BE679392A - - Google Patents

Description

  

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   The present invention relates to refractory dispersions and, in particular, to dispersions comprising molybdenum, tungsten, chromium, rhenium, iron, coba, nickel and their alloys / containing, in dispersion, sodium nitride. silicon, as well as a pressing / adjuvant, selected from magnesium nitride, lithium nitride, aluminum oxide, magnesium oxide, silica, boric oxide and the spines of an oxide divalent, such as magnesium oxide, iron oxide, cobalt oxide, and nickel oxide associated with a trivalent oxide such as aluminum oxide, aluminum oxide, iron and chromium oxide, provided that the divalent oxide and the trivalent oxide are not oxides of the same metal.

   The invention also relates to the preparation of these dispersions and to their use as high temperature refractories as well as as cutting tools.



   Metals suitable for use in the dispersions according to the present invention are molybdenum, tungsten, chromium, rhenium, iron, cobalt, nickel and various alloys. Small amounts of other conventional alloying agents can be used with these metals, as discussed in more detail later in this specification. Silicon nitride can be used alone or in combination with other stable refractory filings,

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The term "pressing aid" refers to an agent which promotes or facilitates pressing or compression.

   As pressing aids suitable for use in the dispersions according to the present invention, there may be mentioned refractory compounds such as magnesium nitride, lithium nitride, aluminum oxide, magnesium oxide, silica, etc. boric oxide and spinels consisting of a divalent oxide, such as magnesium oxide, iron oxide, cobalt oxide and associated nickel oxide, in amounts substantially equimolar to one oxide tri- valent, such as aluminum oxide, iron oxide and chromic oxide, it being understood that the divalent oxide and the trivalent oxide should not be oxides of the same metal. These compounds can be obtained from ordinary commercial sources, provided they exhibit the desired degree of purity.



   The dispersions according to the present invention are prepared by intimately mixing silicon nitride and a pressing aid with the metal, all of these elements being in the form of very fine particles, until a homogeneous dispersion is obtained. This homogeneous powder can be heated and pressed or compressed to the desired shape and degree of density.



   The preparation of the powder dispersions is important, since the properties of the refractory dispersions formed from these powder dispersions depend, to a large extent, on the composition of the powder: Thus, the homogeneity of the metal dispersion , nitride and pressing aid, the size of crystals and final particles of nitride, pressing aid and metal, and the proportions

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 The relative amounts of metal, press aid, and nitrous are important in imparting the desired properties to the refractory dispersions of the present invention and are largely determined by the powder which is used to form the refractory dispersion.



   The particle size of the constituents incorporated in the powder dispersions should be as low as practicable. The preferred maximum particle size is about 50 microns. The desired homogeneity of the dispersion is much easier to achieve as the particle size decreases and it is advantageous if the components are in the form of particles having, on average, less than 10%. microns.



   When the powders dispersed in each other are to be used to form very strong refractory products, such as cutting tools and drill bits, it is preferred that the average particle size is less than 1. micron. Such a particle size contributes significantly to imparting the desired mechanical strength, toughness and wear resistance to refractory dispersions and is necessary for products such as cutting tools.



   The proportion of silicon nitride in the powder dispersions according to the invention is between approximately 1 and 98 parts by volume of silicon nitride per part of metal. If the amount of silicon nitride is less than 1 part by volume per part of metal, the hardness of a refractory dispersion having this composition is less than the desired value.



   Amounts of silicon nitride greater than 98 parts per part of metal tend to significantly reduce the impact resistance of the products.

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 refractories having this composition.



   A preferred amount of silicon nitride is between about 1.5 and 19 parts by volume per part of metal when the metal is molybdenum, tungsten, chromium or rhenium and between about 3 and 50 parts by volume per part of metal, when the metal is iron, cobalt or nickel. When the amount of silicon nitride is reduced to the preferred values, the probability of a continuity of the metallic phase in the refractory dispersion to be formed is increased, which increases the chances of obtaining a continuity. impact resistance, mechanical strength, toughness, as well as other outstanding properties.



