JP2008069031A - Silicon nitride-based sintered body and method for producing the same - Google Patents

Abstract

An object of the present invention is to provide a silicon nitride sintered body that has a fine structure even with a small amount of grain boundary phase components, and is dense and excellent in wear resistance.
Crystal grains of silicon nitride, an amorphous grain boundary phase containing Group 3 elements of the periodic table, aluminum, magnesium, silicon, oxygen, and nitrogen, and a periodic table dispersed in the grain boundary phase A silicon nitride-based sintered body composed of Group 6 element compound particles, wherein the Group 3 element in the periodic table is 0.1% by mass or more in terms of oxide, and the aluminum is 0.1% in terms of oxide. 05-0.5 mass%, containing 0.3 mass% or more of the magnesium in terms of oxide, oxide equivalent of the Group 3 element in the periodic table, oxide equivalent of the aluminum, magnesium The total amount of oxides in terms of oxide is 2.5% by mass or less, the Group 6 element compound of the periodic table is contained in an amount of 0.1 to 2% by mass in terms of oxides, and the silicon nitride sintered body The amount of oxygen contained in is 1.3 mass% or less.
[Selection figure] None.

Description

  The present invention relates to a silicon nitride sintered body excellent in wear resistance used for a cutting tool or the like and a method for producing the same.

  Silicon nitride, sialon, etc., which are conventionally known as engineering ceramics, are not only high strength, high temperature high strength, high toughness, but also excellent in heat resistance, thermal shock resistance, wear resistance and oxidation resistance. Applications are being promoted as heat engine parts such as gas turbines and turbo rotors and cutting tools.

Until now, in order to improve the mechanical and thermal characteristics of the silicon nitride sintered body, the grain boundaries of the silicon nitride particles of the silicon nitride sintered body are used as the metal components, and rare earth elements, silicon, aluminum, and trace amounts of magnesium are added. In addition, an attempt has been made to achieve the above-mentioned purpose by controlling the composition of the grain boundary components to the composition range of the characteristics, including an amorphous grain boundary phase composed of oxygen and nitrogen. (See Patent Document 1).
Japanese Patent No. 3454993

  However, the silicon nitride-based sintered body described in Patent Document 1 has problems such as inferior wear resistance because there are too many grain boundary phase components.

  An object of the present invention is to provide a silicon nitride-based sintered body that has a fine structure even with a small amount of grain boundary phase components and is dense and excellent in wear resistance.

  The silicon nitride-based sintered body of the present invention includes silicon nitride crystal grains, an amorphous grain boundary phase containing Group 3 elements of the periodic table, aluminum, magnesium, silicon, oxygen, and nitrogen, and the grain boundary phase. A silicon nitride sintered body comprising Group 6 element compound particles dispersed in the periodic table, wherein the Group 3 element of the Periodic Table is 0.1% by mass or more in terms of oxide, and the aluminum is contained. 0.05 to 0.5% by mass in terms of oxide, 0.3% by mass or more in terms of oxide in terms of oxide, and in terms of oxide of group 3 element of the periodic table, The oxide equivalent amount, the total oxide equivalent amount of magnesium is 2.5% by mass or less, and contains a Group 6 element compound of the periodic table in a proportion of 0.1 to 2% by mass in terms of oxide, The oxygen content is 1.3% by mass or less.

  In the silicon nitride sintered body of the present invention, the Group 3 element of the periodic table is preferably at least one selected from La, Er, and Lu.

  In the silicon nitride based sintered body of the present invention, it is preferable that the Group 6 element compound of the periodic table is a tungsten compound.

  In the silicon nitride sintered body of the present invention, the average particle size of the Group 6 element compound of the periodic table is desirably 0.05 to 0.2 μm.

  In the silicon nitride sintered body of the present invention, the silicon nitride sintered body preferably has a relative density of 99% or more.

  In addition, the silicon nitride sintered body of the present invention includes needle-like particles of the silicon nitride crystal particles, and the needle-like particles have an aspect ratio of 3 or more and an average minor axis of 2 μm or less. Is desirable.

