JPH0324429B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing ceramic materials. The present invention particularly relates to materials commonly referred to as substituted silicon nitrides, which have high strength and hardness and are useful for making tool tips, gas turbine components, and seals by sintering operations. A typical example of substituted silicon nitride is silicon nitride (Si ₁₂ N ₁₆ ), which has a β-phase lattice structure in which some of the silicon atoms are replaced by aluminum atoms and some of the nitrogen atoms are replaced by oxygen atoms. It will be expanded. However, it is understood that the beta-phase silicon nitride lattice can have substituent elements other than aluminum and oxygen at its atomic positions while maintaining valence balance. Another example of substituted silicon nitride has an alpha-phase silicon nitride lattice, which replaces some of the silicon atoms with aluminum atoms and contains modifying cations such as yttrium, yttrium, etc. in the lattice interstices to achieve valence balance.
It is developed by introducing calcium and lithium. This valence balance is usually achieved through the use of oxides of these modifying cations, eventually leading to the introduction of oxygen to some of the nitrogen positions in the lattice. In this specification, the term substituted silicon nitride should be understood in this way. “α′-Sialon Ceramics” by S.Hampshire, HKPark, DPThompson and KHJack
(Nature, vol 274, No. 5674, pages 880-882,
(August 31, 1978), the X-ray photograph in Figure 5 was
It is shown that α′ reacts with Al ₂ O ₃ to give β′, and this is illustrated by the following formula: However, as pointed out in the earlier British Patent No. 1578434, the strength of β'-sialon begins to decrease when the z-value becomes larger than the order of 1.5, and the above-mentioned
When α'-sialon is converted to high z-value β'-sialon with a second phase containing yttrium, as in the Nature article, such products do not function well as engineering ceramics. Powder containing a high proportion of α-phase substituted silicon nitride with less than 10% by weight of alumina (33% by weight in Nature) and/or at least one silicon nitride (as defined below). By reacting with
It can be made with controlled amounts of other crystalline phases and controlled amounts of glassy phases, so that the strength of the product is acceptable for engineering ceramics and its properties are well maintained at high temperatures (approximately 1200°C). The present inventor found out. The inventors have also found that decreasing the alumina content in the starting mixture below 10% by weight results in sintering in the reduction of β-substituted silicon nitride phases with z-values less than 1.5, with a controlled amount of glass. The α-substituted silicon nitride phase in the product gradually increases, which not only improves the strength at room and high temperatures, but also improves the hardness compared to the hardness of the product without α-phase substituted silicon nitride with the same minimum glass content. I discovered that. However, it has been found that as the alumina content is progressively reduced, it becomes increasingly difficult for the beta-phase substituted silicon nitride to form products with extremely low z values (<0.75). z of β-phase substituted silicon nitride by supplementing or partially or completely replacing the addition of alumina to powders containing a high proportion of α-phase substituted silicon nitride by the addition of silicon nitride.
It has been found that the value can be lowered to less than 0.75. Therefore, by adding silicon nitride or alumina in an amount not exceeding 10% by weight (or by adding both silicon nitride and alumina, provided that the amount of alumina contains a high proportion of α-phase substituted silicon nitride) Ceramic products can be made consisting of β-phase substituted silicon nitride of z-values up to 1.5, with controlled amounts of other crystalline and glassy phases (not exceeding 10% by weight of the powder); It will be appreciated that the phase can include alpha phase substituted silicon nitride.
Although silicon nitride and/or alumina are mentioned above as additives to α-phase substituted silicon nitride, other additives that provide the necessary elements, such as silicon, nitrogen, aluminum, and oxygen, such as silicon oxynitride and/or silicon, can also be used. The so-called polytype, which is silicon aluminum oxynitride having a crystal lattice structure of aluminum nitride, in which valence balance is maintained by partially replacing aluminum atoms and oxygen atoms partially replacing nitrogen atoms, is a suitable addition. It can be a thing. In this specification, the term silicon nitride should be understood in this way. A first object of the invention is a method for making dense ceramic materials of the formula Mx(Si,Al) ₁₂ (O,N) ₁₆ , where x is not greater than 2 and M is a modifying cation, e.g. yttrium, calcium, lithium, magnesium, and cerium) with at least one type of silicon nitride and/or alumina, provided that the alumina is in the mixture. and this mixture is sintered in a non-oxidizing atmosphere at a temperature of 1700 to 1900°C to obtain (1) the general formula Si _6-z Al _z N _8-z O _z (where (2) a dense ceramic material consisting primarily of a β-phase substituted silicon nitride with a small amount of another phase containing a modifying cationic element as described above, or (2) a β-phase as described above. Substituted silicon nitride, a controlled amount (e.g. 0.05% to 90% by weight) of α-phase substituted silicon nitride according to the formula Mx(Si,Al) ₁₂ (O,N) ₁₆ and a small amount containing the modifying cationic element M as described above. (e.g., 0.05% to 20% by weight) of another phase. The required sintering time depends on the sintering temperature, 1900℃
for a sintering temperature of at least 10 minutes, and longer times at lower temperatures in the aforementioned range. Because of the excellent properties of substituted silicon nitride, both the final and intermediate products are extremely difficult to process, and much research has focused on developing methods for producing the final product that minimize processing of the material. has been poured into. In an effort to devise an economical manufacturing route,
Much research has been devoted to ways of simplifying operating parameters, such as avoiding the use of high pressures, reducing time, temperature and also avoiding other costly steps. To make the above-mentioned dense ceramic material (2), the amount of Al ₂ O ₃ in the mixture to be sintered is 7.5% by weight.
