JPH06329473A - Normal-pressure sintering silicon nitride material having abrasion resistance - Google Patents

Abstract

PURPOSE:To prevent the generation of coarse pores in molding and to decrease the number of residual pores in a sintered material by using easily collapsible granulation powder. CONSTITUTION:Silicon nitride powder obtained by imide decomposition process and having a specific surface area of >=10m<2>/g is incorporated with 8-13wt.% of a sintering assistant and 0-5wt.% of a carbide of Ti, Ta, etc., and mixed for 24-60 hr in wet state in the presence of an organic solvent to obtain a slurry. The slurry is incorporated with 0-3.0wt.% of a binder, dried and granulated to obtain granulation powder having particle diameter of <=150mum. The powder is converted to a formed article by CIP forming process under a pressure of >=100Mpa. The formed article is sintered in nitrogen atmosphere at 1700-1800 deg.C for 2-3hr under normal pressure to obtain the objective abrasion-resistant normal-pressure sintering silicon nitride material having a durability of >=1X10<7> cycle by the thrust-type rolling fatigue life test under the maximum contact stress of 6.5Gpa at room temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wear resistant atmospheric pressure sintered silicon nitride material used for silicon nitride bearing members and other mechanical materials.

[0002]

PRIOR ART AND PROBLEM TO BE SOLVED BY THE INVENTION Silicon nitride
Since silicon nitride does not have self-sinterability when sintering the element
This is done by adding a sintering aid. As a sintering aid,
Generally Y₂O₃Rare earth oxides such as Al and ₂O₃, MgO
It is used in combination with oxides such as
Wet-mixing these sintering aids with elementary powder and dry granulating
After that, by molding and sintering, a silicon nitride sintered body is obtained.
Is getting The sintering method is performed under a nitrogen atmosphere at normal pressure.
Normal pressure sintering method, hot press sintering method by mechanical pressure, nitrogen
Atmospheric pressure sintering method and HIP treatment by gas pressure of elemental gas
There is law and so on.

When the sintered body is used as a bearing material or the like, if there are minute defects (pores and the like) in the sintered body, they cause peeling on the surface due to rolling fatigue.
Further, generally, in normal pressure sintering, large pores are likely to remain inside during sintering, and since strength is low, peeling may occur in a very short time even when a life test is performed. Therefore, when it is used as a bearing material or the like, in addition to atmospheric pressure sintering, it is necessary to eliminate the internal pores by an external pressure using a hot press sintering method, an atmosphere pressure sintering method or a HIP treatment method. However, the operation is complicated, and the cost is disadvantageous.

That is, the silicon nitride sintered body used as the bearing material is required to have no defects (pores, etc.) in the sintered body, but the conventional atmospheric pressure sintered body has pores. Since it remained, sufficient rolling fatigue life was not obtained even after the durability test.

Therefore, an object of the present invention is to make the granulated powder in a silicon nitride-based normal pressure sintered body very easily crushed so that it does not have coarse air holes generated at the time of molding and has residual pores in the sintered body. The present invention is to provide a wear resistant atmospheric pressure sintered silicon nitride material which has a small amount and is useful as a bearing material and a wear resistant material.

[0006]

The present inventors have studied the durability of a silicon nitride sintered body after HIP treatment, which has been used as a bearing material until now, and as a result, found 35 μm in the material.
The present invention has been completed as a result of finding that the presence of the above pores (defects such as pores) affects the life, and creating a normal pressure sintered body without pores of 35 μm or more. Came to do.

That is, the present invention provides a wear resistant atmospheric pressure sintered silicon nitride material having durability of 1 × 10 ⁷ cycles or more under a maximum contact stress of 6.5 GPa at room temperature in a thrust type rolling fatigue life test. Is provided.

The wear resistant atmospheric pressure sintered silicon nitride material of the present invention will be described in more detail below. The wear-resistant atmospheric-pressure sintered silicon nitride material of the present invention is 1 × in a thrust type rolling fatigue life test when the wear-resistant atmospheric-pressure sintered silicon nitride material is formed into a ball shape, a plate shape or the like. It is characterized by having a durability (rolling fatigue life) of 10 ⁷ cycles or more.