  The method for producing a silicon nitride sintered body of the present invention comprises silicon nitride crystal particles, Group 3 elements of the periodic table, aluminum, magnesium, and Group 6 element compound particles of the periodic table, and the period The Group 3 element in the table is 0.1% by mass or more in terms of oxide, the aluminum is 0.05% by mass or more in terms of oxide, and the magnesium is 0.3% by mass or more in terms of oxide. In addition, the sum of the oxide equivalent amount of the Group 3 element of the periodic table, the oxide equivalent amount of the aluminum, and the oxide equivalent amount of the magnesium is 3% by mass or less, and the Group 6 element compound of the periodic table is A compact containing 0.1 to 2% by mass in terms of oxide is fired at a temperature of 1650 to 1800 ° C. in an atmosphere containing nitrogen.

  In the method for producing a silicon nitride sintered body of the present invention, it is desirable that the atmosphere containing nitrogen contains oxygen, silicon, and magnesium.

  According to the present invention, the inclusion of a Group 3 element in the periodic table has the effect of increasing the aspect ratio of the silicon nitride particles, and the inclusion of aluminum and magnesium lowers the melting point of the sintering aid and enables firing at a low temperature. The structure can be made finer, and the total amount of oxides of Group 3 elements in the periodic table, oxide equivalents of aluminum, and oxide equivalents of magnesium is 2.5% by mass or less. Thus, even if the amount of the auxiliary agent is small, it can be densified, and can have excellent wear resistance. Furthermore, the Group 6 element compound of the periodic table can be converted to 0 in terms of oxide. Included at a ratio of .1 to 2% by mass has the effect of suppressing a decrease in high-temperature strength and enhancing wear resistance. In addition, it is important that aluminum is 0.05 to 0.5% by mass in terms of oxide, and by making the oxide equivalent of aluminum 0.5% by mass or less, Oxidation resistance and wear resistance can be improved. In addition, it is important that the silicon nitride sintered body has an oxygen content of 1.3% by mass or less, so that the composition of the grain boundary is controlled to improve the oxidation resistance and wear resistance. Can be combined.

  In addition, the wear resistance can be further improved by setting the Group 3 element of the periodic table to at least one selected from La, Er, and Lu.

  In addition, by using a tungsten compound as the Group 6 element compound of the periodic table, W can form silicides and carbides and suppress a decrease in high-temperature strength.

  In addition, by setting the average particle size of the Group 6 element compound of the periodic table to 0.05 to 0.2 μm, the Group 6 element compound of the Periodic Table is prevented from becoming a source of destruction, and the decrease in high-temperature strength is suppressed. can do.

  Moreover, wear resistance can be improved by setting the relative density of the silicon nitride sintered body to 99% or more and obtaining a dense body.

  In addition, the crystal grain of silicon nitride contains acicular particles, the acicular particles have an aspect ratio of 3 or more and an average minor axis of 2 μm or less, thereby increasing fracture toughness and improving strength. As a result, the wear resistance can be improved.

  According to the method for producing a silicon nitride sintered body of the present invention, decomposition and volatilization of the sintering aid component during sintering can be suppressed, and a dense body can be obtained even with a small amount of aid.

  Further, according to the method for producing a silicon nitride sintered body of the present invention, by adding oxygen, silicon, and magnesium to an atmosphere containing nitrogen, it is added as a silicon dioxide component or a sintering aid contained in silicon nitride. It is possible to suppress decomposition and volatilization of the silicon dioxide component, and further to suppress volatilization of MgO.

  Hereinafter, the silicon nitride sintered body of the present invention will be described in detail.