Preferably no more. In making substituted silicon nitride materials, it is advantageous to form an intermediate material, grind it into a powder, and then react the intermediate powder with another powdered component to obtain the final product. Such a method is patented in the UK
No. 1573199, in which a mixture of aluminum, silicon and alumina is heated under a nitriding atmosphere and subjected to a controlled heating schedule to substantially suppress exotherm. Following this, the material is crushed and ground and sintered in a protected environment to create an intermediate product. This is a ceramic material containing silicon aluminum oxynitride that follows a different chemical formula than the desired chemical formula of the final product. This material is polytypic. Following sintering, the intermediate ceramic material is crushed and ground into a powder. This powder is mixed with silicon nitride powder containing silicon as an impurity and a temporary binder. one or more glass-forming oxides, such as magnesium;
Oxides of manganese, iron, boron, lithium, yttrium and other rare earth oxides may be added to the mixture. This mixture is cold pressed to form a preform, which is then spray coated with a protective mixture of boron nitride and silicon in ketone as a carrier fluid. This preform is then open sintered to form the final ceramic material by heating at temperatures of 1200 to 2000°C. It has a crystal structure based on β-silicon nitride, but with increased unit cell size and has the general formula Si _6-z Al _z N _8-z O _z (where z is greater than zero and greater than 5). Contains at least 90% by weight of single-phase silicon aluminum oxynitride according to the following standards. This type of method has numerous advantages. Firstly, the use of aluminum nitride as a starting material can be avoided. Aluminum nitride is extremely hygroscopic and therefore cannot be stored,
It is difficult to handle and requires use under anhydrous conditions. Second, an open sintering process is used to create the final shape of the ceramic material. However, this method requires the use of costly geocrushers during the production of the intermediate ceramic material and on the intermediate material before it is used in the production of the final material. The conventional method using α-phase substituted silicon nitride is
It is possible to use the powder obtained by comminution of such a product as one of the starting materials in the process according to the first subject of the invention, intended to produce a dense and hard product. Yes, but doing so as a manufacturing method is unattractive. It is possible to make prior art α-phase substituted silicon nitrides and avoid all steps in the process that aid in densification, and such an approach facilitates comminution and is the first subject of the present invention. Although the method according to the present invention allows to carry out the method more easily, it still requires a costly comminution step such as a geocrusher.
