Ceramic sintered body made of a sialon material, raw material mixture thereof, and manufacture thereof

Abstract

The present invention relates to a sintered body which is based on β-sialon as well as 15R-sialon and which, as a cutting material, exhibits a high cutting performance compared to workpieces made of nickel-based alloy or Heat Resistant Super Alloys (HRSA). To this end, a ceramic sintered body is disclosed which has a sialon phase and an amorphous or semi-crystalline grain boundary phase. The sialon phase has a proportion of 20 - 80 wt.% 15R-sialon polytypoid. The amorphous or semi-crystalline grain boundary phase optionally comprises a Yb-Al garnet, and constitutes up to 15 wt.% of the total sintered body. The sintered body is manufactured from an inorganic raw material mixture which comprises 40 to 57 wt.% of Si3N4; 40 - 55 wt.% of a mixture of AlN and Al2O3, the ratio of Al2O3 to AlN being in the range of 1-1.5:1, and 3 to 5 wt.% of Yb2O3 as a sintering aid.

Description

[0001] Ceramic sintered body made of a Sialon material, its raw material mixture and production

[0002] The invention relates to a sialon material whose sialon phase comprises ß-sialon and 15R-sialon polytypoid. The sialon material further comprises an amorphous or semi-crystalline grain boundary phase.

[0003] Sintered sialons are well-known, chemically stable materials with high mechanical strength over a wide temperature range. Sialones are therefore used as heat-resistant parts in machinery. Their high mechanical strength leads to low wear in abrasive processes. Sialones are therefore widely used as cutting agents in cutting tools.

[0004] Sintered bodies made of α / β-Sialon, particularly for use as cutting tools, e.g., as cutting agents, are known in the art. Blends of α-Sialon and β-Sialon enable the production of sintered bodies that, on the one hand, exhibit high hardness due to the granular α-Sialon and, on the other hand, also possess good toughness due to the acicular β-Sialon grains.

[0005] The object of the invention is to provide a sialon sintered body that exhibits high chemical resistance, high hardness, and good fracture toughness. The sintered body is primarily intended for use in the machining of nickel-based alloys or heat-resistant super alloys (HRSA). Furthermore, a process for producing a sialon sintered body and the underlying inorganic raw material mixture are to be provided.

[0006] This object is achieved by an inorganic raw material mixture according to claim 1, a sialon sintered molded body according to claim 6, the process according to claim 10, and the use according to claim 14. The subordinate claims specify preferred embodiments. Further preferred embodiments are described below. Embodiments can be freely combined with one another.

[0007] Unless otherwise stated, all percentages are based on weight (wt%).

[0008] Unless otherwise stated, all data in mol% refer to the total mixture.

[0009] All components of the Sialon sintered body and also of the inorganic raw material mixture may contain impurities. The purity of the starting materials is at least > 97%, i.e. each starting material can contain up to 3 wt.% impurities (based on the total amount of the respective starting material). The purity of the starting materials is preferably > 99%, i.e. up to 1 wt.% impurities (based on the total amount of the respective starting material) are possible, particularly preferably the purity is > 99.7%, i.e. up to 0.3 wt.% impurities (based on the total amount of the respective starting material) are possible. Ideally, the purity of the starting materials is > 99.9%, i.e. there are almost no impurities (up to 0.1 wt.%).

[0010] The impurities are preferably foreign metals in amounts of less than 1000 ppm each. In a preferred embodiment, Fe ions are present in the range between 10 and 1000 ppm, preferably between 10 and 500 ppm, particularly preferably between 10 and 100 ppm. A lower Fe content leads to disproportionately high raw material and manufacturing process costs. A higher Fe content leads to the formation of iron silicide, which negatively affects the fracture toughness of the sintered body. The contents of foreign metals are determined by X-ray fluorescence analysis.

[0011] Furthermore, the nitridic components of the raw material mixtures can contain oxygen in amounts of less than 1.5 wt.%, preferably less than 1 wt.%, particularly preferably less than 0.7 wt.%, based on the total amount of the respective starting material.

[0012] The grain sizes of the sialon components in the sintered sintered body are determined using SEM images. The maximum needle length, i.e., the maximum extension of the grains, should not exceed 100 μm. The composition of the sialon sintered body is determined using conventional X-ray analysis methods, such as XRD (DIN EN 13925-1 (2003-07) and DIN 13925-2 (2003-07)). Chemical analyses of the metallic components of the sintered body according to the invention are performed using energy-dispersive X-ray analysis (ISO 15632; DIN EN 1071-4) and X-ray fluorescence analysis (XRF; DIN 51001 (2003-08), DIN 51418-1 (2010-05), DIN 51418-2 (2015-03)). The oxygen content is determined by hot gas extraction (ASTM E 1409:2013).

