JP2014073944A - Method of producing silicon nitride sintered body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a silicon nitride sintered body having stable durability in terms of peeling resistance, and imparting low damage to a mating material.SOLUTION: There is provided the method of producing a silicon nitride sintered body containing Mg and at least one kind of rare earth elements. The method includes a raw material powder preparation step of adding a sintering assistant containing Mg and at least one kind of rare earth elements (RE) to a silicon nitride powder having a 50% cumulative particle diameter (d50) of 0.2 to 3 μm and having a relationship (d90-d10)/d50 among the 50% cumulative particle diameter (d50), 10% cumulative particle diameter (d10) and 90% cumulative particle diameter (d90), the relationship (d90-d10)/d50 being in the range of 0.5 to 8, in such a manner that a ratio (RExOy/MgO) in the case of oxide conversion of Mg and at least one kind of rare earth elements (RE) falls within the range of 0.05 to 50 and mixing them to form the raw powder and a sintering step of sintering molded body which is molded by the raw material, under a pressure of 0.2 to 10 MPa and in nitrogen atmosphere.

Description

  The present invention relates to a method for producing a silicon nitride sintered body.

  For example, various roll members such as rolling rolls, conveyance rolls or support rolls used in steel rolling lines, various engine members such as compressors, turbine blades or cam rollers, rolling elements (balls / rollers), inner rings / outer rings, etc. Sliding members are incorporated as rolling bearing members and sliding bearing members. In recent years, for the purpose of extending the life and energy saving, it has been intensively studied to use a silicon nitride sintered body for these sliding members, and examples thereof are disclosed in the following Patent Documents 1 to 4. ing.

  The silicon nitride-based sintered body disclosed in Patent Document 1 is “a silicon nitride sintered body containing silicon nitride particles and a sintering aid component in the range of 2% by mass to 15% by mass, The silicon nitride particles have needle-like crystal particles having a major axis L of 10 μm or less and a ratio of the major axis L to the minor axis S (L / S) of 5 or more in the crystal structure of the silicon nitride sintered body. 50% to 80% in the ratio, the maximum diameter of the voids existing in the silicon nitride sintered body is 3 μm or less, and the number of the voids is 5 or less within the range of 30 × 30 μm ”. Is the body. According to such a silicon nitride sintered body, when this is applied to a sliding member, it is possible to reduce variations in sliding characteristics typified by rolling life and to improve durability and reliability with good reproducibility. It is described.

  The silicon nitride sintered body disclosed in Patent Document 2 is “a silicon nitride sintered body containing silicon nitride crystal particles and a sintering aid component in the range of 2% by mass to 15% by mass. The silicon nitride crystal particles contain 10% or more of needle-like crystal particles having an area ratio of the major axis L to the minor axis S (L / S ratio) of 5 or more, and the L / S ratio of the acicular crystal particles Is an average value of 6-8, the coefficient of variation is 0.8 or more, and the long diameter L of the needle-like crystal particles is 40 μm or less. ” According to such a silicon nitride sintered body, it is described that it is possible to improve the workability and reduce the manufacturing cost while suppressing the deterioration of the sliding characteristics represented by the strength and the rolling life. .

  The silicon nitride sintered body disclosed in Patent Document 3 is “a silicon nitride sintered body obtained by mixing silicon nitride powder produced by a metal nitriding method and a sintering aid, and a rare earth element as a sintering aid component. A silicon nitride sintered body containing 1.5 to 3% by mass of element, 1 to 3% by mass of Al element, and 5% by mass or less of oxygen element, containing 10 to 3000 ppm of Fe as impurities, and 10% of Ca. The silicon nitride sintered body has a Vickers hardness Hv of 1300 to 1600 and a Young's modulus of 290 GPa or more. In the crystal structure of this silicon nitride sintered body, The area ratio of silicon nitride needle crystal grains having a ratio of 2 or more is 50% or more, the maximum length is 40 μm or less, the porosity of the silicon nitride sintered body is 1% or less, and the maximum pore diameter is 3 μm. Hereinafter, the number of pores having a diameter of 1 μm or more remaining in the surface region of 30 × 30 μm after polishing the silicon nitride sintered body is 5 or less, and segregation of the auxiliary component in the crystal structure of the silicon nitride sintered body The maximum diameter of the agglomerated part is 30 μm or less ”. According to such a silicon nitride sintered body, even if it is formed using a low-purity and inexpensive silicon nitride raw material powder, such as silicon nitride powder produced by a metal nitriding method, the auxiliary component It is possible to control the dispersion state of the material, and it can be uniform and variation in grain boundary strength can be reduced. In addition to mechanical strength, wear resistance, and rolling life characteristics equivalent to or better than those of conventional silicon nitride sintered bodies Further, it is described that a silicon nitride sintered body suitable for a rolling bearing member having excellent workability can be constituted.

  The wear-resistant member (sliding member) made of a silicon nitride-based sintered body disclosed in Patent Document 4 is “a silicon powder containing 0.5 to 10% by mass of a rare earth compound converted to an oxide and a titanium compound. Nitriding formed by forming and sintering mixed raw material powder in which 0.1 to 5% by mass in terms of titanium nitride, 0.1 to 5% by mass of aluminum oxide, and 5% by mass or less of aluminum nitride are added. 0.2 to 5% by mass of titanium nitride particles having a silicon sintered body and having a major axis diameter of 1 μm or less, and 80% of the titanium nitride particles having an aspect ratio of 1.0 to 1.2 Including the above, the silicon nitride sintered body has a porosity of 0.5% or less. ” According to the wear-resistant member, in addition to high strength and high toughness, a wear-resistant member having excellent sliding characteristics, particularly a wear-resistant member capable of imparting suitable characteristics to the bearing member by improving the rolling life. It is stated that it can be done.

WO2008 / 111307 gazette JP 2008-285349 A JP 2011-16716 A JP 2011-132126 A

  The conventional silicon nitride sintered bodies exemplified in Patent Documents 1 to 4 are insufficient in terms of surface peeling resistance when applied as a sliding member. For this reason, the durability of the sliding member when viewed from the viewpoint of peeling resistance is not stable, and practically impedes the application of the silicon nitride sintered body as a sliding member in industrial production. It was a factor.

  Furthermore, the conventional silicon nitride sintered body has a problem in terms of wear of the counterpart material. In other words, wear during sliding on the surface of the sliding member is preferentially worn by the grain boundary phase having low hardness, so even if the surface is smooth before use, the grain boundary phase during sliding is preferred. The silicon nitride particles are exposed due to the general wear and the surface is uneven. Here, since the conventional silicon nitride sintered body is mainly composed of acicular silicon nitride particles having a high aspect ratio, the degree of the unevenness becomes rough. For this reason, when applied to a roll for rolling or a roll for conveyance, scratches are generated on the surface of a steel plate or the like which is the counterpart material due to the above-mentioned convex portions, or the above-mentioned concave portions are printed on the surface of the steel plate or the like. There was a problem that. Further, when applied to a rolling element of a rolling bearing, there is a problem that the sliding surface of the inner ring or outer ring which is the counterpart material is worn or damaged, and the life of the bearing is reduced.

  The present invention has been made by the present inventors intensively examining the above-mentioned problems of the prior art, and is stable in terms of durability from the viewpoint of peeling resistance, and in addition, the silicon nitride material having low damage to the counterpart material It aims at providing the manufacturing method of a sintered compact.

