SNa); and sodium chloride (NaCl). Specifically, the electrolyte comprises 20 to 30 g/1, preferably 22 to 25 g/ of boric acid (H3BO3), 1 to 3 g/1, preferably 2.0 to 2.4 g/1 of sodium saccharin (C7H NO3§Na), 0.1 to 0.3 g/1, preferably 0.1 to 0.2 g/1 of sodium lauryl sulfate (C12H25θ4SNa), and 20 to 40 g/1, preferably 30 to 32 g/1 of sodium chloride (NaCl). The Fe compound and Ni compound in the electrolyte are released in the form of ion and are electro deposited in the form of Fe-Ni during electrodeposition (electroforming). Boric acid is added as a pH buffering agent, sodium saccharin is added as a stress relaxing agent for the Fe-Ni alloy, and sodium chloride is added for enhancing the conductivity of the electrolyte. During electrodeposition (electroforming), the pH of the electrolyte is maintained in a range of 2 to 4, the current density is in a range of 50 to 100 mA/cm2, and the temperature is in a range of 50 to 60 °C.
Tables 1 through 6 show the compositions of electrolytes for forming Fe-Ni alloy sheets having an Ni content in a range of 20 to 50 wt% by electrodeposition (electroforming) under the processing conditions as stated above.
Table 1: Using the solution containing ferrous sulfate (FeSO4 7H2O) and nickel Ssulfate (NiSO4 6H2O)
<for 1 1 of distilled water>
Table 2: Using the solution containing ferrous sulfate (FeSO4 7H
2O) and nickel chloride (NiCl^ 6H
2O)
<for 1 1 of distilled water>
Table 3: Using the solution containing ferrous chloride (FeCl^ 4H20) and nickel sulfate (N1SQ4 6H2O)
Table 4: Using the solution containing ferrous chloride (FeCl^ 4H2O) and nickel chloride (NiCl2 6H2O)
<for 1 1 of distilled water>
Table 5: Using the solution containing ferrous sulfate (FeSO 7H
2O) and nickel sulfamate (Ni(NH
2SO
3)
2)
<for 1 1 of distilled water>
Table 6: Using the solution containing ferrous chloride (FeCl^ 4H2O) and nickel sulfamate (Ni(NH2SO3)2)
<for 1 1 of distilled water>
Table 1 shows the results of Fe-Ni alloys having the desired compositions according to Examples 1 through 10 using electrolytes containing ferrous sulfate (FeSO4 7H2O) and nickel sulfate (N.SO4 6H2) as main components, with using the amounts of nickel sulfate at a constant level of 97 g/1 and the amounts of ferrous sulfate in a range of 28 to 73 g/1.
Table 2 shows the results of Fe-Ni alloys having the desired compositions according to Examples 11 through 17 using electrolytes containing ferrous sulfate
(FeSO 7H2O) and nickel chloride (NiCtø 6H2O) as main components, with using the amounts of nickel chloride at a constant level of 97 g 1 and the amounts of ferrous sulfate in a range of 36 to 70 g/1.
Table 3 shows the results of Fe-Ni alloys having the desired compositions according to Examples 18 through 23 using electrolytes containing ferrous chloride (FeC-2 * 4H2O) and nickel sulfate (MSO4 6H2O) as main components, with using the amounts of nickel sulfate at a constant level of 97 g/1 and the amounts of ferrous chloride in a range of 30 to 70 g/1.
Table 4 shows the results of Fe-Ni alloys having the desired compositions according to Examples 24 through 29 using electrolytes containing ferrous chloride (FeClf 4H2O) and nickel chloride (NiCl^ 6H2O) as main components, with using the amounts of nickel chloride at a constant level of 97 g/1 and the amounts of ferrous chloride in a range of 34 to 65 g/1.
Table 5 shows the results of Fe-Ni alloys having the desired compositions according to Examples 30 through 35 using electrolytes containing ferrous sulfate
(FeSO4 7H O) and nickel sulfamate (Ni(NH2SO3)2) as main components, with using the amounts of nickel sulfamate at a constant level of 97 g/1 and the amounts of ferrous
sulfate in a range of 25 to 52 g/1.
Table 6 shows the results of Fe-Ni alloys having the desired compositions according to Examples 36 through 41 using electrolytes containing ferrous chloride (FeC 4H2O) and nickel sulfamate (Ni(NH2SO3)2) as main components, with using the amounts of nickel sulfamate at a constant level of 97 g/1 and the amounts of ferrous chloride in a range of 22 to 52 g/1.
An apparatus for producing the Fe-Ni alloys having the desired compositions according to the present invention is not particularly limited, and a batch-type electrodeposition (electroforming) apparatus shown in FIG. 1 was used to produce Fe- Ni alloy sheets according to Examples 1 through 41, as shown in Tables 1 through 6. As shown in FIG. 1, electrodeposition (electroforming) was conducted such that an electrolyte 3 according to the present invention was put in an electrodeposition bath 9, and a circulation pump 5 was operated to allow the electrolyte 3 to flow between a cathode 1 and an anode 2, spaced 10 mm apart from each other, at a flow rate of 0.1 to 2.0 m/sec. When a 20 μm thick Fe-Ni alloy was electrodeposited on the cathode 1, a current supply device 4 was stopped, and a desired Fe-Ni alloy sheet was isolated from a cathode surface. According to an aspect of the present invention, the apparatus uses an anode material having different angles of inclination 10 according to flow rate.
The Fe-Ni alloys produced by the above-described processes exhibited coefficients of thermal expansion in a range of about 1 lo about 9 μm/m K according to only the alloy compositions, irrespective of kinds of electrolytes listed in Tables 1 through 6. Table 7 shows coefficients of thermal expansion obtained using a thermal expansion measuring apparatus through several examples. The invar alloy sheets according to the present invention exhibited excellent low thermal expansion properties^ compared to the commercially available invar alloy sheets having coefficients of thermal expansion in a range of 1.2 to 1.5 μm/m Kat the same temperature range.
Table 7: Coefficient of thermal expansion of Fe-Ni alloys according to the present invention at a temperature range of 50 to 100 °C .
According to evaluation by X-ray diffraction, the Fe-Ni alloy has a nanocrystalline structure having a grain size of 5 to 15 nm. The results confirmed that the grain size of the invar alloy composition according to the present invention was very small to be in a range of 5 to 7 nm. If the invar alloy of the present invention has such nanocrystalline structure, the yield strength thereof is about 2,000 MPa, which is much higher than that of the conventional invar alloy being in a range of 260 to 500 MPa. Therefore, the Fe-Ni alloy sheet according to the present invention can be employed for new applications where there is a demand for providing high strength.
According to the present invention, since Fe-Ni alloys having low thermal expansion properties are produced by a single-step electroforming process, the production cost can be greatly reduced. Particularly, since the Fe-Ni alloys according to the present invention have a nanocrystalline structure, they exhibit excellent mechanical properties, thereby creating a new range in industrial uses.