JPH07115932B2 - Homogeneous silicon nitride sintered body and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a high-strength and homogeneous silicon nitride sintered body useful for bearing members, wear resistant members, sliding members and the like, and a method for producing the same.

[Prior Art] It has been conventionally known to use a sintering aid in the production of a silicon nitride sintered body. Then, it is known to add an alkaline earth metal oxide, a rare earth element oxide or the like as the sintering aid.

Of these, the alkaline earth metal oxides have the effect of forming a liquid phase during firing, promoting densification, and strengthening the bonding of the silicon nitride particles. Further, it is known that the rare earth element oxide has an action of promoting the growth of columnar particles of silicon nitride crystals and, when coexisting with an alkaline earth metal, has an effect of contributing to strengthening of the silicon nitride sintered body. Was there.

[Problems to be Solved by the Invention] However, in recent years, there has been a demand for a silicon nitride sintered body having appropriate characteristics as a structural material such as a bearing member, and further strengthening of the silicon nitride sintered body has been demanded. , Densification and homogenization of structure have become necessary.

[Means for Solving Problems] Then, the present inventor has made diligent studies in view of the above problems, and as a result, combines an alkaline earth metal oxide and a rare earth element oxide as a sintering aid. It was found that not only the densification and strength of the silicon nitride sintered body but also the homogenization of the structure are greatly contributed. Furthermore, by combining the manufacturing process of forced drying of the powder after granulation, water content adjustment, and then hot isostatic pressing, the effects of densification, strengthening, and homogenization of the structure by the above-mentioned sintering aid, Due to the synergistic effect of combining the effects of densification, strengthening, and homogenization of the structure due to the specified manufacturing process, further densification, strengthening, and homogenization of the structure are promoted compared to the case of a single case. Therefore, the present invention has been achieved.

That is, according to the present invention, 0.5 to 10 wt% each of one or more rare earth element oxides and 0.5 to 8 wt% each of one or more alkaline earth metal oxides as a sintering aid, the total amount of which is 1.5 to 15w
It is a sintered body of hot isostatic press sintering containing 85 to 98.5 wt% of silicon nitride crystal in a range of t%, the bending strength at room temperature is 100 kg / mm ² or more, and the Knoop hardness is 15.5. A homogeneous silicon nitride sintered body for bearing members, wear resistant members or sliding members characterized by having GPa or more, and a silicon nitride raw material and a sintering aid are mixed, crushed, granulated and then molded. Then, in the method for producing a silicon nitride sintered body by firing the molded body, 0.5 to 10 wt% each of one or more rare earth element oxides and one or more alkaline earth metal oxides are used as sintering aids. 0.5 to 8 wt% each, the total amount of which is added to the range of 1.5 to 15 wt%, and granulated using 85 to 98.5 wt% as the silicon nitride raw material After forcibly drying the granulated powder once Molding, then pre-treating the obtained molded body, hot isostatic pressing under nitrogen atmosphere Process for producing a homogeneous silicon nitride sintered body, characterized the door, is provided.

The homogeneous silicon nitride sintered body according to the present invention contains one or more rare earth element oxides and one or more alkaline earth metal oxides as sintering aids. And, preferably, rare earth element oxide 1 and alkaline earth metal oxide 2
It is effective to select and use the seeds for densification, strengthening and homogenization of the structure of the silicon nitride sintered body. Y ₂ O _{3 is} used as the rare earth element oxide and Mg is used as the alkaline earth metal oxide.
It is particularly preferred to use O and SrO.

The content of the sintering aid is 0.5-10 wt%, preferably 3-8 wt% of one or more rare earth element oxides.
%, One or more alkaline earth metal oxides 0.5 to 8 wt.
%, Preferably 0.5 to 6 wt%, and the total amount of the above sintering aids is 1.
It is used in the range of 5 to 15 wt%, preferably 5 to 13 wt%. And 85 to 98.5 wt% is a crystal of silicon nitride.

Further, it is considered that the above-mentioned sintering aid may not necessarily be in the form of an oxide by forming a solid solution in Si ₃ N ₄ in the sintered body, but the content ratio in that case Is the value converted to oxide.

If the content ratio of the sintering aid deviates from the above range, the densification, the strengthening, and the homogenization of the structure of the silicon nitride sintered body become insufficient, which is not preferable.