  On the other hand, the presence of an amount at least equal to the minimum preferred amount of silicon nitride imparts hardness, wear resistance, chemical resistance, etc., to a refractory dispersion containing this amount of nitride. , which make this dispersion very suitable for obtaining refractory products usable as cutting tools, drill bits and similar devices.



   The amount of the pressing aid contained in the powder dispersions according to the present invention ranges from about 0.02 part to 10 parts by volume per part by volume of metal.



  When the amount of press aid is less than about 0.02 part by volume per part of metal, it is difficult to achieve the desired degree of density in a refractory dispersion containing such quantity of press aid. at temperatures low enough to prevent thermal decomposition of the silicon nitride. Amounts of adjuvant of

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 Pressing greater than about 10 parts by volume per part by volume of metal confers little benefit to a refractory dispersion.



   A preferred amount of pressing aid is between 0.06 part and 7 parts by volume per part of metal. The presence of at least 0.06 part by volume of pressing aid per part of continuous metal in the powder makes it possible to obtain a degree of density which greatly increases the usefulness of the dispersion.
When the amount of the press aid is less than about 7 parts by volume per part of metal, the metal tends to constitute a continuous phase in the refractory dispersion containing that metal.



   One of the preferred embodiments of the invention is a powder dispersion, in which the nitride particles and the particles of the pressing aid are separated from the like particles by particles of metal. This prevents or decreases the agglomeration or joining of the discrete nitride particles and helps to increase the density of the components during the manufacture of the refractory dispersions.



   Another preferred embodiment of the invention is a dispersion in which distinct particles of silicon nitride and pressing aid are uniformly dispersed in the metal which is present as a continuous phase. or a vehicle separating the distinct particles. Such a distribution of the metal ordinarily results in substantially better mechanical properties in a refractory dispersion, making these more suitable for the manufacture of products such as cutting tools and drill bits.

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   It is desirable that the silicon nitride, the pressing aid and the metal used have high chemical purity. Thus, it is, in particular, desirable to avoid the presence of any of the following *. of carbon, oxygen, nitrogen, carbon, silicon or sulfur, both uncombined and in the form of a compound having a free energy of formation per atom less than that of oxides, nitrides , borides, silicides, or corresponding sulphides of molybdenum, tungsten, chromium, rhenium, iron, cobalt or nickel, or the corresponding carbides of molybdenum, tungsten, chromium or rhenium.

   Other such elements, in a form and in amounts capable of reacting with the metal or dissolving the metal used in the manufacture of the refractory dispersion, so as to render the metal unduly brittle, should also be excluded.



   Small amounts of alloying agents commonly used with molybdenum, tungsten, chromium, rhenium, iron, cobalt or nickel can be employed in the dispersions according to the present invention. provided that these alloying elements are retained in the form of a homogeneous solution with the metal, this solution having the crystal structure of the metal.



  Elements such as molybdenum, tungsten, chromium, manganese and others can be used in amounts up to 30% by weight of iron, cobalt or nickel. It is preferred to use molybdenum, tungsten and chromium in amounts of up to about 20% by weight of iron, cobalt or nickel, to form a product having exceptional toughness. desired, elements such as aluminum, titanium, boron and

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 Silicon can be used in amounts of up to 5% by weight of iron, cobalt or nickel. Carbon can be used in amounts up to about 1% by weight.

   Quantities of such alloying agents capable of forming intermetallic compounds or new crystallographic phases should be avoided. The allowable proportions of these agents can be determined, according to this criterion, by consulting the appropriate phase diagrams found in many metallurgical works. Proportions of these agents, such as proportions of up to 10 % iron in tungsten, up to 30% iron in chromium, small percentages of iron, titanium or zirconium in molybdenum and smaller amounts of nickel or cobalt can be used with co @@ positions of molybdenum, tungsten, chromium or rhenium.



