JP2001139380A - Silicon nitride-based composite material and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wear resistant material which is a silicon nitride-based composite material formed by dispersing dispersion particles essentially consisting of nitrides of metals into a matrix essentially consisting of Si3N4, is manufactured by using the Si3N4 raw material having an oxygen quantity of an ordinary level and is practically problem-free in spite of a wide variation in the oxygen quantity of the material to an ordinary level. SOLUTION: The silicon nitride-base composite material which is formed by dispersing the particles essentially consisting of the metal nitride of <=200 nm in an average grain size at 10 to 50 vol.% as the dispersion particles into the matrix consisting of silicon nitride particles of <=200 nm in an average grain size and grain boundary phase and in which the total oxygen quantity in the sintered compact is large within a range from the total oxygen quantity in the raw material powder up to maximum 3 wt.%. The material is obtained by pulverizing and mixing the sintering assistant powder and the metals and/or their nitride powder in such a manner that the average grain size over the entire part attains <=100 nm and the increased oxygen quantity in the powder attains a range of 0.5 to 3 wt.% and sintering the moldings thereof under a nonoxidizing atmosphere containing nitrogen at 1,000 to 1,600 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride-based composite material having high wear resistance useful as wear-resistant members such as various mechanical members and cutting tools and sliding members.

[0002]

2. Description of the Related Art Silicon nitride is excellent in hardness, mechanical strength and heat resistance and is chemically stable, so that it is used for various mechanical members represented by automobile engine parts, cutting tool materials and bearings. -Widely used for sliding members. In recent years, the performance levels imposed on materials in all these fields have become severe. The same applies to fields requiring abrasion resistance.

For example, when a silicon nitride-based composite material is used for specific automobile parts or plastic working tools requiring high wear resistance, a cemented carbide (hard particles composed of WC and a binder phase such as Co) are used. Cermet materials) and remarkably higher wear resistance than conventional materials such as high-speed steel. However, at present, silicon nitride-based composite materials are more expensive than these materials, and the abrasion resistance is not at a satisfactory level corresponding to the price level. In the present invention, “silicon nitride-based” refers to a ceramic containing silicon nitride (Si ₃ N ₄ ) and / or sialon as a main crystal phase. The "silicon nitride-based composite material" refers to a material in which a different component is dispersed and composited in a matrix having such a ceramic as a main crystal phase.

Japanese Unexamined Patent Publication No. Hei 10-338576 discloses such a wear-resistant material in a matrix composed of silicon nitride-based particles having an average particle diameter of 200 nm or less and a grain boundary phase. Titanium nitride (TiN)
A silicon nitride-based composite material in which particles are dispersed is disclosed. This material exhibits high mechanical strength in the middle to low temperature range from room temperature to 900 ° C.

According to the publication, this material is used to form a compact of a mixed powder obtained by mixing a silicon nitride (Si ₃ N ₄ ) powder, a sintering aid powder and a metal Ti powder in a nitrogen atmosphere at 1000 to 1000 μm.
It is obtained by sintering at 1400 ° C. In this case, the mixed metal Ti powder has a function of miniaturizing both the Si ₃ N ₄ and the particles themselves due to its own plastic deformability, and thereby, each of the particles has an average particle diameter. The size is reduced to 200 nm or less. A preferable mixing method is a mechanical alloying method having a high-speed pulverizing effect. Further, at the time of sintering, the metal Ti particles are nitrided to become TiN, and at the same time, the grain growth of the Si ₃ N ₄ particles is suppressed, and a sintered body composed of fine particles as described above is obtained. According to the embodiment of the publication, 1.3 to 2 ..
Those having a high bending strength of 5 GPa are introduced.

[0006]

However, according to a subsequent study by the present inventor, in order to suppress the variation in the abrasion resistance of the material according to this method and to maintain it at a practically acceptable level, the raw material must be sintered. It was found that the amount of increase in oxygen up to the conclusion had to be suppressed to less than 1.5% by weight. It has also been found that for this purpose, the amount of oxygen in the used Si ₃ N ₄ raw material powder must be suppressed to less than 1% by weight. That is, in order to stably obtain the abrasion resistance described in JP-A-10-338576, a special powder having a small oxygen content is selected, or a normal commercial powder is used. It is necessary to remove oxygen while performing a deoxidizing treatment in advance or sintering under special conditions, which raises a problem that a cost increase cannot be avoided. Further, it was also found that the composite material obtained by the method of the same publication tends to have a low wear resistance performance level unless the oxygen content in the raw material is controlled, and that the production variability increases. .