The various conditions in the thrust type rolling fatigue life test are as follows.・ Maximum contact stress: 6.5 GPa ・ Silicon nitride balls: 5/16 "3 balls ・ Rotational speed: 3000 rpm ・ Lubricant: Turbine oil ・ Number of test aborts: 1 × 10 ⁷ cycles The number of times is about 1.5 times the rolling fatigue life of the bearing steel.

The wear resistant atmospheric pressure sintered silicon nitride material of the present invention is not particularly limited as long as it has the above-mentioned durability. For example, a specific surface area of 10 m obtained by the imide decomposition method. 3.2 g / cm2 which was sintered by adding Y ₂ O ₃ , Al ₂ O ₃ as a sintering aid to a silicon nitride powder powder of ² / g or more and further adding carbides such as Ta and Ti.
A wear resistant atmospheric pressure sintered silicon nitride material having a density of ³ or more can be used.

The wear resistant atmospheric pressure sintered silicon nitride material of the present invention can be prepared by the following manufacturing method.

[Manufacturing Method] First, Y ₂ O ₃ and Al ₂ O ₃ as a sintering aid are added to silicon nitride powder in a total amount of 8 to 13% by weight,
Carbides such as Ta and Ti are added as an additive in an amount of 0 to 5% by weight and mixed to obtain a slurry. At this time, for mixing, for example, a wet ball mill is used in the presence of an organic solvent such as ethanol or methanol for 24 to 60 hours, preferably 30 to 48 hours. Here, if the mixing time is shorter than 24 hours, the agglomeration of the silicon nitride powder remains and tends to become a defect at the time of sintering, and if longer than 60 hours, the inclusion of foreign matters from the ball mill increases and the strength of the sintered body decreases. Is not preferred.

Next, polyvinyl butyral (PVB) or the like as a binder was added to the obtained slurry in an amount of 0 to 3.0% by weight, preferably 0.5 to 1.0% by weight, and the mixture was dried and granulated by a spray dryer. Then, it is classified into granulated powder of 150 μm or less. Here, the addition amount of the binder is 3% by weight.
If it exceeds, the granulated powder is hard and difficult to be crushed, and pores are easily generated during molding, which is not preferable.

The use of an organic solvent such as ethanol as a solvent during mixing is because the solvent is likely to evaporate during dry granulation and voids are easily formed between the primary particles to easily collapse. On the other hand, when water is used, the primary particles are densely packed because they are hard to evaporate, the granulated powder is hard and difficult to be crushed, and coarse air holes are easily generated, which is not preferable.

Next, molding is performed. The molding is performed by molding a granulated powder into a mold or filling a rubber mold with a pressure of preferably 100 MPa or more, more preferably 150 to 50.
CIP molding is performed at 0 MPa. Molding pressure is 100MPa
If it is smaller than the above range, the density of the molded body becomes low and the compact is not sufficiently densified during sintering, which is not preferable.

Next, the molded body obtained by the above molding is sintered to obtain a desired sintered body. The sintering conditions are 1700 to 1800 ° C. under normal pressure and nitrogen atmosphere at 1
˜4 hours, preferably 1700 to 1750 ° C., 2-3 hours. If the temperature is lower than 1700 ° C, densification may not occur or strength may not be exhibited, and if it exceeds 1800 ° C, silicon nitride is decomposed, which is not preferable. Further, if the holding time is shorter than 1 hour, β grains of silicon nitride will not grow sufficiently, and if longer than 4 hours, grain growth will be excessive and the strength will decrease, which is not preferable.

The wear resistant atmospheric pressure sintered silicon nitride material of the present invention can be used in various applications requiring durability, and particularly preferably used as a rolling bearing member and the like.

[0018]

EXAMPLES Next, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

[Examples and Comparative Examples] 90% by weight of silicon nitride powder ("SN-E10" manufactured by Ube Industries) and Y ₂ O
₃ (Shin-Etsu Chemical: fine-grained product) 5% by weight, Al ₂ O ₃ (Sumitomo Chemical: “AKP-30”) 4% by weight, TaC
1% by weight of (HC Starch: 0.7 my) was wet mixed with the solvent shown in Table 1 for 36 hours.

