JP4820840B2 - Method for producing wear-resistant member made of silicon nitride - Google Patents

Description

  The present invention relates to a method for manufacturing a wear-resistant member containing silicon nitride as a main component, and in particular, when the wear-resistant member is a rolling bearing member, can exhibit excellent wear resistance, in particular, rolling life characteristics, and durability. The present invention relates to a method for producing a silicon nitride wear-resistant member suitable as a rolling bearing member having excellent properties.

  Wear-resistant members are used in various fields such as bearing members, various roll materials for rolling, engine parts such as compressor vanes, gas turbine blades, cam rollers, and the like. Conventionally, ceramic materials have been used for such wear-resistant members. In particular, a sintered silicon nitride is excellent in mechanical strength and wear resistance, and thus is widely used in various fields.

  Known sintered compositions of silicon nitride sintered bodies include silicon nitride-rare earth oxide-aluminum oxide, silicon nitride-rare earth oxide-aluminum oxide-titanium oxide, and the like. Sintering aids such as rare earth oxides in the above sintered composition generate grain boundary phases (liquid phases) composed of Si-rare earth elements-Al-O-N, etc. during sintering, and densify the sintered body. It is added to increase the strength (see, for example, Patent Document 1).

  A conventional silicon nitride sintered body is formed by adding the above sintering aid as an additive to silicon nitride raw material powder, and the resulting molded body is heated to a high temperature of about 1650 to 1900 ° C. using a firing furnace. Mass-produced by the method of naturally cooling the furnace after firing for a predetermined time. On the other hand, the method of slow cooling is also employ | adopted (for example, refer patent document 2).

  Among the wear-resistant members using the silicon nitride sintered body described above, a bearing member has been generally recognized. Such bearings are used in various applications, and their use as important safety parts is also being studied. For this reason, it is required to further improve the reliability of bearing members made of a silicon nitride sintered body, that is, rolling elements such as balls and rollers.

For example, defects such as scratches and cracks on the surface of the rolling element lead to damage of the entire system using the bearing as well as the bearing itself. Therefore, a process is taken to eliminate such defects as much as possible. . Similarly, pores or the like existing in the vicinity of the surface of the rolling element cause a decrease in reliability, and are therefore removed when processing into a final shape such as a ball or a roller.
JP 2001-328869 A JP-A-11-292632

  However, the silicon nitride sintered body produced by the above conventional method has improved bending strength, fracture toughness, and wear resistance, but is not sufficient, and as a rolling bearing member that requires particularly excellent sliding characteristics. As for the durability of the resin, it is insufficient, and further improvement is demanded.

  In recent years, the demand for ceramic materials as components for precision equipment has increased. In such applications, the characteristics of ceramics, which are high hardness, light weight, and excellent wear resistance, are combined with the properties of high corrosion resistance and low thermal expansion. It's being used. In particular, from the viewpoint of high hardness and wear resistance, the use as a wear resistant member constituting a sliding portion such as a bearing is rapidly expanding.

  However, when a rolling ball such as a bearing is made of a ceramic wear-resistant member, the rolling life of the wear-resistant member is still not sufficient when the rolling ball rolls while repeatedly contacting at a high stress level. Because the surface of the wear-resistant member peels off or cracks due to short-term operation, it is easy to cause an accident that causes vibration or damage to the device equipped with the bearing. There was a problem that durability and reliability as a component material were low.

  In addition, the silicon nitride sintered body based on the conventional manufacturing method has not only the surface but also scratches and cracks that reach the inside relatively at the post-sintering stage. In addition, even if the product does not become defective, the number of manufacturing man-hours (for example, the number of man-hours required for surface polishing until the cracks are substantially eliminated) to remove the cracks and obtain a highly reliable surface increases. This increases the manufacturing cost of the rolling elements.

  That is, when sintering a silicon nitride molded body, impurity oxygen contained in the silicon nitride powder (raw material powder) and part of oxygen contained in the sintering aid are evaporated to generate a gas component. . This gas component is generated almost simultaneously with the start of shrinkage of the silicon nitride molded body during sintering. In the normal sintering method, since densification starts from the surface portion of the sintered body as the compact starts to shrink, it is difficult to remove the gas components inside the sintered body.

When the gas components as described above remain in the sintered body, pores are generated in the silicon nitride sintered body, or oxygen is combined with Si to remain as SiO ₂ . Since the gas component cannot be sufficiently removed by the conventional manufacturing method, pores and SiO ₂ resulting from the gas component remain in a relatively wide range, thereby generating cracks extending toward the inside. In order to remove such cracks, it is necessary to remove the surface of the sintered body to a certain depth, which leads to the occurrence of defects and an increase in manufacturing costs.

  In addition, although the silicon nitride sintered body can be densified by performing, for example, HIP treatment after sintering and filling the pores with a liquid phase formed by a sintering aid, a portion where pores existed In this case, segregation of the liquid phase component occurs. Since the liquid phase component is lower in strength and hardness than the silicon nitride crystal grains, such segregation of the liquid phase component becomes a starting point of breakage when the silicon nitride sintered body is used as a wear resistant member. Therefore, it is necessary to remove such segregated materials.

  In any case, in the conventional method of manufacturing a silicon nitride sintered body, it is inevitable that pores, cracks, segregation of liquid phase components, etc. caused by gas components are distributed to a certain depth of the sintered body. There was a problem. These defects are the cause of defects and the cause of increasing the machining margin (width to be removed by machining) of the sintered body surface when obtaining a surface that can improve the reliability of the rolling elements. These increase the manufacturing cost of wear-resistant members such as rolling elements.

  The present invention has been made in order to cope with the above-described demand for problems, and provides a wear-resistant member having excellent sliding characteristics in addition to high strength and high toughness characteristics, and a method for producing the same. Objective.

  In particular, it is easy to remove the gas components that cause defects and increase the manufacturing cost, which makes it possible to reduce the manufacturing cost in addition to various characteristics required for wear-resistant members, for example. It aims at providing the manufacturing method of a member.

  In order to achieve the above-mentioned object, the inventor of the present invention, when producing a conventional silicon nitride sintered body, the types of silicon nitride raw material powders, the types of sintering aids and additives, and the additions generally used. The effect of these elements on the properties of the sintered body was confirmed by experiments by varying the amount and firing conditions.

  As a result, a raw material mixture obtained by adding a predetermined amount of rare earth oxide, alumina and, if necessary, magnesia, aluminum nitride, titanium oxide, etc., to fine silicon nitride raw material powder is molded and degreased, and the resulting molded body is obtained. After performing deoxygenation treatment (reduction of oxygen concentration) by performing a holding operation under predetermined conditions during sintering, heat is applied under predetermined conditions after performing main sintering or after sintering. It has been found that a wear resistant member made of a silicon nitride sintered body having an excellent rolling life of sliding characteristics in addition to high strength and high toughness characteristics can be obtained when subjected to an isostatic pressing (HIP).

  In addition, when the cooling rate of the sintered body from the sintering temperature to the temperature at which the liquid phase formed by sintering with the rare earth element solidifies is gradually reduced to 100 ° C./hour or less, the sintered body structure It has been found that the pore diameter of can be further reduced.

Furthermore, before reaching the temperature at which final densification and sintering of silicon nitride occurs (1600 to 1850 ° C.), the temperature is raised to a certain temperature in a vacuum and further maintained at such a temperature for a predetermined time. As a result, gas components such as oxygen and SiO ₂ in the sintered body can be moved and discharged to the outside, and finally the oxygen concentration in the outer periphery, that is, defects such as pores and cracks penetrate into the inside. It has been found that the gas component concentration that causes the failure can be reduced.

  The present invention has been completed based on the above findings.

That is, the method for producing a wear-resistant member according to the present invention includes silicon nitride containing oxygen of 1.5% by mass or less, α-phase type silicon nitride of 75 to 97% by mass, and an average particle size of 1.0 μm or less. In the raw powder, the rare earth element is converted to an oxide of 1 to 10% by mass, at least one of aluminum and magnesium is converted to an oxide of 0.2 to 5% by mass, and the aluminum nitride is 5% by mass or less. , Ti, Hf, Zr, W, Mo, Ta, Nb, Cr, at least one selected from the group consisting of oxides, and forming a raw material mixture added with 0.2 to 5 mass% in terms of oxide In the middle of sintering after degreasing and then sintering the obtained molded body, the temperature was 1250 ° C. to 1600 ° C. in a vacuum of 0.01 Pa or less or a temperature of 1500 ° C. to 1600 ° C. in a nitrogen atmosphere . after holding for 5 to 10 hours, a temperature of 165 Sintering is performed at a cooling rate of 100 ° C. or less per hour from the above sintering temperature until the liquid phase formed by sintering with the rare earth element solidifies. Thus, a wear-resistant member made of a silicon nitride sintered body having a total oxygen of 4.5% by mass or less, a porosity of 0.5% or less, and a maximum pore diameter in a grain boundary phase of 0.2 μm or less is prepared. It is characterized by doing.