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has as its object to provide a less expensive material of the same type showing stable and high wear resistance. is there. The composite material of the present invention has an average particle size of 200
In a matrix composed of silicon nitride-based particles having a particle size of 200 nm or less and particles containing metal nitride having a mean particle size of 200 nm or less as a main component, 10 to 50% by volume is dispersed as a dispersed particle. This is a silicon nitride-based composite material in which the total oxygen content in the compact is larger than the total oxygen content in the raw material powder by up to 3% by weight.

[0008] The material of the present invention comprises a step of preparing a silicon nitride powder, a sintering aid powder, and a metal and / or a nitride powder thereof.
nm or less, a step of pulverizing and mixing to obtain a mixed powder so that the increased oxygen amount in the powder is in the range of 0.5 to 3% by weight, a step of molding the mixed powder to form a molded body, 100
And sintering in a non-oxidizing atmosphere containing nitrogen at 0 to 1600 ° C. to form a sintered body.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The composite material of the present invention will be described in detail below, including its manufacturing method. S of the composite material of the present invention
The average particle size of the i ₃ N ₄ particles and the dispersed particles is 200 nm or less. Further, the amount of oxygen contained is controlled by suppressing the increase in the amount of oxygen to 3% by weight or less from the time of the raw material. Therefore, high wear resistance is exhibited by the synergistic effect of the average particle diameter in this range and an appropriate amount of oxygen. If the increase in the average particle size and the amount of oxygen of both particles exceeds these upper limits, the abrasion resistance decreases.

Although the cause is not clear, it is generally considered as follows. Si ₃ N ₄ particles abraded in the air and some silicon oxynitride particles formed in a matrix composed of the same particles and dispersed particles dispersed in the matrix are easily oxidized because they are extremely fine. This is because a fine dense smooth surface is formed. In this case, it is presumed that the amount of the silicon oxynitride is appropriately controlled, probably by controlling the amount of increase in oxygen, which promotes the formation of the smooth surface and also contributes to the prevention of the crystal grains from falling off. Even if the main crystal phase particles fall off, it is presumed that the fineness of these particles weakens the aggressiveness of the particles on the material surface and that the roughening of the material surface does not progress significantly. Is done.

The amount of the dispersed particles is 10 to 50% by volume. If the content is less than 10% by volume, it is impossible to suppress the growth of silicon nitride-based particles and silicon oxynitride particles constituting the matrix, and in particular, the average particle size of Si ₃ N ₄ particles is 200 nm.
You will not be able to control below. On the other hand, if it exceeds 50% by volume,
The dispersed particles agglomerate and coalesce during sintering, which tends to cause grain growth, and the average particle size cannot be controlled to 200 nm or less. The amount is desirably 10 to 40% by volume.

The nitride in the dispersed particles may be a transition metal nitride, but in order to sufficiently achieve the desired effects of the present invention, elements of Group IVa of the periodic table (Ti, Zr and H) are required.
f), Group Va elements (V, Nb and Ta) and VIa
Of group III elements (Cr, Mo and W), especially T
i and Ta nitrides are preferred. The metal nitride in the dispersed particles may contain some carbon or oxygen. For example, carbon and / or oxygen may be partially combined with nitrogen, or carbon and / or oxygen may be present alone. Further, a nitride containing a plurality of metal elements (composite nitride) may coexist. In order to coexist nitrides of a plurality of metal elements in this way, nitride powders of a plurality of metal elements and / or powders of the same metal are mixed in advance. Alternatively, it may be added in a form such as an intermetallic compound or a composite nitride. In this way, by adding in a form containing two or more kinds of metal elements, the dispersed particles containing the added dissimilar metal elements agglomerate with each other, thereby making it difficult for the particles to grow, so that the dispersion average of the dispersed particles is Particle size is
It becomes finer, and the wear resistance of the material is further improved.

