JPH0468058B2 - - Google Patents

Description

[Detailed description of the invention]

When titania (TiO ₂ ) is heated above 1000℃ in a reducing atmosphere, oxygen in TiO ₂ is gradually released.
As titania changes to a lower oxide, titania itself gradually changes in color tone and thermal emissivity. The table shows the degree of oxidation and changes in color tone and thermal emissivity of titania.

【table】

[Table] As shown above, as titania (TiO ₂ ) transitions to a lower oxide, its color tone changes, and naturally its thermal emissivity also changes, resulting in blackened TiO1.75~
TiO1.65 has a high thermal emissivity. By the way, 500
Comparing TiO ₂ measured at ℃ and lower oxides in the composition range of TiO _1.75 to _{TiO 1.65} , there is a difference of about twice as much, and the lower oxide of TiO ₂ has a high thermal emissivity. That is clear. Thus, by applying a low-order oxide of titania with high thermal emissivity to the outer layer of the investment shell mold, heat dissipation from the mold into which the molten metal is poured is improved, resulting in unidirectional solidification of the superalloy. The temperature gradient at the solid phase-liquid phase interface can also be increased. This promotes the growth of crystals having a preferential growth orientation among the crystals constituting the alloy during the solidification process of the molten alloy. Next, the present invention will be explained in detail with reference to Examples. Usually, investment shell molding involves applying a slurry containing an inorganic binder and refractory powder to the surface of a wax model that has the same shape as the part to be manufactured, and applying stucco (sprinkling refractory particles onto the slurry-applied surface).
The process of drying the coating layer covered with slurry and stucco is repeated several times in this order to form a refractory shell layer around the outer periphery of the wax model, and then the wax model is melted and removed to form a shell. A shaped mold is made. Example 1

[Table] In Example 1, of the coating up to the seventh layer on the wax model, the first to fifth layers were coated with a slurry of colloidal alumina binder and alumina powder, and alumina grains were stuccoed. forms a mold using refractory powder of a lower oxide of titania (TiO ₂ ) as a binder of butyl titanate. Butyl titanate is gradually converted from _TiO2 by high temperature calcination.
It takes the form of TiO _2-x , and together with the added lower oxide of titania, it becomes an investment shell mold that has an outer layer with high thermal emissivity. Example 2

[Table] In Example 2, an investment shell mold is formed in the same manner as in Example 1 using the binder and refractory powder particles listed in the table. The mold obtained in Example 2 had a white outer layer before firing, but the outer layer was removed by firing this mold at 1200°C for 1 hour in a reducing atmosphere.
Oxygen is gradually removed from TiO ₂ and it changes to a lower oxide of TiO ₂ , and the outer layer turns black, yielding an investment shell mold with high thermal emissivity. Using the molds obtained in Examples 1 and 2,
When unidirectional solidification casting of Ni-based superalloy (MarM200) was performed under a vacuum of 10 ^-4 Torr,
A cast product of good quality was obtained.

[Brief explanation of the drawing]

FIG. 1 shows a cross-sectional view of the high emissivity investment shell mold with excellent thermal emissivity obtained in Example 1. FIG. 2 shows a cross-sectional view of the manufacturing process of a high emissivity investment shell mold according to Example 2.

Claims (1)

[Claims] 1. A high-emissivity investment shell mold with high thermal emissivity, in which the outer layer of the shell mold is coated with black powder of TiO _1.75 to TiO _1.65 , which is a low-order oxide of titania (TiO ₂ ). 2 A shell mold whose outer layer is coated with titania (TiO ₂ ) is heated to 1000°C or higher in a reducing atmosphere to convert the titania (TiO ₂ ) in the coating layer into a black color, which is a lower oxide of titania. A method for manufacturing a high emissivity investment shell mold in which the thermal emissivity of the mold is increased by changing TiO _1.75 to _{TiO 1.65} .