KR970001065B1 - Sintered body of silicon nitride for cutting tools having high hardness and tension and their preparation - Google Patents

Abstract

Silicon nitrate sinter body for cutting tools having a good hardness and ductility, is manufactured by mixing 45-85 wt.% of SiN4 powder with 8-20 wt.% of Er203, 2-5 wt.% of SiO2 and 5-30 wt.% of TiN and sintering. In an example, a mixture of Er2O3 and SiO2 is grinded in a planetary mill. 8 wt.% of Grinded mixture and 5 wt.% of SiO2 is mixed with 77 wt.% of Si3N4(0.8 microns of particle dia, 16-18m2/g) and 5 wt.% of TiN(1.4 microns of particle diameter) in a ball mill. The obtained mixture is mixed with conventional dispersing agent, binder, and release agent, dried, formed under the pressure of 300-2,000kg/gm2, and sintered at 1,700-1,810 deg.C.

Description

High hardness, high toughness silicon nitride sintered body for cutting tools and manufacturing method thereof

1 is a photograph comparing the cross section (a) of the Si ₃ N ₄ sintered body according to the present invention with the cross section (b) of the Si ₃ N ₄ sintered body according to the prior art.

The present invention relates to a silicon nitride sintered body for high hardness and high toughness cutting tool and a method of manufacturing the same, and particularly, the hardness and toughness of the silicon nitride powder prepared by the addition of Er ₂ O ₃ , SiO ₂ and TiN are high, and the lubricity is excellent, thereby cutting performance. The excellent silicon nitride sintered compact for a cutting tool, and its manufacturing method are related.

In recent years, silicon nitride sintered bodies have been attracting much attention as structural ceramic materials due to their high heat resistance, high thermal shock resistance, chemical stability, and high hardness, and are widely used for cutting tools.

However, although the silicon nitride sintered body has such excellent properties, the covalent bondability is high, the sinterability is bad, and due to the low toughness due to brittle fracture, the silicon nitride sintered body has a great limitation in practical applications.

In order to solve the problems of the silicon nitride sintered body, in Japanese Patent Laid-Open No. 55-32785, Japanese Patent Laid-Open No. 56-73670, an oxide such as Y ₂ O ₃ and Al ₂ O ₃ is added to increase the sinterability of the silicon nitride sintered body. Although the number of applications to propose a method to date, all of which are to added in the process of sintering _{Y 2 O 3, Al 2 O} 3 a SiO ₂ component surface is cooled to form a liquid, reacts with the SiO ₂ remain in the vitreous Therefore, the fracture toughness of the silicon nitride sintered compact is lowered, and the physical properties of the sintered compact have been deteriorated when used at a high temperature for a long time.

In addition, in order to solve the above problems, Japanese Patent Laid-Open No. 4-209763 prepared an sintered compact for cutting tools having excellent strength and wear resistance by adding oxides of Er, Yb, Sc, Dy, and Ho instead of Y ₂ O ₃ .

However, when Er ₂ O ₃ is added as a sintering aid, the liquid phase formation temperature that Er ₂ O ₃ reacts with SiO ₂ to help densification is very high (above 1680 ° C.), so that uniform sintering is difficult, and thus, the normal atmospheric sintering method. The uniformity of the sintering was difficult, and the quality during mass production was not uniform.

Therefore, the present invention provides a silicon nitride sintered compact for homogeneous cutting tools, in which hardness, toughness and lubricity are increased by adding TiN to improve the sinterability and physical properties of the Si ₃ N ₄ sintered compact manufactured by the conventional Er ₂ O ₃ addition. The purpose is to provide a method for producing the same.

Hereinafter, the present invention will be described in detail.

The present invention is prepared by mixing and sintering 20 wt% Er ₂ O ₃ 8 sowl, SiO ₂ 2-5 wt% and TiN 5-30 wt% as a rare earth element to 45 to 85 wt% of Si ₃ N ₄ powder. Silicon nitride sintered body for cutting tools.

