JPS58136702A - Production of molded and sintered parts of powder - Google Patents

Abstract

PURPOSE:To obtain sintered parts of intricate shapes having homogeneous quality and high density by sintering moldings of raw materials powder obtained from female molds of desired shapes molded by using meltable and fusible patterns by a hot hydrostatic pressing method. CONSTITUTION:Slurry prepd. by mixing refractory powder, silicate compds. and dispersion is coated on patterns of desired shapes manufactured of easyly dissolvable or fusible materials and is solidified whereby female mold shells are formed. Said patterns are melted away to obtain female molds having the cavities of the pattern shapes and 10-60% porosities. The slips prepd. by mixing desired metallic raw material powder or ceramic raw material powder and dispersion is charged into the cavities of such female molds. The dispersion in the slips is removed through the walls of the female molds to dry and solidify the moldings of the raw material powder and the moldings are heated up to the m.p. of the silicate compd. in the female mold materials to make the moldings hermetic. Such hermetic moldings are subjected to hot hydrostatic pressing to sinter the moldings under pressure; thereafter, the female molds are removed and the sintered parts are obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a method for manufacturing precision mechanical parts made of metal or ceramics with complex shapes in a high-density and homogeneous manner using powder raw materials, such as gas turbines, diesel engines, superchargers, etc. If parts with complex shapes or curved surfaces can be mass-produced using heat-resistant, corrosion-resistant, and wear-resistant materials, it will greatly contribute to improving the lifespan and performance of mechanical devices that use these parts.

By the way, it is known that precision parts with complex shapes that are difficult to form by forging or casting can be easily manufactured by powder metallurgy or by applying this method, but it is generally not possible to apply pressure during sintering. Therefore, the strength and quality of the obtained sintered body lacked reliability.

By the way, instead of the conventional sintering method, a method was developed that uses hot isostatic pressing to sinter while applying pressure from all four sides.
In principle, this method allows parts with complex shapes to be sintered under pressure, but the technology has not yet been fully established, and for example (a) it is generally possible to deform the required powder in an airtight manner. It is necessary to fill the powder into a container and seal it, and the packing density of the powder is small, resulting in large sintering shrinkage and low dimensional accuracy.

(b) If the powder is molded into the desired shape in advance, it is difficult to handle the fragile powder compact, and furthermore, when it is sealed in a container and pressure sintered, the compact and the container wall are in close contact with each other. Otherwise, the sintered body is likely to crack or deform.

□ eU There are problems such as the difficulty of creating a container material that has appropriate deformation characteristics at the desired sintering temperature of ceramics or metals.

An object of the present invention is to provide a method for forming and sintering metal powder or ceramic powder, which solves the above-mentioned problems.

Next, the method of the present invention will be explained step by step with reference to the accompanying drawings.

(1) Making a model using a soluble or meltable substance: A male model with the desired shape is made. This model needs to be removed after forming the female shell in step 5, which will be described later. Therefore, it must be easily dissolved in a solvent that does not soak the female mold material, or at a temperature higher than the temperature at which the female mold material softens and deforms. It is also necessary that the material be made of a material that melts and flows easily at low temperatures.

Since a slurry containing a mixture of refractory powder and silicate compound powder and a binder is used to apply it on the model to form the female shell, low melting point wax or alloy is used as a material that satisfies the above requirements. Or use a wax that dissolves in water or an organic solvent.

The model may be manufactured by a known method such as melting a desired material and pouring it into a mold for casting, injection molding, or machining. The dimensions of this model must be made larger than the dimensions of the final product by the amount of shrinkage in anticipation of shrinkage of the raw material powder compact during the subsequent hot isostatic pressing process.

(2) Formation of the female shell: The material for the female shell is a mixed powder of a refractory that does not melt at the sintering temperature of the required sintered body and a silicate compound that melts at a temperature below the sintering temperature, and a binder. and a dispersion liquid are used. For example, in the case of a nickel alloy or steel whose sintering temperature is 1000 to 1400°C, materials such as silica, alumina, and zirconia (Zr(h)), whose melting points are sufficiently higher than 1400°C, are used as refractories.

