JPH0254733A - Manufacture of ti sintered material - Google Patents

Abstract

PURPOSE:To manufacture the title material having high density and low C and O2 content at low cost by adding and mixing a binder into Ti fine powder, subjecting the mixture to injection molding, thereafter heating away the binder in a nonoxidizing atmosphere and successively subjecting it to two stage sintering at low temp. and high temp. CONSTITUTION:Thermoplastic resin such as polyethylene and polypropylene or paraffin, etc., as a binder, is mixed, in the ratio of 0.5 to 3.0wt.%, into Ti fine powder having <=30mum average grain size and the mixture is subjected to injection molding into the desired shape. The molded body is heated in a nonoxidizing atmosphere such as N2 at 5 to 20 deg.C/hr heating speed to remove the binder in the molded body away. After that, the molded body is firstly heated to 1050 to 1200 deg.C in vacuum of about 1X10<-3>torr to execute sintering; the sintered body is successively subjected to secondary sintering, by which the Ti sintered material having low C and O2 content and high density can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing a Ti sintered material produced by a powder metallurgy method.

<Prior Art> In recent years, methods for manufacturing sintered parts using powder metallurgy have shown remarkable growth, and the materials used range from conventional ferrous metals to non-ferrous metals.

Ti has a lower specific gravity than steel materials, and its strength is fully comparable to that of steel, so it is used as an aircraft material in a wide variety of parts. It is also used as a medical device because it is compatible with human tissue and does not cause any harm.

However, the yield of machining parts from melted lumber is low, resulting in high costs and low productivity. Therefore, by using the injection molding method, which can mass produce parts with complex shapes,
Although high productivity can be achieved at low cost, since Ti is a very active metal, there is a problem in that it is difficult to obtain a material with high density and low impurities using normal sintering methods.

On the other hand, hot isostatic pressing, pressure sintering, and the like have been proposed as methods for producing high-density sintered alloys.

For example, as shown in Japanese Patent Application Laid-Open No. 63-500874, there is a method that attempts to achieve high density by applying pressure within a pressure range of 70 to 211 kg/c+n'.

<Problems to be Solved by the Invention> However, the above method requires the use of low C2, low O Ti powder as a raw material, which makes the raw material powder highly pure and expensive, making it difficult to achieve the economic efficiency of the powder metallurgy method. It damages the

Furthermore, when using the injection molding method, it is necessary to use a binder in addition to the raw material powder, and since it is difficult to completely remove this binder in the post-process, the resulting molded product has a high C1 and high 0. must be sintered, and it is impossible to remove impurities.

In addition, the hot isostatic pressure method has the problem of being economically disadvantageous because the equipment is complicated, which increases the working time, and the equipment is expensive.

The present invention aims to solve the above problems and provide a method for manufacturing a Ti sintered material with high density and low impurity by using an ordinary vacuum furnace without requiring special equipment. .

Means for Solving the Problems> In order to achieve the above object, according to the present invention, Ti powder with an average particle size of 30 μm or less is used as a raw material, a binder is added to the powder, mixed, and injection molded. After that, the binder in the molded body was removed by heating in a non-oxidizing atmosphere, and then heated for 10 minutes.
A method for producing a Ti sintered material is provided, which comprises sintering at a temperature of 50 to 1200°C and a pressure of I x 10 -3 Torr or less, and further sintering at a temperature of 1200 to 1400°C.

In addition, the binder in the molded body is removed by heating, and the C10 molar ratio in the molded body is adjusted to 0.5 to 3.0 in advance during sintering.
It is preferable to adjust to

The invention will now be described in more detail.

In the present invention, a powder having an average particle size of 3 mm or less is used as the raw material powder for the following reasons.

As the particle size of the powder becomes smaller, the sinterability improves and the density increases. If the average particle size exceeds 30 μm, not only will high density not be obtained, but the fluidity during molding will be reduced, the filling of the molded product will be non-uniform, and there will be disadvantages such as deformation and poor dimensional accuracy. Therefore, the upper limit is 30 μm
And so.

Since the present invention uses the above-mentioned fine powder, during injection molding, the desired fluidity cannot be obtained with just the metal powder, making molding impossible.

Therefore, we added a binder to prevent these defects from occurring.
Mix and shape. The binder may be a thermoplastic resin such as polyethylene, vopropylene or polystyrene, a wax such as paraffin, microwax or carnauba, or a mixture of both may be used for molding. Of course, the present invention is not limited to these binders.

