JPH04367564A - Silicon nitride-based pressed compact and its production - Google Patents

Abstract

PURPOSE:To provide a silicon nitride-based sintered compact requiring abrasion resistance at high temperatures and a method for producing the above-mentioned sintered compact. CONSTITUTION:The subject method is a method for producing a silicon nitride- based sintered compact composed of sintering mixed powder composed of 0.3-5wt.% zirconium oxide powder and/or samarium oxide powder having <=3mum average particle size with 3-30wt.% silicon carbide whisker, a sintering assistant in an amount of 3-15wt.% based on the silicon nitride powder and the remainder composed substantially of silicon nitride powder at a sintering temperature within the range of 1550-1700 deg.C under >=200kg/cm<2> pressure. Furthermore, the silicon nitride-based sintered compact obtained by the aforementioned method is provided.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is expected to be applied to parts that require wear resistance particularly at high temperatures, such as cams for automobile engines, wear-resistant parts of tappet boilers, wear-resistant parts of steel manufacturing equipment, etc. The present invention relates to wear-resistant silicon nitride ceramics and a method for producing the same.

0002

BACKGROUND OF THE INVENTION Silicon nitride ceramics have been widely used as ceramics that have excellent wear resistance, especially in high-temperature regions. Although many methods have been used to improve wear resistance, the most common method has been to sinter the material using a hot press method to improve hardness. Addition of hard particles or whiskers has also been proposed as a method to improve hardness, but adding such additives reduces sinterability and does not densify unless hot press sintered at high temperatures. However, there was a problem in that the additives, such as hard particles and whiskers, reacted with the sintering aid, making it impossible to fully demonstrate its properties. In other words, the properties of the added hard particles and whiskers cannot be fully demonstrated, so the amount added must be increased, but doing so will reduce sinterability, necessitate sintering at a higher temperature, and increase cost. There were other problems.

0003

[Problems to be Solved by the Invention] In view of the above-mentioned state of the art, the present invention is capable of achieving sufficient densification even at a low sintering temperature, and that even if the amount of added hard particles and whiskers is small, the addition effect can be sufficiently exhibited. It is an object of the present invention to provide a pressed sintered body of silicon nitride and a method for manufacturing the same, which can exhibit the following effects.

0004

[Means for Solving the Problem] As a method for lowering the sintering temperature, the present inventors used aluminum oxide (Al2O3, alumina), which is commonly used as a sintering aid,
In addition to yttrium oxide (Y2O3, yttria), we considered adding a third component compound, and as a result, we found that zirconium oxide (ZrO2, zirconia) and samarium oxide (Sm2O3, samaria) can be used at low sintering temperatures. The present inventors confirmed that it is an effective additive compound that is effective in reducing oxidation and has little deterioration in properties (bending strength, hardness, etc.) at high temperatures.Based on this knowledge, the present invention was completed. . That is, the present invention provides (1) zero zirconium oxide and/or samarium oxide.
．． 3 to 5% by weight of silicon carbide whiskers, 3 to 15% by weight of a sintering aid based on silicon nitride, and the remainder substantially silicon nitride. Pressed sintered body.

(2) 0.3 to 5% by weight of zirconium oxide powder and/or samarium oxide powder with an average particle size of 3 μm or less, 3 to 30% by weight of carbide whiskers, and 3 to 15% by weight of silicon nitride powder. A mixed powder consisting of a sintering aid and the remainder substantially silicon nitride powder was pressed at a pressure of 200 kg/cm.
2. A method for producing a pressed sintered body of silicon nitride, characterized in that sintering is carried out at a sintering temperature in the range of 1,550 to 1,700°C. It is.

[0006]

[Function] According to the present invention, it is possible to lower the sintering temperature by approximately 100°C compared to the case where only the commonly used alumina-yttria-based sintering aid is added, and the added hard Particles and whiskers can be effectively used to improve wear resistance, and there is little deterioration in properties at high temperatures, resulting in a dramatic improvement in wear resistance from room temperature to high temperature.

[0007]

EXAMPLES The effects of the present invention will be explained in detail in the following examples. The silicon nitride powder used in the test had an average particle size of 0.5 μm (
The powder had a crystallite diameter of approximately 0.2 μm or less. As sintering aids, aluminum oxide (Al2O3) has an average particle size of 0.8μm, and yttrium oxide (Y2O3)
The particles used had an average particle size of 1.2 μm. The following test was conducted using the basic composition of the sintering aid as 93% by weight of silicon nitride powder, 2% by weight of aluminum oxide, and 5% by weight of yttrium oxide.