Further, in the wear-resistant member, the silicon nitride sintered body has a three-point bending strength of 900 MPa or more and a fracture toughness value of 6.5 MPa · m ^1/2 or more, and is composed of this silicon nitride sintered body. Three SUJ2 rolling steel balls having a diameter of 9.525 mm are arranged on a track having a diameter of 40 mm set on the upper surface of the wear-resistant member, and rotated with a load of 400 kg applied to the rolling steel balls. A wear resistant member having a rolling life defined by the number of revolutions until the surface of the silicon nitride wear resistant member peels when it is rotated under a condition of several 1200 rpm is 1 × 10 ⁸ times or more; It is also possible to do.

Furthermore, the crushing strength of the silicon nitride sintered body is 200 MPa or more, the fracture toughness value is 6.5 MPa · m ^1/2 or more, and the diameter of the wear-resistant member made of this silicon nitride sintered body is 9. While preparing three rolling balls of 525 mm, the above three rolling balls are arranged on a 40 mm diameter track set on the upper surface of the SUJ2 steel plate, and the maximum contact of 5.9 GPa with the rolling balls Rolling fatigue life defined by the time until the surface of the rolling ball made of a silicon nitride sintered body is peeled when rotating under the condition of a rotational speed of 1200 rpm with a load applied so that stress acts. It is also possible to use a wear-resistant member having a length of 400 hours or longer.

As a method for measuring wear resistance (rolling fatigue life) when the wear-resistant member has a ball shape, a ball having a diameter of 9.525 mm (= 3/8 inch) is cited as a reference value. Is not limited to this size. For example, when the ball size is different from 9.525 mm (= 3/8 inch) in diameter, the maximum contact stress is changed according to the ball size and measured. In this case, since the unit Pa is 1 Pa = 1.02 × 10 ⁻⁵ kgf / cm ² , the change in the maximum contact stress is calculated by proportional calculation according to the size of the ball to be measured. . In addition, the wear resistant member of the present invention has a rolling fatigue life of 400 hours or more even if the ball size is different.

  In the wear-resistant member obtained in the present invention, the silicon nitride sintered body preferably contains 5% by mass or less of at least one of aluminum and magnesium in terms of oxide. The silicon nitride sintered body preferably contains 5% by mass or less of aluminum nitride. Furthermore, it is preferable that the silicon nitride sintered body contains at least one selected from the group consisting of Ti, Hf, Zr, W, Mo, Ta, Nb, and Cr in an amount of 5% by mass or less in terms of oxide.

  Further, when the wear-resistant member made of the silicon nitride sintered body is a rolling bearing member, it is possible to exhibit particularly excellent sliding characteristics and durability.

  In the wear-resistant member obtained in the present invention, the silicon nitride sintered body is a sintered body containing silicon nitride as a main component and containing a small amount of oxygen, and the oxygen concentration is 0 compared to the central portion. It is preferable to have an outer peripheral portion with a low oxygen concentration reduced in a range of 2% by mass or more and 2% by mass or less. The silicon nitride sintered body preferably has a Vickers hardness of Hv 1200 or higher.

  In this way, by reducing the oxygen concentration in the outer peripheral portion of the silicon nitride sintered body, the penetration depth of defects such as pores and cracks becomes shallow, and the occurrence of defects due to these defects can be suppressed, Costs and labor required for surface processing can be reduced. By these, the manufacturing cost at the time of producing wear-resistant members, such as a rolling element, from a silicon nitride sintered compact can be reduced.

  In the outer peripheral portion of the silicon nitride sintered body used in the present invention, the concentration difference of the metal component in the sintering aid relative to the central portion is preferably less than 0.2% by mass. As described above, the silicon nitride sintered body used in the present invention has realized removal of unnecessary oxygen to the last, and the distribution of other metal components is the same as that of the conventional sintered body. The original properties (strength, sliding properties, etc.) as a knot are maintained.

  In the silicon nitride sintered body used in the present invention, if the difference in oxygen concentration between the outer peripheral portion and the central portion is 0.2% by mass or more and 2% by mass or less, the above-described operations and effects can be obtained. However, if the oxygen concentration of the entire sintered body is too high, the original characteristics of the silicon nitride sintered body may be impaired. Therefore, the oxygen concentration of the entire sintered body is preferably 6% by mass or less. . Particularly preferred is 4.5% by mass or less.

  In the wear-resistant member, it is preferable to form an intermediate portion having a difference in oxygen concentration with respect to the central portion of 1% by mass or less. By providing such an intermediate portion, the gradient of the oxygen concentration can be made gentler, and the defect occurrence rate of members and the cost required for surface processing can be further suppressed.

  The method for producing a wear-resistant member of the present invention comprises a step of molding a raw material composition mainly composed of silicon nitride powder into a desired shape, and a molded body obtained by the molding step, having a pressure of 0.01 Pa or less. The temperature is raised to a temperature in the range of 1200 to 1500 ° C. in a vacuum, and the step of holding the temperature in the range of 1200 to 1500 ° C. for 1 to 10 hours, and the molded body after the vacuum treatment in a nitrogen atmosphere And sintering at a temperature in the range of 1600 to 1800 ° C.

  The wear resistant member of the present invention is characterized by comprising a silicon nitride sintered body prepared as described above. The wear-resistant member of the present invention is effective for a bearing member (rolling element) such as a bearing ball, and is particularly effective for a relatively large bearing ball having a diameter of 9 mm or more.

  As a preferred embodiment of the present invention, the silicon nitride sintered body is a sintered body containing silicon nitride as a main component and containing a small amount of oxygen, and 0 between the center portion and the outer peripheral portion of the sintered body. There is an oxygen concentration difference of 2% by mass or more and 2% by mass or less. That is, the outer peripheral portion is a low oxygen concentration region in which the oxygen concentration is reduced in the range of 0.2% by mass or more and 2% by mass or less compared to the central portion.

  FIG. 2 is a view schematically showing regions having different oxygen concentrations in the silicon nitride sintered body obtained by the present invention. FIG. 2 shows a silicon nitride sintered body 2 having a ball shape as an example, and the present invention is not limited to this. Here, the range from the center O of the silicon nitride sintered body to 5% of the radius R is defined as the center portion A. Further, the outer peripheral portion B is in the range from the outer surface S of the silicon nitride sintered body to 1% of the radius R, in other words, from 99% to 100% of the radius R from the center O. In addition, about board | plate materials etc., the same area | region shall be shown on the basis of thickness.

When the oxygen concentration in the central portion A of the silicon nitride sintered body is C ₁ (mass%) and the oxygen concentration in the outer peripheral portion B is C ₂ (mass%), the oxygen concentration C _{2 in the} outer peripheral portion B is (C _{1 -2)} range of ~ (C 1 -0.2), i.e. _{(C 1 -2) ≦ C 2} ≦ (C 1 -0.2) < is to satisfy _{C 1.} The oxygen concentration difference (concentration difference of 0.2% by mass or more) between the central portion A and the outer peripheral portion B is caused by the manufacturing method of the present invention described later in detail, that is, final densification and sintering of silicon nitride. Before reaching the generated temperature, the temperature is raised to a certain temperature in vacuum and a process of holding the temperature at such a temperature for a predetermined time is carried out, so that gas components such as oxygen and SiO ₂ in the sintered body are exposed to the outside. This is achieved by moving the substrate toward the outside and further discharging it out of the sintered body.

The formation of the low oxygen concentration region in the outer peripheral portion B of the silicon nitride sintered body means that the amount of residual oxygen in the outer peripheral portion B and the amount of SiO ₂ produced by combining it with Si are small. Therefore, the depth of penetration of defects such as pores and cracks caused by gas components such as oxygen and SiO ₂ becomes shallow, and the occurrence of defects due to these defects can be suppressed, and the cost and labor required for surface processing can be reduced. Can be reduced. That is, it becomes possible to reduce the manufacturing cost of the silicon nitride sintered body and the wear resistant member using the same.

Here, when the difference in the oxygen concentration C ₂ of the oxygen concentration C ₁ and the outer peripheral portion B of the central portion A is less than 0.2 wt%, to confer the effect of the low oxygen concentration region described above on the outer peripheral portion B I can't. On the other hand, the oxygen concentration difference exceeding 2% by mass means that the oxygen concentration in the outer peripheral portion B is extremely reduced, and the densification of the outer peripheral portion B may not proceed sufficiently. On the contrary, the strength and wear resistance of the outer peripheral portion B are lowered. The difference in oxygen concentration between the central portion A and the outer peripheral portion B is more preferably in the range of 0.5 to 1.5 mass%.