  The silicon nitride sintered body of the present invention has a structure composed of crystal grains of silicon nitride as a main component and a grain boundary phase, and silicon nitride mainly consists of a β-silicon nitride crystal phase. In this β-silicon nitride crystal phase, β-sialon may be formed by slightly dissolving aluminum. The silicon nitride crystal particles are present as needle-like crystals, preferably having an average minor axis of 2 μm or less and an average aspect ratio (major axis / minor axis) of 3 or more. This is because by setting the average minor axis to 2 μm or less, degranulation is less likely to occur during cutting, and even if degranulation occurs, the effect is small and abnormal wear does not occur. In addition, by setting the average aspect ratio to 3 or more, the toughness of the sintered body increases, the crystal grains do not fall off, and the fracture resistance increases.

  According to the present invention, the grain boundary phase constituting the sintered body is composed of Group 3 elements of the periodic table, aluminum, magnesium, silicon, oxygen, and nitrogen, and is composed of these elements in an amorphous state. . The composition of the elements constituting this grain boundary phase is at least 0.1% by mass in terms of oxides of Group 3 elements of the periodic table, 0.05 to 0.5% by mass in terms of oxides of aluminum, The oxide equivalent of magnesium is 0.3 mass%, the total oxide equivalent of group 3 elements in the periodic table, the oxide equivalent of aluminum, and the oxide equivalent of magnesium is 2.5 mass% or less. It is important to be. The reason for limiting the composition as described above is that when the composition of the element composed of each element includes at least the above-mentioned added amount, the sintering proceeds sufficiently, the strength of the sintered body is improved, and the acicular crystals This is because the toughness is increased. Moreover, the fall of the hardness of a sintered compact can be suppressed and abrasion resistance can be improved by making the conversion amount of the composition which consists of these elements into 2.5 mass% or less. In addition, it is important that the silicon nitride sintered body has an oxygen content of 1.3% by mass or less, so that the composition of the grain boundary is controlled to improve the oxidation resistance and wear resistance. Can be combined.

  In the silicon nitride sintered body of the present invention, the Group 3 element of the periodic table is preferably at least one selected from La, Er, and Lu. By containing at least 0.1% by mass or more of these elements in terms of oxide, the compact can be smoothly densified without causing spots called spots, and the hardness of the grain boundary phase can be easily increased. .

  In the silicon nitride sintered body of the present invention, the relative density of the sintered body with respect to the theoretical density is preferably 99% or more. When the relative density is 99% or more, there are almost no voids in the sintered body, and the wear resistance is further improved. Furthermore, since there are almost no voids in the sintered body, the fracture resistance is improved.

  In the silicon nitride sintered body of the present invention, it is important that the grain boundary phase contains a Group 6 element compound of the periodic table as the third component. It is important that this Periodic Table Group 6 element compound is contained in an amount of 0.1 to 2% by mass in terms of oxide, particularly 0.5 to 2% by mass, and the average minor axis is 0.05 to 0.2 μm. It is desirable that When the added amount is 0.1% by mass or more, or when the average minor axis is 0.05 μm or more, a sufficient pinning effect on the grain boundary phase softening at a high temperature by these particles can be obtained, and the strength at high temperature does not decrease. . On the other hand, when the addition amount is 2% by mass or less, or when the average minor axis is 0.2 μm or less, the enlargement of the particles can be suppressed, and the particles themselves can be prevented from becoming a destruction source.

  Further, the group 6 element compound of the periodic table includes a chromium compound, a molybdenum compound, and a tungsten compound, and any of them can be used. However, a tungsten compound is desirable for ease of handling. The tungsten compound can suppress a decrease in high-temperature strength by being present as a carbide or silicide.

Next, a method for manufacturing the silicon nitride sintered body described above will be described. First, as a starting material, silicon nitride powder and an oxide (RE ₂ O ₃ ), silicon dioxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), magnesium oxide (MgO), a Group 3 element of the periodic table, Prepare powder of Group 6 element compound of periodic table. As the silicon nitride raw material powder, any of α-silicon nitride, β-silicon nitride, or a mixture thereof can be used. These particle sizes are preferably 2 μm or less, particularly 1 μm or less. Further, the Group 6 element compound of the periodic table is preferably a tungsten compound. The tungsten compound may be any oxide, carbide, silicide, nitride, etc., but an oxide is desirable because it is inexpensive and easily obtains a fine powder. These raw material powders are weighed at a predetermined ratio, mixed and pulverized by a ball mill or the like. A binder is appropriately added to the mixed powder and granulated by a spray drying method or the like.