The material of the present invention is prepared so that the total oxygen content is up to 3% by weight than the total oxygen content in the raw material powder. The term “total oxygen content in the sintered body” as used herein refers to the total amount of oxygen present in the sintered body regardless of whether or not it is chemically bonded. The “total amount of oxygen in the raw material powder” is the total amount of oxygen present in the raw material powder regardless of whether or not it is chemically bonded. Since an oxide is often used as a sintering aid, most of the oxygen exists in the grain boundary phase of the sintered body. The difference between the two, that is, the amount of increase in oxygen during the manufacturing process is generally controlled to 3% by weight or less. If there is no difference in this amount or if oxygen decreases through the manufacturing process, vacancies are likely to be formed in the material, and the amount of open pores on the surface of the material increases. As a result, wear resistance is reduced. In order to improve wear resistance, the amount of open pores is
It is desirable to keep it to 0.5% or less. On the other hand, this amount difference is 3
If the content is more than 10% by weight, much of the oxygen present in the raw material and oxygen taken in from the outside during the subsequent manufacturing process will be collected in the grain boundary phase, so that the glass phase forming the grain boundary phase will increase.
In addition, abnormal grain growth of the matrix and the dispersed particles during sintering is likely to occur, and it becomes impossible to control the average particle diameter within the above range. This difference in the amount of oxygen is preferably 1.5 to 2% by weight. Some of these oxygens precipitate as silicon oxynitride in the matrix of the sintered body.

Further, the material of the present invention comprises a step of preparing a silicon nitride powder, a sintering aid powder, and a metal and / or a nitride powder thereof; A step of pulverizing and mixing the mixed powder so that the amount of oxygen in the powder is in the range of 0.5 to 3% by weight to form a mixed powder; a step of molding the mixed powder to form a molded body; Sintering in a non-oxidizing atmosphere containing nitrogen at 1600 ° C. to form a sintered body.

As the raw material powder, any of commercially available powders may be used, but it is preferable to use Si ₃ N ₄ powder having an oxygen content of 1 to 2% by weight. Oxygen content is less than 1% by weight or 2
If the content is more than 10% by weight, grain growth is likely to occur, and it may be difficult to control the size of the main crystal phase particles, and the abrasion resistance tends to decrease. The crystal form may be either α-type or β-type. For both the Si ₃ N ₄ powder and the sintering aid powder, the average particle diameter is desirably small as it is easy to control the particle diameter and the abrasion resistance is improved, but the particle diameter is preferably 5 μm or less, more preferably 2 μm or less. The smaller the average particle size of the metal powder or the nitride powder added as the dispersed particles, the better, but it is preferably about 10 μm or less, more preferably 5 μm or less.

These powders have a total average particle size of 100 n.
m or less, and pulverized and mixed so that the increased oxygen amount in the powder is in the range of 0.5 to 3% by weight to obtain a mixed powder. If the average particle size after pulverization exceeds 100 nm, the average particle size of the main crystal phase particles and the dispersed particles after sintering does not become 200 nm or less. Mixing is desirably performed by a method such as a ball mill or an attritor that involves grinding. For example, Japanese Patent Application Laid-Open No.
As described in JP-A-338576, mechanical alloying is performed using this type of mixing apparatus. According to this method, a fine mixed powder having an average particle diameter of 100 nm or less can be obtained due to the plastic deformation ability of the metal powder added as a dispersed particle source as described above. Conditions such as the acceleration of the pulverization, the charge amount ratio between the powder and the pulverizing medium, and the pulverization time are appropriately selected according to the initial average particle size level of the raw material powder. Further, in order to control the oxygen content of the powder after pulverization within the above range, it is desirable to adjust the pulverization atmosphere to an inert gas atmosphere such as nitrogen gas. The Si ₃ N ₄ powder, the sintering aid powder, and the metal nitride powder to be dispersed particles produce extremely fine particles from a metal or an organic or inorganic salt thereof by chemical or physical means in advance. May be. Examples of such means include a method of obtaining a coprecipitate from an organic salt of a metal, a method of producing a coprecipitate from an inorganic composite compound such as a Si—Ti—N system by heat treatment, and the like. In addition to the above-mentioned grinding means, there is a vibration-type grinding method and the like.