For example, when silicon nitride (SiaN4) ceramic is a raw material powder for a sintered body, the sintering temperature is 1600~1
Since the temperature is 850° C., materials that do not melt in the above temperature range, such as alumina, zirconia, and silicon carbide, are used as refractories.

As the silicate compound to be mixed with these refractories, it is necessary to select a material that melts or softens at the above-mentioned sintering temperature of the metal or ceramic. For example, in the case of nickel alloys and steel, Pyrex glass, etc. are used, and in the case of silicon nitride ceramics and silicon carbide ceramics, borosilicate glass, quartz glass, or cordierite (2M
It is preferable to use a silicate compound that melts or softens at the sintering temperature of ceramics, such as pO.2AJ203.5SiO2).

The mixing ratio of silicate compounds to refractories is 50% or more.
The following shall apply. If this is less than 5%, there is not enough to close the gaps between the refractory particles, making it impossible to achieve complete airtightness.On the other hand, if it is more than 50%, when gas is pressurized, the female mold wall In addition to deformation, the melt between refractory particles infiltrates into the interior.
Since press-fitting becomes noticeable, it is necessary to appropriately select the mixing ratio of the silicate compound.

By appropriately selecting this mixing ratio, the female mold wall acts as an airtight and deformable pressure transmission wall that applies pressure isotropically to the raw material powder compact, resulting in uniform sintering shrinkage and improved dimensional and shape accuracy. A high-density, high-quality sintered body can be obtained.

In order to easily apply the refractory powder and silicate compound powder to the model, they are mixed with a dispersion of water, ethanol, etc.
After drying, it is made into a slurry mixed with a binder such as water glass, aluminum phosphate, colloidal silica, or alumina cement to give it strength. After applying this slurry to a model and drying and curing it, it is necessary to obtain a porosity of 10 to 60%. If the porosity exceeds 60 inches, the strength of the female mold will decrease and it will be easily damaged, while if the porosity is less than 10 inches, it will be difficult for the dispersion to ooze out after pouring the raw material slip, which is not preferable.

(3) Removal of the model: The model in the female mold is melted or dissolved in a solvent and removed from the female mold to create a cavity with the same shape as the model in the female mold shell. If it is removed by dissolving it with a solvent, it is then thoroughly dried.

(4) Preparation of sintering raw material powder If the raw material powder for making the intended sintered parts is metal powder, the average particle size is several 17.
) Spherical particles having a diameter of 10 to 100 microns and made by an atomization method or a rotating electrode method are desirable from the viewpoint of filling properties.

When the raw material powder is ceramic, the average particle size is at most several microns, preferably 1 micron or less, from the viewpoint of sinterability, and spherical particles are desirable from the viewpoint of filling properties.

Further, in the case of ceramics such as silicon nitride and silicon carbide, which have insufficient sinterability by themselves, it is preferable to add a sintering accelerator. In the case of silicon nitride, A-2 is used as a sintering accelerator.
03, AiN, Y2O3, MpO1CeO2, etc. are suitable.

In addition to the above, cermets such as WC-Co or TiN-Ni, and ceramic powders such as A-203 can be used to
Dispersion strengthened alloys dispersed in metals such as alloys, or C
Powder of fiber-reinforced alloy in which fibers such as or SiC are dispersed in metal can also be used as the sintering raw material powder.

(5) Production of slip from sintering raw material powder: A dispersion liquid is mixed with the sintering raw material powder to form a slip.

(8) Water is generally used as the dispersion liquid, but if the sintering raw material powder causes a chemical reaction with the dispersion liquid or coagulates, an organic solvent such as ethanol or propatool may be used.

Further, if necessary, a deflocculant, a binder, a mold release agent, and the like are added to stabilize the slip, and the pH is adjusted. In the case of ceramic powder, water glass or ammonium alginate is used as a deflocculant, and methyl heptylose or polyvinyl alcohol is used as a binder.