  One aspect of the present invention that achieves the above object is a method for producing a silicon nitride-based sintered body containing 0.5 to 20% by mass of Mg and at least one rare earth element in terms of oxides, wherein 50% cumulative particles The diameter (d50) is 0.2 to 3 μm, and is a relationship between the 50% cumulative particle diameter (d50), the 10% cumulative particle diameter (d10), and the 90% cumulative particle diameter (d90) (d90-d10). / Sintering aid containing Mg and at least one rare earth element (RE) in a silicon nitride powder with a d50 of 0.5-8, and Mg and at least one rare earth element (RE) as oxides The ratio (RExOy / MgO) is added so as to be in the range of 0.05 to 5 and mixed to form a raw material powder, and a compact formed from the raw material powder is 0.2 to Nitrogen atmosphere under 10 MPa pressure In a method for producing a raw material silicon nitride sintered body having a firing step of firing.

  In addition, in the said baking process, it is desirable to have the temperature range which heats a molded object for the predetermined time in the range of (H3-200 degreeC)-(H3 + 200 degreeC) with respect to temperature H3 from which the shrinkage rate of a molded object will be 90%. .

  Furthermore, in the said baking process, it has the temperature range which heats a molded object for the predetermined time in the range of (H1-300 degreeC)-(H1-10 degreeC) with respect to temperature H1 which liquid phase conversion of a sintering adjuvant starts. It is preferable.

  In addition, in the firing step, it is more preferable to have a temperature range in which the compact is heated for a predetermined time in a range of H1 to (H1 + 200 ° C.) with respect to the temperature H1 at which the liquid phase of the sintering aid starts.

  According to the silicon nitride sintered body according to the present invention, as will be described in detail below, the durability from the viewpoint of peel resistance is stable, and in addition, the silicon nitride sintered with low damage to the counterpart material A method of manufacturing a body can be provided.

It is a figure which shows the temperature profile in a baking process. It is a figure explaining the method of calculating | requiring the temperature H2 used as the reference | standard of the heating temperature of a 4th temperature range. It is a schematic block diagram of an abrasion testing machine.

The method for producing a silicon nitride sintered body according to the present invention comprises:
(1) A method for producing a silicon nitride sintered body containing 0.5 to 20% by mass of Mg and at least one rare earth element in terms of oxide,
(2) The 50% cumulative particle size (d50) is 0.2 to 3 μm, and the relationship between the 50% cumulative particle size (d50), the 10% cumulative particle size (d10), and the 90% cumulative particle size (d90) (D90-d10) / d50 having a silicon nitride powder with a range of 0.5 to 8,
(3) The ratio (RExOy / MgO) when the sintering aid containing Mg and at least one rare earth element (RE) is converted to an oxide of Mg and at least one rare earth element (RE) is 0.05. A raw material powder adjusting step of adding and mixing to form a raw material powder, and (4) a molded body formed of the raw material powder in a nitrogen atmosphere under a pressure of 0.2 to 10 MPa. This is a method for producing a silicon nitride sintered body having a firing step of firing. Hereinafter, the manufacturing method of the silicon nitride sintered body according to the present invention will be described along the steps.

[Raw material powder adjustment process]
First, the silicon nitride powder will be described. As the silicon nitride powder to be prepared, silicon nitride powder having a particle size distribution in which d50 is 0.2 to 3 μm and (d90−d10) / d50 is in the range of 0.5 to 8 is used. In addition, said d10, d50, and d90 are based on JIS Z 8825-1, and are each 10% cumulative particle diameter in the volume-based cumulative distribution when the particle size distribution of silicon nitride powder is measured with a laser type particle size measuring device. , 50% cumulative particle size, 90% cumulative particle size. Thus, according to the silicon nitride powder having a range of (d90-d10) / d50 of 0.5 to 8, a silicon nitride-based sintered body having a desired long axis length range can be obtained. The desirable range of (d90-d10) / d50 is 1-5.

  The d10 of the silicon nitride powder is desirably in the range of 0.1 to 1 μm. When d10 is less than 0.1 μm, fine particles are relatively increased, and thus abnormal grain growth is likely to occur during sintering, and as a result, coarse pores may be generated in the silicon nitride sintered body. There is. On the other hand, when d10 exceeds 1 μm, the ratio of silicon nitride particles having a relatively large particle size increases, and the strength of the obtained silicon nitride-based sintered body may be reduced. Furthermore, d90 of the silicon nitride powder is desirably in the range of 0.8 to 10 μm. If d90 is less than 0.8 μm, the difference from d50 is small, and the silicon nitride particles are too uniform in size, so that a desired packing density cannot be obtained and coarse pores may be generated. . On the other hand, when d90 exceeds 10 μm, the ratio of silicon nitride particles having a relatively large particle size increases, and the strength of the obtained silicon nitride-based sintered body may be reduced. For the above reasons, more preferable ranges of d10 and d90 of the silicon nitride powder are 0.1 to 0.5 μm and 0.9 to 8 μm, respectively.

  The oxygen content of the silicon nitride powder is 5% by mass or less, more preferably 0.2 to 3% by mass in consideration of the sinterability and the mechanical characteristics of the silicon nitride sintered body. In addition, from the same point of view, the alpha conversion rate, which is the ratio of the α-type silicon nitride particles in the silicon nitride powder, is preferably 60% or more, and more preferably 70% or more. Furthermore, in order to produce a silicon nitride sintered body having desired mechanical properties at a low cost, the silicon nitride powder or the sintering aid may contain 5 to 3000 ppm of an Fe component in terms of Fe element.

  Next, the sintering aid added to the silicon nitride powder will be described. The sintering aid containing at least Mg and at least one rare earth element (RE) is generally used as a compound such as an oxide, oxynitride, carbide, nitride, silicide, or boride of these elements. It is added to the raw material powder in the form of a powder containing Mg (hereinafter sometimes referred to as Mg powder) and a powder containing a rare earth element (hereinafter sometimes referred to as RE powder). The rare earth element (RE) used as the sintering aid is not particularly limited, but Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm , Yb, and Lu can be suitably used, but among these, Y, Ce, Sm, Dy, Er, Yb, and Lu are desirable from the viewpoint of mechanical properties, and Y is particularly desirable from the viewpoint of densification. Most desirable. In addition, it is preferable that the average particle diameter (d50) of Mg powder and RE powder (hereinafter, both may be collectively referred to as a sintering aid powder) is 0.1 to 3 μm.

  Furthermore, in addition to the sintering aid, a metal element (M) may be added to the raw material powder as an additive for improving the mechanical properties of the silicon nitride sintered body. This metal element (M) is also generally a powder as a compound such as an oxide, oxynitride, carbide, nitride, silicide, boride, etc. (hereinafter, a powder containing a metal element may be referred to as M powder). Is added to the raw material powder in the form of The metal element (M) is not particularly limited. For example, hafnium (Hf), titanium (Ti), zirconium (Zr), tungsten (W), molybdenum (Mo), tantalum (Ta), niobium ( Nb) and at least one metal element M selected from chromium (Cr) can be used, and it is particularly preferable to use Ti from the viewpoint of mechanical strength. Moreover, it is preferable that the average particle diameter (d50) of M powder shall be 0.1-3 micrometers.