The bending strength is 100 kg / mm ² or more, preferably 110
It is at least kg / mm ² . This is because if the bending strength is 100 kg / mm ² or more, resistance to mechanical stress increases and it becomes difficult to break during use.

Further, in the homogeneous silicon nitride sintered body of the present invention, it is necessary that the Knoop hardness is 15.5 Gpa or more in order to improve rolling fatigue life and wear resistance, and it is further preferable that it is 16.0 Gpa or more. Is.

The homogeneous silicon nitride sintered body having the composition and characteristics as described above is used in a silicon nitride raw material of 85 to 98.5 wt% and 0.5 to 10 wt% of each of one or more rare earth element oxides as a sintering aid and an alkaline earth metal. One or more oxides are added in an amount of 0.5 to 8 wt% each so that the total amount is 1.5 to 15 wt% and pulverized and mixed. Preferably, the raw materials are pulverized and then sieved to 32 μm or less before granulation. Then, after forcibly drying the granulated powder, water is added if necessary and sieved, and then molded, and then the obtained molded body is subjected to a pretreatment and under a nitrogen atmosphere. It can be manufactured by subjecting the steel to hot isostatic pressing. That is, particularly important points in the method for producing the homogeneous silicon nitride sintered body of the present invention are forced drying of the granulated powder and specification of the sintering aid to be used. If this forced drying is not performed, in the subsequent molding process,
Since the granulated powder does not uniformly disintegrate due to the molding pressure, it is not possible to obtain a homogeneous molded body with few pores. Therefore, coarse pores remain even after hot isostatic pressing (HIP).
A homogeneous, dense, high-strength fired product cannot be obtained.

In addition, after forcibly drying the granulated powder, adding water as necessary and further sieving can obtain a more uniform granulated powder without the difference in water content between the granulated powders. It is preferable because it is possible.

Furthermore, it is preferable to pass the raw material after pulverization through a sieve of 32 μm or less before granulation. It is preferable to use a sieve with a mesh size larger than this to effectively remove coarse particles after pulverization and foreign substances contained in raw materials. This is because it cannot be eliminated and it is difficult to maintain the uniformity of the granulated powder.

Also, an important point in the present invention is to use two or more kinds of sintering aids, one or more rare earth element oxides and one or more alkaline earth metal oxides in total. At least one of Y ₂ O ₃ , CeO ₂ , Yb ₂ O ₃ etc. is used as the rare earth element oxide, and at least one of MgO, SrO, BeO, BaO etc. is used as the alkaline earth metal oxide. It is preferable that the rare earth element oxide is one kind and the alkaline earth metal oxide is two kinds, that is, three kinds in total, more preferably the rare earth element oxide is Y ₂ O ₃ and the alkaline earth metal oxide is MgO, It is SrO. As the content ratio of the sintering aid,
One or more rare earth element oxides are each 0.5 to 10 wt%, preferably 3 to 8 wt%, one or more rare earth element oxides are each 0.5 to 8 wt%, preferably 0.5 to 6 wt%, and the total amount is 1.
It is used at 5 to 15 wt%, preferably 5 to 13 wt%.

By incorporating the above-mentioned two or more kinds as the sintering aid in the above-mentioned content ratio, in combination with the subsequent forced drying operation of the granulated powder, densification of the sintered body, strengthening, homogenization of the structure Is achieved.

The starting materials for these sintering aids are not particularly limited to oxides, and salts such as nitrates may be used.

In the present invention, the molding is performed after the forced drying, and then the pretreatment and the hot isostatic pressing treatment are performed.
Of these, the pretreatment process can be divided into two processes: a process of primarily firing the molded product (primary sintering process) and a process of encapsulating the molded product in capsules (capsule processing process). Among the pretreatment steps, in the primary sintering step, the molded body, preferably under normal pressure nitrogen atmosphere, 1400 ~
It is primarily fired at 1600 ° C. If the firing temperature is lower than 1400 ° C, open pores will not disappear even after firing, and a dense sintered body will not be obtained even after hot isostatic pressing. Also, the firing temperature is 1600
If the temperature is higher than 0 ° C, the decomposition reaction of silicon nitride proceeds, and a dense and high-strength sintered body cannot be obtained even after hot isostatic pressing.

On the other hand, in the capsule treatment step, the molded body is preferably vacuum degassed and then sealed in glass containing SiO ₂ as a main component. The glass is preferable as the capsule because it is excellent in deformability and sealing property as a capsule during hot isostatic pressing.