[0013] Sialones are typically produced by sintering a powdered mixture and consist primarily of silicon nitride, aluminum oxide, and other inorganic starting materials, such as sintering aids. The sintered body, i.e., the material, the sintered body made from the starting materials, comprises a sialon phase and an amorphous or at least semi-crystalline grain boundary phase. The sialon phase comprises ß (beta) - sialon (Si-zAlzOzNs-z where 0 < Z < 4.2) and 15R-sialon polytypoid (SiAUOzN^). The proportion of 15R-sialon polytypoid is 20 - 80 wt.%, preferably 30 - 70 wt.%, particularly preferably 40 - 60 wt.% based on the total weight of the sialon phase. The proportion of ß-sialon is preferably at least 10 wt.%, particularly preferably at least 35 wt.%. A proportion of ß-sialon of 40 wt.% is particularly preferred. The proportion of ß-sialon is a maximum of 80 wt.%.

[0014] The proportion of 15R polytypoid results in a sintered body that exhibits high chemical inertness, meaning that chemical reactions with or on the sintered body are avoided by a high proportion of 15R polytypoid. However, a high proportion of 15R polytypoid leads to high brittleness of the sintered body. An optimal ratio of chemical inertness to fracture toughness of the sintered body can be achieved in the range of 40 to 60 wt.% 15R.

[0015] The detection limit for the X-ray analysis method for determining the composition of the sialon phase and for determining the individual sialons present in the sintered body is approximately 5 wt.%. The sialon phase may contain up to 10, preferably up to 5 wt.% additional sialons, preferably selected from the list comprising α (alpha)-, 12H-, 21R-, and / or 27R-sialon.

[0016] The sintered body consists of > 80 wt.%, preferably > 85 wt.%, of the sialon phase and up to 20 wt.%, preferably up to 15 wt.%, of the amorphous or at least semi-crystalline grain boundary phase, based on the total weight of the sintered body. Particularly preferably, the sintered body consists of > 90 wt.% of the sialon phase.

[0017] Preferably, the proportion of grain boundary phase in the total weight of the sintered body is <12 wt.%, particularly preferably <10 wt.%. In a preferred embodiment, the sintered body consists of the sialon phase and the grain boundary phase, i.e., the sum of the proportions of the sialon phase and the grain boundary phase equals 100 wt.%. In order to produce the densest possible sintered body, sintering aids, for example, are added as additives. The amount of additives added influences the amount of grain boundary phase. In a preferred embodiment, the proportion of grain boundary phase is at least 5 wt.%.

[0018] The sintered body according to the invention is produced by heat treatment, or sintering, of a starting material mixture. This starting material mixture comprises an inorganic raw material mixture and organic components. An inorganic raw material mixture for the production of sialons comprises the components SiSn4, AlN, Al2O3, and sintering aids.

[0019] For the production of the sintered molded body according to the invention, an inorganic raw material mixture is proposed to which Yb2Ü3 is added as a sintering aid.

[0020] The use of Yb2Ü3 results in a sintered body with high fracture toughness. This makes the sintered body according to the invention highly suitable as a cutting tool for machining metallic workpiece materials. The high fracture toughness leads to increased cutting edge stability. Thus, the sintered body can withstand the stresses encountered during machining, even at high cutting speeds, increased feed rates, and / or greater cutting depths, even in interrupted cuts.

[0021] The sintered body according to the invention, the sialon, is obtained from an inorganic raw material mixture which comprises the following components:

[0022] 40 - 57 wt.% SisN4 40 - 55 wt.% of a mixture of AIN and AI2O3, wherein the ratio of AI2O3 to AIN is in the range 1 - 1.5:1, preferably 1 - 1.25:1, particularly preferably 1 - 1.2:1,

[0023] 3 - 5% by weight of Yb2O3 as a sintering aid.

[0024] In a preferred embodiment, the sum of the inorganic components is 100 wt.% and the inorganic raw material mixture consists only of the components SisN4, AIN, AI2O3 and Yb2O3 as sintering aids.

[0025] The inorganic raw material mixture comprises all inorganic components used to produce the sintered body according to the invention. To produce the sintered body, further organic components are added, such as dispersants, pressing aids, and binders, which are completely combusted during heat treatment, debinding, and sintering. These organic components preferably contain no metallic components. Thus, in a preferred embodiment, ammonium salts are used instead of sodium salts of the organic components.