Furthermore, in the silicon nitride sintered body obtained by the present invention, the oxygen concentration C ₃ in the intermediate portion (region C in the silicon nitride sintered body shown in FIG. 1) between the central portion A and the outer peripheral portion B is the central portion A. The oxygen concentration C ₁ has a concentration difference of 1% by mass or less. As described above, in the silicon nitride sintered body used in the present invention, the oxygen concentration gradually decreases from the central portion A toward the outer peripheral portion B, that is, the concentration is inclined. As a result, the defect occurrence rate of the silicon nitride sintered body and the cost and labor required for surface processing can be further suppressed.

In the silicon nitride sintered body obtained in the present invention, the specific oxygen concentration is preferably 6% by mass or less as an average value of the entire sintered body. When the total oxygen concentration (total oxygen amount) in the silicon nitride sintered body exceeds 6% by mass, the original characteristics of the silicon nitride sintered body are likely to be impaired. In addition, the specific oxygen concentration in the outer peripheral portion B is preferably in the range of 3 to 4% by mass in order to suppress the occurrence of defects such as pores and cracks due to gas components such as oxygen and SiO ₂ . Also, the total oxygen concentration range described above is effective in reducing the depth of defect penetration. The oxygen concentration is particularly preferably 4.5% by mass or less.

  In addition, as for each oxygen concentration of the center part A, the intermediate part C, and the outer peripheral part B, three arbitrary measurement points are selected from each region, and the oxygen concentration at each measurement point is measured with EPMA or the like, and these measured values are measured. The average value is shown. The total oxygen concentration (total oxygen amount) in the sintered body is a value determined by an oxygen analyzer according to the inert gas melting-infrared absorption method. Further, the total oxygen amount of the sintered body in the present invention indicates the total amount of oxygen constituting the silicon nitride sintered body in mass%. Therefore, when oxygen is present in the silicon nitride sintered body as a metal oxide or oxynitride, not the amount of the metal oxide (and oxynitride) but the metal oxide (and oxynitride) It focuses on the amount of oxygen.

  In a preferred aspect of the present invention, the silicon nitride sintered body has a concentration difference between the central portion A and the outer peripheral portion B with respect to the oxygen concentration as described above, and further, the sintered body as a whole has a concentration gradient. However, the other components, that is, the metal components in the compound added as a sintering aid, are uniformly distributed in the same manner as in the conventional sintered body, and the metal components in the central portion A and the outer peripheral portion B. The concentration difference is less than 0.2% by mass.

  As described above, the silicon nitride sintered body obtained by the present invention has realized removal of unnecessary oxygen, and the distribution of other metal components is equivalent to that of the conventional sintered body. Since the microstructure of the basic sintered body composed of the elementary crystal grains and the grain boundary phase (glass phase) existing between them is maintained, the original characteristics of the silicon nitride sintered body, ie, strength and hardness The fracture toughness value, sliding characteristics (rolling life characteristics, etc.) are maintained.

  Regarding the hardness required for the wear-resistant member, it is preferable that the Vickers hardness has a characteristic of Hv 1200 or more. When the hardness of the silicon nitride sintered body is less than Hv 1200 in terms of Vickers hardness, the wear resistance is significantly reduced. In particular, the sliding characteristics (rolling life characteristics) required for bearing balls and the like cannot be sufficiently satisfied. The Vickers hardness of the silicon nitride sintered body is more preferably Hv1300 or more.

  The method for producing a wear resistant member made of silicon nitride according to the present invention contains 1.5% by mass or less of oxygen, 75 to 97% by mass of α-phase type silicon nitride, and an average particle size of 1.0 μm or less. A raw material mixture obtained by adding 1 to 10% by mass of a rare earth element in terms of oxide to the silicon nitride powder is prepared to prepare a molded body, and after the obtained molded body is degreased and sintered After holding at a temperature of 1250 ° C. to 1600 ° C. for a predetermined time, main sintering is performed at a temperature of 1650 ° C. to 1850 ° C.

  Furthermore, in the above production method, by slowly cooling the sintered body at a cooling rate of 100 ° C. or less per hour from the sintering temperature to a temperature at which the liquid phase formed by sintering with the rare earth element solidifies. The pore diameter can be further reduced.

  Moreover, in the said manufacturing method, it is preferable to add 5 mass% or less in conversion of an oxide at least one of aluminum and magnesium to the said silicon nitride powder. Further, it is preferable to add 5% by mass or less of aluminum nitride to the silicon nitride powder. Further, it is preferable that at least one selected from the group consisting of Ti, Hf, Zr, W, Mo, Ta, Nb, and Cr is added to the silicon nitride powder in an amount of 5% by mass or less in terms of oxide.

  Moreover, it is preferable to implement a hot isostatic pressing (HIP) process at a temperature of 1600 ° C. to 1850 ° C. in a non-oxidizing atmosphere of 300 atm or higher after sintering.

According to the above manufacturing method, when preparing the silicon nitride sintered body constituting the wear-resistant member, the silicon nitride formed body is subjected to the holding operation under predetermined conditions during the sintering, and then the main sintering is performed. Therefore, the oxygen concentration of the sintered body is effectively reduced, generation of pores due to this oxygen is suppressed, and the maximum pore diameter can be made extremely small. And since the pore which tends to become a starting point of fatigue failure when stress acts is reduced, a wear resistant member excellent in fatigue life and durability can be obtained. Further, even if the deoxidation action by the holding operation proceeds, the sinterability is improved and the pores are reduced, so that the total oxygen amount is 6% by mass or less, preferably 4.5% by mass or less, and the silicon nitride crystal structure A grain boundary phase containing a rare earth element or the like is formed therein, the maximum pore diameter in the grain boundary phase is 0.3 μm or less, the porosity is 0.5% or less, and the three-point bending strength is 900 MPa or more at room temperature. In addition, a wear resistant member made of silicon nitride excellent in mechanical properties having a fracture toughness value of 6.5 MPa · m ^1/2 or more and a crushing strength of 200 MPa or more is obtained.

  The silicon nitride powder used in the method of the present invention and constituting the main component of the silicon nitride sintered body constituting the wear-resistant member includes oxygen, taking into consideration sinterability, bending strength, fracture toughness value and rolling life. The α-phase type silicon nitride having a content of 1.5% by mass or less, preferably 0.5 to 1.2% by mass is contained in an amount of 75 to 97% by mass, preferably 80 to 95% by mass, and the average particle size is It is preferable to use fine silicon nitride powder of 1.0 μm or less, preferably about 0.4 to 0.8 μm.

  Further, when silicon nitride powder having an impurity oxygen amount exceeding 1.5 mass% is used, the oxygen concentration difference between the central portion and the outer peripheral portion is increased, but the oxygen concentration as a whole of the sintered body is increased, and the pores are increased. The strength of the silicon nitride sintered body tends to be reduced due to an increase in the rate. In other words, in the present invention, since a sufficient effect can be obtained even if the silicon nitride raw material powder contains impurity oxygen of up to 1.5 mass%, it is not always necessary to use a high-purity raw material powder. Cost reduction. A more preferable oxygen content of the silicon nitride raw material powder is in the range of 0.5 to 1.2% by mass.

  As the silicon nitride raw material powder, α-phase type and β-phase type powders are known, but the α-phase type silicon nitride raw material powder tends to have insufficient strength when formed into a sintered body. On the other hand, β-phase type silicon nitride raw material powder requires high-temperature firing, but a high-strength sintered body in which silicon nitride crystal particles having a high aspect ratio are complicated is obtained. Accordingly, in the present invention, the α-phase type raw material powder is fired at a high temperature, and the silicon nitride sintered body is preferably a sintered body mainly composed of β-phase type silicon nitride crystal particles. .

  In the present invention, the reason why the blending amount of the α-phase type silicon nitride powder is limited to the range of 75 to 97% by mass is that the bending strength, fracture toughness value and rolling life of the sintered body are markedly within the range of 75% by mass or more. This is because the excellent characteristics of silicon nitride become remarkable. On the other hand, considering the sinterability, the range is up to 97% by mass. Preferably it is set as the range of 80-95 mass%. More preferably, it is the range of 85-90 mass%.

  As a result, the silicon nitride starting material powder has an oxygen content of 1.5% by mass or less, preferably 0.5 to 1% in consideration of sinterability, bending strength, fracture toughness, and rolling life. Use a fine silicon nitride powder that is 2% by mass, contains α-phase type silicon nitride of 90% by mass or more, and has an average particle size of 1.0 μm or less, preferably about 0.4 to 0.8 μm. Is preferred.