   Chemically stable refractory compounds can be used to replace silicon nitride in dispersions according to the present invention in amounts less than 50% of the volume of silicon nitride. Among these nitrides, mention may be made of titanium nitride, aluminum nitride, zirconium nitride, hafnium nitride, tantalum nitride, uranium nitride, cerium nitride and sodium nitride. thorium.

   These nitrides can replace part of the silicon nitride. Stable carbides, such as titanium carbide, zirconium carbide, tungsten carbide, hafnium carbide, chromium carbide, tantalum carbide , molybdenum carbide and niobium carbide, as well as silicides and disilicides of chromium, molybdenum and

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 tungsten, can be used in similar amounts. It is, however, essential that silicon nitride always constitutes more than 50% of the non-metallic constituents of the dispersions according to the present invention.

   It is also essential, as has already been pointed out, not to use refractory compounds which may react with the metal in such a way as to make it brittle or brittle or which may decompose so as to form similar elements, including presence cannot be admitted for the same reason,.



   Preparation of metals.



   Metals which can be used in the dispersions according to the present invention with the desired degree of hardness can be obtained from commercial sources or can be prepared in a routine manner. A suitable process for the preparation of these metals for incorporation into the dispersions according to the present invention is the process of reduction with low temperature hydrogen of the corresponding metal oxide.



   Iron, cobalt and nickel can be prepared by reduction with hydrogen of the corresponding metal oxide or carbonate at temperatures between about 600 C and 1200 C.



   For the preparation of molybdenum and tungsten, the oxides of which are somewhat volatile at other temperatures, it is better to carry out the reduction in phases. The oxide is first reduced to a lower valence oxide, such as tungsten dioxide or molybdenum bi: xide at a temperature below the melting point of the oxide, for example at 600 Ce The reduction is, then completed at a higher temperature, eg, 900 ° C, this temperature being sufficiently low to avoid excessive sintering of the powdered metal.

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   The reduction is followed by grinding in an inert liquid medium and, if necessary, purification with hydrochloric acid. In this way, the pure metal can be obtained in the form of a powder having, preferably, a specific surface area greater than 1 m2 per gram, which makes the metal suitable for subsequent dispersal with it. silicon nitride. Are the grinding elements used during operations desireable? of grinding materials are made of the same metal as that which is prepared, so that no foreign matter is introduced into this metal, by attribution of the grinding elements or bodies.



     Preparation of silicon nitride.



   Silicon nitride can be prepared by any conventional method, for example by nitrating powdered metallic silicon which has been ground so that the particles are less than 10 microns, at a temperature of .900 to 16000C in. a gaseous atmosphere of nitrogen or cracked ammonia.



   One method is to nitride the silicon powder at a temperature below 1400 C, to prevent the melting of the silicon, for 1 to 5 hours.,
The temperature can then be raised to a value greater than the melt weight of the silicon, ie up to a value of 1450 to 1600 ° C., to complete the reaction.



   In the event that some aggJomeration occurs during the preparation of the silicon nitrides, it is possible to degglomerate the particles, for example by grinding them in a ball mill, in an inert solvent.

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   After grinding, it may be desirable to purify the nitride, for example by treatment with an acid, to remove impurities absorbed during grinding by attrition of the grinding bodies or elements. To avoid the need for such purification, it is preferred to use grinding bodies, such as balls, made of the same metal as that with which the nitride is subsequently interdispersed.



   When it is desired to obtain a very low oxygen content, the silicon nitride can be reduced in an atmosphere, such as a cracked ammonia atmosphere, to remove any oxygen which may be absorbed during the process. purification.



     Preparation. powder dispensations.



   Interdispersions of the metals with silicon nitride, pressing aid, and other refractory compounds, if desired, as an egg-laying form constitute one of the preferred embodiments of the present invention. . The silicon nitride, the pressing aid and any other refractory compounds which may be desired can be interdispersed with the powdered metal, in any suitable manner, for example by mixing, within a hydrocarbon serving as a solvent. or acetone, in a colloid mill or in a ball mill. A grinding or mixing time of between 24 and 500 hours has been found to be satisfactory.