It must also be noted that the comminution process, apart from increasing manufacturing costs, introduces impurities into the reactants, which adversely affects the reproducibility of the final product. A second object of the present invention is to provide a method for producing ceramic powder containing a high proportion of alpha-phase silicon nitride as described above, which does not require a costly grinding step such as a geocrusher. It is to be. A second object of the invention is a method for producing ceramic materials in which powder mixtures of silicon, aluminum, alumina and oxides or nitrides of modifying cationic elements (for example yttrium, calcium, lithium, magnesium, cerium) are used. carrying out the first stage nitriding by heating the first stage nitriding mixture at a temperature below the melting point of aluminum under a nitriding atmosphere until the first stage nitriding is substantially complete; heating at a temperature below the melting point of silicon until the second stage nitridation is substantially complete, thereby producing a friable material; comminution of the material; and subsequently the comminution of the comminuted friable material
Sintering while maintaining a non-oxidizing atmosphere at temperatures between 1650°C and 1900°C gives the formula Mx(Si,Al) ₁₂ (O,N) ₁₆ where x is not greater than 2 and M is for modification. It is a cationic element.) α-phase substituted silicon nitride according to
Friable ceramic materials containing more than 50% by weight, or α-phase substituted silicon nitride as described above and according to the formula Si _6-z Al _z N _8-z O _z , where z is greater than zero and not greater than 1.5. mixture with β-phase substituted silicon nitride
A process for producing ceramic materials comprising steps of obtaining a brittle ceramic containing more than 50% by weight. The relative proportion of α-phase substituted silicon nitride to β-phase substituted silicon nitride depends on the temperature of the sintering step;
The higher the temperature within the range of 1500℃ to 1900℃,
For a given treatment time the proportion of alpha phase material will be large. The powder mixture used in the method described above may contain silicon nitride and/or aluminum nitride. Preferably, the brittle ceramic material comprising a mixture of alpha and beta phases of substituted silicon nitride contains greater than 50% by weight alpha phase material. This is preferably done by carrying out the final sintering step at a temperature between about 1700°C and 1900°C. The proportions of the components of the powder mixture used will, of course, depend on the type of friable ceramic product required. Most preferably, the proportions of the components of the powder mixture are selected such that the resulting friable ceramic material consists essentially entirely of alpha phase material or substantially entirely a mixture of alpha and beta phase material. Ru. If calcium is used as the modifying element, the α-phase ceramic material may have the formula Ca _0.5 Si _10.5 Al _1.5 O _0.5 N _15.5 or the formula Ca _0.8 Si _9.2 Al _2.8 O _1.2 N _14.8 . When the cationic element for modification is lithium, α
Phase ceramic materials typically have the formula LiSi ₁₀ Al ₂ ON ₁₅ . When the modifying cationic element is yttrium, the α-phase ceramic material can have the formula Y _0.4 Si ₁₀ Al ₂ O _0.8 N _15.2 or the formula Y _0.6 Si _9.2 Al _2.8 O _1.1 N _14.9 . That is, the proportions of the components are preferably substantially balanced according to a suitable formula. The friable ceramic material formed by the method according to the second subject of the invention is a dense ceramic material consisting essentially of the aforementioned β-phase material and a small proportion of other phases comprising the aforementioned modifying cationic elements;
or the aforementioned β-phase materials, in controlled amounts (e.g.
It is suitable as an intermediate for the formation of dense ceramic materials consisting essentially of α-phase materials (0.05% to 90% by weight) and small proportions of other phases containing the aforementioned modifying cationic elements. The required sintering time depends on the sintering temperature, 1900℃
for at least 10 minutes; longer times are required if lower temperatures within the ranges mentioned above are employed. Conveniently, the ceramic powder is 5 to 96.5% by weight of the mixture containing the ceramic powder. Conveniently, the ceramic powder is present in an amount of less than 30% by weight of the mixture containing the ceramic powder;
and at least one glass-forming metal oxide selected from yttrium oxide, calcium oxide, lithium oxide, cerium oxide, rare earth element oxides and lanthanide series element oxides, magnesium oxide, manganese oxide, and iron oxide, It is contained in a mixture containing the ceramic powder described above. Most conveniently, the at least one glass-forming metal oxide as described above is included in an amount of less than 10% by weight of the mixture comprising the ceramic powder as described above. Preferably, silicon nitride represents an amount of up to 75% by weight of the mixture containing the ceramic powder described above, more preferably from 5 to 75%. Conveniently, the product after cooling is reheated, preferably at a temperature not exceeding 1400° C., in order to devitrify the glass phase. In Example 1 according to the first subject of the invention,
Silicon nitride powder with an average particle size of 2 microns and containing 5% by weight silicon as an impurity (approximately 90% α
Contains phases. ) (supplied by Lucas Syalon under the designation Si ₃ N ₄ (K ₂ )), aluminum nitride powder (Stark Company:
7.7% by weight of yttrium oxide (supplied by Rare Earth Products) with a particle size of approximately 1 micron.
% by weight was ball milled for 24 hours using alumina balls. This resulted in an increase of 2% by weight of alumina in addition to the alumina contained in the aluminum nitride powder. The mixed powder was then placed in a furnace in loose form and the temperature of the furnace was slowly increased to 1820°C in the presence of a nitriding atmosphere.