  Then, the mixed powder adjusted at a predetermined ratio as described above is molded into an arbitrary shape by known molding means such as die press molding, casting molding, extrusion molding, injection molding, cold isostatic pressing, etc. . After the obtained molded body is fired at a temperature of 1650 to 1800 ° C. by a known firing means, for example, an atmospheric pressure firing method, a gas pressure firing method, a hot press method or the like in an oxidizing atmosphere or a non-oxidizing atmosphere, The corrosion-resistant ceramic member of the present invention can be obtained by cooling.

  It goes without saying that the atmosphere used for the firing is mainly composed of nitrogen and may contain a small amount of oxygen as long as the silicon nitride sintered body is not oxidized. Further, it may contain a component such as Si, Al, or Mg that evaporates from a silicon nitride sintered body or a so-called material.

Furthermore, as described above, in order to reduce the average minor axis of the silicon nitride particles and increase the average aspect ratio, after firing at 1650 ° C. to 1800 ° C. in a nitrogen atmosphere, 9.8 MPa to 294 MPa, 1500 It is desirable to perform hot isostatic baking at ˜1700 ° C.

In the method for producing a silicon nitride sintered body according to the present invention, the oxidizing firing atmosphere or the non-oxidizing atmosphere is preferably an atmosphere containing nitrogen, oxygen, silicon, and magnesium. It is important to contain SiO, MgO. By firing in such an atmosphere, decomposition of SiO ₂ added as a sintering aid is suppressed, and volatilization of MgO is suppressed. Furthermore, even if a part of the sintering aid is volatilized from the molded body, if the molded body is placed in the above atmosphere, the components present as the atmosphere are taken into the molded body and volatilized. Minutes are supplemented. As a result, a dense sintered body can be produced even with a small amount of added sintering aid. Such an atmosphere can be obtained by, for example, mixing Si, SiO _2, and MgO powder, placing the sample in a baking pot with the sample, laying down, or placing the sample around the sample, and then baking the sample together with Si or Mg. It can be realized by evaporating.

  The silicon nitride-based sintered body of the present invention can be suitably used for cutting tools and the like that require high toughness, high hardness, and wear resistance.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, this invention is not limited to a following example.

As starting materials, silicon nitride powder having an average particle size of 0.7 μm and Er ₂ O ₃ , Lu ₂ O ₃ , La ₂ O ₃ having an average particle size of 0.9 μm as oxides of Group 3 elements of the periodic table, periodic rule WSi ₂ , WC, WN, and MoSi ₂ powders having an average particle size of 0.1 μm were prepared as Group 6 element compound particles. Silicon dioxide (SiO ₂ ) was converted from the amount of oxygen contained in the silicon nitride raw material powder.

  The amount of oxygen was measured by an infrared absorption method by grinding a silicon nitride sintered body into a powder form.

  Using these raw material powders, a final sintered body was prepared together with a binder so as to have the composition shown in Table 1, and then pulverized and mixed with a ball mill for 72 hours. After mixing, press molding was performed at a pressure of 98 MPa to obtain a molded product for the tool shape SNGN120212.

This molded body was degreased, fired at 1750 ° C., 5 Hr, N ₂ atmosphere under normal pressure conditions, and then fired at 1600 ° C. for 2 hours at 196 MPa under hot isostatic pressure to obtain a sintered body.

  The density of the sintered body was measured by the Archimedes method for the obtained sintered body, and the value is shown in Table 1.

  Moreover, the minor axis length and major axis length of the silicon nitride crystal particles in the photograph were measured with a ruler by an electron micrograph on the sintered body, and the average minor axis and average aspect ratio of the silicon nitride crystal particles were obtained. .