  Next, an organic binder and a solvent are added to the silicon nitride powder, the sintering aid powder and, if necessary, the M powder, and these are mixed by a mixing device such as a ball mill using a silicon nitride ball to obtain a raw material slurry. Form. In order to improve the dispersibility of the silicon nitride powder and the sintering aid powder in the solvent, a dispersant may be added. Here, the silicon nitride powder and the sintering aid powder are blended so that Mg and the rare earth element are contained in an amount of 2 to 20% by mass in terms of oxide, but the ratio in the case of Mg and rare earth element (RE) in terms of oxide is mixed. Mg powder and RE powder are adjusted so that (RExOy / MgO) is in the range of 0.05 to 5. Thereby, a silicon nitride-based sintered body in which silicon nitride particles having a predetermined size have a desired aspect ratio (L / S) can be obtained.

  In addition, it is desirable to adjust Mg and rare earth elements (RE) to be 0.1 to 15% by mass and 0.1 to 15% by mass, respectively, in terms of oxide. Furthermore, when adding M powder, it is desirable to adjust and mix | blend a metal element (M) so that it may become 0.01-15 mass% in conversion of an oxide.

  As said organic binder, high molecular compounds, such as polyvinyl alcohol, polyvinyl butyral, polyethyleneglycol, methylcellulose, an acrylic resin, can be used individually or in mixture of 2 or more types. Moreover, as a solvent, organic solvents, such as methyl alcohol, ethyl alcohol, and isopropyl alcohol, water (pure water), etc. can be used individually or in mixture of 2 or more types. The raw material slurry is mixed by adding 0.1 to 20 parts by mass of the organic binder and 30 to 1000 parts by mass of the solvent with respect to 100 parts by mass of the total amount of silicon nitride powder and sintering aid powder. Can be obtained.

[Granulation process]
The raw material slurry obtained in the raw material adjustment step is dried by a granulating apparatus such as a spray dryer to form granulated powder.

  The granulated powder formed by the spray dryer or the like is classified by, for example, sieving to form a granulated powder having a predetermined particle size distribution. Here, the average particle size (d50) of the granulated powder is desirably 10 to 300 μm. When the average particle size (d50) is less than 10 μm, the fluidity of the granulated powder is poor and the filling rate into the mold is reduced, and the transferability of the molding pressure is lowered. May not be able to get. On the other hand, when it exceeds 300 μm, the pores formed between the granulated powders become relatively large when the granulated powder is filled in the molding die or the like in the molding process, and as a result, coarse pores are formed. There is a possibility that coarse pores remain in the resulting silicon nitride sintered body. From the same viewpoint, the desirable range of the average particle diameter (d50) of the granulated powder is 20 to 150 μm.

[Molding process to degreasing process]
Using the granulated powder formed in the granulation step, a molded body is formed (molding step). The molding method may be either dry molding or wet molding. For example, the molding can be performed by a dry molding such as a press molding method or CIP (cold isostatic pressing). And the molded object formed at the shaping | molding process is heated in an atmospheric condition, and the organic binder contained in a molded object is removed (degreasing process). In addition, you may process the molded object after a degreasing process as needed, and may adjust a molded object in the shape approximated to the sliding member which is a product.

[Baking process]
The molded body that has undergone the degreasing step is fired in a firing furnace to form a silicon nitride sintered body. As shown in FIG. 1, the firing step of firing the compact to form the silicon nitride sintered body is arranged after the first to sixth temperature regions P1 to P6 and the sixth temperature region P6 which are heating regions. While controlling the temperature with the temperature profile P provided with the cooling region P7, the atmosphere in the furnace is controlled in each of the temperature regions P1 to P6 to form a silicon nitride sintered body. Here, in FIG. 1, the horizontal axis is the elapsed time, the vertical axis is the heating temperature of the firing furnace, and the furnace atmosphere is displayed below the graph. Moreover, although the diagram which shows each temperature range P1-P6 is drawn as a horizontal straight line in FIG. 1, the temperature of each temperature range P1-P6 may change within the allowable temperature range. Hereinafter, the temperature ranges P1 to P7 of the temperature profile P will be described in detail.

[First temperature range]
The first temperature range P1 is heated in a vacuum atmosphere, preferably at a constant temperature, and the molded body is heated to volatilize gasifiable components contained in the molded body. This is a temperature range for suppressing the generation of coarse pores due to the remaining gas. In order to enhance the degassing effect, it is preferable to heat the molded body under a pressure of 50 Pa or less, and the molded body may be heated in a vacuum atmosphere also in the second temperature range P2 described below. In addition, from the same viewpoint, the range of the temperature t1 in the first temperature range P1 is preferably 800 to 1400 ° C., and the heating time is preferably 0.5 to 10 hours. In order to enhance the degreasing effect, the temperature rising rate from room temperature to the first temperature range P1 is preferably 0.2 to 20 ° C./hour.

[Second temperature range]
The second temperature range P2 is a pre-stage of the third temperature range P3 to be described below, preferably by heating the molded body for a certain period of time within a predetermined temperature range while maintaining the temperature at a constant temperature. This is the temperature range to make uniform. Here, in the range of the temperature t2 in the second temperature range P2 set to a temperature exceeding the heating temperature t1 in the first temperature range P1, the liquid phase of the Mg compound added as the sintering aid component starts. The temperature H1 to be set is set as a reference. Specifically, the temperature range is preferably in the range of (H1-300 ° C) to (H1-10 ° C). The temperature H1 varies depending on the particle size and composition of the silicon nitride powder and the sintering aid powder. For example, when the sintering aid is MgO, the temperature H1 is in the range of 1200 to 1700 ° C. Further, in order to make the temperature of the molded body uniform, the heating time in the second temperature range P2 is 0.5 hours or more, and the rate of temperature increase from the first temperature range P1 to the second temperature range P2 is 0. 2 to 20 ° C./hour is preferable. In addition, although the upper limit of heating time is not specifically limited, It is desirable to set it as 5 hours or less from the surface of industrial production cost. Further, the atmosphere in the second temperature range P2 may be a nitrogen atmosphere, but as described above, it is preferable to use a vacuum atmosphere following the first temperature range P1.

[Third temperature range]
The third temperature range P3 is a temperature range set to a temperature at which the Mg compound and RE compound added as a sintering aid component react with SiO ₂ or the like on the surface of the silicon nitride particles to start liquid phase formation. is there. That is, in the third temperature range P3, the temperature of the molded body heated in the second temperature range P2 is increased, and thereafter, the liquid phase of the Mg compound and the RE compound is preferably maintained at a constant temperature. However, by heating the molded body for a certain time in a predetermined temperature range, the liquid phase formation of the Mg compound and the RE compound proceeds uniformly as the entire molded body. Here, as described above, the molded body is heated uniformly in the second temperature range P2, and the effect is also superimposed, and the uniformity of the liquid phase formation of the Mg compound and the RE compound is further enhanced.

  The range of the temperature t3 in the third temperature range P3 set to a temperature exceeding the heating temperature t2 in the second temperature range P2 is set with reference to the temperature H1 at which the liquid phase starts, but the temperature range is , H1 to (H1 + 200 ° C.) is preferable. Furthermore, in order to make the liquid phase uniform, the heating time of the third temperature range P3 is set to a range of 0.5 to 10 hours, and the rate of temperature increase from the second temperature range P2 to the third temperature range P3 is 0.2 to 20 ° C./hour is preferable.

  The atmosphere in the third temperature range P3 may be a vacuum atmosphere in order to obtain the effect of degassing, but it reduces the decomposition of the silicon nitride particles and suppresses the evaporation of the liquid phase Mg compound having a low vapor pressure. In order to prevent generation of coarse pores, a nitrogen atmosphere is preferable. The pressurizing condition is preferably 0.2 to 10 MPa, more preferably 1 to 10 MPa, including the fourth to sixth temperature ranges P4 to P6 described below. The reason will be described later.