And it was held for 5 hours. The cooled product has a high proportion (98%) and a small amount (estimated to be on the order of 2%) of α-phase substituted silicon nitride, where yttrium is the modifying cation. Si _6-z Al _z N _8-z It was found to consist of β-phase substituted silicon nitride of O _z (z is of the order of 0.3). The sintered product was a hard sintered cake, and it was necessary to use a diyoke crusher to convert it into an intermediate powder that could be subjected to subsequent processing. 90 parts by weight of the intermediate powder crushed on a geocrusher was then mixed with 10 parts by weight of the silicon nitride used earlier and ball milled again using an alumina ball until the alumina increase was 8.45 parts by weight. . The resulting powder is then isotropically
It was pressed at 20,000 psi (140 MN·m ^-2 ) and sintered in a furnace containing a nitriding atmosphere. Furnace temperature is 1750
℃ and held for 5 hours. The crystalline phases detected in the product consist of β-phase substituted silicon nitride occupying on the order of 96%, about 3% of the polytype crystalline phase called 12H, and the B phase (Y ₂ SiAlO ₅ N) of the cons. . The z-value of the main component of the β phase was on the order of 1.5, and the modulus of failure in three-point bending was on the order of 90,000 psi (620 NM m ^-2 ). This experiment confirmed the method of the first object of the present invention for producing a material containing β-phase substituted silicon nitride with a z value of 1.5 or less from an intermediate powder in which α-phase substituted silicon nitride is the main constituent. However, all the following experiments were carried out using an intermediate powder made according to the second subject of the invention, a friable powder that does not require costly comminution. In the second experiment, which is a control example for the second object of the present invention, 29.5% by weight of silicon powder (supplied by Kema Nord, Sweden) with a particle size smaller than 20 microns, aluminum powder (supplied by Kema Nord, Sweden), aluminum powder (Johnson and Bloy 10.6% by weight of silicon nitride with an average particle size of 2 microns (contains approximately 90% by weight of alpha phase and 5% by weight of silicon as impurities).
Si ₃ N ₄ (K ₂
(supplied as ALCOA XA15 by the company)
1.4% by weight, and 9.5% by weight of yttrium oxide powder (supplied by Rare Earth Products) with a particle size of approximately 1 micron.
Mixed uniformly with a Nautamix mixer. weight%
were adjusted so that the atomic ratios of the elements followed the formula Y _0.4 Si ₁₀ Al ₂ O _0.8 N _15.2 . Yttrium oxide was present to provide the modifying cation. The mixture was placed in a nitriding furnace and the temperature was increased to about 10°C per minute under a nitriding atmosphere of nitrogen and hydrogen.
Raised to 640°C at a rate of ~15°C. At this temperature, an antithermal reaction began and the mixture was nitrided at 640°C for 20 hours. The exothermic reaction is controlled by monitoring the temperature of the mixture and the temperature of the furnace walls and diluting the nitriding atmosphere with argon when necessary to prevent the exothermic reaction from occurring too violently to exceed the required temperature of 640°C. It was done. That is, it was ensured that the temperature of the mixture did not rise above the melting point of aluminum (approximately 660°C). When the heat generation is no longer detected by the temperature detection of the mixture and walls as described above,
This was taken to indicate that the first stage of the nitriding process was completed. The temperature in the furnace was then increased to 1200°C while maintaining the same nitriding atmosphere used in the first stage. Keep the mixture at this temperature for 10 hours, then
Raised to 1250℃, kept for 5 hours, then raised to 1300℃,
It was kept for 5 hours, then raised to 1350°C, kept for 5 hours, and finally raised to 1400°C and kept at this temperature for 10 hours. The progress of the reaction at this stage is monitored as in the first stage nitridation by monitoring the temperature of the mixture and furnace walls, and when necessary diluting the atmosphere with argon to prevent the temperature from becoming too high. controlled. In this second stage of nitriding, the disappearance of reaction heat was understood to indicate that the nitriding was complete. The resulting material was a friable, nitrided mixture that was easily crushed by simple steel ball milling after cooling. There is no need to use costly comminution means such as a geocracker at this stage. The powdered material thus obtained was placed in a graphite pot and heated in a furnace to 1600 DEG C. at a heating rate of 10-15 DEG C. per minute in a non-oxidizing atmosphere. In this example, the non-oxidizing atmosphere is nitrogen at 1 atmosphere. This material was kept at this temperature for 5 hours during which time it reacted. After the reaction, the material was removed from the furnace and allowed to cool to room temperature. The resulting ceramic material was friable and required only a small amount of force to powder it for subsequent use. However, the X of this substance
Line spectral analysis shows that it contains 30% by weight of α-phase substituted silicon nitride of formula Y _0.4 Si ₁₀ Al ₂ O _0.8 N _15.2 , and 50% by weight of β-phase substituted silicon nitride of formula Si _4.6 Al _1.4 N _6.6 O _1.4 , and further 15 It was shown to consist of % by weight of unreacted alpha silicon nitride and 5% by weight of yttrium oxide. This product does not contain a high proportion of α'-phase substituted silicon nitride and therefore does not fall within the scope of the present invention, and it is considered as a control experiment for the examples below. Experiment (2) above was repeated for several samples (Examples 3-6). However, in the final sintering step, the temperature of each sample was set higher in sequence,
As in Example 2, it was kept at the specified temperature for 5 hours. The results of these experiments are shown in Table 1.