  In particular, by using fine raw material powder with an average particle size of 0.7 μm or less, it is possible to form a dense sintered body with a porosity of 0.5% or less even with a small amount of sintering aid. It is. The porosity of this sintered body can be easily measured by the Archimedes method.

  Further, the total amount of oxygen contained in the silicon nitride sintered body constituting the wear resistant member obtained in the present invention is specified to be 6% by mass or less. If the total oxygen content of the sintered body exceeds 6% by mass, the maximum pore diameter in the grain boundary phase becomes large and tends to be the starting point of fatigue failure, and the rolling (fatigue) life of the wear-resistant member is reduced. Preferably it is 4.5 mass% or less.

  The “total oxygen content of the sintered body” defined in the present invention indicates the total amount of oxygen constituting the silicon nitride sintered body in mass%. Therefore, when oxygen is present in the silicon nitride sintered body as a metal oxide, oxynitride, or the like, not the amount of the metal oxide (and oxynitride) but the metal oxide (and oxynitride) ) Is focused on the amount of oxygen in it.

  Furthermore, the maximum pore diameter in the grain boundary phase of the silicon nitride sintered body constituting the wear resistant member obtained in the present invention is defined to be 0.3 μm or less. When the maximum pore diameter exceeds 0.3 μm, it is particularly likely to become a starting point of fatigue failure, and the rolling (fatigue) life of the wear-resistant member is reduced. Preferably, it is 0.2 μm or less.

  The rare earth element added as a sintering aid to the silicon nitride raw material powder includes oxides such as YHo, Er, Yb, La, Sc, Pr, Ce, Nd, Dy, Sm, and Gd, or sintering operations. These oxide substances may be used alone or in combination of two or more kinds. These sintering aids react with the silicon nitride raw material powder to form a liquid phase and function as a sintering accelerator.

  The amount of the sintering aid added is in the range of 1 to 10% by mass with respect to the raw material powder in terms of oxide. When the amount added is less than 1% by mass, densification or increase in strength of the sintered body is insufficient, and in particular, when the rare earth element is an element having a large atomic weight such as a lanthanoid element, it is relatively low. A strong and relatively low thermal conductivity sintered body is formed. On the other hand, when the added amount exceeds 10% by mass, an excessive amount of grain boundary phase is generated, and the amount of pores generated increases or the strength starts to decrease, so the above range is set. In particular, it is desirable to set it as 2-8 mass% for the same reason.

Also, at least one oxide (Al ₂ O ₃ , MgO) of aluminum (Al) and magnesium (Mg) used as a selective additive component in the present invention promotes the function of the rare earth element sintering accelerator. In order to improve the mechanical strength such as the bending strength and fracture toughness value of the Si ₃ N ₄ sintered body by performing densification at a low temperature and controlling the grain growth in the crystal structure, Add in range. When the addition amount of Al and Mg is less than 0.2% by mass in terms of oxide, the effect of addition is insufficient. On the other hand, when the excess amount exceeds 5% by mass, the oxygen content increases. The addition amount is 5% by mass or less, preferably 0.2 to 5% by mass. In particular, the content is desirably 0.5 to 3% by mass.

  Furthermore, aluminum nitride (AlN) as another optional additive component serves to suppress the evaporation of silicon nitride during the sintering process and further promote the function of the rare earth element as a sintering accelerator. It is desirable that it is added in the range of 5% by mass or less.

  When the amount of AlN added is less than 0.1% by mass, sintering at a higher temperature is required, whereas when the amount exceeds 5% by mass, an excessive amount of grain boundary phase is generated, Alternatively, since the solid solution starts to be dissolved in silicon nitride, the pores are increased and the porosity is increased, so that the addition amount is set to 5 mass% or less. In particular, in order to ensure good performance in terms of sinterability, strength, and rolling life, it is desirable that the addition amount be in the range of 0.1 to 3% by mass.

In the present invention, Ti, Hf, Zr, W, Mo, Nb, and Cr may be added as oxides, carbides, nitrides, silicides, and borides as other optional additive components. These compounds promote the function of the rare earth element as a sintering accelerator, and also serve to enhance the mechanical strength of the Si ₃ N ₄ sintered body by performing a dispersion strengthening function in the crystal structure. A compound of Ti and Mo is preferred. When the addition amount of these compounds is less than 0.1% by mass in terms of oxide, the addition effect is insufficient, whereas when the excess amount exceeds 5% by mass, the mechanical strength and rolling life are reduced. For this reason, the addition amount is set to a range of 5 mass% or less. In particular, the content is desirably 0.2 to 3% by mass.

  The compounds such as Ti and Mo also function as a light-shielding agent that imparts opacity by coloring the silicon nitride ceramic sintered body black.

  Further, since the porosity of the sintered body greatly affects the rolling life and strength of the wear-resistant member, it is manufactured so as to be 0.5% or less. When the porosity exceeds 0.5%, the number of pores that become the starting point of fatigue failure increases rapidly, and the rolling life of the wear-resistant member is reduced, and the strength of the sintered body is reduced.

  Further, as described above, the porosity of the silicon nitride sintered body is 0.5% or less, the maximum pore diameter in the grain boundary phase formed in the silicon nitride crystal structure is 0.3 μm or less, and the total amount of oxygen is In order to obtain a silicon nitride sintered body that gives a predetermined rolling life when a thrust type rolling wear test apparatus is used, the silicon nitride molding prepared with the above raw material is used. After the body is degreased, it is held at a temperature of 1250 to 1600 ° C. for 0.5 to 10 hours in the course of sintering, and then subjected to atmospheric pressure sintering or pressure sintering at a temperature of 1650 to 1850 ° C. for about 2 to 10 hours. is important. In addition, the pore diameter can be further reduced by gradually cooling the sintered body immediately after completion of the sintering operation at a cooling rate of 100 ° C. or less.

  In particular, during the sintering process, the oxygen concentration in the liquid phase (grain boundary phase) generated by holding at a temperature of 1250 to 1600 ° C. for 0.5 to 10 hours is reduced to increase the melting point of the liquid phase. It is possible to suppress the generation of bubble-like pores generated when the phases are melted and to minimize the maximum pore diameter, thereby improving the rolling life of the sintered body. This holding operation in the middle of sintering exhibits a remarkable effect particularly when the treatment is performed in a vacuum atmosphere at a temperature of 1350 to 1450 ° C., but the same effect can be obtained even in a treatment in a nitrogen atmosphere at a temperature of 1500 to 1600 ° C. Demonstrated.

  In addition, when the cooling rate of the sintered body that reaches the temperature at which the liquid phase solidifies after sintering is set to 100 ° C./hour or lower and the temperature is gradually cooled, the oxygen concentration in the liquid phase is further reduced. A sintered body with improved life can be obtained.

  When the sintering temperature is less than 1650 ° C., the sintered body is not sufficiently densified and the porosity is 0.5 vol. %, The mechanical strength and rolling life are both reduced. On the other hand, if the sintering temperature exceeds 1850 ° C., the silicon nitride component itself tends to evaporate and decompose. In particular, when pressureless sintering is performed instead of pressure sintering, decomposition and evaporation of silicon nitride starts from around 1800 ° C.

  The cooling rate of the sintered body immediately after completion of the above sintering operation is an important control factor for reducing the pore diameter and crystallizing the grain boundary phase, and rapid cooling such that the cooling rate exceeds 100 ° C. per hour. In this case, the grain boundary phase of the sintered body structure becomes amorphous (glass phase), and the oxygen concentration in the liquid phase generated in the sintered body is insufficiently reduced. Rolling life characteristics will deteriorate.

  The temperature range in which the cooling rate should be strictly adjusted is sufficient from the predetermined sintering temperature (1650 to 1850 ° C.) to the solidification of the liquid phase generated by the reaction of the sintering aid. . Incidentally, the liquid phase freezing point in the case of using the above sintering aid is about 1600 to 1500 ° C. And by controlling the cooling rate of the sintered body at least from the sintering temperature to the liquid phase solidification temperature to 100 ° C./hour, preferably 50 ° C. or less, more preferably 25 ° C. or less, The amount of oxygen is 6% by mass or less, the maximum pore diameter is 0.3 μm or less, the porosity is also 0.5% or less, and a silicon nitride sintered body excellent in rolling life characteristics and durability can be obtained. It is more effective when combined with the above-mentioned midway holding treatment at 1300 to 1600 ° C.