[0026] In a preferred embodiment, the inorganic raw material mixture according to the invention comprises

[0027] 45 - 54.5 wt% Si3N4,

[0028] 42-50 wt.% of a mixture of AIN and AI2O3, wherein the ratio of AI2O3 to AIN is in the range 1-1.5:1, preferably 1-1.25:1, particularly preferably 1-1.15:1.

[0029] - 3.5 - 5 wt% Yb2O3.

[0030] In a preferred embodiment, the sum of the inorganic components is 100 wt.%.

[0031] In a particularly preferred embodiment, the inorganic raw material mixture according to the invention comprises

[0032] - 47.5 - 51.5 wt.% Si3N4,

[0033] 45 - 48 wt.% of a mixture of AIN and AI2O3, wherein the ratio of AI2O3 to AIN is in the range 1 - 1.5:1, preferably 1 - 1.25:1, particularly preferably 1 - 1.2:1.

[0034] - 3.5 - 4.5 wt% Yb2O3.

[0035] In a preferred embodiment, the sum of the inorganic components is 100 wt.%.

[0036] The raw material mixture comprises Yb2O3 as a sintering aid, which serves to produce high-density ceramics. Using more than 5 wt.% Yb2O3 based on the total sintered body reduces the heat resistance, toughness, and hardness of the sialon sintered body. In one embodiment, the proportion of Yb2O3 with respect to the inorganic raw material mixture according to the invention is 0.4-1.5 mol%, preferably 0.6-1.5 mol%, and particularly preferably 0.6-1 mol%.

[0037] The sintered molded body is produced from the inorganic raw material mixture according to the invention. First, the inorganic raw material mixture is prepared. One or more organic additives are added.

[0038] The raw materials are first mixed and / or ground in a solvent. In one embodiment, the solvent is water. In another embodiment, the solvent is an organic solvent, a mixture of several organic solvents, or a mixture of one or more organic solvents and water. The solvent mixtures are preferably single-phase, i.e., the solvents completely dissolve in each other in the required amounts.

[0039] The powdered inorganic raw material mixture should comprise particles with an average particle size of 10 pm or less, preferably 5 pm or less, more preferably 3 pm or less. The inorganic raw material mixture is preferably placed in a mixing and grinding machine, such as a ball mill or a SiN pot mill with SiN grinding balls, and a solvent is added to the material that does not, or at least substantially does not, dissolve the powdered raw material. The grain sizes of the raw material mixture are referred to as agglomerates or primary particles, depending on the processing step. The D50 value of the primary particles, the ground raw materials, is determined by centrifugal sedimentation using a particle distribution analyzer (DIN EN 725-5:2007, ISO 13320:2020-01).

[0040] The mixture is then ground and mixed until a slurry is formed and the desired primary grain size, i.e., the grain size of the raw material after grinding and before shaping, is achieved. The mixing and grinding process typically lasts at least 5 minutes, preferably 30 minutes, particularly preferably 1 hour, up to a maximum of 300 hours, preferably a maximum of 200 hours, particularly preferably a maximum of 100 hours.

[0041] In one embodiment, the SiA / N powder has a primary grain size D50 of 0.25 < x < 2.5 pm, preferably 0.25 < x < 2.0 pm, particularly preferably D50 of 0.35 < x < 1.0 pm. The primary grain size influences the shaping and sintering activity.

[0042] In a further embodiment, the Si3N4 has a primary grain size D50 of 1.5 < x < 2.0 pm.

[0043] After grinding, other organic additives can also be added and mixed with the above-mentioned components.

[0044] The organic auxiliaries to be added before or after grinding can be dispersants, binders, pressing aids, and / or plasticizers. In one embodiment, the organic auxiliaries are added to the powdered raw material mixture or the resulting slurry in an amount of 1 to 30 wt.%, based on the weight of the inorganic raw material mixture.

[0045] The prepared mixture, the slurry, comprising the inorganic and organic raw materials in a solvent mixture is, in one embodiment, subjected to granulation by a suitable process, such as spray drying.

[0046] The mixture or granules are then shaped. All state-of-the-art shaping methods are applicable. In a preferred embodiment, the granules are shaped by pressing, preferably axial pressing, at 50 to 200 MPa. In a further embodiment, shaping is carried out by isostatic pressing.

[0047] Molding can also be done using other processes such as injection molding, extrusion molding or slip casting.