[Table] From Examples 2 to 5 in Table 1, it can be seen that the ratio of α-phase material to β-phase material in the ceramic materials made can be controlled by the temperature of the last sintering step, and for a constant sintering The higher the temperature in time, the more α
It can be seen that the amount of phase substances increases. Under the above conditions, that is, under 1 atmosphere of nitrogen in the above experiment, the maximum temperature at which the maximum amount of α-phase substituted silicon nitride was formed was:
The temperature was on the order of 1820℃. The lowest temperature at which a high proportion of α-phase substituted silicon nitride is present, ie greater than 50%, was determined to be on the order of 1650°C. A further series of experiments were carried out using the pre-sintered samples according to Example 2 to study the effect of time on temperature and of temperatures higher than the maximum temperature used in the experiments in Table 1. The results are shown in Table 2.

[Table] From the above table, for example, from Examples 11, 8, and 6, it can be seen that the α/β phase ratio increases as the time at a given temperature increases. However, from Examples 8 and 9, the α/β phase ratio begins to decrease when the temperature is raised to 1870°C for 2 hours under the condition of 1 atm nitrogen, while from Example 10, dissociation does not occur after 2 hours at 1900°C. It can be seen that other phases begin to appear in the friable product. In conclusion, therefore, α-phase-rich products can be made at temperatures up to on the order of 1900°C, and temperatures on the order of 1820°C can produce accurate products with reasonable sintering times (on the order of 5 hours). It seems that it allows for a lot of control. It is also understood that the absolute value of such temperature will also be influenced by other conditions within the furnace, e.g. pressure, and in order to quantify the conditions of the manufacturing equipment to be used some It may be useful to perform preliminary experiments. Although silicon, aluminum, silicon nitride, alumina, and yttrium oxide were used as starting materials in the examples described above, useful brittle ceramic materials may be prepared using yttrium nitride and/or other modifying cations such as calcium, Lithium, magnesium or cerium oxides and/or
Or it will be understood that it can be obtained using nitrides. Furthermore, it will be appreciated that the use of silicon nitride as one of the starting materials is not essential. However, since the nitriding operation is antithermal, it is advantageous to include silicon nitride. This is because this not only helps to control the exothermic reaction, but also allows high nitriding temperatures to be used without thermal runaway, thus allowing an overall highly efficient nitriding step. It is from. For the same reason, aluminum nitride can be included as one of the starting materials in addition to or instead of aluminum. However, as the amount of silicon nitride and/or aluminum nitride is progressively increased while decreasing silicon and/or aluminum, respectively, the effectiveness of the present invention decreases. Therefore, preferably silicon nitride and/or
Alternatively, it is contemplated to include aluminum nitride in an amount such that the weight ratio of silicon nitride to silicon or aluminum nitride to aluminum is not greater than 3:1. In a series of examples according to the subject of the invention, a high proportion of α-phase substituted with 72% by weight of α′ phase and 28% by weight of β′ phase (β-phase substituted silicon nitride) was prepared according to Example 4. 800 g of a friable intermediate powder sample with silicon nitride was ground using a spherical mill containing various Al ₂ O ₃ balls (i.e. 1/4″, 1/2″, 3/4″) over a period of 24 h. 3.47 wt _{% Al2O3}
Increase or grind for 24 hours in a cylindrical mill
It gave _{an Al2O3} increase of 5.41% by weight. Another 800 g sample was each processed in a cylindrical mill using 1/4" diameter balls, increasing Al ₂ O ₃ by 6.88% by weight in 24 hours, 48
Grinded to give an Al ₂ O ₃ increase of 9.19% by weight in time. All treatments were performed using isopropyl alcohol (i
-p-a) was used as the carrier liquid. Dry each slurry in an air oven at 120℃, sieve the powder, and then
It was isotropically pressed at 20,000 psi (140 MN·m ^-2 ) to form a billet for sintering under a nitrogen atmosphere.
Table 3 shows the processing conditions, the products obtained and their properties.