  The silicon nitride sintered body constituting the wear-resistant member obtained by the present invention is manufactured through the following process, for example. That is, for a fine silicon nitride powder having the predetermined fine particle size and low oxygen content, a predetermined amount of sintering aid, necessary additives such as an organic binder, and Al, Mg as required , AlN, Ti, etc. are added to adjust the raw material mixture, and then the obtained raw material mixture is molded to obtain a molded body having a predetermined shape. As a forming method of the raw material mixture, a known forming method such as a general-purpose uniaxial pressing method, a die pressing method, a doctor blade method, a rubber pressing method, or a CIP method can be applied.

  In the case of forming a molded body by the above-mentioned mold pressing method, it is necessary to set the molding pressure of the raw material mixture to 120 MPa or more in order to form a grain boundary phase in which pores are not easily generated particularly after sintering. is there. When this molding pressure is less than 120 MPa, a portion where the rare earth element compound, which is a component that mainly constitutes the grain boundary phase, is easily aggregated, and a sufficiently dense molded body cannot be formed, and cracks are generated. Only a large number of sintered bodies can be obtained. Since the location where the grain boundary phase is aggregated is likely to be a starting point of fatigue failure, the life durability of the wear-resistant member is lowered. On the other hand, if the molding pressure is excessively set to exceed 200 MPa, the durability of the molding die is lowered, so that the productivity is not necessarily good. Therefore, the molding pressure is preferably in the range of 120 to 200 MPa.

  Subsequent to the above molding operation, the molded body is heated in a non-oxidizing atmosphere at a temperature of 600 to 800 ° C. or in air at a temperature of 400 to 500 ° C. for 1 to 2 hours to sufficiently remove the organic binder component added in advance. Remove and degrease.

  Next, vacuum processing is performed in which the inside of the firing furnace is depressurized during the sintering of the degreased compact.

That is, the temperature is raised to a temperature in the range of 1250 to 1600 ° C. in a vacuum of 0.01 Pa or less, and held at a temperature in the range of 1250 to 1600 ° C. for 0.5 to 10 hours. By carrying out such a vacuum treatment, it is possible to move gas components such as oxygen and SiO ₂ in the sintered body to the outside, and to discharge the gas components to the outside. Since the discharge of the gas component occurs particularly from the outer peripheral portion, it is possible to finally reduce the oxygen concentration in the outer peripheral portion.

  If the temperature during the vacuum treatment is less than 1250 ° C., the discharge of gas components does not proceed sufficiently, and the oxygen concentration in the outer peripheral portion of the final sintered body may not be sufficiently reduced. On the other hand, if the temperature during the vacuum treatment exceeds 1600 ° C., there is substantially no difference from the main sintering, and densification starts early from the outer peripheral portion, so that the removal of gas components such as the intermediate portion may not be performed. . The same applies to the holding time during the vacuum treatment, and if it is out of the above range, the gas component may be insufficiently discharged or the gas component may be excessively discharged.

  Next, following the vacuum treatment (holding operation), the compact is sintered at atmospheric pressure or atmospheric pressure at a temperature of 1650 to 1850 ° C. for a predetermined time in an inert gas atmosphere such as nitrogen gas or argon gas. I do. As the pressure sintering method, various pressure sintering methods such as atmospheric pressure sintering, hot pressing, and HIP treatment are used.

  The above sintering step may be performed subsequent to the vacuum processing step, or once cooled in the furnace to room temperature or a temperature in the vicinity thereof, then nitrogen is introduced into the furnace, and then the temperature is raised to the sintering temperature again. May be implemented.

  In addition, after the sintering, the obtained silicon nitride sintered body is further subjected to a hot isostatic pressing (HIP) treatment at a temperature of 1600 ° C. to 1850 ° C. in a non-oxidizing atmosphere of 300 atm or higher, Since the influence of the pores of the sintered body that becomes the starting point of fatigue fracture can be further reduced, a wear-resistant member having further improved sliding characteristics and rolling life characteristics can be obtained.

  In particular, when the silicon nitride sintered body is applied to a bearing member such as a bearing ball, it is effective to perform HIP treatment after atmospheric pressure sintering or atmospheric pressure sintering.

  The silicon nitride wear-resistant member manufactured by the above method has a total oxygen amount of 6% by mass or less, a porosity of 0.5% or less, a maximum pore diameter of 0.3 μm or less, and a three-point bending strength. Excellent mechanical properties of 900 MPa or more at room temperature.

It is also possible to obtain a silicon nitride wear-resistant member having a crushing strength of 200 MPa or more and a fracture toughness value of 6.5 MPa · m ^1/2 or more.

  Furthermore, according to the production method of the present invention, the Vickers hardness is Hv 1200 or more, and an oxygen concentration difference of 0.2% by mass or more and 2% by mass or less is provided with respect to the central portion of the sintered body. Thus, a silicon nitride sintered body (abrasion resistant member) having an outer peripheral portion, that is, an outer peripheral portion defined as a low oxygen region can be obtained with good reproducibility.

  According to the method for manufacturing a wear-resistant member according to the present invention, the oxygen concentration of the sintered body is reduced because the main body is formed after performing a predetermined holding operation during the sintering process. In addition, the generation of pores is suppressed, the maximum pore diameter can be made extremely small, and a wear-resistant member having excellent rolling life characteristics and durability can be obtained. Therefore, when this wear-resistant member is used as a rolling bearing member and a bearing portion is prepared, it is possible to maintain good sliding rolling characteristics over a long period of time, and operational reliability and durability. It is possible to provide an excellent rotating device. In addition, as other applications, it can be applied to various fields that require wear resistance, such as engine parts, various jigs and tools, various rails, and various rollers.

  That is, although the silicon nitride sintered body used in the present invention can be used for various applications, it is particularly effective for wear-resistant members. Examples of wear-resistant members to which this silicon nitride sintered body can be applied include bearing members, various roll materials for rolling, engine parts such as compressor vanes, gas turbine blades, cam rollers, etc. It is effective for a bearing member (rolling element) whose entire surface is a sliding portion like a bearing ball. In particular, the present invention is effective for a relatively large bearing ball having a diameter of 9 mm or more.

  Needless to say, the silicon nitride sintered body used as the wear-resistant member may be subjected to finish processing such as surface polishing or coating treatment as necessary. In other words, when the silicon nitride sintered body can be used as it is as a wear resistant member, the silicon nitride sintered body becomes a direct wear resistant member.

  According to the wear-resistant member and the method of manufacturing the same according to the present invention, since the main body is formed after performing a predetermined holding operation during the sintering process, the oxygen concentration of the sintered body is reduced. Thus, the generation of pores is suppressed and the maximum pore diameter can be minimized, and a wear-resistant member having excellent rolling life characteristics and durability can be obtained. Therefore, when this wear-resistant member is used as a rolling bearing member and a bearing portion is prepared, it is possible to maintain good sliding rolling characteristics over a long period of time, and operational reliability and durability. It is possible to provide an excellent rotating device.

  Next, the embodiments of the present invention will be specifically described with reference to the following examples.

[Examples 1-2]
As Example 1, the amount of oxygen was 1.1% by mass and the Si ₃ N ₄ (silicon nitride) raw material powder having an average particle size of 0.55 μm containing α-phase type silicon nitride 97% was sintered to 86% by mass. As a binder, 5% by mass of Y ₂ O ₃ (yttrium oxide) powder having an average particle size of 0.9 μm, 5% by mass of Al ₂ O ₃ (alumina) powder having an average particle size of 0.7 μm, and an average particle size of 1. 2% by mass of 0 μm AlN (aluminum nitride) powder and 2% by mass of TiO ₂ (titanium oxide) powder having an average particle size of 0.5 μm were added, and a silicon nitride ball was used as a grinding medium in ethyl alcohol for 96 hours. After wet mixing, the raw material mixture was prepared by drying.

Next, a predetermined amount of an organic binder is added to the obtained raw material powder mixture to prepare a blended granulated powder, which is then press-molded at a molding pressure of 130 MPa, and a molded product of 50 mm × 50 mm × thickness 5 mm as a sample for measuring bending strength. A large number of compacts having a diameter of 80 mm and a thickness of 6 mm were produced as rolling life measurement samples. Next, after degreasing the obtained molded body in an air stream at 450 ° C. for 4 hours, heating from room temperature and carrying out a holding operation for half an hour at a temperature of 1400 ° C. in a vacuum atmosphere of 10 ⁻² Pa or less. After sintering for 4 hours at a temperature of 1750 ° C. in a nitrogen gas atmosphere of 0.7 MPa, the cooling rate until the temperature drops to 1500 ° C. is adjusted to 100 ° C./hr, respectively, and the sintered body is gradually adjusted. Chilled. Next, the obtained sintered body is subjected to a hot isostatic pressing (HIP) treatment in which a pressure of 100 MPa is applied at a temperature of 1700 ° C. for 1 hour in a nitrogen gas atmosphere, whereby the silicon nitride according to Example 1 is obtained. A raw wear-resistant member was prepared.

