JPS63264261A - Casting method for rare earth metal - Google Patents

Abstract

PURPOSE:To obtain a casting product of high quality in a stable by casting the molten metal of a rare earth metal in a specific height into the mold forcibly cooling the bottom face. CONSTITUTION:The bottom face of a mold is made of the structure capable of forced cooling, the liquid cooling by water, oil, etc., is usually used and in the case of water cooling a cooling water 5 is sufficiently flowed for cooling. The height of the side face frame 2 of the mold can optionally be selected by the thickness of the necessary casting product. The molten metal of a rare earth metal is cast into this forcibly cooled mold so as to become of the height less than 1/2 length of the longest line part dividing the bottom face. The casting product of high quality is obtd. in stable.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for casting rare earth metals. Specifically, the present invention relates to a method for casting rare earth metals mainly composed of columnar crystals suitable for sputtering targets and the like.

[Conventional technology and its problems]

As a method for casting rare earth metals, it is known to use a vertical mold whose temperature can be controlled from the side (for example, Japanese Patent Application Laid-Open No. 1023-33). In this method, if the molten rare earth metal is rapidly cooled by cooling the side surface, there is an inconvenience that a shrinkage cavity will occur in the center of the mold. No nests occur, but the crystals become coarse. In addition, if casting is performed in an air-cooled state, there will be many columnar crystals, but the shape of the crystals differs widely between near the side wall surface and in the center), making it difficult to obtain a cast product with uniform crystals.

Sputtering, such as sputtering used in magneto-optical disk manufacturing, requires a sputtering surface with a uniform fFK film thickness, but if a rare earth metal with coarse crystals is used as a sputtering target, the crystals will be oriented in a dependent manner and the same sputtering force will be affected. Even if sputtering is performed under such conditions, the film thickness will change and a uniform product cannot be obtained.

Furthermore, if there is a cavity in the sputtering target, abnormal discharge will occur during sputtering, which will not only damage the uniformity of the product but also make it impossible to continue sputtering.

[Means for solving problems]

As a result of intensive research to obtain cast products suitable for use as sputtering targets, the inventors of the present invention have found that rare earth metals can be cast with a stable and high performance by using a casting mold with a specific structure. The present invention was completed based on the knowledge that high quality castings can be obtained.

Specifically, the purpose of the present invention is to produce rare earth metal products of great industrial value, and this purpose is to:
This is achieved by pouring a molten rare earth metal into a mold whose bottom surface is forcibly cooled so as to reach the height below the A long plate of the longest line dividing the bottom surface.

The present invention will be explained in detail below. .

The rare earth metals referred to in the present invention refer to atomic number! It includes 7 to 7/7 lanthanides, yttricum and scandium. These metals may be used alone or may be alloys of these metals. First, the rare earth metal of the present invention includes a small amount of metal other than the rare earth metal,
For example, it may contain 10 or less transition metals.

Next, the mold used in the present invention will be explained.

The bottom surface of the mold can be arbitrarily selected, such as flat or recessed, as long as it has a structure that allows forced cooling. There are no restrictions on the material, and various metals, ceramics, etc. can be used, but steel and stainless steel are preferred.

Although the forced cooling method can be arbitrarily selected, water cooling and liquid cooling using oil or the like are usually used. Also,
Air cooling using cooling fins may also be used.

It is preferable to cool the bottom of the mold before pouring the molten metal. For example, in the case of water cooling, it is preferable to cool the bottom of the mold by sufficiently flowing cooling water.

The amount of cooling water depends on the amount of molten metal, temperature, bottom area of the mold, etc., so the flow rate cannot be specified, but the cooling water should be supplied so that the outlet temperature of the cooling water is 0℃ or less, preferably 7θ℃ or less. It is preferable to supply.

□The side frame of the mold is made of nine metal I! ! 2! In consideration of removal, it is preferable to make the mold separately from the bottom, but please consider ways to remove the cast metal, such as slanting the side frames so that the top of the mold is wider than the bottom. Alternatively, it may be one that is integrated with the bottom surface. Materials include those that are difficult to form alloys on molten rare earth metals, rust, stainless steel,
Cast iron and ceramics such as boron nitride are preferred.

゛The side frame may be cooled by air or forced cooling like the bottom, but the heat capacity must be such that when molten metal is poured, the surface temperature rises at the temperature R''* at which it forms an alloy with the molten metal. On the other hand, if the surface temperature does not reach the level of alloy formation, it is preferable to let it cool.Also, if the side frame is made of ceramics, it will not form a compound with ordinary metals. You can leave it to cool.