[Table] It can be seen from Examples 12-15 that useful engineering ceramics with good density, strength and hardness properties were made. It is estimated that for Al ₂ O ₃ increases of more than 7.5% by weight, no α' phase is detected, but the predominant phase in this condition is the β' phase on the order of 85% by weight. Alumina content is about 7.5% by weight
As the amount becomes smaller, the amount of α' phase gradually increases. If, in the examples herein, the intermediate phase contains on the order of 28% by weight β' phase, making a dense final product containing less than this amount of β' phase without adding aluminum nitride to the mixture I can't. If a product containing less than 28% by weight β' phase is required in the final product, the intermediate phase must have an appropriate amount of β' phase or an appropriate amount of aluminum nitride must be added. The alumina content is less than the order of 10% by weight,
And by increasing the amount to more than 7.5% by weight, there are many β' phases with a z value of 0.75 < z < 1.5,
It can be ensured that a product with a controlled amount of other crystalline phases is obtained. In Example 16 according to the subject of the invention, in order to extend the range of materials obtained, and in particular to be able to control the z-value of the β' phase to a lower value than can be obtained with alumina increase alone, alumina powder is added. In addition, silicon nitride powder was used. 75 parts by weight of the intermediate powder according to Example 5 was added to
It was mixed with 25 parts by weight of silicon nitride powder supplied by Kennametal and ball milled in isopropyl alcohol using alumina balls for 72 hours.
At this point the starting mixture was found to have an alumina gain of 8.89 parts by weight. The fine powder thus produced was then dried, isostatically pressed as in Examples 12-15 and sintered under nitrogen atmosphere at 1600°C for 2 hours followed by 1750°C for 5 hours. The resulting product contains β' phase material as the main constituent, along with 12H on the order of 3% by weight, has a density of 3.23 gcc ^-1 and a three-point bending modulus of failure of 89800 psi at room temperature.
(620 MNm ^-2 ), exhibiting Rockwell A hardness of 92.
The z value of the β′ phase material was found to be 0.8. Additionally, samples were made using Si ₃ N ₄ and Al ₂ O ₃ as in Example 13, and using the brittle intermediate of Example 5. The treatments and materials obtained are shown in Table 4.

Table: Examples 16-19 consistently make it possible to produce products with a high proportion of β' phase while allowing the z value to be lowered to less than that obtained with alumina alone. It will be noted that in Example 19 Y ₂ O ₃ was added to the starting materials. This is because the amount of intermediate phase is small (28.6 parts by weight) and therefore yttrium from the α' phase is insufficient in glass formation to aid in densification. Y ₂ O ₃ was therefore added to compensate for this deficiency. However, it will be understood that other glass-forming metal oxides or nitrides may also be added, such as oxides or nitrides of magnesium, manganese, iron, lithium, calcium, cerium and the lanthanide series and other rare earth elements. . These additives can be in the form of compounds which can be transformed into the required state, but preference is given to using oxides of metals which form cations of the α' phase. According to the comparison of Examples 18 and 19, the final β′ phase z
An increase in value can be achieved by increasing the amount of alumina and intermediate phase and decreasing the amount of silicon nitride. In Examples 18 and 19, the total amount of yttrium is substantially the same. Examples 16 and 17 were modified to create an α′ phase in the final product, and the alumina content was adjusted accordingly.
Reduce to 6.13 and 8.1% by weight and repeat. The product obtained contains an α′ phase and is 15% by weight when using the starting material of Example 16 but with a lower Al ₂ O ₃ content.
It was found to contain 5% by weight of α' phase when using the starting material of Example 17 but with a lower Al ₂ O ₃ content. Example 16 (ie, high proportion of intermediate powder and high α' phase content) was repeated with the amount of alumina reduced to 2% by weight. The product obtained contained 80% by weight of α' phase. In Example 20 of the present invention, 95 parts by weight of a brittle ceramic material made according to Example 5 (92.6% α' phase, 7.4% β' phase) were combined with 5 parts by weight of silicon nitride from Example 1. Mixed and the mixture was ground to fine particles in a colloid mill. It will be appreciated that in colloid milling, component enrichment from the grinding media does not occur as occurs in alumina ball milling. The powder was placed in a 2 inch (51 mm) diameter graphoid die (which is richly coated with boron nitride) and heated to 4600 psi (31.7 MPa).