0.5 to 1.0% by weight of the binder shown in Table 1 was added to the obtained slurry, and the mixture was granulated and dried by a spray dryer. The granulated powder is sieved through a sieve, 150
Those having a size of μm or less were used. 50 x 50 x 5 of this granulated powder
After CIP molding with a pressure of 150 MPa into a plate shape of mm,
Sintering was carried out under atmospheric pressure in a nitrogen atmosphere at 1750 ° C. for 2 hours under atmospheric pressure.

The rolling fatigue life test surface of the obtained pressureless sintered body (test piece) was finished by grinding to Rmax = 0.3 μm or less, and then subjected to a thrust type rolling fatigue life test. Figure 1 shows the thrust type rolling fatigue life test.
Will be described with reference to. Here, FIG. 1 is a schematic diagram showing a thrust type rolling fatigue life test apparatus. As shown in FIG. 1, a thrust type rolling fatigue life test apparatus 10 includes a test tank 6 having a recess for fixing the test piece 1 in the center of the inner surface thereof, a cage 3 for equally distributing the silicon nitride balls 2. It comprises an inner ring 4 having a groove formed in a portion in contact with the silicon nitride ball 2, and a rotary shaft 7 to which the inner ring 4 is attached. Further, as the lubricating oil, turbine oil 5 is added so that the test piece 1, the silicon nitride balls 2, the cage 3 and the inner ring 4 are immersed. Then, after applying a load in the direction of arrow A to the test tank 6, the test can be performed by rotating the rotary shaft 7 in the direction of arrow B at a predetermined rotation speed.

The test conditions for the thrust type rolling fatigue life test are as follows.・ Maximum contact stress: 6.5 GPa ・ Silicon nitride balls: 5/16 ”3 balls ・ Rotational speed: 3000 rpm ・ Lubricant oil: Turbine oil ・ Cutoff frequency: 1 × 10 ⁷ cycles

The bending strength of the sintered body is JIS-R-1.
It is the three-point bending strength measured by 601. The results are shown in Table 1.

[0024]

[Table 1]

As is clear from the results shown in Table 1, in the wear resistant atmospheric pressure sintered silicon nitride material of the present invention, the residual pores inside the sintered body are 20 μm or less and the bending strength is 1000 M.
Reached Pa or higher. The rolling fatigue life test result of this pressureless sintered body exceeded 1 × 10 ⁷ cycles and had durability that could be used as a bearing material. On the other hand, in the comparative example in which ion-exchanged water is used as the solvent and the binder is acrylic resin or PVA, the granulated powder is hard and is difficult to be crushed, so that 50 μm residual pores exist in the atmospheric pressure sintered body. The bending strength was low at 800 to 900 MPa. As a result of rolling fatigue life test of these, 1 × 10
Peeling occurred in ⁶ cycles or less.

Therefore, it is understood that the wear resistant atmospheric pressure sintered silicon nitride material has very small residual pores and excellent strength and durability against rolling fatigue due to the crushing of the granulated powder.

[0027]

EFFECTS OF THE INVENTION The wear-resistant atmospheric pressure sintered silicon nitride material of the present invention has coarse atmospheric holes generated at the time of molding in a silicon nitride atmospheric pressure sintered body by making the granulated powder very easily crushed. In other words, the sintered body has few residual pores and is useful as a bearing material and a wear resistant material.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a thrust type rolling fatigue life test apparatus.

[Explanation of symbols]

 1 Test piece (sintered body under pressure) 2 Silicon nitride balls 3 Cage 4 Inner ring 5 Turbine oil 6 Test tank 7 Rotating shaft 10 Thrust type rolling fatigue life tester

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Youji Kukai 5 1978, Ogushi, Ube City, Yamaguchi Prefecture 5 1978, Ube Industries Ltd. Inorganic Materials Research Laboratory (72) Inventor Katsumi Nishihara 55, Sakuradori, Kuwana City, Mie Prefecture (72) Inventor Kiyohara, Koichi Mie Prefecture, Kuwana City, Tozai 22224, Toho, Akebono Dormitory

Claims (1)

[Claims] 1. In a thrust type rolling fatigue life test, 1 × 10 ⁷ under a maximum contact stress of 6.5 GPa at room temperature.
A wear-resistant atmospheric pressure sintered silicon nitride material that has durability over a cycle.