[0048] The shaped mixture of starting materials is then debindered and sintered. In a preferred embodiment, sintering takes place under a protective gas, such as nitrogen and / or argon.

[0049] Typically, debinding and sintering takes place in a heating device. The gas atmosphere during debinding and sintering is inert in one embodiment and comprises N2, argon, or a mixture of N2 and other inert gases, preferably Ar.

[0050] The debinding preferably takes place at 400 to 800°C and preferably lasts at least 5 min, preferably 30 min, particularly preferably 1 h to a maximum of 100 h, preferably a maximum of 50 h, particularly preferably a maximum of 30 h.

[0051] The precise contents of the individual sialon phase components and the proportion and composition of the amorphous or semi-crystalline grain boundary phase are adjusted by the selected sintering parameters. During the production of the sintered body, during sintering of the inorganic raw material mixture, the sintering aid Yb2O3 is converted, among other things, to Yb-Al garnet, Yb3Al5Oi2, and accumulates in the amorphous or semi-crystalline grain boundary phase. The lowest possible proportion of Yb-Al garnet in the grain boundary phase is preferred. The lower the proportion of Yb-Al garnet in the grain boundary phase of the sintered body, the higher the wear and abrasion resistance of the sintered body. In a preferred embodiment, a maximum of 1.4 wt. % Yb-Al garnet is detectable in the grain boundary phase.

[0052] The Yb-Al garnet as a crystalline portion stabilizes the grain boundary phase by increasing the softening temperature compared to a completely amorphous grain boundary phase. In a preferred embodiment, at least 0.02 wt. % Yb-Al garnet is detectable in the grain boundary phase. The amount of Yb-Al garnet is influenced by the sintering parameters, such as the sintering temperature. At sintering temperatures up to 1950 °C, lower amounts of Yb-Al garnet are obtained; at lower sintering temperatures, a higher amount of Yb-Al garnet is obtained (see also Table 2). The amount of Yb-Al garnet in the sintered body is preferably between 0.01 and 5 wt. %, particularly preferably between 0.015 and 3 wt. %, most preferably between 0.02 and 1.4 wt. % based on the amount of crystalline phases in the sintered body.

[0053] A lower sintering temperature increases the proportion of crystalline grain boundary phase, and thus also the proportion of Yb-Al garnet in the grain boundary phase. In addition, a sintering temperature that is too low leads to a less dense sintered body with increased porosity and, consequently, lower abrasion resistance. Therefore, the sintering temperature is preferably above 1600 °C.

[0054] In addition to the sintering temperature, the cooling rate also affects the proportion of Yb-Al garnet in the amorphous and / or semi-crystalline grain boundary phase. The slower the cooling, the higher the proportion of Yb-Al garnet. Therefore, the cooling rate is preferably higher than 1000°C in 14 hours, particularly preferably higher than 1000°C in 12 hours, and especially preferably higher than 1000°C in 10 hours. In one embodiment, the cooling rate is slower than 1000°C in 4 hours; preferably, the cooling rate is in the range of 1000°C in 4-8 hours.

[0055] In addition to the proportions of crystalline phases, the sintering temperature also affects the grain size of the crystallites. These can be refined using Rietveld refinement based on an X-ray diffractogram of the sintered body. Table 2 shows the average grain size of the individual crystalline phases (crystallite size). This is the average length of the congruently scattering domains in the sintered body. For the ß-sialon phase, the higher the sintering temperature, the larger the crystallite size of the ß-sialon phase. Furthermore, the crystallite size of the Yb-Al garnet phase in the sintered body according to the invention is smaller than the average crystallite size of the sialon phases. Preferably, the crystallite size of the Yb-Al-Grant phase is at least 5 times smaller than the average crystallite size of the sialon phases, particularly preferably the crystallite size of the Yb-Al-Grant phase is at least 10 times smaller than the average crystallite size of the sialon phases.

[0056] The shaped mixture of starting materials is sintered at a temperature between 1600 °C and 1950 °C, preferably between 1650 °C and 1900 °C, particularly preferably between 1750 °C and 1875 °C. At these sintering temperatures, a sintered body with the highest possible density is obtained (> 99% of the theoretical density), and the proportion of Yb-Al garnet is in the preferred range.

[0057] In a preferred embodiment, the sintering takes place in a gas pressure sintering furnace under a pressure of at least 10 bar, preferably at least 50 bar, particularly preferably at least 75 bar and preferably at most 150 bar, particularly preferably at most 100 bar.