  The composition of the sintered body was calculated from the ICP emission analysis and oxygen analysis. Moreover, the remainder which pulled the grain boundary phase from the whole was made into silicon nitride amount.

  The crystal phase was determined by identifying the peak obtained from X-ray diffraction.

Further, after grinding into a tool shape, a cutting test was performed under the conditions of work material: FCD-450, cutting speed: 500 m / min, feed amount: 0.2 mm / rev, cutting depth: 2.0 mm, cutting time: 120 sec. . In the evaluation, the flank wear amount of the blade edge was calculated by taking a photograph using a microscope with a length measuring device and measuring the average value of the wear amount. Further, the chipping of the cutting edge was performed by observing the cutting edge with a microscope after the test. These results are shown in Table 1.

  According to Table 1, sample no. 2-7, 9-13, 15, 17-20, 22, 23, 27-31 all showed excellent cutting performance with a small amount of wear and no chipping of the cutting edge.

On the other hand, sample no. 8, 14, 16, 21, and 33 showed increased wear in the cutting test. In addition, the sample No. outside the scope of claims of the present invention. 1, 24 to 26 and 32 were damaged during testing.

  As described in detail above, the silicon nitride sintered body of the present invention controls the grain size and aspect ratio of the silicon nitride particles in the sintered body, and the third composition existing in the grain boundary phase and the grain boundary phase. The presence of particles can prevent cutting and wear during cutting, improve cutting characteristics and extend the tool life.

Claims (8)

Crystal grains of silicon nitride, an amorphous grain boundary phase containing Group 3 elements of the periodic table, aluminum, magnesium, silicon, oxygen, and nitrogen, and Group 6 elements of the Periodic Table dispersed in the grain boundary phase A silicon nitride-based sintered body composed of compound particles, wherein the Group 3 element of the periodic table is 0.1% by mass or more in terms of oxide, and the aluminum is 0.05 to 0.00 in terms of oxide. 5 mass%, containing 0.3 mass% or more of the magnesium in terms of oxide, oxide equivalent of the Group 3 element of the periodic table, oxide equivalent of the aluminum, oxide equivalent of the magnesium The total amount is 2.5% by mass or less, the periodic table group 6 element compound is contained in a proportion of 0.1 to 2% by mass in terms of oxide, and oxygen contained in the silicon nitride sintered body Silicon nitride based sintering characterized in that the amount is 1.3% by mass or less . 2. The silicon nitride based sintered body according to claim 1, wherein the Group 3 element of the periodic table is at least one selected from La, Er, and Lu. The silicon nitride-based sintered body according to claim 1 or 2, wherein the Group 6 element compound of the periodic table is a tungsten compound. 4. The silicon nitride based sintered body according to claim 1, wherein an average particle diameter of the Group 6 element compound of the periodic table is 0.05 to 0.2 μm. 5. The silicon nitride sintered body according to any one of claims 1 to 4, wherein a relative density of the silicon nitride sintered body is 99% or more. The crystal grain of the silicon nitride includes acicular particles, and the acicular particles have an aspect ratio of 3 or more and an average minor axis of 2 μm or less. The silicon nitride sintered body described. It contains silicon nitride crystal particles, Group 3 elements of the periodic table, aluminum and magnesium, and Group 6 element compound particles of the periodic table. 1 mass% or more, 0.05 mass% or more in terms of oxide in terms of aluminum, 0.3 mass% or more in terms of oxide in terms of magnesium, and oxide equivalent of Group 3 elements in the periodic table The sum of the amount, the oxide equivalent amount of the aluminum, and the oxide equivalent amount of the magnesium is 3% by mass or less, and the Group 6 element compound of the periodic table is 0.1 to 2% by mass in terms of the oxide. A method for producing a silicon nitride-based sintered body, which comprises firing the contained compact in an atmosphere containing nitrogen at a temperature of 1650 to 1800 ° C. The method for producing a silicon nitride-based sintered body according to claim 7, wherein the atmosphere containing nitrogen contains oxygen, silicon, and magnesium.