JPH05277621A - Ti or ti alloy casting mold material and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide Ti or Ti alloy casting mold material, which is molten Ti that is a casting metal or whose reaction against Ti alloy is very little, and the manufacture thereof. CONSTITUTION:The material is Ti composed of a powdery yttrium oxide Y2O3-x (0.08<=X<=0.12) with semi-stoichiometry composition in which oxygen is short, or Ti alloy casting mold material. The grain diameter of Y2O3-x is appropriately 1 to 40mum. The powdery Y2O3-x is manufactured by heating powdery Y2O3 which is mixed with excess powdery Y, in the temperature range of 1830K or above and 2080K or less, and crushed by means of a crushing device made of nitride and/or carbide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a mold material used for casting Ti or Ti alloy.

[0002]

2. Description of the Related Art Titanium or titanium alloy is particularly in a liquid state.
It is active in, and has a strong affinity with oxygen,
It is considered one of the most difficult materials to make. Strong with oxygen
Affinity is due to the fact that Ti oxide is thermodynamically stable
Also, the solubility of oxygen in Ti is very high.
It Therefore, it is as stable as Ti oxide or more stable.
Al ₂O₃ And ZrO₂When these coexist with Ti,
The reduced and dissociated oxygen contaminates and hardens the Ti casting.
Therefore, these cannot be used as a mold material. Oxide
Other refractory materials, nitrides, refractory metals, sulfides, etc.
Although it has been tried as a color template material, molten Ti
No stable mold material has been obtained.

Under these circumstances, CaO and Y ₂ O ₃ have recently received attention. All of them are thermodynamically very stable and have low solubility in Ti, so that they have come to be used as template materials. The use of Y ₂ O ₃ as a casting material for casting Ti or Ti alloys is a known technique.
Then, a technique of using a rare earth-based binder having a low reactivity also in the slurry for molding a mold (Japanese Patent Laid-Open Nos. 03-8533 and 03-8534) makes it possible to obtain a cast body having a small reaction layer with the mold material. It was

[0004]

However, CaO must be handled carefully with water, and CaO,
All of Y ₂ O ₃ are suitable for small cast products, but especially for large products, it takes a long time to cool down and the reaction time becomes long, which is not sufficient for obtaining a sound product.

The present invention uses a refractory material that is thermodynamically stable and has a very low solubility in Ti, so that a Ti or Ti alloy casting mold material that reacts very little with molten Ti or a Ti alloy that is a casting metal. And a method for manufacturing the same.

[0006]

SUMMARY OF THE INVENTION The present invention provides a substoichiometric oxygen-deficient yttrium oxide Y ₂ O _3-x (0.0
8 ≦ x ≦ 0.12) A Ti or Ti alloy casting mold material made of powder is provided. The yttrium refractory powder preferably has a particle size in the range of 1 to 40 μm.

In order to produce such yttrium oxide powder, it was mixed with an excess of Y powder in a temperature range of 1830 K or less and 2080 K or less in a vacuum or an inert atmosphere.
Heat Y ₂ O ₃ powder. After that, the yttrium oxide powder is pulverized in a vacuum or in an inert atmosphere using a pulverization device made of nitride and / or carbide to adjust the particle size to a predetermined range.

The present invention will be described in more detail below. Yttrium oxide, the stoichiometric composition Y ₂ O ₃ oxygen has been known that sub-stoichiometric composition Y ₂ O _3-x where insufficient slightly present in comparison with, also the standard free energy Is also given. Literature RJ Ackerman, EG Rauh
: J. Chem. Thermodynamics, 5 (1973), 331
See. Therefore, first, this data and molten Ti (hereinafter T
i (l)) Y and O activities (reference M. Hoch:
Titanium Sci. Technol., 3 (1985), 143
From 1), the solubility of Y ₂ O _3-x in Ti (l) at 1973K is determined. For comparison, Y ₂ O ₃ and Al ₂ O ₃ are similarly calculated for solubility at 1973K.

The standard free energies of formation of each substance at 1973K are as follows.

[Equation 1] However, at 1973K, Y ₂ O _3-x becomes Y ₂ O _2.888 (x = 0.1
12).

The activity of Y and O in solid solution in Ti (l) is reported in the literature (RJ Ackerman et al .: J. Chem. T.
hermodynamics, 5 (1973), 331),
Further, the activity of Al is obtained by converting from the Racult standard to the 1 wt% standard, and the equilibrium solubility in Ti (l) is calculated from these as follows.

[Equation 2]

From the above, the equilibrium solubility in Ti (l) is
Y ₂ O _3-x (Y ₂ O _{2.888 at 1973K} ) is overwhelmingly small,
It turns out that it is stable. Especially when casting large products, the heat capacity is large and the cooling rate is small, so even if Y ₂ O ₃ is used,
It is concluded that Y ₂ O _{3 -x} is hardly reduced, although it may enter the casting surface.

[0012] be used as a mold material for such Y ₂ O ₃ substoichiometric composition of oxygen is insufficient slightly compared to Y ₂ O _3-x Ti or Ti alloy casting, Ti (l ) Does not react with Y ₂ O _{3-x of the} mold material, so that the casting surface of the cast product of Ti or Ti alloy can be finished beautifully,
The product surface finishing step can be largely omitted, which is extremely useful.