Further, as Example 2, the holding operation in the middle of sintering was carried out under the same conditions as Example 1 except that the holding operation was carried out in a nitrogen gas atmosphere of 1 × 10 ⁴ Pa at a temperature of 1600 ° C. for 2 hours. Thus, a silicon nitride wear-resistant member according to Example 2 was prepared.

[Comparative Examples 1-3]
As Comparative Example 1, a silicon nitride wear-resistant member according to Comparative Example 1 was prepared by processing under the same conditions as in Example 1 except that the intermediate holding operation at a temperature of 1400 ° C. was not performed in a vacuum atmosphere. Further, as Comparative Example 2 which is an example outside the preferable range of the present invention, the holding operation during the sintering was performed at a temperature of 1600 ° C. for 2 hours in a nitrogen gas atmosphere of 1 × 10 ⁴ Pa, further sintering. A silicon nitride wear-resistant member according to Comparative Example 2 was prepared by treating under the same conditions as in Example 1 except that the subsequent cooling rate was 500 ° C./hr, which was furnace cooling by conventional natural cooling. Further, as Comparative Example 3, except that Si ₃ N ₄ (silicon nitride) raw material powder having an oxygen content of 1.7 mass% and an average particle size of 1.5 μm containing 91% α-phase type silicon nitride was used. Were treated under the same conditions as in Example 1 to prepare a silicon nitride wear-resistant member according to Comparative Example 3.

  For each silicon nitride wear-resistant member according to Examples 1 and 2 and Comparative Examples 1 to 3 thus obtained, the total oxygen content, porosity, maximum pore diameter in the grain boundary phase, and three-point bending strength at room temperature The results shown in Table 1 were obtained by measuring the fracture toughness value and rolling life according to the Shinhara method in the microindentation method.

  The porosity of the sintered body is measured by the Archimedes method, while the maximum pore diameter in the grain boundary phase is selected from three sections of a unit area of 100 μm × 100 μm from the cross section of the sintered body. The largest pore diameter was measured from the enlarged photograph. As the maximum pore diameter, the longest diagonal line shown in the enlarged photograph was adopted.

  Further, the total oxygen amount in the silicon nitride sintered body was measured with an oxygen analyzer according to an inert gas melting-infrared absorption method.

  For the three-point bending strength, a bending test piece of 3 mm × 40 mm × thickness 4 mm was prepared from the sintered body, the span (fulcrum distance) was set to 30 mm, and the load application speed was set to 0.5 mm / min. Measured with

The rolling characteristics of each wear-resistant member were measured using a thrust type rolling wear test apparatus as shown in FIG. The test apparatus includes a flat wear-resistant member 2 disposed in the apparatus main body 1, a plurality of rolling steel balls 3 disposed on the upper surface of the wear-resistant member 2, and the rolling steel balls 3. A guide plate 4 disposed at the top, a drive rotary shaft 5 connected to the guide plate 4, and a cage 6 that regulates the spacing between the rolling steel balls 3 are configured. The apparatus main body 1 is filled with lubricating oil 7 for lubricating the rolling part. The rolling steel balls 3 and the guide plate 4 are made of high carbon chromium bearing steel (SUJ2) defined by Japanese Industrial Standards (JIS G 4805). As the lubricating oil 7, paraffinic lubricating oil (viscosity at 40 ° C .: 67.2 mm ² / S) or turbine oil is used.

The rolling life of the plate-like wear-resistant member according to this example is obtained by measuring three SUJ2 rolling steel balls having a diameter of 9.525 mm on a track having a diameter of 40 mm set on the upper surface of the wear-resistant member 2. The above-mentioned silicon nitride wear-resistant member is arranged and rotated under conditions of 1200 rpm with a load of 400 kg applied to the rolling steel balls 3 under oil bath lubrication conditions of turbine oil. The number of rotations until the surface of 2 was peeled was measured as the rolling life. Each measurement result is shown in Table 1 below.

As is clear from the results shown in Table 1, the silicon nitride wear-resistant member according to each example is formed by carrying out main sintering after performing a predetermined holding operation during the sintering process. Therefore, the oxygen concentration of the sintered body is reduced, the generation of pores is suppressed, the maximum pore diameter is miniaturized, the strength characteristics are good, the rolling life is more than 10 ⁸ times, and the durability is excellent A wear resistant member made of silicon nitride was obtained.

  On the other hand, in Comparative Example 1 in which the holding operation in the middle of the sintering process was not performed, the effect of reducing oxygen was small and many pores remained, resulting in a decrease in strength characteristics and rolling life.

  On the other hand, when the cooling rate of the sintered body was set large as in Comparative Example 2 and cooled rapidly, the deoxygenation effect was not sufficient, and the effect of reducing the maximum pore diameter was reduced, resulting in a reduction in rolling life.

  Further, in Comparative Example 3 in which the amount of oxygen in the raw material powder is excessive, the porosity and the maximum pore diameter are increased even if the holding operation and slow cooling during the sintering are performed, so that the strength and rolling life are increased. It was found that both decreased.

  Next, the case where the wear resistant member according to the present invention is applied to a rolling ball of a bearing material will be specifically described with reference to the following examples and comparative examples.

[Examples 1B to 2B and Comparative Examples 1B to 3B]
Each of the prepared granulated powders prepared in Examples 1 and 2 and Comparative Examples 1 to 3 was filled and pressed into a mold to prepare a spherical preform. Further, each preform was subjected to a rubber press treatment at a molding pressure of 120 MPa to prepare spherical molded bodies having a diameter of 11 mm as samples for crushing strength measurement and rolling life measurement.

  Next, each spherical molded body was degreased under the same conditions as in Example 1, and then processed under the holding conditions, sintering conditions, cooling rate after sintering, and HIP conditions shown in Table 2. Further, the obtained sintered bodies were polished to form balls having a diameter of 9.525 mm and a surface roughness of 0.01 μmRa, so that Examples 1B to 2B and Comparative Examples 1B to 3B were formed. A rolling ball for a bearing as a wear-resistant member according to the above was prepared. The surface roughness was measured as the center line average roughness (Ra) obtained by measuring the equator of the rolling ball using a stylus type surface roughness measuring instrument.

  For the rolling balls as wear-resistant members according to the examples and comparative examples prepared as described above, the total oxygen content, the porosity, the maximum pore diameter in the grain boundary phase, the crushing strength, the fracture toughness value, and The rolling fatigue life was measured.

  The rolling fatigue life was measured using a thrust type rolling wear test apparatus shown in FIG. Here, in Example 1 or the like, the evaluation object is the flat wear-resistant member 2, and the ball rolling on the surface of the wear-resistant member 2 was SUJ2 rolling steel ball 3. In order to evaluate the rolling balls 8 made of silicon nitride of Examples 1B to 2B and Comparative Examples 1B to 3B, a bearing steel plate 9 made of SUJ2 was arranged instead of the wear resistant member 2.

The rolling fatigue life of each rolling ball is as follows. The three rolling balls 8 having a diameter of 9.525 mm are prepared from each wear-resistant member as described above, while the diameter set on the upper surface of the SUJ2 steel plate 9 is set. The three rolling balls 8 are arranged on a 40 mm track, and a load is applied so that a maximum contact stress of 5.9 GPa acts on the rolling balls 8 under the oil bath lubrication conditions of the turbine oil. When rotating under the condition of 1200 rpm, the rolling fatigue life was measured as the time until the surface of the silicon nitride sintered body rolling ball 8 was peeled off. The measurement results are shown in Table 2 below.

  As is clear from the results shown in Table 2 above, the silicon nitride rolling balls according to the respective examples are formed by carrying out the main sintering after performing a predetermined holding operation during the sintering process. Therefore, the oxygen concentration of the sintered body is reduced, the generation of pores is suppressed, the maximum pore diameter is miniaturized, the crushing strength is high, the rolling fatigue life exceeds 400 hours, and the silicon nitride has excellent durability. A rolling ball was obtained.

  On the other hand, in Comparative Example 1B in which the holding operation in the middle of the sintering process was not carried out, the effect of reducing oxygen was small and many pores remained, and the crushing strength and rolling fatigue life were reduced.

  On the other hand, when the cooling rate of the sintered body is set to a large value as in Comparative Example 2B and rapidly cooled, the deoxygenation effect is not sufficient, and the effect of reducing the maximum pore diameter is reduced and the rolling fatigue life is reduced. .

  Further, in Comparative Example 3B in which the amount of oxygen in the raw material powder is excessive, the porosity and the maximum pore diameter are increased even if the holding operation and slow cooling during the sintering are performed, so that the crushing strength and rolling are increased. It was found that both fatigue lives were reduced.