[Fourth temperature range]
The fourth temperature range P4 is a temperature range in which rearrangement of the silicon nitride particles is promoted in the liquid phase of the liquid phase Mg compound and RE compound. By providing the fourth temperature range P4, in the molded body that contracts in the liquid phase, the silicon nitride particles are formed before the grain growth of the silicon nitride particles in the fifth temperature range P5 and the sixth temperature range P6 described below. Rearrangement is promoted in the liquid phase. As a result, the resulting silicon nitride sintered body is improved in density, resulting in a silicon nitride sintered body with fewer coarse pores and further improved pore dispersibility. It is formed.

  Here, the range of the temperature t4 in the fourth temperature range P4 set to a temperature exceeding the heating temperature t3 in the third temperature range P3 is the amount of change in shrinkage rate per unit temperature in the heated molded body. The temperature H2 at which a certain shrinkage rate (unit:% / ° C) is the highest is set as a reference, and the temperature range is desirably (H2-50 ° C) to (H2 + 50 ° C), preferably constant. It is desirable to heat while maintaining this temperature. Further, in order to sufficiently rearrange the silicon nitride particles, the heating time of the fourth temperature range P4 is set to a range of 1 to 10 hours, and the temperature rise from the third temperature range P3 to the fourth temperature range P4. The speed is preferably 0.2 to 20 ° C./hour. For the same reason as in the third temperature range P3, the atmosphere in the fourth temperature range P4 is preferably a nitrogen atmosphere. Further, the pressurizing condition is preferably 0.2 to 10 MPa, and more preferably 1 to 10 MPa.

  In the present invention, the temperature H2 at which the shrinkage rate of the heated molded body is highest is obtained by the following method. Since this temperature H2 varies depending on the specifications or blending ratio of the silicon nitride powder and the sintering aid powder, as shown in the conceptual diagram of FIG. 2, the temperature range t3 of the third temperature range P3 to the sixth temperature range P6. The range of t6 is divided into 10 and the temperatures ta to ti are selected. And after omitting the said 1st temperature range P1 and the 2nd temperature range P2, it heats a molded object to the temperature ta-ti selected in 0.2 MPa nitrogen atmosphere, and furnace-cools after that, and is obtained. The linear shrinkage rate of the molded body was measured. And as shown in FIG. 2, let the temperature of the point with the largest inclination among the diagrams which plotted the correlation of heating temperature and shrinkage | contraction rate be H2. In addition, if the usable temperature of the linear dilatometer is within the range of t3 to t6, the above H2 creates a diagram in which the correlation between the heating temperature and the shrinkage rate is plotted using the linear dilatometer, and has the highest inclination. The temperature at a large point may be H2.

[Fifth temperature range]
The fifth temperature range P5 is a final stage of the heating zone, which is the last stage of the sixth temperature range P6, which will be described below, desirably heating the molded body for a predetermined time in a predetermined temperature range while maintaining a constant temperature, This is a temperature range where the body contraction is uniform throughout. By providing the fifth temperature range P5 in the preceding stage of the sixth temperature range P6, it is possible to form a silicon nitride-based sintered body that is more dense and has fewer coarse pores.

  Here, the range of the temperature t5 of the fifth temperature range P5 set to a temperature exceeding the heating temperature t4 of the fourth temperature range P4 is based on the temperature H3 at which the contraction rate of the heated molded body is 90%. However, it is desirable that the temperature range be in the range of (H3−200 ° C.) to (H3 + 200 ° C.), and it is desirable to heat while maintaining a constant temperature. The temperature H3 at which the contraction rate of the heated molded body becomes 90% can be obtained in the same manner as in the fourth temperature range P4. Further, for uniform shrinkage of the molded body, the heating time of the fifth temperature range P5 is set to a range of 0.1 to 10 hours, and the rate of temperature increase from the fourth temperature range P4 to the fifth temperature range P5. Is preferably 0.2 to 20 ° C./hour. Similarly to the above, the atmosphere in the fifth temperature range P5 is preferably a nitrogen atmosphere. The pressurizing condition is preferably 0.2 to 10 MPa, and more preferably 1 to 10 MPa.

[6th temperature range]
The sixth temperature range P6, which is the final stage of the heating range, is a temperature range in which the phase transition of the silicon nitride particles to the β phase is completed and densification is completed. Here, the heating temperature t6 and the heating time in the sixth temperature range P6 set to a temperature exceeding the heating temperature t5 in the first temperature range P5 are the sizes of the silicon nitride particles contained in the obtained silicon nitride-based sintered body. The heating temperature is suitably set to 1500 to 2000 ° C. in consideration of the influence on the characteristics of the silicon nitride sintered body, such as the formation of pores due to the sheath ratio or the volatilization of the sintering aid. The heating time is preferably in the range of 0.1 to 20 hours, and it is preferable to heat while maintaining at a constant temperature. Similarly to the above, the atmosphere in the sixth temperature range P6 is preferably a pressurized nitrogen atmosphere. The pressurizing condition is preferably 0.2 to 10 MPa, and more preferably 1 to 10 MPa.

[Cooling area]
The cooling region P7 is a temperature region in which the liquid phase formed through the heating regions P1 to P6 is solidified to form a grain boundary phase. In order to suppress crystallization of the sintering aid component and to form a grain boundary phase mainly composed of the glass phase, the cooling rate of the cooling zone P7 is preferably 0.2 ° C./hour or more. As a result, the area ratio in the grain boundary phase existing in the silicon nitride-based sintered body can be 97% or more as the glass phase, and the silicon nitride-based sintered body excellent in mechanical characteristics, particularly wear resistance. Can be obtained.

According to the method for producing a silicon nitride-based sintered body according to the above embodiment, a silicon nitride-based sintered body containing 0.5 to 20% by mass of Mg and at least one rare earth element in terms of oxide, The ratio (RExOy / MgO) when having a grain boundary phase containing silicon particles and Mg and at least one kind of rare earth element, and each of Mg and rare earth element (RE) in terms of oxide is 0.05 to The average value of the major axis length L of silicon nitride particles existing in a 20 × 20 μm region arbitrarily set on the processed surface is 5.0 μm or less, and the major axis length L with respect to the minor axis length S is The average value of the ratio (L / S) is 5 or less, and in an area of 300 × 300 μm arbitrarily set on the processed surface, pores each having an area of 0.01 μm ² or more are 0.01 to ² in area ratio. 5%, the most adjacent among the pores It is possible to obtain a silicon nitride sintered body in which the average value of the distance between the centers of gravity of the pores in contact is 5 μm or more and the variation coefficient of the distance between the centers of gravity is 1.5 or less. Hereinafter, a specific configuration of the silicon nitride sintered body that can be obtained by the method for manufacturing a silicon nitride sintered body according to the present invention will be described.

  The silicon nitride sintered body obtained by the above production method contains 0.5 to 20% by mass of Mg and at least one rare earth element (RE) in terms of oxides, and includes silicon nitride particles, the Mg and at least one kind. It has a grain boundary phase containing rare earth elements (RE).

  Here, the silicon nitride-based sintered body is a sintered body mainly composed of silicon nitride. The silicon nitride-based sintered body that can be effectively used for constituting the sliding member is desirably a high-density sintered body having a relative density of 90% or more, preferably 95% or more. When the relative density is less than 90%, it is not preferable as a sliding member requiring high sliding characteristics.