(1) First, a test was conducted to select a compound to be added to lower the sintering temperature. The basic composition of the sintering aids was 93% by weight of silicon nitride, 5% by weight of yttria, and 2% by weight of alumina. As the compound to be added, oxides of rare earth elements were mainly selected as candidates. Specifically, lanthanum oxide (La2O3), samarium oxide (Sm2O3), eurobium oxide (Er)
2 O3 ), gadolinium oxide (Gd2 O3 ), ytterbium oxide (Yb2 O3 ), dysprosium oxide (Dy2 O3 ), neobium oxide (Nb2
Powders of cerium oxide (CeO2), zirconium oxide (ZrO2), and cerium oxide (CeO2) were tested. The average particle size of these powders is about 1-0.5 μm.

After weighing silicon nitride powder, aluminum oxide powder, and yttrium oxide powder at a predetermined mixing ratio, a predetermined amount of the above-mentioned additive compound was weighed and added to the mixture. This mixture was mixed for 48 hours using a ball mill using ethanol as a solvent. After mixing, it was dried and sintered using a hot press. Hot press sintering conditions are sintering temperature 1500-1750℃, pressing force 250kg/cm2
and sintered at a constant rate. The test was conducted with the holding time at the predetermined sintering temperature constant at 2 hours. A test piece was cut out from the obtained sintered body and subjected to a bending strength test (room temperature and 1200°C).
Characteristic evaluation tests such as hardness test (room temperature) and density measurement were conducted. For comparison, a similar test was also conducted on silicon nitride as an additive compound.

First, in order to narrow down the types of compounds to be added, hot press sintering was performed at each temperature with the added amount of the compound fixed at 1% and 3% by weight, and the density of the sintered body was measured. We conducted this process to select compounds that are effective in lowering the sintering temperature. The results of these tests are summarized in Table 1. Table 1 shows the sintering temperature at which the relative density becomes 99% or more when hot-press sintering silicon nitride without addition of compounds, and the sintering temperature is 1650°C.

[Table 1]

As is clear from Table 1, zirconium oxide, cerium oxide, and samarium oxide are densified to a relative density of 99% or more at a low temperature of 1550° C. compared to a silicon nitride sintered body with no compound added. This is the case when . Gadolinium oxide, lanthanum oxide, neobium oxide,
When eurobium oxide and dysprosium oxide are added, the relative density is 99% unless hot pressed at 1650°C, which is almost the same sintering temperature as silicon nitride without compound additions.
Do not densify to a certain degree. In addition, when ytterbium oxide is added, the sintering temperature at which the relative density is densified to 99% or more is higher than that of silicon nitride with no compound added.
℃, and no effect of addition for lowering the sintering temperature was observed.

From the above results, it has become clear that zirconium oxide, cerium oxide, and samarium oxide are effective compounds for lowering the sintering temperature of silicon nitride. becomes 1550℃ and 1
A bending strength test and a hardness test were conducted under two fixed conditions of 600° C., and a test was conducted to select an additive compound with excellent properties. The amount of the compound added was 1 as in the above test.
% by weight and 3% by weight. Table 2 summarizes these results.
Shown below. For comparison, silicon nitride without compound addition was used at 165
Table 2 also shows the characteristic values of the samples hot-press sintered at 0°C.

[Table 2]

As is clear from Table 2, the addition of the compound improves the bending strength and hardness at room temperature. This is thought to be because these additive compounds functioned as a kind of sintering aid and effectively worked to further densify the structure. On the other hand, the bending strength at a high temperature of 1200°C has different trends depending on the type of compound added, and when zirconium oxide and samarium oxide are added, the high-temperature bending strength is almost the same as when no compounds are added. The results were about the same or slightly improved. On the other hand, when cerium oxide is added, the bending strength at high temperatures is significantly reduced. This is also confirmed from the test results mentioned above (see Table 1).
When cerium oxide was added, the relative density was significantly improved compared to when other compounds were added, even at the lowest sintering temperature in the sintering test, 1500°C. It can be inferred that the formation of a liquid phase during silicon nitride sintering is promoted by this. Conversely, in high-temperature bending strength tests, the glass phase present at the grain boundaries easily softens, resulting in a result in which the high-temperature bending strength is inferior to that obtained when other compounds are added. considered to be a thing.