  In addition, when measuring the rolling fatigue life of the silicon nitride rolling balls according to each of the above examples, three rolling balls having a diameter of 9.525 mm were used. Even in the case of changing, it has been confirmed that rolling characteristics corresponding to the load conditions and rolling conditions can be obtained.

  Next, a plate-like wear-resistant member prepared according to a composition or processing conditions other than the above-described examples will be specifically described with reference to the following examples and comparative examples.

[Examples 3 to 27]
The silicon nitride raw material powder used in Example 1 as Examples 3 to 27, Y ₂ O ₃ powder, Al ₂ O ₃ powder, and an average particle size of 0.9 to 1.0 μm as shown in Table 3 In addition to various rare earth oxide powders, Table 3 shows MgO powder having an average particle size of 0.5 μm and various compound powders having an average particle size of 0.4 to 0.5 μm in addition to AlN powder having an average particle size of 1.0 μm. The raw material mixtures were prepared by blending so as to achieve the composition ratio shown.

  Next, each raw material mixture obtained was molded and degreased under the same conditions as in Example 1, followed by holding operation under the conditions shown in Table 3 during sintering, followed by main sintering, and further HIP treatment As a result, silicon nitride wear-resistant members according to Examples 3 to 27 were produced.

[Comparative Examples 4 to 9]
On the other hand, as shown in Table 3 as Comparative Examples 4 to 9, Y ₂ O ₃ was added in an excessive amount (Comparative Example 4), Y ₂ O ₃ was added in an excessive amount (Comparative Example 5), and TiO ₂ was excessive. (Comparative Example 6), Al ₂ O ₃ added excessively (Comparative Example 7), AlN added excessively (Comparative Example 8), MgO added excessively (Comparative Example 9) ) Raw material mixtures were prepared.

  Next, each obtained raw material mixture was molded and degreased under the same conditions as in Example 3, and then held in the course of sintering under the conditions shown in Table 3, followed by main sintering and further HIP treatment. Thus, silicon nitride wear-resistant members according to Comparative Examples 4 to 9 were produced.

For each silicon nitride wear-resistant member according to each of the examples and comparative examples thus manufactured, the total oxygen content, the porosity, the maximum pore diameter in the grain boundary phase, and three points at room temperature under the same conditions as in Example 1. The bending strength, fracture toughness value and rolling life were measured and the results shown in Table 3 below were obtained.

As is clear from the results shown in Table 3 above, a holding operation is performed under predetermined conditions in the course of the sintering process of the raw material compact that includes a predetermined amount of rare earth element and has an oxygen content defined, and is gradually cooled after sintering. In the wear-resistant member according to each of the examples manufactured as above, the oxygen concentration of the sintered body is reduced, the generation of pores is suppressed, the maximum pore diameter is miniaturized, and the strength characteristics are good. Further, a wear resistant member made of silicon nitride having a rolling life exceeding 10 ⁸ times and excellent in durability has been obtained.

  On the other hand, as shown in Comparative Examples 4 to 9, in the sintered body in which the addition amount of the rare earth component is outside the preferable range specified in the present invention, the holding operation during the sintering and the slow cooling after the sintering are performed. However, the rolling life of the surface of the wear-resistant member is low, and the characteristic requirements specified in the present invention are satisfied in any of the characteristics such as the total oxygen content, porosity, maximum pore diameter, and three-point bending strength of the sintered body. It can be confirmed that it is not.

  Next, the case where the wear-resistant members according to Examples 3 to 27 and Comparative Examples 4 to 9 are applied to rolling balls of bearing materials will be specifically described with reference to the following Examples and Comparative Examples.

[Examples 3B to 27B and Comparative Examples 4B to 9B]
Each of the prepared granulated powders prepared in Examples 3 to 27 and Comparative Examples 4 to 9 was filled and pressed into a mold to prepare a spherical preform. Further, each preform was subjected to a rubber press treatment at a molding pressure of 100 MPa to prepare spherical molded bodies having a diameter of 11 mm as samples for crushing strength measurement and rolling life measurement.

  Next, each spherical molded body was degreased under the same conditions as in Example 1, and then treated under the holding conditions, sintering conditions, cooling rate after sintering, and HIP conditions shown in Table 4. Further, the obtained sintered bodies were polished to form balls having a diameter of 9.525 mm and a surface roughness of 0.01 μmRa, so that Examples 3B to 27B and Comparative Examples 4B to 9B were obtained. A rolling ball for a bearing as a wear-resistant member according to the above was prepared. The surface roughness was measured as the arithmetic average roughness (Ra) obtained by measuring the equator of the rolling ball using a stylus type surface roughness measuring instrument.

For the rolling balls as wear-resistant members according to the examples and comparative examples prepared as described above, the total oxygen content, the porosity, the maximum pore diameter in the grain boundary phase, the crushing strength, the fracture toughness value, and The rolling fatigue life was measured in the same manner as in Example 1B. The measurement results are shown in Table 4 below.

  As is clear from the results shown in Table 4 above, a holding operation is performed under predetermined conditions in the course of the sintering process of the raw material compact that includes a predetermined amount of rare earth elements and has a specified amount of oxygen, and is gradually cooled after sintering. In the rolling ball according to each example manufactured as described above, the oxygen concentration of the sintered body is reduced, the generation of pores is suppressed, the maximum pore diameter is miniaturized, and the crushing strength characteristics are good. The rolling fatigue life exceeds 400 hours, and a silicon nitride rolling ball excellent in durability is obtained.

  On the other hand, as shown in Comparative Examples 4B to 9B, in the sintered body in which the addition amount of the rare earth component is out of the range specified in the present invention, the holding operation during the sintering and the slow cooling after the sintering are performed. However, the rolling fatigue life of the rolling ball is low, and the characteristic requirements specified in the present invention are not satisfied in any of the characteristics such as the total oxygen content, porosity, maximum pore diameter, and three-point bending strength of the sintered body. Can be confirmed.

  Next, specific examples of the wear resistant member of the present invention in which parts having different oxygen concentrations are formed and the evaluation results thereof will be described.

[Examples 101 to 105 and Comparative examples 101 to 102]
To the silicon nitride (Si ₃ N ₄ ) powder having an oxygen content of 1.2% by mass, a rare earth compound powder and an aluminum compound powder as a sintering aid, and other metal compound powders are added in the composition shown in Table 5. Then, they were mixed using a wet ball mill and then dried to prepare respective raw material mixtures.

  Next, a predetermined amount of an organic binder was added to and mixed with each of the obtained raw material mixtures, and then spherical molded bodies were produced by the CIP method (molding pressure = 100 MPa). Each obtained molded body was degreased in an air stream at 450 ° C., and then heated in a vacuum of 0.01 Pa or less from room temperature to a temperature of 1200 to 1500 ° C., and further held at the same temperature for 2 to 6 hours. . Subsequently, nitrogen gas was introduced into the furnace and sintered at 1600 to 1700 ° C. for 2 to 5 hours to obtain spherical sintered bodies (silicon nitride sintered bodies) each having a diameter of 10 mm.

  In addition, as Comparative Example 101 with the present invention, spherical firing was performed in the same manner as in Example 102, except that sintering was performed by raising the temperature from room temperature in a nitrogen atmosphere without performing heating and holding in vacuum. A sintered body (silicon nitride sintered body) was produced. Further, as Comparative Example 102, a spherical sintered body (silicon nitride sintered body) was produced in the same manner as Example 101, except that the composition ratio was such that the total oxygen amount exceeded 6 mass%.

  For each of the spherical sintered bodies according to Examples 101 to 105 and Comparative Examples 101 to 102 obtained in this manner, the oxygen concentration and Vickers hardness at the central part and the outer peripheral part were measured. Regarding the measured value of the oxygen concentration, in the cross section of the spherical sintered body, three arbitrary measurement points were selected from the central portion and the outer peripheral portion, the oxygen concentration at each measurement point was measured with EPMA, and these measured values were averaged. Indicates. Vickers hardness was measured according to JIS R-1610 (test load 98.07 N).

Furthermore, the concentration difference in the amount of metal component of the sintering aid at the center and the outer periphery of each spherical sintered body was also determined. Moreover, about each spherical sintered compact, the defect generation rate by the crack after a sintering and a chip was investigated. These measurement results are shown in Table 5. In each measurement, the sintered body was measured in a state where the burned-up surface was left as it was.

  As can be seen from Table 5, each silicon nitride sintered body according to the example of the present invention has a large difference in oxygen concentration between the central portion and the outer peripheral portion. And since there is little gas component amount which becomes the cause of generation | occurrence | production of a defect in an outer peripheral part, it turns out that the defect generation rate by the crack of a sintered compact, a crack, etc. is low. Furthermore, since there are few defects in the outer peripheral portion, labor and cost required for surface processing can be reduced. In addition, about the silicon nitride sintered compact by each Example, when the total oxygen amount was measured with the oxygen analyzer according to an inert gas fusion-infrared absorption method, all the total oxygen amount was 6 mass% or less.