  Magnesium (Mg) and rare earth elements (RE) as sintering aid components are main components constituting the grain boundary phase. The total content of Mg and rare earth element (RE) in the silicon nitride sintered body is in the range of 0.5 to 20% by mass in terms of oxide. When the total content is less than 0.5%, the proportion of the grain boundary phase that functions to bond silicon nitride particles is small, the densification is insufficient, and the relative density is lowered. When this is applied as a sliding member, the desired peel resistance cannot be satisfied. On the other hand, in the case of 20% or more, since the ratio of the grain boundary phase to the silicon nitride particles is increased, the strength and hardness of the silicon nitride sintered body is lowered, and when this is applied as a sliding member Similarly, the desired peel resistance cannot be satisfied. In addition, it is preferable that content of Mg is the range of 0.1-15 mass%. Further, the rare earth element (RE) content in the silicon nitride sintered body is preferably in the range of 0.1 to 15% by mass.

  Furthermore, the aspect ratio of the silicon nitride particles described below is realized by setting the ratio (RExOy / MgO) when Mg and rare earth elements (RE) are converted to oxides in the range of 0.05 to 5. .

  The silicon nitride sintered body obtained by the above manufacturing method has an average value of the major axis length L of silicon nitride particles existing in a 20 × 20 μm region arbitrarily set on the processed surface, of 5.0 μm or less, The average value of the ratio (L / S) of the major axis length L to the minor axis length S is 5 or less. Thus, the silicon nitride sintered body according to the present invention is composed of silicon nitride particles having the long axis length L and the average value of the aspect ratio (L / S) in the above range. Thereby, this silicon nitride sintered body reduces the size of the pores present therein, and also uniformizes the dispersed state of the pores to suppress the generation of adjacent pores.

That is, in the silicon nitride sintered body, among pores existing in a 300 × 300 μm region arbitrarily set on the processed surface, pores each having an area of 0.01 μm ² or more are 0.01 by area ratio. Contains ~ 5%. The pores having this area are pores that may become a starting point of destruction when the silicon nitride sintered body is applied as a sliding member. By making the area ratio 5% or less, the silicon nitride The strength of the sintered material is ensured. In order to obtain a silicon nitride sintered body having an area ratio of pores of less than 0.01%, an operation such as HIP treatment is required for increasing the density, and the manufacturing cost of the silicon nitride sintered body is high. Become. Furthermore, when high pressure is applied in the firing process, a dense portion of pores is likely to be formed, and this dense portion apparently behaves as one large void, so that the silicon nitride sintered body having the dense portion is slid. When used as a member, cracks may occur starting from this dense portion, and peeling may occur.

  Further, in the silicon nitride sintered body, the average value of the distance between the centers of gravity of the pores adjacent to each other among the pores is 5 μm or more, and the variation coefficient of the distance between the centers of gravity is 1.5 or less. In the silicon nitride sintered body according to the present invention, the pores having such a size that can be the starting point of the fracture are uniformly distributed in a state where they are dispersed at a certain distance. As a result, when this silicon nitride-based sintered body was applied as a sliding member, the adjacent pores apparently formed one large pore and suppressed from becoming the starting point of destruction, and applied as a sliding member. In this case, it is possible to ensure the peel resistance in the case. The coefficient of variation can be obtained by dividing the standard deviation of the distance between the centers of gravity of the most adjacent pores by the average value.

  In addition, the silicon nitride sintered body obtained by the above manufacturing method is mainly composed of silicon nitride particles having a long axis length and an average aspect ratio in the above range. There is less unevenness on the surface. As a result, when the silicon nitride sintered body according to the present invention is applied as a sliding member, wear of the counterpart material sliding with the sliding member is suppressed.

In the present invention, the area of pores existing in a 300 × 300 μm region on the processed surface, the area ratio in the region, and the distance between the centers of gravity of adjacent pores are measured by the following procedure. First, when the silicon nitride sintered body has a sintered skin, the surface is ground with a # 180 diamond grindstone to remove the sintered skin to obtain a processed skin. Next, the processed skin is lapped with diamond abrasive grains having an average particle size of 1 μm or less so that the surface roughness (Rz) specified in JIS B0601 is 0.07 μm or less. Any three places on the surface after lapping are imaged with an SEM or a laser microscope. Next, an image of pores existing in a 300 × 300 μm region of the photographed photograph is specified, the area is obtained by image processing, and the area ratio in the region of pores having an area of 0.01 μm ² or more is obtained. Then, the center of gravity of those pores is obtained by image processing, the distance between the centers of gravity of the most adjacent pores is calculated, and the average value and standard deviation are obtained. Note that pores partially included in the 300 × 300 μm region are excluded from the objects of confirmation.

  In the present invention, the major axis length L and the aspect ratio (L / S) of the silicon nitride particles are measured by the following procedure. First, the surface after the lapping is plasma etched, and then the plasma-etched surface is imaged with an SEM or a laser microscope at any three locations on the surface of the silicon nitride sintered body. The major axis length L and minor axis length S of silicon nitride particles present in a 20 × 20 μm region of the photographed image are measured. The major axis length L refers to the size of the longest portion of the silicon nitride particles, and the minor axis length S refers to the size of the shortest portion of the silicon nitride particles. And the average value of the major axis length L and aspect ratio (L / S) of a silicon nitride particle is calculated | required from these measurement results. Here, the silicon nitride particles that are partially included in the periphery of the 20 × 20 μm region are excluded from the objects of confirmation.

  In order to further improve the peel resistance and further reduce the wear resistance of the counterpart material, the major axis length L of the silicon nitride particles is 1. in a 20 × 20 μm region arbitrarily set on the processed surface. In the region of 300 × 300 μm arbitrarily set on the processed surface containing 50 to 150 silicon nitride particles of 0 to 4.0 μm and an aspect ratio (L / S) of 4 or less, the area ratio of the pores Is 0.01 to 2%, the average value of the distance between the centers of gravity is preferably 5 to 425 μm, and the coefficient of variation of the distance between the centers of gravity is preferably 0.5 to 1.5.

  In addition, when a dense part having a distance between the centers of gravity of the pores of less than 5 μm is present, the diameter of the surrounding circle of the dense part is preferably 5 to 40 μm. In this way, when there are dense pores on the surface of the silicon nitride sintered body having a distance between the centers of gravity of less than 5 μm, adjacent pores apparently constitute one pore, and the silicon nitride sintered When the body is applied as a sliding member, the dense portion is highly likely to be a starting point of destruction. Therefore, in the silicon nitride-based sintered body according to the present invention, by setting the diameter of the surrounding circle surrounding the dense portion to 40 μm or less, the dense portion is prevented from starting to break down, and the silicon nitride-based sintered body is suppressed. The strength of the knot is further improved. The encircling circle of the dense part is defined as a circle having the smallest diameter including the pores constituting the dense part. Further, the lower limit of the diameter of the dense portion is not particularly limited, but when it is less than 5 μm, an operation such as HIP treatment is required for increasing the density, and as described above, the manufacturing cost is increased and the peel resistance is increased. descend. Therefore, the lower limit of the diameter of the dense part is preferably 5 μm or more.