The amount of binder varies depending on the molding method. In addition to conventional mold presses, the molding machines used include extrusion molding machines, powder rolling machines, and injection molding machines.

The binder is 0.5 to 3. 0% by weight
However, the injection molding method, which can mold products with complex shapes, requires about 10% by weight of a binder.

After molding, the temperature is raised and maintained at a constant rate in a non-oxidizing atmosphere to remove the binder. If the heating rate at this time is too high, the product will crack or bulge, so 5-b After removing the binder, the product is sintered to achieve high density. Although the binder remains without being completely removed, the amount of C10, which is an impurity in the final sintered body, is reduced by promoting the reaction between the carbon of this residual binder and the oxygen of the oxide film present on the surface of the Ti powder. Reduce as much as possible. At that time, the degree of removal of the binder may be adjusted, or after removal and before sintering, the heating temperature and oxygen potential in the atmosphere may be adjusted.
By adjusting the 10 molar ratio to an optimum value, the amount of C10 is reduced.

Thereafter, sintering is performed at 1050 to 1200° C. in a vacuum of 1×10 −3 Torr or less. followed by 1
By sintering at 200 to 1400°C, a high-density sintered body with a sintered density ratio of 92% or more can be obtained.

The Ti powder according to the present invention is a very active metal and has a high affinity for oxygen, so it is difficult to reduce it in a hydrogen atmosphere used in a normal sintering process.

Therefore, in the present invention, a method was adopted in which the reduction was easily promoted by the action of the contained C through vacuum sintering.

The sintering action begins at the point of contact between particles and proceeds by the solid-state diffusion of atoms. However, if the powder surface is covered with oxides, the diffusion of atoms is blocked and densification does not proceed, resulting in the formation of a sintered body. High density is not achieved. In other words, in order to obtain high density, it is necessary to reduce the oxides on the powder surface.

For this purpose, it is sintered under reduced pressure. t×10-3 Tor
If the value exceeds r, the reduction reaction of the oxide is difficult to proceed, so the upper limit was set at I X 10 '''' Torr.

As mentioned above, the reduction reaction of the oxide can be easily promoted by the contained C, but in this case, it is necessary to appropriately adjust the C10 molar ratio in the compact before sintering. This is because the reduction of C and O in the sintered body is achieved by the progress of the reaction C+ o → CO C+20 ”Co2.

If the C10 molar ratio is inappropriate, the sintered body will have an excessive amount of C or O, and if the lower limit of the C10 molar ratio is less than 0.5, the O in the sintered body will exceed 0.5% by weight. , no increase in sintered density was observed. On the other hand, when the C10 molar ratio exceeds 3.0, the sintered body becomes hard and brittle because the amount of C exceeds 0.1% by weight. Therefore, 070 in the compact before sintering
The molar ratio was defined in the range of 0.5 to 3.0.

The temperature range for the first stage vacuum sintering is 1050-1200℃.
This is because at temperatures lower than 1050° C., the oxide is not sufficiently reduced, so the oxide remains and inhibits subsequent sintering. Furthermore, since a large amount of C remains, there is a risk of carbide formation, so the lower limit was set at 1050°C.

On the other hand, the upper limit was set at 1200°C because if this temperature was exceeded, the pores would rapidly become blocked, CO1Co2 gas would remain inside the sintered body, and the amount of impurities in the final sintered body would increase. . In other words, the upper limit of the sintering temperature for the first stage of sea urchin is 12
The temperature was set at 00°C.

Subsequently, densification is achieved by heating and maintaining the temperature to 1200 to 1400°C.

At temperatures below 1200° C., the diffusion rate of Ti is slow and high density cannot be obtained, and as a result, many pores remain, resulting in poor mechanical properties and chemical stability. Therefore, the lower limit is 120
The temperature was 0°C.

If the temperature exceeds 1400° C., the shrinkage of pores due to solid-phase sintering has finished, so that no significant density increase effect can be obtained. Furthermore, the refractories and heating elements in the vacuum furnace are rapidly consumed, which impairs economic efficiency. Therefore, the upper limit is 14
The temperature was set at 00°C.

Sintering at a temperature of 1200 to 1400° C. is preferably carried out in an atmosphere of high purity inert gas or under vacuum conditions to prevent contamination of impurities.