The mixed powder prepared as described above can be formed by a known molding method such as a conventional dry press molding method, an extrusion molding method, a doctor blade molding method, and an injection molding method. In addition, the most desirable molding method in terms of quality and production may be selected. Prior to molding, the mixed powder after pulverization and mixing may be granulated to increase its bulk density in advance to enhance moldability.

The compact is placed in a non-oxidizing atmosphere containing nitrogen.
Sintering is performed in a temperature range of 1000 to 1600 ° C. The composition and pressure of the atmosphere gas are adjusted according to the oxygen content of the above-mentioned pulverized mixed powder and the content of metal in the powder to be dispersed particles. For example, when the former is relatively close to 3% by weight or the latter is 50% by weight or more, only nitrogen gas or its partial pressure is increased, or nitrogen gas of higher pressure is used. As the heating means for sintering, ordinary normal pressure sintering may be used, but a means such as a pulse discharge sintering method or a high frequency induction heating type sintering method capable of heating and uniformly heating the compact in a short time is used. desirable. The sintering may be performed by pressurizing with an atmospheric gas or by applying an external pressure mechanically and applying pressure.

[0019]

Example 1 A dispersed particle source powder composed of a Si ₃ N ₄ powder, a sintering aid powder, and a metal or metal nitride described in Table 1 was prepared. Both powders are commercially available. Note that Y ₂ O ₃ and Al ₂ O ₃
Each of the powders had an average particle size of 1 μm. In the table, the amounts of the Si ₃ N ₄ powder and the sintering aid powder are indicated by weight% of the total amount of both, not including the dispersed particle source powder. The raw material powder to be the matrix and the dispersed particle source powder were mixed such that the latter was the volume% in the table and the remainder was the volume% of the former. For example, in sample 1, 70% by volume of a matrix powder composed of Si ₃ N ₄ powder and sintering aid powder in the weight ratios shown in the table, 10% by volume of metallic Ti powder and 10% by volume of metallic Ta powder, and TiN powder Was 10% by volume. The conversion into the weight value at the time of weighing was performed using the respective theoretical densities. The same applies to the following embodiments.
For example, in the case of this embodiment, the same density value is Si ₃ N ₄ , Y
G / g in the order of ₂ O ₃ , Al ₂ O ₃ , Ti, Ta and TiN.
3.40, 5.03, 3.9 in cm ³ units
8, 4.60, 7.70 and 5.40.

[0020]

[Table 1]

The oxygen content of the whole raw material powder before mixing was at the level described in the column "Total oxygen content" in Table 2. In addition, this oxygen amount X was made into the total sum using the chemical analysis value of each raw material powder.

[0022]

[Table 2]

The weighed raw material powders of each sample were pulverized and mixed using a planetary ball mill whose container and balls (pulverizing medium) were made of silicon nitride. The ball was added twice as much as the powder in bulk. After charging the powder and the ball, the mixture was pulverized for 5 hours at an acceleration of 150 G while flowing nitrogen gas. The average particle size of the mixed powder is calculated using the "X-ray structural analysis" written by Waseda and Matsubara.
Pp. 119-126 (April 10, 1998, published by Uchida Rokaku Toho) and calculated from the X-ray diffraction data of the sample. Further, the oxygen increase amount ΔX was obtained by obtaining the total oxygen amount by chemical analysis, and subtracting the initial amount X from this amount. Table 2 also shows the above results.

The mixed powder is added with 3% by weight of paraffin as a binder, and then subjected to embossing and granulation to obtain granules. After sintering these granulated powders, a four-point bending strength test specified in JIS R1601 is performed. It is molded into a size that can take a piece, and the molded body is placed in a high-frequency induction heating type furnace.
The temperature was raised in 1 MPa of nitrogen, and kept at 1400 ° C. for 15 minutes to produce a sintered body. Each of the obtained sintered bodies was evaluated for each item described in Table 3, and the results were summarized in the same table. All the samples were densified to almost 99% or more of the theoretical density. Vickers hardness is 14 ~
It was between 17 GPa.