The height of the side frame can be arbitrarily selected depending on the desired thickness of the casting. Usually, the W of the longest line segment (diameter in the case of a circle) that is formed by the side frame and divides the bottom of the hole.
When manufacturing a sputtering target at #, where the height below the long plate is preferable, the longest line dividing the bottom is not necessary.
It is preferable to choose from the Akinaga range.

In the casting of the present invention, the top surface of the mold may be open, but it is preferable to keep the top surface warm for the purpose of preventing the formation of shrinkage cavities and promoting the growth of columnar crystals or equiaxed crystals. As for the upper surface of the mold, metal plate, ceramic plate,
Examples include a method of placing a cover made of an inorganic heat insulating material or a combination thereof. Specifically, a method of covering with a metal plate such as tantalum or niobium, or a heat insulating plate such as a ceramic plate can be mentioned.

To cast rare earth metals, the molten rare earth metal is poured into the mold described above, but the temperature of the molten metal is the melting point of the metal. The temperature is preferably θ°C, preferably 100°C higher. If the temperature of the molten metal is too low, the flow of the molten metal will be poor, causing solidification at the casting opening and shrinkage cavities due to uneven water flow.

First, it is preferable to pour the molten metal to a height that is equal to or lower than the length of the longest line dividing the bottom surface. When targeting an IPIK sputtering target, it is preferable to cast at a height between the nominal length and the optical length of the longest line segment that divides the bottom surface.

〔Example〕

The present invention will be explained below with reference to examples.

Example 1 As shown in Fig. 1, a ring-shaped stainless steel frame was placed on a water-cooled copper plate, and the inner diameter was //! A simple mold was made, a cover made of tantalum plate was placed on the top, and terbium metal was poured into it at 14 tjθ℃ to a diameter of 4 tOtm and a thickness of 10w.
m disks were obtained.

When we examined the structure of the obtained metal plate, we found that the size of the crystal grains was at the bottom! It was an equiaxed crystal with a diameter of 0-100μ and /σθ~−〇〇μ at the top. In addition, an X-ray photograph of the inside revealed that there were no nests.

Therefore, a disk with a thickness of 7wm was cut out from the lower part, and a sputtering target with a diameter of /2j■ and a thickness of j was obtained by lathe processing.The size of the crystal grains in this part is !θ ~ /
θθμ, and using this sputtering target, sputtering was performed under the following conditions.

The results are shown in Table 1.

Equipment used for sputtering conditions Magnetron type sputtering equipment
Force 1) 0 2θOOOWθ Puttering time 30 seconds Press batter / θ minutes Distance between metal and get substrates 100van Substrate used Polycarbonate comparative example/Metal TV ram with thickness O0! ■Made from tantalum and has a diameter of 90 cm! Shizuku, height! The mixture was placed in a Q■ crucible and heated to 10°C/minute in a vacuum induction furnace to melt it, and then cooled to its edge at a cooling rate of ♂°C/minute to solidify.

Then, use a lathe to cut the mental crucible to a diameter of lλ.
! Fin, thick! A simple sputtering target was obtained.

When we investigated this metal mwt, we found that the crystal grain size was /
,! It was an equiaxed crystal of ~3. In addition, when the inside was examined using X-ray photographs, it was found that there was a hive nest.

Using this sputtering target, sputtering was performed on a polycarbonate plate under the same conditions as in the example.

As shown in Table 1, it was found that the film obtained in Comparative Example/ had a large change in film thickness and was not suitable as a sputtering target.

〔Effect of the invention〕

The castings obtained according to the present invention have equiaxed crystals or granular crystals with uniform diameters, or have cavities inside and are strong.
Suitable for sputter link targets and other uses.

[Brief explanation of drawings]

FIG. 1 shows the mold used in Example 1 of the present invention. / is a copper water-cooled plate, ko is a stainless steel side frame, 3 is a tantalum crack cover, gu is a casting hole, ! indicate the flow of cooling water. Applicant: Mitsubishi Chemical Industries, Ltd. Agent: Patent attorney: Yo Hase - (1 other person) Figure 1

Claims (2)

[Claims] (1) A method for casting rare earth metals, which is characterized by pouring molten rare earth metal into a mold whose bottom surface is forcibly cooled to a height that is less than 1/2 the length of the longest line dividing the bottom surface. (2) The rare earth metal casting method according to claim 1, wherein the upper surface of the mold is kept warm.