(6) Slip injection 2 The slip prepared as described above is injected into the female mold having the cavity of the desired shape. At this time, it is desirable to hold the female mold in a powder-packed bed for the purpose of holding the thin female mold and absorbing the slip dispersion liquid leached from the female mold. In this way, the dispersing liquid in the slip injected into the female mold leaches out through the pores of the female mold wall and is absorbed into the surrounding powder packed bed, promoting leaching.

When the injection of the slip is completed, the injection port of the female mold is closed and sealed with the material for the female mold. After the dispersion liquid has been leached from the female mold, the female mold is removed from the powder-filled bed and dried by air drying or gradual heating. By sufficiently drying, the sintering raw material powder becomes When the silicate compound is melted and the spaces between the refractory particles of the female shell are completely filled with the silicate compound melt, the female shell is made airtight.

Since this heating does not leave any gas remaining in the female shell,
Although it is preferable to carry out the process in a vacuum, the process may also be carried out at normal pressure in an atmosphere that does not oxidize the raw material powder.

(8) Hot isostatic press: After making the female mold completely airtight, place it in a hot isostatic press machine and pass gas through it to bring the gas pressure inside the machine to approximately 100 to 2000 atmospheres. The female mold is heated while pressurized with gas to raise the temperature to the appropriate temperature for sintering the raw material powder, and the pressurization increases density and sintering. If the gas pressure is lower than 100 atm, the pressure applied to the compact during sintering will be insufficient and the effect of hot isostatic pressing will be insufficient. Further, the use of a pressure higher than 2000 atm is limited by the current hot isostatic press capability.

An appropriate amount of a silicate compound is mixed in the female mold material (therefore, the female mold wall acts as an airtight yet deformable pressure transmitting wall that applies isotropic pressure to the raw material powder compact filled inside. .

(9) Removal of the female mold: After sintering, the female mold is removed from the sintered body by a mechanical method such as wind blasting, impact, vibration, or grinding, or a chemical method such as high-temperature, high-pressure alkaline solution treatment. The mold shell is removed and the sintered body is taken out.

Next, an example will be described.

Example 1゜Nickel alloy (14%Co-94Cr-5,5%7-
)～4.7'l'i-3%M O-N i) Atomized spherical powder (average particle size 100 microns) is used as raw material powder, and mixed with an equal amount of ethanol by apparent volume to form a molding material. It was a slip. Meanwhile, a wax model of an engine turbine blade was made by injection molding. For the female shell, 300 mesh of fused quartz powder was mixed as the refractory material, and Pyrex glass powder was mixed as the silicate compound in a ratio of 60% = 40% by weight, and colloidal silica was dispersed in this as a binder in a ratio of 15% by weight. A slurry was prepared by mixing 35% by weight of water, and the slurry was applied onto a wax model to form a shell approximately 2 mm thick. This was heated to about 120° C. to melt the wax inside the shell, flow it out, and remove it, forming a female mold with a porosity of 40%.

The previously prepared slip of nickel alloy powder is injected into the cavity of this female mold, and the ethanol in the slip is leached through the pores of the wall of the female mold, and the raw material powder remaining in the cavity of the female mold is removed from the cavity. The slurry for the female mold was applied to the injection port of the female mold to seal the injection port, and after the whole was sufficiently dried, it was placed in a hot isostatic press machine, and the inside of the machine was heated to 10" Torr. After the vacuum was removed, the temperature was heated to 1,100°C, and the Pyrex glass was melted to fill the gaps between the refractory particles in the female shell to make it airtight. Argon gas was then introduced into the device and heated to 1,100°C.
Atmospheric pressure was applied, and the temperature was further increased to 1200° C., and hot water pressure pressing was performed for 1 hour.

After cooling, the female mold filled with the sintered body was taken out and sandblasted to remove the female mold material on the surface to obtain a product sintered body.

The density of the sintered body is almost densified to the theoretical density,
It was found that the sintered body had significantly fewer defects such as pores than conventional precision cast turbine blades.

Example 2゜ Average particle size 0.7 microns, containing 95% or more α-type crystals,
A slip was prepared by mixing silicon nitride powder containing 1.5 grams of oxygen as an impurity.