[0025]

[Table 3]

The crystal form of the main crystal phase and the formation phase of the dispersed particles in the table were confirmed by X-ray diffraction. As shown in Table 3, the crystal forms of the main crystal phases were all α-type S
It was a mixed crystal of i ₃ N ₄ (shown as α in the table) and α-sialon (shown as α ′ in the table). The same applies to the following examples, but silicon oxynitride was also confirmed. As a result of chemical analysis, the component ratio of the matrix including the grain boundary phase was almost maintained at the same ratio when the raw materials were blended. The average particle size of the main crystal phase particles and the dispersed particles was confirmed by taking an image of the polished surface of the sample by an electron microscope at a magnification of 50,000 and performing statistical processing by a line segmentation method in the visual field. The volume ratio of the dispersed particles (the total amount of the dispersed particles in Table 3 and the indicated value) was determined by checking the area ratio in the same visual field of the electron microscope, and this was defined as the volume ratio.
The total amount of oxygen Y was confirmed by chemical analysis. The oxygen amount difference was obtained by subtracting the above X from this Y. In addition, the four-point bending strength was determined based on the finished strength test piece specified in JIS R1601. The open porosity was confirmed by the procedure of JIS R1634.

[0027]

[Table 4]

Next, the wear resistance of each of the above sintered bodies was evaluated by a cutting test and a sliding test. Table 4 shows the results. Evaluation of the wear amount by the cutting test was performed as follows. Each sintered body sample was prepared as SNMG1240
8 and fixed to a steel shank, using S45C steel as the work material, peripheral speed 200 m / min, feed 0.5 mm / rotation, cutting depth 2 m
The test cutting was performed for 5 minutes under the condition of m. The wear amount Vb of the flank of each chip sample after cutting was confirmed. On the other hand, the amount of wear in the sliding test was determined by cutting a ball having an outer diameter of 5 mm from each sample, applying a load of 10 N (Newton) to the ball, and applying a pin-on-desk method in an atmosphere at a temperature of 25 ° C. and a humidity of 60%. Made by. The specific wear in this case is
The wear volume (mm ³ ) is measured by the load (N) and the total mileage (m)
m). The unit of the wear amount in the table is [
10 ⁻⁸ mm / N].

The following can be understood from the above results.
(1) When the average particle size of the raw material Si ₃ N ₄ exceeds 5 μm or the oxygen content exceeds 2% by weight, the average particle size of the main crystal phase tends to increase and the wear resistance tends to decrease. However, even if the average particle size and the oxygen content exceed these values, if the increase ΔX in the oxygen content after mixing is controlled to 0.5 to 3% by weight, the reduction in wear resistance does not pose a practical problem. It is. (2) S forming the main crystal phase of the matrix
The amount of i ₃ N ₄ (blended amount) is preferably at least 90% by weight of the matrix in view of mechanical strength and abrasion resistance.
(3) The average particle size of the dispersed particle source powder is desirably 10 μm or less in terms of mechanical strength and abrasion resistance. (4) If the amount of the dispersed particles is less than 10% by volume or exceeds 50% by volume, the abrasion resistance decreases.

Example 2 With the raw material composition of Sample 3 of Example 1, sample powders having various average particle diameters and increasing amounts of oxygen were prepared during mixing and pulverization, in particular, only the pulverization time was different from that of Example 1. These powders were molded and sintered in the same manner as in Sample 3 of Example 1. The physical properties and abrasion resistance of the sintered body were evaluated in the same manner as in Example 1. Table 6 and Table 7 show the characteristics of the sintered body and the results of the wear test, respectively.
Shown in Each sintered body was densified to 99% or more of the theoretical density, and their Vickers hardness was 14 to 17 GP.
a.

From the above results, (1) If the average particle size of the mixed powder after the mixing and pulverization exceeds 100 nm, the average particle size of both the main crystal particles and the dispersed particles in the sintered body exceeds 200 nm. It can be seen that the mechanical strength and abrasion resistance are remarkably reduced, and that (2) the abrasion resistance is particularly reduced if the amount of oxygen after mixing and pulverization is too large.

[0032]

[Table 5]

[0033]

[Table 6]

[0034]

[Table 7]

Example 3 Using the matrix composition of Sample 3 of Example 1 and changing the source of the dispersed particles as shown in Table 8, mixed powders as shown in Table 9 were prepared. Then, various sintered bodies were prepared.