After hot pressing at ₁₇₅₀ °C for 1 hour under the _pressure of
A dense product was formed consisting of % β' phase (z value = 0.2), 2% glass containing yttrium and no trace of free silicon. Although high density was achieved in this example by heat pressing, it is possible to achieve the same density without using pressure by ensuring that some alumina is included in the mixture, for example by alumina ball milling. I can do it. However, the incorporation of such alumina reduces the weight proportion of α-phase substituted silicon nitride of the general formula Yx(Si,Al) ₁₂ (O,N) ₁₆ in the final product. Although examples are shown using yttrium as the cation-modifying element, the methods and products of the invention are equally accomplished using other cation-modifying elements such as calcium, lithium, magnesium, and cerium. Although in the examples described above alumina and/or silicon nitride were added to the intermediate containing the α' phase, silicon, nitrogen, aluminum and oxygen may be used in place of or in conjunction with the compounds described above. It will be understood that it can be introduced by For example, silicon oxynitride or the polytype mentioned at the beginning could be used. In Example 21 of the present invention, 12 parts by weight of the intermediate powder according to Example 7 (containing 87% by weight of α' phase and 13% by weight of β' phase) were combined with 76 parts by weight of silicon nitride, 7 parts by weight. 21R of UK Patent No. 1573199, and 5 parts by weight of Y ₂ O ₃ (added due to the small amount of intermediate as described in Example 19) and the whole is mixed with alumina medium. Milled in a ball mill, resulting in an increase of 2.91 parts by weight. Sintering at 1750℃ for 5 hours and followed by
By baking at 1400℃ for 5 hours, it can be heated at room temperature.
99700psi (690MNm ^-2 ), 52200psi at 1200℃
A product with a modulus of (360 MNm ^-2 ) and a Rockwell A hardness of 92 was obtained. This confirms a high proportion of β' phase and approximately 5% by weight of α' phase. The z value of the β′ phase was 1.2. Control of the z-value can be achieved by increasing the z-value by decreasing the silicon nitride and increasing the amount of polytype and/or alumina by that amount, and vice versa for decreasing the z-value. Also, if an increase in the α' phase content in the final product is desired, this can be done by increasing the amount of intermediate while decreasing the amount of silicon nitride, and by decreasing the alumina content; or by adding Y ₂ O. This can be achieved by increasing the intermediate content while decreasing the amount of ₃ .
When reducing the α' phase of the final product, it is desirable not to reduce the amount of intermediates below 5% of the starting mixture and to keep the weight proportion of the intergranular glass layer within acceptable limits. Examples 12 to 21 contain α-phase substituted silicon nitride in the starting mixture made by the second method of the invention (i.e., a method that does not require an expensive comminution process and provides a more friable powder). Although the powder containing a high proportion was used, the powder was prepared using other methods such as Example 1.
can be made by the method described in , and is a good product obtained according to the first subject of the invention. However, it is clearly preferred to use powders made according to the second subject of the invention. Examples include controlled beta-phase substituted silicon nitride, and good products with or without alpha-phase substituted silicon nitride include alpha-phase substituted silicon nitride with or without beta-phase substituted silicon nitride. Although it has been exemplified that it can be made from a powder, it is preferred to use a starting powder that is rich (>90%) in alpha-phase substituted silicon nitride, as this enhances the thermodynamic behavior of the reactants. Another reason why a high proportion of alpha-phase intermediates is preferred is that it provides greater control over the composition of the resulting product compared to products obtained by routes using polytypic intermediates in the absence of alpha-phase intermediates. The goal is to make it possible to make it wider.

Claims (1)

[Claims] 1. A high proportion of α-phase substituted silicon nitride according to the formula Mx (Si, Al) ₁₂ (O, N) ₁₆ (where x is not greater than 2 and M is a modifying cation). mixing ceramic powder containing at least one silicon nitride and/or alumina, provided that the alumina does not exceed 10% by weight of the mixture; and heating the mixture at 1700°C to 1900°C.
sintered in a _non -oxidizing _atmosphere at _{a temperature} of (2) a high-density ceramic material consisting primarily of β-phase substituted silicon nitride and a small amount of another phase containing the above-mentioned modifying cation M; or (2) the above-mentioned β
High density consisting mainly of phase-substituted silicon nitride, a controlled amount of α-phase substituted silicon nitride according to the formula Mx(Si,Al) ₁₂ (O,N) ₁₆ , and a small amount of another phase containing the above-mentioned modifying cation M. A method for producing a high-density ceramic material, comprising the steps of making a ceramic material. 2. The method according to claim 1, wherein the modifying cation is yttrium, calcium, lithium, magnesium, or cerium. 3. A method according to claim 1, wherein the dense ceramic material (2) contains from 0.05 to 90% by weight of alpha-phase substituted silicon nitride according to the formula Mx(Si,Al) ₁₂ (O,N) ₁₆ . 4 Ceramic substance (1) or ceramic substance (2)