Next, the influence of the particle size of the powder of the compound to be added was investigated. The compound studied was samarium oxide. The powder particle size of samarium oxide is 0.5
μm, 1.0μm, 2.0μm, 3.0μm and 5.0
Five types of μm were prepared. The amount added was 1% by weight, and the sintering temperature was 1550°C. Table 3 shows the sintered density and room temperature bending strength of sintered bodies to which samarium oxide of various particle sizes was added. As is clear from this table, when the powder particle size of samarium oxide is 5.0 μm, the sintered body density is slightly lowered and the room temperature bending strength is also lowered. From this result, the characteristics of the sintered body of the present invention can be maintained by setting the powder particle size of the compound to be added to 3.0 μm or less, and more preferably setting the average particle size of the compound to 1.0 μm or less. It turns out that the above is a necessary condition.

[Table 3]

(2) As a result of the above tests for selecting additive compounds for lowering the sintering temperature, it became clear that zirconium oxide and samarium oxide are effective in lowering the sintering temperature. We decided to conduct a sintering test on silicon nitride to which silicon carbide whiskers were added. First of all,
The amount of silicon carbide whiskers added was fixed at 10% by weight, and the appropriate amounts of zirconium oxide and samarium oxide to be added were investigated. The test method, test conditions, characteristic evaluation method, etc. are the same as the above-mentioned test. Figure 1 shows the dependence of sintered compact density, room temperature bending strength, high temperature bending strength, and hardness on the amount of zirconium oxide added when zirconium oxide is added.
Shown below. Similarly, dependence on the amount of samarium oxide added is shown in FIG. Regarding the sintering temperature, the sintering temperature of silicon nitride with no compound added and 10% by weight of silicon carbide whiskers is 17
Based on the test results described above, it is thought that the sintering temperature can be lowered by about 100°C by adding a compound, so the test was conducted with the sintering temperature fixed at 1650°C.

As is clear from FIG. 1, when zirconium oxide is added, the physical properties are comparable to or better than when no zirconium oxide is added in the range of 0.3% to 5% by weight. In particular, the properties are significantly improved when the amount added is in the range of 0.5% by weight to 3% by weight. When the amount added is large, these compounds react with the added sintering aid and form a glass phase that exists at the grain boundaries, but as the amount of this glass phase increases, the high temperature bending strength decreases. it is conceivable that. Furthermore, as is clear from Figure 2, when samarium oxide is added, the tendency is almost the same as when zirconium oxide is added, but the amount of addition at which a significant improvement in properties is recognized is 0.5. It ranges from 3% to 3% by weight. Note that the combined addition of samarium oxide and zirconium oxide is similarly effective.

Next, the optimum amount of silicon carbide whiskers to be added was investigated. The added compound was zirconium oxide, and the amount added was 1% by weight. Further, the sintering temperature was set at 1650° C., and the amount of silicon carbide whiskers added was varied from 1% by weight to 40% by weight. FIG. 3 shows the dependence of the sintered density, room temperature bending strength, high temperature bending strength (1200° C.), and hardness on the amount of silicon carbide whisker added of the obtained sintered body.

As is clear from FIG. 3, when the amount of silicon carbide whiskers added is 3% by weight or more, the high temperature bending strength is improved and the hardness is also significantly improved. However, if the amount of silicon carbide added is 30% by weight or more, the sintered body will not be sufficiently densified at a sintering temperature of 1650° C., resulting in a decrease in the density of the sintered body. The optimum amount of silicon carbide whiskers to be added is determined from the fact that the high temperature bending strength and hardness are significantly improved, and the room temperature bending strength is approximately the same or higher than that of silicon nitride without silicon carbide whiskers. The total amount is from 5% to 20% by weight.

Next, the hot press sintering conditions were investigated. Silicon carbide whisker addition amount is 10% by weight
, 1% by weight of zirconium oxide as an additive compound
As a result, the sintering temperature was 1650°C and the pressure was 50°C.
A sintering test was conducted by varying the weight from kg/cm2 to 500 kg/cm2. Figure 4 shows the dependence of sintered density, room temperature bending strength, and hardness on pressing force.

As is clear from FIG. 4, a pressure of 200 kg/cm2 or more is required during hot press sintering, and no improvement in properties is observed even if hot press sintering is performed with a pressure higher than this. Conversely, if the pressure is lower than this, the sintering temperature will not sufficiently densify, and the purpose of adding a compound to lower the sintering temperature and preventing damage to silicon carbide whiskers during sintering will not be achieved. Therefore, it has become clear that a minimum pressure of 200 kg/cm2 is required during hot press sintering.

Furthermore, for confirmation, the influence of hot press sintering temperature was investigated. The amount of silicon carbide whiskers added was 10% by weight, the additive compound zirconium oxide was 1% by weight, and the pressing force was 250 kg/c.
A hot press sintering test was conducted under the conditions of m2. Figure 5 shows the dependence of the sintered body density, room temperature bending strength, and hardness on the sintering temperature.