In addition, the present invention is 45 to 85% by weight of Si ₃ N ₄ powder Er ₂ O ₁ 3 8 to 20% by weight with an average particle diameter of 0.6㎛, SiO ₂ 2 to 5% by weight with an average particle diameter of 0.6㎛ and 1㎛ to 5-30% by weight of 2 µm TiN together with an organic molding formulation, followed by shaping, and then sintering under a nitrogen atmosphere at a temperature of about 1750 to 1850 ° C. for 2 to 6 hours. It is a manufacturing method of a silicon nitride sintered compact.

Hereinafter, the present invention will be described in more detail.

That is, the present invention is mixed with 45 to 85% by weight of Si ₃ N ₄ powder Er ₂ O ₃ 8 to 20% by weight, SiO ₂ 2 to 5% by weight and TiN 5 to 30% by weight with a conventional organic molding formulation To grind.

Here, Er ₂ O ₃ and SiO ₂ powder is separated and milled in a centrifugal mill to adjust the average particle size of about 0.6㎛, TiN using a powder having an average particle diameter of 1㎛ to 2㎛, each raw material The powder is weighed to the composition and mixed together with the appropriate organic molding preparation.

At this time, as the organic molding aid to be used, conventional dispersing agents, binders, mold release agents, alcohols such as methanol and the like used in the silicon nitride sintered body are used.

After the mixed raw material slurry is combined, it is molded into a cutting tool shape of a certain shape by pressure molding, injection molding, injection molding or extrusion molding, and the added organic substance is removed by heat sintering.

In the above process, the sintering temperature is in the temperature range of 1750 to 1850 ℃, the sintering time is carried out in the N ₂ atmosphere for 2 to 6 hours. In addition, the primary sintered sintered body is subjected to a Sinter-HIP (Sinter-HIP) process to obtain a denser sintered body.

The sintered liquid phase generated when sintering only Er ₂ O ₃ and SiO ₂ is transferred to the surface by changing the content, mixing method, and particle size of the secondary phase TiN existing after sintering the manufacturing process according to the present invention as described above. Wetting can be prevented to produce a product having the properties of a homogeneous sintered body.

In addition, when TiN is added in less than 5% by weight, or 30% by weight or more in the manufacturing process, and when the average particle diameter of TiN is out of the above range, it is impossible to produce a uniform sintered body.

That is, in order to help the sinterability of the sintered body and to prevent the sedimentation during the ingredient material treatment, the sweating shape is increased by adding and mixing TiN with a larger particle size than that of Er ₂ O ₃ and SiO ₂ , which has reduced the average particle diameter. You can prevent it. The reason is that when only Er ₂ O ₃ is added, the liquid phase formation temperature is high, and since the redistribution of the liquid phase formed during the subsequent sintering process does not occur uniformly, it plays a role of redistribution of the liquid phase formed by TiN addition. .

That is, when a liquid phase is present between the spheres with a radius r, the liquid phase is transferred to the surface by a capillary pressure of P = 2γ / r. When TiN particles having a large particle diameter (r) exist according to the present invention, It serves to reduce the capillary pressure relatively to prevent the rapid transfer of liquid to the surface, and thus to prevent the sweating phenomenon to the surface of the sintered body to solve the heterogeneous phenomenon of the sintered body.

In addition, the liquid phase formed between Er ₂ O ₃ and SiO ₂ causes crystallization during natural cooling (Er ₂ Si ₃ N ₄ O ₃ crystal phase formation), the higher temperature strength and hardness than the addition of Y ₂ O ₃ , Al ₂ O ₃ It is high, the residual stress caused by the difference in thermal expansion coefficient between the known phase SiO ₂ and the dispersed phase TiN plays a role of lengthening the crack path, it is possible to manufacture a material resistant to mechanical impact, TiN itself It is possible to improve the cutting performance of the sintered body by lighting that the friction coefficient is lower than that of Si ₃ N ₄ modification and high lubricity.

Hereinafter, the present invention will be described in detail with reference to Examples.

Example 1

The powder of Er ₂ O ₃ and SiO ₂ ground in a centrifugal mill was milled for 90 minutes using a plane mill to increase the particle size distribution, and the particle size was reduced to about 0.6 μm. Ball mill with reduced 1 (8% by weight) and SiO ₂ (5% by weight) 77% by weight of Si ₃ N ₄ (particles 0.8 to 0.95 μm, 16 to 18 m 2 / g) and 5% by weight of TiN (particle size 1.4 μm) (Ball mill) was mixed.