This Y ₂ O _3-x can be manufactured as follows. That is, first, Y ₂ O ₃ powder is held together with excess Y powder at a temperature of 1830 K or more and 2080 K or less in an inert atmosphere such as Ar or in a vacuum, and preferably heated for 10 hours or more and 20 hours or less. This is because if the upper limit of the temperature time is larger than that, sintering tends to proceed excessively, and pulverization tends to be difficult, and if the lower limit is smaller than that, Y ₂ O _3-x is not reduced. The heat treatment is performed in an inert atmosphere or vacuum because Y ₂ O ₃ is preferentially decomposed and evaporated if the atmosphere is reducing.

After heating, after sufficiently cooling to room temperature, in an inert atmosphere or in a vacuum, a mortar or ball mill made of a nitride and / or a carbide such as BN, Si ₃ N ₄ , WC, etc. until the desired particle size is obtained. Smash.

The range of x of Y ₂ O _3-x used in the present invention and the reasons for limitation are as follows. That is, thermodynamically stable Y ₂
O _3-x is determined for each temperature, and the above-mentioned heating temperature 1830
The composition range corresponding to ≦ T ≦ 2080 is 0.08 ≦ x ≦
This is because it is 0.12.

The reason for crushing using a non-oxide crusher such as BN, Si ₃ N ₄ or WC in vacuum or in an inert gas atmosphere is that the sample is oxidized during crushing and Y ₂ O _{3 is used.} The reason why it is preferable to adjust the particle size to 1 to 40 μm is that if it is finer than 1 μm, cracks will be generated when molding as a mold material, and if it is rougher than 40 μm, it will be cast. This is because the casting surface properties of the product deteriorate.

[0017]

EXAMPLES The present invention will be specifically described below based on examples.

(Example 1) Y ₂ O ₃ powder having a particle size of ₂ to 10 μm was mixed with excess metal Y powder in an Ar atmosphere to obtain 1830K to 2K.
After heating at 080 K for 20 hours, the powder was crushed using a mortar in a glove box filled with Ar gas to prepare Y ₂ O _{3 -x} powder. The composition was identified by a double-focusing high-resolution mass spectrometer. A powder having a particle size of 1 to 40 μm was selected from the pulverized powder, and a binder containing SiO ₂ sol as a main component was mixed so as to have a mass ratio of 5% and stirred to prepare a precision casting slurry. 12 pieces of 30 × 30 × 150 mm rectangular parallelepiped product are used as a tree face-shaped mold face coat to a thickness of 2 mm, and the outer layer is 5 m thick.
It was coated with zircon + morokite + SiO ₂ sol slurry until the thickness became m, sufficiently dried and then baked at 1573K for 3 hours. The cast alloy is a Ti-6Al-4V alloy (main components are Al 6.50%, V 4.08%, O
0.12%, Fe 0.20%) and melted in an electron beam melting furnace. The dissolution conditions were 100 KW × 10 minutes, and 200 g of pure Al lumps were added before the appearance to adjust the components. The casting weight is 10 kg, and the cooling rate of the product after casting is W-5.
As measured by Re / W-26Re thermocouple, 0.2 ° C / s
It was ec (vacuum furnace cooling).

The product was taken out of the furnace at 573 K, and the Vickers hardness of the cross section of the product portion, the thickness of the oxygen enriched layer obtained by EPMA analysis, and the maximum concentration were compared for comparison.
Table 1 shows the results when a mold having a face coat of Y ₂ O ₃ and Al ₂ O ₃ powder slurry was used. However, a portion where the amount of oxygen was larger than that of the bulk was used as the concentrated layer. From this, Y ₂
The mold using O _3-x was in contact with the molten Ti alloy
It was found that Y ₂ O _3-x did not react and a casting with a sound surface could be obtained.

(Example 2) Of the Y ₂ O _3-x (x = 0.112) grains prepared in the same manner as in Example 1, those having a changed grain size distribution were used to mold a mold, and casting experiments were conducted. went. Particle size distribution is 1 μm or less, 1 to 40 μm, 40 μm to 100 μ
3 conditions of m. The results are shown in Table 2. From this, it is understood that the particle size distribution of 1 to 40 μm, which is the claimed range of the present invention, is the most suitable as the molding condition for the mold.

[0021]

[0022]

[0023]

EFFECT OF THE INVENTION A mold using Y ₂ O _{3 -x} as a face coat material for the mold has a large size and a T ratio even if the cooling rate is very slow.
Since it does not react with the molten i alloy, a casting with a sound surface can be obtained. This can reduce the cost because the post-process for removing the reaction layer can be omitted, and the dimensional accuracy is further improved.

Claims (4)

[Claims] 1. A Ti or Ti alloy casting mold material made of Y ₂ O _{3 -x} (0.08 ≦ x ≦ 0.12) powder having a quasi-stoichiometric composition and lacking oxygen. 2. The particle size of yttrium oxide powder is 1 to 40 μm.
The mold material for casting Ti or Ti alloy according to claim 1, wherein m is m. 3. The method for producing the yttrium oxide powder according to claim 1 or 2, wherein Y ₂ O mixed with an excess of Y powder in a temperature range of 1830 K or less and 2080 K or less in a vacuum or an inert atmosphere. T characterized by heating ₃ powders
The manufacturing method of the i or Ti alloy casting mold material. 4. When producing the yttrium oxide powder according to claim 1 or 2, the yttrium oxide powder obtained in claim 3 is vacuumed using a crushing device made of nitride and / or carbide. Alternatively, the method for producing a Ti or Ti alloy casting mold material according to claim 3, wherein the grain size is adjusted within a predetermined range by pulverizing in an inert atmosphere.