A method according to claim 1, comprising from 0.05 to 20% by weight of another phase. 5. The method according to claim 1, wherein the alumina content of the mixture containing ceramic powder is 7.5% by weight or less. 6. The method of claim 1, wherein the ceramic powder is 5 to 96.5% by weight of the mixture containing the ceramic powder. 7 Ceramic powder is present in an amount less than 30% by weight of the mixture containing the ceramic powder, and the mixture containing the ceramic powder contains yttrium oxide, calcium oxide, lithium oxide, cerium oxide, rare earth element oxide and 2. The method of claim 1, further comprising at least one glass-forming metal oxide selected from oxides of lanthanide elements, magnesium oxide, manganese oxide, and iron oxide. 8. A method according to claim 7, wherein the at least one glass-forming metal oxide is present in an amount of less than 10% by weight of the mixture comprising ceramic powder. 9. A method according to any one of claims 1 to 8, wherein silicon nitride is present in an amount of up to 75% by weight of the mixture comprising ceramic powder. 10. The method of claim 9, wherein the silicon nitride is present in an amount of 5 to 75% by weight of the mixture containing the ceramic powder. 11. The method according to any one of claims 1 to 10, wherein the product is reheated after cooling to devitrify the glass phase. 12. The method of claim 11, wherein the reheating temperature is not higher than 1400°C. 13. Heating a powder mixture of silicon, aluminum, alumina, and an oxide or nitride of a modifying cation under a nitriding atmosphere at a temperature below the melting point of aluminum until this first stage nitridation is substantially complete. carrying out a first stage nitriding by heating the first stage nitrided mixture at a temperature below the melting point of silicon while maintaining a nitriding atmosphere until this second stage nitriding is substantially complete; carrying out a second stage of nitriding, thereby producing a friable material; comminution of the friable material thus obtained; and subsequent pulverization of the finely divided friable material at a temperature between 1650°C and 1900°C. Sintering while maintaining a non-oxidizing atmosphere results in α-phase substitution according to the formula Mx(Si,Al) ₁₂ (O,N) ₁₆ , where x is not greater than 2 and M is a modifying cation. silicon nitride 50
Friable ceramic material containing more than % by weight,
or a mixture of the α-phase substituted silicon nitride described above and the β-phase substituted silicon nitride according to the formula Si _6-z Al _z N _8-z O _z , where z is greater than zero and not greater than 1.5.
To obtain a friable ceramic material containing more than 50% by weight; mixing a ceramic powder formed from the aforementioned friable ceramic material with silicon nitride and/or alumina, provided that the alumina is more than 10% by weight of the mixture; and this mixture is sintered at a temperature between 1700 and 1900°C under a non-oxidizing atmosphere for at least 10 minutes at 1900°C to obtain (1) the general formula Si _6-z Al _z N _8-z O _z (where z is greater than zero and not greater than 1.5) and a small amount of another phase containing the above-mentioned modifying cation M; or ( 2) β mentioned above
phase-substituted silicon nitride, consisting primarily of a controlled amount of α-phase substituted silicon nitride according to the above-mentioned formula Mx(Si,Al) ₁₂ (O,N) ₁₆ , and a small amount of another phase containing the above-mentioned modifying cation M A method for manufacturing ceramic materials, comprising the steps of creating a high-density ceramic material. 14. The method according to claim 13, wherein the modifying cation is yttrium, calcium, lithium, magnesium or cerium. 15. A method according to claim 13, wherein the dense ceramic material (2) comprises from 0.05 to 90% by weight of alpha-phase substituted silicon nitride according to the formula Mx (Si, Al) ₁₂ (O, N) ₁₆ . 16 Ceramic substance (1) or ceramic substance (2)
14. A method according to claim 13, comprising from 0.05 to 20% by weight of another phase. 17 Claim 13, wherein the alumina content of the mixture containing ceramic powder is 7.5% by weight or less
The method described in section. 18. The method of claim 13, wherein the ceramic powder is 5 to 96.5% by weight of the mixture containing the ceramic powder. 19 Ceramic powder is present in an amount less than 30% by weight of the mixture containing the ceramic powder, and in the mixture containing the ceramic powder, yttrium oxide, calcium oxide, lithium oxide, cerium oxide, rare earth element oxide and Claim 1 contains at least one glass-forming metal oxide selected from oxides of lanthanide elements, magnesium oxide, manganese oxide, and iron oxide.
The method described in Section 3. 20. The method of claim 19, wherein the at least one glass-forming metal oxide is present in an amount less than 10% by weight of the mixture comprising ceramic powder. 21. A method according to any one of claims 13 to 19, wherein silicon nitride is present in an amount up to 75% by weight of the mixture comprising ceramic powder. 22. The method of claim 21, wherein silicon nitride is present in an amount of 5 to 75% by weight of the mixture containing ceramic powder. 23 Claims 13 to 22, in which the product is reheated after cooling to devitrify the glass phase.
The method described in any one of the paragraphs. 24. The method of claim 23, wherein the reheating temperature is not higher than 1400°C.