The above component mixture was dispersed in methanol with an organic molding preparation, for example, a conventional dispersant, a binder, a mold release agent and the like, and then milled.

After drying and assembly of the slurry obtained above were press-molding into a shaped body of a predetermined shape, and then press-molding by compression 300kg / cm ^2, the press-molding was isotropic to 2000kg / cm ^2.

The molded article prepared as described above was heated up to 1810 ° C. and sintered under an N ₂ atmospheric pressure atmosphere, whereby powder of the same composition as the molded article was embedded to prevent decomposition of Si ₃ N ₄ . In addition, the produced sintered compact was subjected to Sinter-HIP (Sinter-HIP) under a condition of 1750 bar during one trial at 1700 ° C to obtain a product having better physical properties.

The results of the composition and mechanical properties of the sintered body prepared as described above are shown in Table 1 below.

Examples 2 to 3

The same procedure as in Example 1 was carried out except that the sintered compact was produced at the composition ratios shown in Table 1.

The results of the composition and mechanical properties of the sintered compact of each example are shown in Table 1 below.

Comparative Examples 1 to 4

The same procedure as in Example 1 was carried out except that the sintered body was produced at the composition ratio shown in Table 1 (Comparative Examples 3 and 4 are methods known from Japanese Patent Application Laid-Open No. 4-209763).

The results of the composition and the mechanical properties of the sintered compact of each comparative example are shown in Table 1 below.

Experimental Example 1

The hardness and toughness measured in Table 1 showing the characteristics of the sintered compacts prepared by the above Examples and Comparative Examples were measured by measuring the surface area of the manufactured sintered compact, and the sintered compact and TiN were not added according to the present invention. In order to compare the internal characteristics (hardness and toughness characteristics of the specimen) of the sintered body, the characteristics of the sintered body prepared in Example 2 and Comparative Example 1 were measured, and the results are shown in Table 2 below.

In Table 2, when only ErO was added as in Comparative Example 1, the physical properties of the internal parts of the sintered body were measured to have low hardness and toughness compared to the sintered body according to Example 1 to which TiN was added. In order to confirm this fact actually, the cross section of the sintered compact of Example 2 and the sintered compact of Comparative Example 1 was image | photographed like FIG. That is, it was confirmed that the sintered compact of Example 2 (FIG. 1a) to which 10 weight% of TiN was added formed a more uniform sintered layer than the sintered compact of Comparative Example 1 (FIG. 1B) not added.

That is, as compared with the case where only ErO is added as described above, by adding both ErO and TiN simultaneously, a uniform sintered layer is formed inside the sintered body (there is almost no difference in the Er content between the inside and the outside of the specimen). Production of products with improved physical properties was possible.

Test Example 2

In order to compare the cutting performance of the sintered compact manufactured by the Example and the comparative example which concerns on this invention, the sintered compact of Example 2 and the sintered compact corresponding to Comparative Example 1 and Comparative Example 2 were made into the shape of a cutting tool, and the upper and lower surfaces After the corner processing, the cutting test was performed under the following conditions.

Cutting condition

Crisp Lipids: FS 25

Cutting speed: 883m / min

Feed speed: 0.3mm / rev

Cutting depth: 2.0mm

Total processing period: 200 minutes

The test results are shown in Table 3 below. Table 3 shows the cutting performance relative to the number of cuttable workpieces of one cutting tool when the workpiece is processed for 8 seconds per piece.

The sintered compact for SiO-based cutting tools manufactured by the addition of ErO and TiN of Example 2 according to the present invention in the comparative test results based on the cutting performance of Comparative Example 2 based on 100 was Comparative Example 1 and Comparative Example 2 Compared to the above, it was found that the cutting performance was excellent, and the cutting performance of the SiN-based sintered compact was greatly improved by the addition of ErO and further by the addition of TiN.

Claims (1)

45 to 85% by weight of Si ₃ N ₄ powder is a cutting tool, characterized in that by mixing and sintering Er ₂ O ₃ 8 to 20% by weight, SiO ₂ 2 to 5% by weight and TiN 5 to 30% by weight as a rare earth element Silicon nitride sintered body.