As is clear from FIG. 5, as the sintering temperature is increased, the bending strength tends to decrease slightly. The problem is hardness, and when the sintering temperature is 1700° C. or higher, the hardness tends to be lower than that without the addition of silicon carbide whiskers, and the effect of adding silicon carbide whiskers is no longer recognized. Judging from the above results, when producing silicon nitride-based wear-resistant ceramics to which these silicon carbide whiskers are added, the hot press sintering temperature should be kept at 1700°C or lower (this temperature is lower than the hot (This is 50°C lower than the press sintering temperature of 1750°C.)
It became clear that this needed to be done.

(3) From the above test results, the manufacturing conditions for silicon nitride-based wear-resistant ceramics to which silicon carbide whiskers have been added have been clarified.The effectiveness of these wear-resistant ceramics was tested in the following tests. Evaluation was made by a wear test.

[0024] In the test, fused silica powder was sprayed onto the ceramic using compressed air to abrade the ceramic.
The wear resistance was evaluated by measuring the amount of wear. The test conditions were as follows: fused silica powder with a particle size of about 40 μm was used, the powder concentration was 50 g/Nm 3 , the blowing speed was 100 m/sec, the blowing angle was 90 degrees, and the test temperature was room temperature. The ceramics used in the test had 10% by weight of silicon carbide whiskers added, 1% by weight of zirconium oxide or samarium oxide as an additive compound, a sintering temperature of 1650°C, and a pressing force of 250kg/cm2.
Hot press sintered with 10% by weight of silicon carbide whiskers but no additive compounds, hot press sintered at a sintering temperature of 1750°C and a pressure of 250 kg/cm2, and silicon carbide whiskers and A total of four types were prepared by hot press sintering at a sintering temperature of 1650° C. and a pressure of 250 kg/cm 2 without any additive compounds. The test results are summarized in Table 4.

[Table 4]

[0025] From Table 4, the ceramics according to the present invention to which silicon carbide whiskers and additive compounds are added are dramatically superior to those to which only silicon carbide whiskers are added and to which no additive silicon whiskers are added. The wear resistance was improved, demonstrating the effectiveness of the present invention. especially,
When silicon carbide whiskers are added and no additive compounds are added, there is almost no difference in wear resistance compared to when silicon carbide whiskers are not added. The addition of is effective in lowering the sintering temperature, which prevents damage to the silicon carbide whiskers during sintering and fully demonstrates the effects of the silicon carbide whiskers, dramatically improving wear resistance. It is thought that the characteristics have improved.

[0026]

[Effects of the Invention] The wear-resistant ceramics according to the present invention have significantly improved wear resistance compared to conventional silicon nitride-based ceramics, which are said to have excellent wear resistance. By applying ceramics to various parts that require wear resistance, such as the wear-resistant parts of automobile engine cams, tappets, and boilers, and the wear-resistant parts of steel-making machinery, the service life of these parts can be dramatically extended. It has great effects on the industrial field, such as improving machine reliability, simplifying maintenance, and reducing costs.

[Brief explanation of the drawing]

[Figure 1] Chart showing the results of a test to optimize the amount of compound (zirconium oxide) added

[Figure 2] Chart showing the results of a test to optimize the amount of compound (samarium oxide) added

[Figure 3] Chart showing the results of a test to optimize the amount of silicon carbide whiskers added

[Figure 4] Chart showing the results of a test for optimizing the pressing force during hot press sintering of the ceramics of the present invention

[Figure 5] Chart showing the results of a test to optimize the sintering temperature during hot press sintering of the ceramics of the present invention

Claims (2)

[Claims] Claim 1: 0.3 to 5% by weight of zirconium oxide and/or samarium oxide and 3 to 3% by weight of silicon carbide whiskers.
1. A pressurized sintered body of silicon nitride, characterized in that the sintering aid comprises 0% by weight of silicon nitride, 3 to 15% by weight of a sintering aid based on silicon nitride, and the remainder substantially silicon nitride. 2. Calcined zirconium oxide powder and/or samarium oxide powder with an average particle size of 3 μm or less in an amount of 0.3 to 5% by weight, carbide whiskers in an amount of 3 to 30% by weight, and silicon nitride powder in an amount of 3 to 15% by weight. A mixed powder consisting of a binder and the remainder substantially silicon nitride powder was pressed at a pressure of 200 kg/cm2.
The method for producing a pressed sintered body of silicon nitride is characterized in that sintering is carried out at a sintering temperature in the range of 1,550 to 1,700°C.