  Furthermore, the silicon nitride sintered body may contain 5 to 3000 ppm of an iron (Fe) component in terms of Fe element. Here, the Fe component refers to a component containing Fe as an element, such as an Fe compound such as iron oxide or iron nitride. This Fe component is usually derived from impurities contained in the silicon nitride powder or sintering aid powder as a raw material, but may be added as necessary. Here, when the Fe component is less than 3 ppm in terms of Fe element, high-purity silicon nitride powder or sintering aid powder is required, and the production cost of the silicon nitride-based sintered body increases. On the other hand, if it exceeds 3000 ppm, the desired mechanical properties of the silicon nitride sintered body cannot be satisfied, and if this is applied as a sliding member, the sliding properties may not be realized. There is. Here, the Fe component contained in the silicon nitride-based sintered body easily forms a segregation part that becomes a starting point of fracture, and lowers the peel resistance when applied as a sliding member. However, as will be described below, in the silicon nitride sintered body according to the present invention, by controlling the size and dispersion state of the segregation part and optimizing them, the decrease in peel resistance is suppressed. Yes.

  That is, in the silicon nitride sintered body containing the Fe component, 5 to 50 Fe segregation portions having a maximum diameter of 0.1 to 10 μm in a measurement region of 200 × 200 μm arbitrarily set on the processed surface. In addition, the average value of the distance between centroids between adjacent Fe segregation parts is 5 μm or more, and the variation coefficient of the distance between centroids is 1.2 or less. Here, when the maximum diameter of the Fe segregation portion is less than 0.1 μm, or the number thereof is less than 5, it is necessary to use high-purity silicon nitride raw material powder or sintering aid powder, which is disadvantageous in terms of cost. It becomes. On the other hand, when the maximum diameter of the Fe segregation part exceeds 20 μm or the number thereof exceeds 50, the strength is reduced, and the fracture starting from the Fe segregation part is likely to occur.

  In addition, content of the said Fe component can be measured in the following procedures. First, after the silicon nitride sintered body is finely pulverized and powdered, hydrofluoric acid or the like is added and heated to about 180 ° C. in a pressure vessel to form a solution. Next, after rinsing off hydrofluoric acid with sulfuric acid, the solution is subjected to ICP emission analysis to determine the content of Fe component.

  Here, as described above, the silicon nitride sintered body produced by the production method according to the present invention is mainly composed of silicon nitride particles having the major axis length and the average aspect ratio in the above range. In addition, the Fe segregation part is also uniformly arranged in a state of being separated by a certain distance. That is, in the silicon nitride sintered body of this preferred embodiment, in the 200 × 200 μm measurement region arbitrarily set on the processed surface, the average distance between the centers of gravity between the most adjacent Fe segregation portions among the Fe segregation portions The value is 5 μm or more, and the variation coefficient of the distance between the centers of gravity is 1.2 or less. Thereby, it is suppressed that the adjacent Fe segregation part becomes one Fe segregation part apparently and becomes the starting point of fracture, and as a result, a silicon nitride-based sintered body with higher peeling resistance is configured.

  In addition to the Mg, rare earth elements and Fe components, the silicon nitride sintered body includes hafnium (Hf), titanium (Ti), zirconium (Zr), tungsten (W), molybdenum (Mo), tantalum (Ta). ), Niobium (Nb), and chromium (Cr), at least one metal element (M) may be contained as a simple metal element or as a compound of the metal element. These metal components (M) are arbitrarily added as additives for improving the mechanical properties of the silicon nitride sintered body.

  Here, the metal component (M) is an element that is optionally added. By dispersing the M compound in the silicon nitride sintered body, the mechanical strength of the silicon nitride sintered body is improved. It is possible to improve the sliding characteristics when applied as a sliding member. Of the metal elements (M), titanium (Ti) is preferably applied particularly from the viewpoint of mechanical properties. The content of the metal element M in the silicon nitride sintered body is preferably in the range of 0.01 to 15% by mass in terms of the metal element (M) in terms of oxide. If the content of the metal element M exceeds 15% by mass, the mechanical strength may decrease. On the other hand, when the amount is less than 0.01% by mass, the effect of improving the mechanical strength may not be obtained.

  Thus, when the metal element (M) is contained in an amount of 0.01 to 15% by mass in terms of an oxide, a segregated part (hereinafter referred to as an M segregated part) segregated with the metal component (M) as a main component. .) May be generated, and the silicon nitride sintered body may be destroyed starting from the M segregated portion. Therefore, in the silicon nitride-based sintered body according to a preferred embodiment, in a 40 × 40 μm region arbitrarily set on the processed surface, the M segregation portion includes 50 or less M segregation portions having a maximum diameter of 5 μm or less. The average value of the distance between the centers of gravity between the most adjacent M segregating parts is 2 μm or more, and the coefficient of variation of the distance between the centers of gravity is 1.5 or less. Here, when the maximum diameter of the M segregation part exceeds 5 μm or the number thereof exceeds 50, the strength is reduced, and the breakage starting from the M segregation part is likely to occur. On the other hand, the maximum diameter and the lower limit of the number of M segregation parts are not particularly limited, but in order to produce a silicon nitride sintered body having a maximum diameter of less than 0.05 μm, the particle diameter is very fine. It is necessary to improve the dispersibility of the raw material powder in the silicon nitride powder and the addition of the raw material powder, which is disadvantageous in terms of industrial production. Therefore, the lower limit of the maximum diameter of the M segregation part is preferably 0.05 μm. Further, the lower limit of the number of M segregation parts is desirably two for the same reason.

  In the present invention, the maximum diameter and the number of the Fe segregation part and the M segregation part are confirmed by the following procedure. First, a 200 × 200 μm or 40 × 40 μm region arbitrarily set on the processed surface of the silicon nitride-based sintered body is subjected to surface analysis with EPMA, and Fe and a predetermined metal element (M ) Distribution. Of the Fe segregation part and M segregation part present in the surface analysis image, the number of those having the maximum diameter in a predetermined range is measured. Note that the maximum diameters of the Fe segregation part and the M segregation part refer to the maximum diameter of each Fe segregation part and M segregation part. Next, only the Fe segregation part and M segregation part having the maximum diameter in the above range are specified, the center of gravity is obtained by image processing, the distance between the center of gravity of the most adjacent Fe segregation part and M segregation part is calculated, and the average Find the value and coefficient of variation. Here, the Fe segregation part and the M segregation part partially included in the periphery of the region are excluded from the objects of confirmation.

  In the silicon nitride sintered body produced by the production method according to the present invention, the phase present at the grain boundary between the silicon nitride particles is preferably mainly a glass phase. Specifically, it is preferable that the ratio of the crystal phase existing at the grain boundary between the silicon nitride particles is less than 3% by area ratio and 97% or more is the glass phase. By constituting the phase present at the grain boundary between the silicon nitride particles mainly with the glass phase, it is possible to improve the peel resistance as the sliding member. Here, in the present invention, the crystal phase refers to a material containing an Fe component or a metal element (M) as a main component and existing at a grain boundary between silicon nitride particles separately from the glass phase.

  In the present invention, the area ratio of the glass phase existing at the grain boundary between the silicon nitride particles is determined by the following procedure. First, the processed surface is analyzed by X-ray diffraction to identify the composition of the crystal phase. Subsequently, about the element which comprises the crystal phase which identified the composition as mentioned above, a 200 * 200 micrometer area | region is surface-analyzed by EPMA, The distribution of the said element is confirmed based on the image of the surface analysis. Based on the results of this surface analysis, the area of the crystal phase containing the element is obtained. Further, the 200 × 200 μm region is imaged by SEM, and the areas of the glass phase and the crystal phase existing at the grain boundaries are obtained. The value (100 fraction) obtained by subtracting the area of the crystal phase from the total area of both and dividing by the total area is defined as the area ratio (%) of the glass phase.