The method for producing a Ti sintered material of the present invention combines adjusting the C10 of the compact, vacuum sintering at a relatively low temperature, and subsequent high-density sintering at a relatively high temperature under the above conditions. This is a two-stage sintering method that allows the production of high-density, low-impurity sintered bodies in an ordinary vacuum furnace.

<Example> The present invention will be specifically described below based on Examples.

(Examples 1 to 3, Comparative Examples 1 to 3) Ti powder having the average particle size shown in Table 1 was prepared as a raw material powder, a thermoplastic resin and wax were added as a binder, mixed, and the mixture was pressurized. It was kneaded using a kneader.

This was crushed into granules and used as a molding raw material.

Using an injection molding machine, it was molded into a plate shape with a thickness of 2 mm, and heated to 600 °C at a temperature increase rate of 10 °C/h in a nitrogen atmosphere.
Thereafter, the temperature and the oxygen potential in the atmosphere were adjusted so that the C10 molar ratio in the molded body was 0.5 to 1.0.

This was held in vacuum (<10-3 Torr) at the temperature shown in Table 1 for more than 1 hour, and then the temperature was raised to 1300°C and held for 3 hours.

After cooling, the density ratio was determined from the density and true density by the Archimedes method, and the amount of C and O in the sintered body was analyzed.

The results are shown in Table 1.

In Example 1.2, the average particle diameter of the raw material powder was 10 μm, and the first stage sintering temperatures were 1080° C. and 1150° C., so that a sintered body with high density and a low amount of impurities was obtained.

In Example 3, the diameter was 25 μm, which was larger than that in Example 1.2, so that a sintered body with a density of 95% and roughly low C1 and low O was obtained.

In Comparative Example 1, the sintering temperature in the first stage was as low as 1000°C, and the transition to high-temperature sintering occurred before sufficient decarburization and deoxidation progressed, resulting in a high C and O content in the final sintered body. It is thought that

In Comparative Example 2, the sintering temperature in the first stage was as high as 1250° C., so the pores were blocked, and CoXCO2 gas remained, presumably resulting in a high C10 content in the final sintered body.

In Comparative Example 3, the sintering temperature in the first stage was 1150°C, and the removal of C1 and O0 was progressing, but since the raw material powder was a coarse powder with an average particle size of 35 μm, a high-density sintered body could not be obtained. There wasn't.

(Examples 4 and 5, Comparative Examples 4 and 5) Molded bodies were produced in the same manner as in Examples 1 to 3, and treated with a debinding agent. After that, the C10 molar ratio in the molded body was 0.
．． It was adjusted to be between 2 and 4.0.

Thereafter, it was sintered in the same manner as in Examples 1 to 3, and the density and the amount of C and zero in the sintered body were analyzed.

The results are shown in Table 2.

In Example 4.5, since the C10 molar ratio was within the range of the present invention, a sintered body with high density and low impurity content was obtained.

In Comparative Example 4, it is thought that because the C10 molar ratio was too small, that is, because Off was too large, oxides remained and inhibited the increase in density.

In Comparative Example 5, the C10 molar ratio was too large, that is, the amount of residual C was large, and it is considered that a large amount of unreacted C remained in the final sintered body even after the reduction reaction.

Table 1 Table 2 <Effects of the Invention> Since the present invention is configured as described above, a molded body is prepared before sintering in a normal vacuum furnace using powder with an average particle size of 30 μm or less as a raw material. By combining C10 adjustment and low-temperature sintering under reduced pressure and high-temperature sintering, it is possible to produce a Ti sintered material with high density and low C1 and low O.
Thereby, Ti sintered parts can be manufactured at low cost and with excellent productivity.

Claims (2)

[Claims] (1) Using Ti powder with an average particle size of 30 μm or less as a raw material, a binder is added to the powder, mixed and injection molded, and then the binder in the molded body is heated in a non-oxidizing atmosphere. removed, followed by a temperature of 1050-1200℃, 1 x 10^
- Sintered at a pressure of 3 Torr or less, and further 1200 ~
A method for producing a Ti sintered material, characterized by sintering at a temperature of 1400°C. (2) The binder in the compact is removed by heating, and the C/O molar ratio in the compact is adjusted to 0.5 to 3.0 in advance during sintering.
The method for producing a Ti sintered material according to claim 1, wherein the Ti sintered material is adjusted to