[Examples 106 to 110 and Comparative Example 103]
Bearing ball balls each having a diameter of 10 mm were produced using the same composition as each of the silicon nitride sintered bodies of Examples 101 to 105 and Comparative Example 101. For sintering of each element ball, HIP treatment was further applied to those sintered in the same manner as in Examples 101 to 105 and Comparative Example 101. For each of these elementary spheres, the oxygen concentration at the three locations of the outer peripheral portion of 30 μm from the surface, the intermediate portion of 1 mm from the surface, and the central portion was measured in the same manner as in Example 101. The results are shown in Table 6. Each elementary sphere was polished to have a diameter of 9.525 mm and a surface roughness Ra of 0.3 μm to obtain finished spheres.

  As is apparent from Table 6, in each bearing ball (finishing ball) according to the embodiment of the present invention, the oxygen concentration decreases from the central portion to the outer peripheral portion, and the oxygen concentration is substantially inclined. I understand.

[Examples 111 to 113 and Comparative Examples 104 to 108]
By applying the same composition and manufacturing method as in Example 107, bearing ball balls each having a diameter shown in Table 7 were produced. Further, for Comparative Example 104, the same composition and manufacturing method as in Example 107 were applied to produce a ball bearing ball having a diameter of 2 mm. As Comparative Examples 105 to 108, the same composition and manufacturing method (without vacuum temperature increase and holding) as in Comparative Example 103 were applied to produce bearing ball base balls having the diameters shown in Table 7, respectively. The oxygen concentration in the outer peripheral part, the intermediate part, and the central part of each elementary sphere was measured in the same manner as in Example 101. Moreover, it measured also about the defect incidence rate of the sintered compact after sintering. As the defect occurrence rate of the sintered body, the ratio of those that could be confirmed visually to have cracks on the surface of the sintered body after sintering was measured. The results are shown in Table 7.

  As is clear from Table 7, it can be seen that a clear difference in oxygen concentration occurs between the central portion and the outer peripheral portion of the ball bearing ball having a diameter of 9 mm or more. And it turns out that these elementary spheres (silicon nitride sintered body) have a low defect occurrence rate. On the other hand, in the ball bearing ball having a diameter of 2 mm, almost no oxygen concentration gradient occurs. This is because in the case of a small ball having a diameter of 2 mm, since the volume of the ball is small, there are relatively few unnecessary gas components present therein, and the effect of the vacuum treatment is small. It can also be seen that bearing ball base balls (silicon nitride sintered bodies) that are not subjected to vacuum treatment as in Comparative Examples 105 to 108 have a high defect occurrence rate. From this, it can be seen that the present invention is particularly effective for bearing balls having a diameter of 9 mm or more.

  In addition, Comparative Example 104, which is an example outside the preferable range of the present invention, is an example showing that the inclination of the oxygen concentration is not observed even when vacuum treatment is performed on a small ball having a diameter of 2 mm. As an example, a bearing ball having a diameter of 2 mm is not excluded from the present invention. For example, as can be seen from comparison between the comparative example 104 and the comparative example 108, it can be said that the comparative example 104 subjected to the vacuum treatment has a smaller defect occurrence rate, and the present invention is effective for a small ball.

[Examples 114 to 115]
5% by mass of yttrium oxide powder, 3% by mass of aluminum oxide powder, 4% by mass of aluminum nitride powder, and titanium oxide with respect to 87.2% by mass of silicon nitride powder having an oxygen content of 0.8% by mass 0.8% by mass of powder was added and mixed to prepare a raw material mixture.

  Next, a predetermined amount of an organic binder was added to and mixed with the obtained raw material mixture, and then spherical molded bodies were produced by the CIP method (molding pressure = 100 MPa). Each obtained compact was degreased in an air stream at 450 ° C., and then subjected to vacuum temperature increase and vacuum treatment under the conditions shown in Table 8. Thereafter, sintering was performed in a nitrogen atmosphere under conditions of 1650 ° C. × 5 hours, and further HIP treatment was performed to obtain bearing balls (silicon nitride sintered bodies) each having a diameter of 15 mm.

With respect to each of the elementary spheres thus obtained, the oxygen concentration at three locations of the outer peripheral portion, the intermediate portion, and the central portion was measured in the same manner as in Example 101. Further, each element ball was polished so that the surface roughness Ra was 0.1 μm, and then an abrasion resistance test was performed. In the abrasion resistance test, a thrust tester shown in FIG. 1 was used, and the time until the surface of the bearing ball was thinned was measured. These results are shown in Table 8.

  As can be seen from Table 8, it can be seen that the bearing ball using the silicon nitride sintered body of the present invention is excellent in wear resistance.

  According to the silicon nitride sintered body constituting the wear-resistant member of the above embodiment, for example, while satisfying various characteristics required for the wear-resistant member, it is possible to reduce the defect occurrence rate and to process it. Costs required can be reduced. Therefore, by using the silicon nitride sintered body according to each embodiment, it is possible to provide a wear-resistant member that is excellent in reliability and life characteristics and that is reduced in manufacturing cost.

Sectional drawing which shows the structure of the thrust type | mold rolling wear test apparatus for measuring the rolling life characteristic of the wear-resistant member obtained by this invention. The figure which shows each area | region where oxygen concentration differs in the silicon nitride sintered compact which comprises the wear-resistant member obtained by this invention in a schematic diagram.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Apparatus body 2 Wear-resistant member 3 Rolling steel ball 4 Guide plate 5 Drive rotary shaft 6 Cage 7 Lubricating oil 8 Rolling ball (made of silicon nitride)
9 Bearing steel plate (SUJ2)
A Center part B Outer part C Middle part

Claims (9)

In the case of silicon nitride powder containing oxygen of 1.5 mass% or less and α-phase type silicon nitride of 75 to 97 mass% and having an average particle size of 1.0 μm or less, rare earth elements are converted into oxides and 1 to 10% by mass, 0.2 to 5% by mass in terms of oxide of at least one of aluminum and magnesium, 5% by mass or less of aluminum nitride, Ti, Hf, Zr, W, Mo, Ta, Nb, A raw material mixture is prepared by converting at least one selected from the group consisting of Cr into an oxide and 0.2 to 5% by mass is added to prepare a molded body, and after degreasing the obtained molded body During sintering, after holding at a temperature of 1250 to 1600 ° C. in a vacuum of 0.01 Pa or less or at a temperature of 1500 to 1600 ° C. for 0.5 to 10 hours in a nitrogen atmosphere, at a temperature of 1650 to 1850 ° C. From the sintering temperature, the main sintering By slowly cooling the sintered body at a cooling rate of 100 ° C./hour or less until the liquid phase formed during sintering with the rare earth element solidifies, the total oxygen is 4.5% by mass or less and the porosity is 0. A method for producing a wear-resistant member made of silicon nitride, characterized by preparing a wear-resistant member made of a sintered silicon nitride having a maximum pore diameter of 5% or less and a grain boundary phase of 0.2 μm or less . The hot isostatic pressing (HIP) treatment is performed on the silicon nitride sintered body at a temperature of 1600 ° C to 1850 ° C in a non-oxidizing atmosphere of 300 atm or higher after sintering. The manufacturing method of the wear-resistant member made from silicon nitride of description. 2. The method for producing a wear-resistant member according to claim 1, wherein the wear-resistant member made of the silicon nitride sintered body is a rolling bearing member. The silicon nitride sintered body is a sintered body containing a small amount of oxygen, and has a low oxygen concentration in which the oxygen concentration is reduced in the range of 0.2% by mass or more and 2% by mass or less compared to the central part. 2. A method for manufacturing a wear-resistant member according to claim 1, wherein an outer peripheral portion is formed. The method for manufacturing a wear-resistant member according to claim 1, wherein the silicon nitride sintered body has a Vickers hardness of Hv 1200 or higher. 5. The method for producing a wear-resistant member according to claim 4 , wherein the outer peripheral portion has a concentration difference of a metal component in the sintering aid with respect to the central portion of less than 0.2% by mass. Manufacturing method of member. 5. The method for manufacturing a wear-resistant member according to claim 4 , wherein an intermediate portion in which the difference in oxygen concentration with respect to the central portion is 1% by mass or less is formed. 5. The method for manufacturing a wear-resistant member according to claim 4 , wherein the wear-resistant member is a bearing ball. 9. The method for manufacturing a wear-resistant member according to claim 8 , wherein a diameter of the bearing ball is 9 mm or more.

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