After performing these pretreatments, hot isostatic pressing treatment, preferably under a nitrogen atmosphere of 200 to 1500 atm, 1500 to 1
Perform at 900 ° C.

Using the combination of the specific sintering aids as described above, the forced drying step of the granulated powder, and the pretreatment step and hot isostatic pressing treatment step of the molded body obtained thereby are further preferably combined. By performing the sieving step after crushing the raw material, a homogeneous silicon nitride sintered body having the characteristics of the present invention could be manufactured.

The silicon nitride sintered body according to the present invention is suitable for use as a bearing member such as a rolling bearing and a sliding bearing, and also as a sliding member such as an air slide and a lathe bed, and a moving body such as gas, liquid or particles. It can also be preferably used as a wear resistant member used in a contacting portion (eg, cobblestone, nozzle).

[Examples] Hereinafter, the present invention will be described in detail based on Examples, but it will be apparent that the present invention is not limited to these Examples.

The drawing is a flow chart showing an embodiment of the method for producing a homogeneous silicon nitride sintered body of the present invention. As shown in the drawings, each step is represented by step 1 to step 9.

First, a silicon nitride raw material is mixed with one or more rare earth element oxides and one or more alkaline earth metal oxides as a sintering aid, for a total of two or more species, and pulverized (step 1), and preferably used during pulverization. In order to remove foreign matters such as cobblestone fragments and coarse particles, a material having an average particle diameter of 1 µm or less is preferably passed through a sieve of 32 µm or less (step 2).

Next, after granulating this raw material (step 3), the granulated powder is forcibly dried, preferably at a temperature of 60 to 100 ° C., to reduce the difference in the water content of the granulated powder and to obtain a homogeneous granulated powder. (Step 4). Next, if necessary, 0.5 to 5.0% by weight of water is added to the granulated powder (step 5) to obtain a granulated powder having a uniform water content, which is further sieved and aggregated by adding water. Coarse particles are removed (step 6). The obtained granulated powder is molded by a usual method (step 7), then the molded body is subjected to pretreatment (step 8), and then fired by hot isostatic pressing treatment (step 9). The homogeneous silicon nitride sintered body of can be manufactured.

Hereinafter, more specific examples will be described.

Example 1 A sintering aid was first added to α-type silicon nitride powder having an average particle size of 0.9 μm.
Add and mix in the types and proportions shown in the table, and add water to it 60
%, And mixed and pulverized by a batch type pulverizer, and then sieved through a sieve having an opening of 20 μm to obtain a slurry having an average particle diameter of 0.7 μm. Add polyvinyl alcohol (PV
A) 2% by weight was added, and a granulated powder was obtained using a spray dryer. This granulated powder was forcibly dried at 60 ° C. for 24 hours, added with 4% by weight of water, and further passed through a sieve having an opening of 149 μm. Thereafter, cold isostatic pressing was performed at a pressure of 5 ton / cm ² to obtain a compact. After degreasing this molded body at 500 ° C for 3 hours, it is vacuum-sealed in a silica glass capsule, and this capsule is placed in a HIP device at a pressure of 300at.
By hot isostatic pressing (HIP) sintering at m and a temperature of 1600 ° C., sintered bodies of the present invention and comparative examples were obtained. The characteristics of the obtained sintered body are shown in Table 1.

The bending strength was measured by the four-point bending strength method of JIS R-1601 "Test method for bending strength of fine ceramics".
The Knoop hardness was measured under a load of 300 g and a holding time of 15 seconds based on JIS Z-2251 "Micro hardness test method".

The rolling fatigue life test is 50 mm
A (φ) × 10 mm (thickness) disk is cut out and mirror-polished, then Hertz stress 500 k is measured by a 6-ball type thrust bearing tester.
A rolling fatigue test was conducted at g / mm ² for evaluation.

As is clear from Table 1, the sintering aid of the present invention, and a manufacturing process in which HIP sintering is performed using the adjusted raw material in which water is added if necessary after forced drying and then sieved. By combining, high strength compared to conventional products,
It was found that a sintered body having high hardness and excellent mechanical properties can be obtained.