[0036]

[Table 8]

[0037]

[Table 9]

Each of these sintered bodies was first evaluated for its properties in the same manner as in Example 1. Table 10 shows the results. Further, a wear test was performed in the same manner as in Example 1, and the results are shown in Table 11. Each sintered body was densified to almost 99% or more of the theoretical density, and their Vickers hardness was in the range of 14 to 17 GPa.

From the above results, (1) the same results as in Example 1 can be obtained even if the components of the dispersed particle source are changed;
(2) When only one kind of metal is added to the dispersed particles (no nitride is added), compared to the case where a plurality of kinds of metals are dispersed,
The average particle size after mixing and grinding increases. As a result, it was found that the abrasion resistance was particularly reduced as compared with the case where a plurality of kinds were dispersed.

[0040]

[Table 10]

[0041]

[Table 11]

Example 4 Using the mixed powder of Sample 3 of Example 1 and placing it in the same high-frequency induction heating furnace as that of the sample, sintered bodies were prepared under various sintering conditions shown in Table 12. . These sintered bodies were evaluated in the same manner as in Example 1, and the results are shown in Tables 13 and 14. The sample 38 had a density of about 97% of the theoretical density, and had a Vickers hardness as low as about 12 GPa.
On the other hand, in the sample 43 having a high sintering temperature, the average particle diameter of both the main crystal particles and the dispersed particles exceeded 200 nm. Therefore, both samples had low mechanical strength and abrasion resistance. Other samples densified to almost 99% or more of theoretical density,
Vickers hardness was also in the range of 14-17 GPa.
In addition, as another attempt of the short-time heating method, sintering by heating in the pulse discharge heating method was also attempted, but almost the same result as this result was confirmed. A sample prepared by the same procedure using a Si ₃ N ₄ raw material powder having the same composition and a β-type crystal as the raw material powder has a crystal phase of β (β-type Si ₃ N ₄ ) and β ′
(Β-sialon), but the performance was almost the same as that shown in the table.

[0043]

[Table 12]

[0044]

[Table 13]

[0045]

[Table 14]

[0046]

According to the present invention, fine dispersed particles mainly composed of a metal nitride are dispersed in a fine matrix mainly composed of Si ₃ N ₄ , and the raw material and the raw material during the production process are dispersed. By devising the mixing and pulverizing method and controlling the amount of increase in oxygen, even if the amount of oxygen and the average particle diameter of the raw materials vary, there is practically no problem with the silicon nitride composite material having excellent wear resistance. Can be provided at a lower cost than ever before.

Continued on the front page F-term (reference) 3C046 FF33 FF43 FF47 FF55 3J011 SB20 SD03 SE10 4G001 BA03 BA09 BA32 BA37 BA38 BA53 BA57 BA61 BA73 BB03 BB09 BB32 BB37 BB38 BB51 BB52 BB53 BB57 BB73 BC13 BC14 BE14

Claims (4)

[Claims] In a matrix comprising silicon nitride-based particles having an average particle size of 200 nm or less and a grain boundary phase, 10 to 10 particles as a dispersed particle are mainly composed of a metal nitride having an average particle size of 200 nm or less. A silicon nitride-based composite material that is dispersed by 50% by volume and has a total oxygen content in the sintered body that is larger than the total oxygen content in the raw material powder by up to 3% by weight. 2. The silicon nitride-based composite material according to claim 1, wherein a main component of the dispersed particles is at least one kind of a nitride of a group IVa, Va, or VIa element. 3. A step of preparing a silicon nitride powder, a sintering aid powder, and a metal powder and / or a nitride powder thereof, wherein the powder has a total average particle size of 100 nm or less;
A step of pulverizing and mixing to obtain a mixed powder so that the amount of oxygen in the powder is in the range of 0.5 to 3% by weight; a step of molding the mixed powder to form a molded body;
Sintering in a non-oxidizing atmosphere containing nitrogen at 0 ° C. to form a sintered body. 4. The method for producing a silicon nitride-based composite material according to claim 3, wherein the metal is at least one of group IVa, Va and VIa elements.