[Example]
Hereinafter, the present invention will be specifically described based on Examples 1 to 24 and Comparative Examples 1 to 6. In addition, this invention is not limited to Examples 1-24.

  First, Examples 1-12 and Comparative Examples 1-6 will be described. In Examples 1 to 12 and Comparative Examples 1 to 6, a silicon nitride-based sintered body was manufactured by the method described below, and the state of the silicon nitride particles and pores, as well as the peel resistance and the wear resistance of the counterpart material were evaluated. Went.

In each of the examples and comparative examples, magnesium oxide was used for silicon nitride powder having d10 to d90 and (d90-d10) / d50, oxygen content of 1.5%, Fe content of 300 ppm, and α conversion of 97% shown in Table 1. (MgO), yttrium oxide (Y ₂ O ₃ ), cesium oxide (Ce ₂ O ₃ ), or erbium oxide (Er ₂ O ₃ ) in a powder state added in a proportion shown in Table 1 to 100 parts by mass of the raw material powder On the other hand, 2 parts by weight of polyvinyl butyral as an organic binder and 100 parts by weight of ethyl alcohol as an organic solvent were placed in a resin-lined container and mixed with a silicon nitride ball in a ball mill for 24 hours to prepare a raw material slurry. . The average particle size (d50) of each powder of magnesium oxide (MgO), yttrium oxide (Y ₂ O ₃ ), cesium oxide (Ce ₂ O ₃ ) and erbium oxide (Er ₂ O ₃ ) added as a powder is 1.2 μm.

  In each Example and Comparative Example, after adjusting the viscosity of the obtained raw material slurry, it was dried with a spray dryer to form granulated powder. The obtained granulated powder was classified by sieving and adjusted so as to be a granulated powder having an average particle size (d50) of 80 μm. Then, the granulated powder was press-molded at a molding pressure of 200 MPa to produce a large number of disk-shaped molded bodies having a diameter of 80 mm and a thickness of 6 mm.

The molded body was degreased by heating at 700 ° C. for 12 hours in the air, and then sintered in a sintering furnace at the temperature and atmosphere pattern shown in FIG. 1, and the diameter was 64 to 66 mm and the thickness was 4.8. A number of test pieces made of a silicon nitride-based sintered body in a range of ˜5 mm were prepared. The furnaces in the second temperature range P2 to the sixth temperature range of the second temperature range P2, the fourth temperature range P4, the fifth temperature range P5, the temperatures t2, t4, and t5 and the respective heating times and the nitrogen atmosphere. The pressure was set as shown in Table 1. The sintering conditions other than the above are as follows. The rate of temperature increase between the temperature ranges was 2.0 ° C./hour.
(1) First temperature range P1 Temperature t1: 900 ° C., heating time: 2 hours, atmosphere: vacuum, pressure: 10 Pa
(2) Second temperature region P2 Temperature t2 and heating time: shown in Table 1 (3) Third temperature region P3 Temperature t3: 1300 ° C., Heating time: 1 hour (4) Fourth temperature region P4 Temperature t4: Table 1 Heating time: 2 hours (5) 5th temperature range P5 Temperature t5 and heating time: shown in Table 1 (6) 6th temperature range P6 Temperature t6: 1850 ° C., heating time: 3 hours (7) 7th Temperature range P7 Cooling rate: 0.5 ° C / hour

The front and back surfaces of the test pieces of each Example and Comparative Example were ground with a # 180 diamond grindstone to a thickness of 4.2 mm to remove the sintered skin to obtain a processed skin, and then the surface defined in JIS B0601 The processed skin was lapped with diamond abrasive grains having an average particle size of 1 μm or less so that the roughness (Rz) was 0.07 μm or less. Any three places on the surface after the lapping are picked up with an SEM or a laser microscope, an image of pores existing in a 300 × 300 μm region of the photographed photo is specified, the area is obtained by image processing, and the area is 0 The area ratio in the region of pores of 0.01 μm ² or more was determined. Then, the center of gravity of those pores was obtained by image processing, the distance between the centers of gravity of the most adjacent pores was calculated, and the average value, standard deviation, and the diameter of the surrounding circle when there was a dense portion were obtained. Note that pores partially included in the 300 × 300 μm region were excluded from the objects of confirmation. The results are shown in Table 2.

  Furthermore, the surface of the test piece after the lapping was plasma etched, and then the plasma etched surface was imaged with an SEM or a laser microscope at any three locations on the surface of the silicon nitride sintered body. The major axis length L and minor axis length S of silicon nitride particles existing in a 20 × 20 μm region were measured. From these measurement results, the average value of the major axis length L and the aspect ratio (L / S) of the silicon nitride particles, the major axis length L is 1.0 to 4.0 μm, and the aspect ratio (L / S) is 4. The number of predetermined silicon nitride particles as follows was determined. Note that the silicon nitride particles partially contained in the 20 × 20 μm region were excluded from the objects of confirmation. The results are shown in Table 2.

  In the present invention, the peel resistance shown in Table 2 and the wear resistance of the mating material were confirmed using the test apparatus 10 shown in FIG. The test apparatus 10 includes a disk-shaped test piece 12 arranged in the apparatus main body 11, a plurality of rolling steel balls 13 arranged on the upper surface of the test piece 12, and an upper part of the rolling steel balls 13. The guide plate 14 is arranged, a drive rotary shaft 15 connected to the guide plate 14, and a cage 16 that regulates the arrangement interval of the rolling steel balls 13. The apparatus main body 11 was filled with lubricating oil 17 for lubricating the rolling part. The rolling steel balls 13 and the guide plate 14 were made of high carbon chrome bearing steel (SUJ2) defined by Japanese Industrial Standard (JIS G 4805). As the lubricating oil 17, a paraffinic lubricating oil (viscosity at 40 ° C .: 67.2 mm 2 / S) was used. The test piece 12 was the same as the test piece for measuring silicon nitride particles and pores, and was processed under the same conditions as those before the measurement of the silicon nitride particles and pores.

  The conditions at the time of evaluating the peel resistance of the disk-shaped test piece according to the present example and the comparative example and the degree of wear of the counterpart material were as follows. Three SUJ2 rolling steel balls having a diameter of 9.35 mm are arranged as mating members on a 40 mm diameter track set on the upper surface of the test piece 12, The rolling steel ball 13 was rotated under the condition of a rotational speed of 1200 rpm with a load of 39.2 MPa applied. And about peeling resistance, the time until the surface of the test piece 12 peels is calculated | required, and when it is less than 100 hours, it is "x", when it is 100 hours or more and less than 700 hours, "(triangle | delta)", 700 hours Above, less than 2000 hours were evaluated as “◯”, and over 2000 hours were evaluated as “◎”. Table 2 shows the evaluation results of the peel resistance of each example and comparative example.

  Moreover, the conditions at the time of evaluating the wear resistance of the counterpart material which concerns on a present Example and a comparative example made the rolling steel ball 13 rotate for 500 hours on the conditions similar to the above and the peeling resistance evaluation method. The wear resistance of the mating material was evaluated as follows. The diameter of the rolling steel balls before and after the test is measured at 10 locations with a micrometer. And when it is set as the average value D1 of the diameter of 10 places obtained with the rolling steel ball before a test, and the smallest diameter among the diameters of 10 places obtained with the rolling steel ball after the test is set to the minimum diameter D2. Degree of wear (%) = ((D1−D2) / D1 × 100), the wear resistance of the counterpart material was evaluated. Here, when the degree of wear was 0.01% or more, “x”, 0.005 % Or less and less than 0.01% were evaluated as “△”, 0.001% or more and less than 0.005% as “◎”, and less than 0.001% as “「 ”. The evaluation results of the wear properties of the counterpart materials of the examples and comparative examples are shown in Table 2. In addition, the wear properties of the counterpart materials were not confirmed for samples in which the test piece peeled off in less than 100 hours.