On the other hand, a model in the shape of a turbo supercharger wheel was made by injection molding water-soluble soluble wax, and slurry for the female shell was applied onto it. This slurry is a mixture of -300 mesh silicon carbide powder as a refractory powder and borosilicate glass powder as a silicate compound at a ratio of 2:1 (weight ratio), and an ethanol solution in which colloidal silica as a binder is dispersed. A slurry was prepared by mixing 35% by weight. After applying the slurry to the model and drying and solidifying it to form a female shell with a thickness of about 1 mrrl, it is immersed in water to dissolve and remove the soluble wax on the model to form a model-shaped cavity, It was made into a female type with a porosity of about 30%.

This female mold is held in a bed filled with silica sand powder, the slip containing silicon nitride as a main component is injected into the female mold, the dispersion liquid is leached through the female mold wall, and the raw material powder remains in the female mold cavity.
It was filled, dried, and solidified. Next, after sealing the slip inlet using a slurry of female mold material, it is placed in a hot isostatic press apparatus, and the apparatus is evacuated to 1O-3 Torr.
r, the female mold was heated to 1550°C K to melt the borosilicate glass in the female mold material, and the pores of the female mold were filled with the borosilicate glass melt to make it airtight, and then heated under hot water pressure. Argon gas was passed through the press equipment to raise the pressure to 1000 atm, and the female mold was heated in the press at 1750° C. for 2 hours to perform hot isostatic pressing.

After cooling, the female mold was taken out from the apparatus and subjected to autoclave treatment with an aqueous alkaline solution to dissolve and remove the borosilicate glass in the female mold shell. The density of the obtained sintered body is 3.15
At 97 cc, it was sufficiently densified and had no cracks or other defects.

As explained above, in the conventional powder metallurgy method, powder is usually formed and sintered using a uniaxial press, which makes it difficult to manufacture not only mechanical parts with complex shapes but also sintered bodies with uniform density. However, according to the method of the present invention, since hot isostatic pressing is used for sintering, pressure can be applied from all sides during sintering, resulting in high density and even complex sintering. It becomes possible to mass produce parts with various shapes.

In addition, as a sealed container, refractory powder that does not soften and melt at the sintering temperature of the raw material powder is mixed with a silicate compound that melts below the sintering temperature to form a slurry, and the model is coated with +lk to form a shell, and the model is melted or melted. Since the container is melted and removed to form a female mold having a cavity of the desired shape, it is easy to seal the container before pressure sintering.

In addition, the required metal or ceramic powder is injected in the form of a slip into the cavity of the female mold, and the dispersion liquid is leached out through the pores of the wall of the female mold, leaving the raw material powder in the slip inside the cavity and filling it. By drying and solidifying the powder, a molded product with the desired shape can be obtained, and there is no need for conventional press molding to obtain the desired shape.Also, since the dispersion liquid is leached using the pores of the female mold, the raw material powder can be transferred into the female mold cavity. It has extremely great practical effects, such as being easy to fill inside.

[Brief explanation of drawings]

The accompanying drawings are diagrams showing a flow sheet of the method of the present invention.

Claims (1)

[Claims] In a method for manufacturing molded and sintered parts of metal powder or ceramic powder, a dispersion of refractory powder and silicate compound powder is applied to a model of a desired shape made of a material that is melted or easily melted. The mixed slurry is applied and solidified to form a female shell, which is immersed in a solvent or heated to dissolve or melt the model and removed from the female shell, having a model-shaped cavity and pores. A female mold with a ratio of 10 to 60q6 is manufactured, a dispersion liquid is mixed with the desired metal raw material powder or ceramic raw material powder to form a slip, the slip is injected into the cavity of the female mold, and the slip dispersion is poured into the female mold. The raw material powder compact remaining filled in the cavity is dried and solidified, and the injection port of the female mold is sealed, and the melting point of the silicate compound in the female mold material is heated in a heating furnace. The pores of the female mold are sealed to form a sealed body.The sealed body is heated to the sintering temperature while being pressurized with a hot isostatic press device, and the raw material powder compact in the sealed body is pressurized. A method for producing a molded and sintered part of ceramics or metal powder, which comprises removing a female mold after sintering to obtain a sintered body.