JPH067882A - Manufacture of imvestment shell mold with high emissivity for molding uni-directional solidified super alloy - Google Patents

Abstract

PURPOSE:To obtain a mold with excellent thermal emissivity and to manufacture Ni-base super alloy by coating the external layer part of a mold with the particulate of specific composition and executing the firing of the mold at high temperature, and thereby improving the cooling effect of the mold. CONSTITUTION:After either the particulate where 1-10mol% antimony oxide is added to titania, or the particulate where 0.1-5mol% lithium oxide is added to nickel oxide or cobalt oxide is coated on the external layer part of a shell mold, the firing of this mold is executed at the temperature of 1000 deg.C or higher, the thermal emissivity of this coated layer is increased, and the cooling effect of the mold is improved. This arrangement allows manufacture of an investment shell mold with high thermal emissivity to obtain uni-directional castings of Ni-base super alloy with high quality.

Description

Detailed Description of the Invention

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BACKGROUND OF THE INVENTION The present invention is used for obtaining a directionally solidified cast product of a superalloy which is excellent in corrosion resistance and creep resistance at high temperatures.

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2. Description of the Related Art Conventionally, refractory materials such as alumina, zircon, and mullite have been used as molds for unidirectional solidification casting of superalloys. Since the molds made of these refractories have a low thermal emissivity, the cooling effect of the molds is poor when the superalloy melt is subjected to unidirectional solidification casting under vacuum. Therefore, it was difficult to increase the temperature gradient with respect to the solidification direction of the molten metal, and it was difficult to preferentially grow crystals in a specific orientation for the purpose of increasing the strength of the superalloy.

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In order to improve the thermal emissivity of a mold by using a newly developed refractory having a high thermal emissivity as a mold material instead of the conventional refractory for a mold, This is a technique for obtaining a high quality unidirectionally solidified cast product by giving a high temperature gradient during solidification of the molten metal inside to promote crystal growth in a specific orientation.

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The titania containing antimony oxide, nickel oxide or cobalt oxide containing lithium oxide in place of the refractory materials such as alumina, zircon, and mullite which have been used conventionally are once heated to 1000 ° C.
When heated above, the thermal emissivity increases. For example, titania powder (TiO ₂ ) containing 1 mol% of antimony oxide (Sb ₂ O ₅ ), nickel oxide (NiO) containing 1 mol% of lithium oxide (Li ₂ O), and cobalt oxide (Co).
Table 1 shows the results of measuring the thermal emissivity at 800 ° C. of each powder of (O) that was formed into a tablet at 100 kgf / cm ² and fired at 1100 ° C. for 1 hour. As shown in Table 1, TiO ₂ was converted into S by high temperature firing.
It is clear that the refractory materials of NiO and CoO in which b ₂ O ₅ and Li ₂ O in NiO and 1 mole% of Li ₂ O in CoO are solid-dissolved have high thermal emissivity. Therefore, if these refractory materials are used in place of conventional refractory materials to form a mold and preheat to 1000 ° C. when pouring the superalloy molten metal, the thermal emissivity of the mold is remarkably improved. Is promoted and a good quality unidirectionally solidified cast product is obtained.

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【Example】

Example 1 In this example, the refractory materials shown in Table 2 were used. The investment shell mold was manufactured as follows. The coating of the slurry prepared by mixing Al ₂ O ₃ powder with colloidal alumina as the binder for the 1st to 3rd layers around the prototype wax model and the Al ₂ O ₃ grain stucco (to the slurry coated surface) Sprinkle Al ₂ O ₃ grains). Succeedingly, from the 4th layer to the 6th layer, Sb was added to the colloidal silica binder
The coating of the slurry containing the TiO ₂ powder added with the ₂ O ₅ powder and the stucco of Al ₂ O ₃ grains are performed. Finally, after coating the same slurry as the sixth layer and drying, the wax model wrapped in the coating layer is removed by heating to form a shell-shaped mold. The shell mold manufactured as described above is preheated at around 1500 ° C. before pouring the molten alloy. At this time, in the outer layer portion (fourth to seventh layers) of the mold, Ti containing Sb ₂ O ₅ as a solid solution was used.
It is composed of O ₂ and Al ₂ O ₃ grains, and the layer has excellent heat radiation due to the effect of TiO ₂ containing Sb ₂ O ₅ . Then, under a vacuum of 10 ⁻⁴ Torr, 15
When a molten Ni-base superalloy melted at 60 ° C was poured into this mold and unidirectional solidification casting was performed at a temperature gradient of 60 ° C / cm and a drawing speed of 20 cm / h, crystals in the <001> orientation proceeded to solidify. Good quality castings were obtained which grew preferentially in the direction.

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Example 2 In this example, the refractories shown in Table 3 were used. In this example, NiO powder added with L ₂ iO was used in place of the TiO ₂ powder used in the fourth to seventh layers of Example 1. The manufacturing method of the shell mold is the same as that of the first embodiment. The mold of Example 2 also becomes a mold excellent in heat radiation due to the effect of NiO containing Li ₂ O in the outer layer of the mold during preheating at 1500 ° C.,
The cooling capacity of the mold is improved. Next, under a vacuum of 10 ⁻⁴ Torr, the molten Ni-base superalloy melted at 1600 ° C. was poured into this mold, and unidirectional solidification casting was performed. As a result, a good quality cast product was obtained.

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Example 3 In this example, the refractories shown in Table 4 were used. In this example, Li ₂ O was used instead of the Li ₂ O-containing NiO powder used in Example 2.
The CoO powder which added the powder was used. The manufacturing method of the shell mold is the same as that of the first embodiment. The mold manufactured according to Example 3 also has good heat radiation from the outer layer of the mold containing CoO containing Li ₂ O during preheating at 1500 ° C., and thus has excellent cooling ability. When a molten Ni-base superalloy melted at 1600 ° C. was poured into this mold and unidirectional solidification casting was performed, a cast product with excellent quality was obtained.

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Claims (1)

[Claims] 1. A powder or granular material comprising 0.1 to 10 mol% of antimony oxide (Sb ₂ O ₅ ) added to titania (TiO ₂ ), nickel oxide (NiO) or cobalt oxide (CoO).
After coating the outer layer part of the shell mold with one of the powdery particles added with 0.1 to 5 mol% of lithium oxide (Li ₂ O), the mold is baked at a high temperature of 1000 ° C. or higher to A method for producing a high emissivity investment shell mold, in which the thermal emissivity of the coating layer of the above is increased to improve the cooling effect of the mold.