Example 2 Powders of Y ₂ O ₃ , MgO, and SrO as sintering aids were added and mixed at a ratio shown in Table 2 to α-type silicon nitride powder, and 60% of water was added thereto.
After pulverizing and mixing with a batch type pulverizer, the slurry was sieved. At this time, in order to examine the influence of the average particle diameter after pulverization and the sieve opening of the slurry after pulverization, various changes were made as shown in Table 2. Further, 2 wt% of polyvinyl alcohol (PVA) was added to this slurry, and a granulated powder was prepared using a spray dryer. Then, using a constant temperature dryer to investigate the forced drying temperature of the granulated powder, the amount of water added after the forced drying, and the effect of the sieve opening after the water addition, the granulated powder at the forced drying temperature shown in Table 2 was used. After being dried for 24 hours, water addition and sieving after water addition were carried out as needed as shown in Table 2.

The granulated powder thus obtained was molded and degreased in the same manner as in Example 1 and then subjected to normal pressure sintering for 3 hours at 1550 ° C. in a nitrogen atmosphere (primary sintering step), and then in a nitrogen atmosphere. And second
HIP treatment was performed at the pressures and temperatures shown in the table to obtain silicon nitride sintered bodies of the present invention and comparative examples.

From Table 2, it was found that the range of the sintering aid of the present invention is more preferable due to the forced drying of the granulated powder and the synergistic effect thereof combined with the subsequent HIP treatment.

[Effects of the Invention] As described above, according to the present invention, a specific combination of sintering aids is used, and forced drying of granulated powder and subsequent pretreatment and HIP treatment are combined. More preferably, by performing sieving after crushing the raw material, a silicon nitride sintered body having a more dense and high strength and a uniform structure can be obtained. Therefore, the silicon nitride sintered body of the present invention can be used very effectively as a wear resistant member, a sliding member, etc. in addition to a bearing member.

[Brief description of drawings]

The drawing is a flow chart showing an embodiment of the manufacturing method of the present invention.

Claims (11)

[Claims] 1. A sintering aid comprising one or more rare earth element oxides in an amount of 0.5 to 10 wt% and one or more alkaline earth metal oxides in an amount of 0.5 to 8 wt%, respectively, the total amount being 1.5 to 15 wt%. It is a sintered body of hot isostatic press sintering consisting of 85 to 98.5 wt% of silicon nitride crystals, with bending strength at room temperature of 100 kg / mm ² or more and Knoop hardness of 15.5 GPa or more. A homogeneous silicon nitride sintered body for a bearing member, a wear resistant member or a sliding member, which is characterized by being present. 2. The silicon nitride sintered body according to claim 1, wherein the rare earth element oxide is one kind and the alkaline earth metal oxide is two kinds. 3. The silicon nitride sintered body according to claim 1, wherein the rare earth element oxide is Y ₂ O ₃ and the alkaline earth metal oxides are MgO and SrO. 4. A method for producing a silicon nitride sintered body by mixing a raw material of silicon nitride and a sintering aid, pulverizing, granulating, molding, and then firing the compact, in the method of producing a rare earth element as a sintering aid. 0.5 to 10 wt% each of elemental oxides and 0.5 to 8 wt% of alkaline earth metal oxides, respectively, in a total amount of 1.5 to 15 wt%, and a silicon nitride raw material of 85 to The granulated powder granulated using 98.5 wt% is forcibly dried once and then molded, and then the obtained molded body is subjected to pretreatment and hot isostatic pressing in a nitrogen atmosphere. A method for producing a homogeneous silicon nitride sintered body, which comprises: 5. The production method according to claim 4, wherein one kind of rare earth element oxide and two kinds of alkaline earth metal oxide are added. 6. The method according to claim 4, wherein the rare earth element oxide is Y ₂ O ₃ and the alkaline earth metal oxides are MgO and SrO. 7. After forcibly drying the granulated powder,
The production method according to claim 4, wherein water is added if necessary, and the powder is sieved to obtain a uniform granulated powder having a predetermined water content. 8. The method according to claim 4, wherein the raw material after pulverization is passed through a sieve of 32 μm or less before granulation. 9. The production method according to claim 4, wherein the average particle size after pulverization is 1 μm or less. 10. The pretreatment is performed in a nitrogen atmosphere at 1400-1600.
The production method according to claim 4, wherein the firing is performed primarily at a temperature of ° C. 11. The manufacturing method according to claim 4, wherein the pretreatment is to encapsulate the molded body.