[0058] The sintering time is preferably at least 30 minutes and preferably at most 3 hours, particularly preferably the sintering time is 45 minutes to 2.5 hours.

[0059] The finally sintered Sialon sintered body can then be removed. Final machining is carried out according to methods known in the art. In one embodiment, the sintered body is further processed by grinding to produce indexable inserts or solid-end milling cutters. The sintered body according to the invention can be processed into a cutting medium that reacts only slightly with the workpiece material to be machined, e.g., nickel-based alloys or steels. Chemically resistant, hard cutting materials are required for the machining of Ni-based alloys. The alloys are highly heat-resistant and hard; very high temperatures are generated during machining, which leads to reactions and rapid wear with conventional cutting materials. When machining nickel-based alloys or Heat Resistant Super Alloys (HRSA), no built-up edge is formed, i.e.The material of the workpiece to be machined adheres little to no to the cutting fluid. In addition, the high proportion of 15R Sialon polytypoid results in a sintered body with very high chemical resistance.

[0060] The present invention relates to a sintered body based on ß-Sialon and 15R-Sialon, which, as a cutting material, exhibits high cutting performance compared to workpieces made of nickel-based alloys or Heat Resistant Super Alloys (HRSA). For this purpose, a ceramic sintered body is shown that has a Sialon phase and an amorphous or semi-crystalline grain boundary phase. The Sialon phase has a proportion of 20-80 wt.% 15R-Sialon polytypoid. The amorphous or semi-crystalline grain boundary phase optionally comprises a Yb-Al garnet and accounts for up to 15 wt.% of the entire sintered body.

[0061] The Yb2O3 from the raw material mixture, along with the Al-based additives and the SiO2 contained in the Si3N4 raw material, serves as a sintering aid. While the Al-based additives and the SiO2 can also be incorporated into the crystal lattice of the described sialon phases during the sintering process, the Yb remains in the grain boundary phase of the sintered body. This, and the Yb content, influence the properties of the grain boundary phase, such as the glass transition point and the bonding of the sialon phases with the grain boundary phase. This bonding determines the dominant mechanisms for crack propagation in the sintered body and is therefore crucial for the fracture toughness of the sintered body. Therefore, the grain boundary phase of the sintered body according to the invention contains at least 1.5 wt.%, preferably 2 wt.%, particularly preferably 2.5 wt.% and at most 5 wt.% Yb, calculated in the form of the sequioxide Yb2Ü3 and in relation to the total weight of the sintered body.

[0062] The sintered body is produced from an inorganic raw material mixture containing 40 to 57 wt.% SiSn4; 40-55 wt.% of a mixture of AlN and AlO3, with the ratio of AlO3 to AlN being in the range 1-1.5:1; and 3 to 5 wt.% YbO3 as a sintering aid. Examples of embodiments:

[0063] The following inorganic raw material mixtures (RM) were provided for the synthesis of sintered bodies.

[0064] Tab. 1 Composition of the inorganic raw material mixture

[0065] The starting materials, see Table 1, were mixed. SiSn4 with an a-SiN4 content of > 95%, an average grain diameter of > 0.45 pm and an oxygen content of 1.2 - 1.4 wt.%, as well as YbO3 with a purity of > 99.9%, an average grain diameter of approximately 5 pm, AlO3 with a purity of > 99.9%, an average grain diameter of 0.3 pm and AlN with an oxygen content of 0.6 - 1% and an average grain diameter of 1.2 - 1.7 pm were weighed, mixed with water and ground for at least 30 minutes in a stirred ball mill. The organic components were then added. The resulting ceramic slip (slurry) was granulated by spray drying. The molded bodies were axially pressed at a pressure of approximately 1000 bar and debindered at 500 °C for 2 hours. Subsequent sintering was carried out according to the parameters in Table 2.

[0066] The sintered mold bodies were ground into cutting plates.