According to Examples 1-12, the silicon nitride-based sintered body obtained by producing the particle size distribution of silicon nitride particles, the mixing ratio of Mg and rare earth elements and the pressure in the firing step within the scope of the present invention. The average value of the major axis length L of silicon nitride particles existing in a 20 × 20 μm region arbitrarily set on the processed surface of a certain test piece is 5.0 μm or less, and the ratio of the major axis length L to the minor axis length S ( L / S) has an average value of 5 or less, and in an area of 300 × 300 μm arbitrarily set on the processed surface, pores each having an area of 0.01 μm ² or more are 0.01 to 5% by area ratio. And a silicon nitride sintered body of a silicon nitride sintered body in which the average value of the distance between the centers of gravity of the pores adjacent to each other among the pores is 5 μm or more and the variation coefficient of the distance between the centers of gravity is 1.5 or less Could get. As a result, the peel resistance of the silicon nitride sintered body and the wear resistance of the counterpart material were both good.

  Furthermore, in each of Examples 1 to 12, the ratio (RExOy / MgO) in the case of converting each of Mg and rare earth elements (RE) into oxides was in the range of 0.05 to 5, and was additionally processed. In a 20 × 20 μm region arbitrarily set on the surface, it contains 50 to 150 silicon nitride particles having a major axis length L of 1.0 to 4.0 μm and an aspect ratio (L / S) of 4 or less. In the 300 × 300 μm region arbitrarily set on the formed surface, the area ratio of the pores is 0.01 to 2%, the average value of the distance between the centroids is 5 to 425 μm, and the variation in the distance between the centroids The coefficient was 0.5 to 1.5.

  On the other hand, in Comparative Examples 1 to 6 in which the particle size distribution of silicon nitride particles, the blending ratio of Mg and rare earth elements, and the pressure in the firing process were manufactured outside the scope of the present invention, the test that is the obtained silicon nitride sintered body The shape (major axis length / aspect ratio) of the piece of silicon nitride particles or the area ratio / dispersion state of the pores are poor, and therefore the peeling resistance and the wear resistance of the counterpart material are lower than those of Examples 1-12. It was.

  Next, Examples 13 to 24 will be described. In Examples 13 to 24, a silicon nitride-based sintered body was manufactured by the same production method as in Examples 1 to 12 except that the level of Fe content in the silicon nitride powder as a raw material was changed. The silicon nitride particles and the generation state of the Fe segregation part, the peel resistance, and the wear resistance of the counterpart material were evaluated.

In each of the examples and comparative examples, magnesium oxide (MgO) and yttrium oxide (Y ₂ O ₃ ) were respectively added to the silicon nitride powders having d10 to d90 and (d90-d10) / d50 and Fe content shown in Table 3. The raw material powder added in the ratio shown in Table 2 in the state of powder was prepared, and the raw material slurry was produced on the same conditions as the said Examples 1-12. Then, using this raw material slurry, a disk-shaped molded body having a diameter of 80 mm and a thickness of 6 mm is prepared under the same conditions as in Examples 1 to 12, and the molded body is sintered to sinter silicon nitride. A number of test pieces made of ligations were prepared.

  About the obtained test piece, it processed similarly to the said Examples 1-12, and calculated | required the long axis length L and the short axis length S, the aspect-ratio (L / S), and pore distribution of the silicon nitride particle | grains after that. Furthermore, peeling resistance and wear resistance of the counterpart material were evaluated using the test piece. In addition, as shown in Table 4, the pore size distribution (area ratio, etc.) is the same as that in Examples 1 to 12, in which the particle size distribution of silicon nitride particles, the mixing ratio of Mg and rare earth elements, and the pressure in the firing step are the same. It was almost the same.

  Here, in Examples 13 to 24, the distribution of the Fe segregation part was confirmed. On the surface of the test piece processed in the same manner as in Examples 1 to 12, a 200 × 200 μm region set arbitrarily was subjected to surface analysis with EPMA, and the distribution of Fe was confirmed based on the image of the surface analysis. And the number whose maximum diameter is 0.1-10 micrometers among the Fe segregation part which exists in the image of this surface analysis was measured. Next, only the Fe segregation part having the maximum diameter in the above range was specified, the center of gravity was determined by image processing, the distance between the center of gravity of the most adjacent Fe segregation parts was calculated, and the average value and coefficient of variation were determined. The results are shown in Table 4. In addition, the Fe segregation part partially contained in the 200 × 200 μm region was excluded from confirmation.

  According to Examples 13 to 24, even when the Fe component is 3000 ppm or less and the Fe component has a segregated Fe part, the maximum is obtained in a 200 × 200 μm region arbitrarily set on the processed surface. 5 to 50 Fe segregating parts having a diameter of 0.1 to 10 μm, the average value of the distance between the centers of gravity between the most adjacent segregating parts among the Fe segregating parts is 5 μm or more, and the coefficient of variation of the distance between the centers of gravity is A silicon nitride sintered body whose structure was controlled to be 1.2 or less could be obtained. As a result, the peel resistance of the silicon nitride sintered body and the wear resistance of the counterpart material were both good.

DESCRIPTION OF SYMBOLS 10 Test apparatus 11 Apparatus main body 12 Test piece 13 Rolling steel ball 14 Guide plate 15 Drive rotary shaft 16 Cage 17 Lubricating oil

Claims (4)

  A method for producing a silicon nitride-based sintered body containing 0.5 to 20% by mass of Mg and at least one rare earth element in terms of oxide, wherein the 50% cumulative particle size (d50) is 0.2 to 3 μm. The nitriding is a relationship between the 50% cumulative particle size (d50), the 10% cumulative particle size (d10) and the 90% cumulative particle size (d90) (d90-d10) / d50 in the range of 0.5-8. The ratio (RExOy / MgO) when a sintering aid containing Mg and at least one kind of rare earth element (RE) is converted into an oxide in terms of Mg and at least one kind of rare earth element (RE) is 0. A raw material powder adjusting step of adding and mixing to form a raw material powder in a range of 05 to 5, and a molded body formed of the raw material powder is fired in a nitrogen atmosphere under a pressure of 0.2 to 10 MPa Silicon nitride having a firing step Manufacturing method of the sintered body.   The said baking process WHEREIN: It has the temperature range which heats a molded object for the predetermined time in the range of (H3-200 degreeC)-(H3 + 200 degreeC) with respect to temperature H3 from which the shrinkage | contraction rate of a molded object becomes 90%. A method for producing a silicon nitride sintered body.   The said baking process WHEREIN: It has the temperature range which heats a molded object for the predetermined time in the range of (H1-300 degreeC)-(H1-10 degreeC) with respect to temperature H1 which liquid phase conversion of a sintering adjuvant starts. 3. A method for producing a silicon nitride sintered body according to 2.   4. The silicon nitride material according to claim 3, wherein in the firing step, the silicon nitride material has a temperature range in which the molded body is heated for a predetermined time in a range of H1 to (H1 + 200 ° C.) with respect to a temperature H1 at which the liquid phase of the sintering aid starts. A method for producing a sintered body.

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