[0067] 5 Tab. 2 Composition and properties of the sintered bodies

[0068] * the information refers to the proportion of crystalline phases and was determined by Rietveld refinement, Topaz Vers. 4.2, cif-files 00-048-1616, 00-042-0160, 00 023-1476

[0069] ** the information refers to the result of the Rietveld refinement carried out to determine the crystalline phases (see *), the Crystallite Size was refined according to Gaus

[0070] 10 '“Results from experiments on machining nickel-based alloys (Inconel 718)

[0071] The measured values ​​were determined according to the following standards: XRF: DIN 51001 (2003-08), DIN 51418-1 (2010-05), DIN 51418-2 (2015-03); XRD: DIN EN 13925-1 (2003-07), DIN 13925-2 (2003-07); Density: DIN EN 623-2 (1993-11), ISO 18754 (2020-04); Hardness: DIN EN 843-3 (2005-08), ISO 14705 (2016-12), ASTM C 1327 (2015); Fracture toughness: ISO 14627 (2012-07)

Claims

Patent claims 1. Inorganic raw material mixture comprising: 40 - 57 wt% Si3N4 40 - 55 wt% of a mixture of AIN and AI2O3, wherein the ratio of AI2O3 to AIN is in the range of 1 - 1.5:1, and 3 - 5 wt% Yb2O3, where the sum of the inorganic components amounts to 100 wt%.

2. Raw material mixture according to claim 1, wherein the ratio of AI2O3 to AIN is 1 - 1.25:1, preferably 1 - 1.12:

1.

3. Raw material mixture according to one of the preceding claims, comprising 45 - 54.5 wt% Si3N4, 42 - 50 wt% of a mixture of AIN and Al2O3, - 3.5 - 5 wt% Yb2O3 4. Raw material mixture according to one of the preceding claims, comprising - 47.5 - 51.5 wt% Si3N4, 45 - 48 wt% of a mixture of AIN and Al2O3, - 3.5 - 4.5 wt% Yb2O3 5. Raw material mixture according to one of the preceding claims, wherein the Si3N4 powder has a primary particle size D50 0.25 < x < 2.5 pm, preferably D50 0.25 < x < 2.0 pm, particularly preferably D50 0.35 < x < 1.0 pm or 1.5 < x < 2.0 pm.

6. Ceramic sintered body comprising a sialon phase comprising β-sialon and 15R-sialon, wherein the proportion of 15-R-sialon polytypoid is 20-80 wt.% of the sialon phase, and an amorphous or semi-crystalline grain boundary phase, wherein the grain boundary phase constitutes up to 15 wt.% of the total sintered body, and wherein the grain boundary phase contains a maximum of 5 wt.% Yb, calculated in the form of the sequioxide Yb2Ü3 and in relation to the total weight of the sintered body.

7. Ceramic sintered body according to claim 6, wherein the grain boundary phase comprises at least 1.5 wt. %, preferably 2 wt. %, particularly preferably 2.5 wt. % Yb, calculated in the form of the sequioxide Yb2O3 and with respect to the total weight of the sintered body.

8. Ceramic sintered body according to claim 6 or 7, wherein the proportion of 15R- sialon polytypoid is 30 - 70 wt.%, preferably 40 - 60 wt.% based on the total weight of the sialon phase.

9. Ceramic sintered body according to claim 8, wherein the sialon phase additionally contains up to 10 wt.% 12H-, 21R-, 27R- or α-sialon, preferably up to 5 wt.% 12H-, 21R-, 27R- or α-sialon.

10. Ceramic sintered body according to one of claims 6 to 9, wherein the proportion of Yb-Al garnet in the sintered body is between 0.01 and 5 wt.%, particularly preferably between 0.015 and 3 wt.%, particularly preferably between 0.02 and 1.4 wt.%, based on the amount of crystalline phases in the sintered body.

11. Ceramic sintered body according to one of claims 6 to 10, wherein the Crystallite Size of the Yb-Al-garnet phase is smaller than the mean Crystallite Size of the Sialon phases, preferably at least 5 times smaller, particularly preferably at least 10 times smaller.

12. Method for producing the sintered sintered mold body according to any one of claims 6 to 11, comprising the process steps: (a) Providing a mixture of raw materials according to any one of claims 1 to 5 (b) Addition of one or more organic additives (c) Mixing and grinding the raw materials, preferably in at least one liquid selected below water and / or at least one organic solvent and optionally adding one or more further organic additives (d) Shaping the mixture (e) Debinding and sintering (f) Removal of the sintered sintered mold body 13. Method according to claim 12, wherein the sintering in process step (e) is carried out at 1600 °C to 1950 °C, preferably between 1650 °C and 1900 °C, particularly preferably at 1750 °C to 1875 °C.

14. Method according to claim 12 or 13, wherein the gas atmosphere is selected from N2 and / or a protective gas, preferably selected from N2 or a mixture of N2 and Ar and / or where sintering takes place at a pressure between 10 and 100 bar.

15. Use of the ceramic sintered body according to one of claims 6 to 11 as a cutting means, preferably as an indexable insert or full-shank end mill.

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