   Since the silicon nitride used in the context of the invention is difficult to purify, it is desirable to use grinding bodies, such as balls, made of the same metal as that with which the silicon nitride. must be inter-dispersed. Grace

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 to this extent, foreign matter cannot get into the dispersion, owing to the attraction of the grinding bodies. The mill may be a mill lined with an elastomeric material, such as neoprene, which is not softened or attacked by the fluid in which the milling takes place. The grinding conditions, such as the volume of the charges of the grinder and the speed of rotation of the latter, should be chosen so as to be optimal, as indicated further in the examples given below.



   After kneading or grinding the mixture until it is homogeneous, the grinding fluid can be removed, by washing with a suitable solvent, such as hexane, and drying in vacuo. Chemical analysis can be performed at this time and, if appreciable amounts of oxygen, carbon or nitrogen are combined with the metal, in any form other than that of the stable refractory compounds mentioned above, the powders. can be reduced to remove these impurities. This reduction is preferably carried out at a temperature below 1000 ° C., using pure and very dry hydrogen.



   The average particle size can easily be determined: by examining the interdisperse powders by means of an ordinary microscope for the larger particles and by means of an electron microscope for the smallest particles. The term "average particle size" refers to the average diameter of the particles.



  In preferred powder dispersions, the area per cm3 of the solid particles is between about 3 and 180 m2. The area per m3 can be determined by dividing the specific area, measured by techniques

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 absorption of nitrogen, by the density of solids contained in the disperaion.



     Preparation of refractory dispersions.



   The interdisportions of the metals with the silicon nitride, the ad @ before pressing and any other reactive compounds which may be desired, in the form of solid or solid matter, constitute another form. preferred embodiment of the present invention. An exemplary method of forming such dispersions includes heating and pressing or compressing the powdered dispersions to substantially the theoretical density, if desired, in a nitrogen atmosphere.



   The temperature at which the compression takes place depends on the amount of metal used, its state of subdivision, as well as / the composition and state of subdivision of the silicon nitride and the pressing aid. . In general, temperatures will be between @ / 10 and 9/10 of the melting point, expressed in degrees Kelvin, of the metallic component and must be at least 1600 C, without exceeding 18500C, in the case of molybdenum, tungsten - ne, chromium or rhenium and at least 10000C. preferably about 16000C to 18500C in the case of iron, cobalt or nickel.



   The time during which the compact compressed product resided at the maximum temperature used and remained subjected to the maximum pressure used varies according to the temperature of the compression or of the pressing, according to the composition and to the state of dispersion. In general, this duration can be between a few seconds and several hours, for example 4 hours or more.

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   The pressure used also depends on the above-mentioned variable factors, but is generally between 35 and more than 420 kg / cm2.



   The various possible combinations of compressing or pressing conditions will be further illustrated in the examples given later.



   Another method of interdispersing the constituents with each other, prior to the preparation of a solid interdispersion - is to precipitate the metal to be used on previously prepared fine particles of silicon nitride and. pressing or compression aid. The metal can be precipitated, for example, in the form of a hydrous metal hydroxide or carbonate, and the resulting nogenous mixture can then be reduced in an atmosphere both high in nitrogen and in nitrogen. hydrogen, such as an atmosphere of cracked ammonia. This allows the reduction of the oxides of the metals present without causing a change in the silicon nitride used.



   When a refractory dispersion has been prepared, the particle size of the constituents of that dispersion can be determined by preparing a section, metallographically, etching this section with an appropriate chemical and examining the surface with a hand. microscope, using an optical microscope or an electron microscope, as required. When an electron microscope is to be used, a carbon or plastic replica of the surface is first prepared and measurements made on this replica.



   The nature of the interdispersion of the metal nitride and the pressing aid with the metal, as well as the dimensions of the metal in the refractory dispersions according to the present invention are a function of the conditions.

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 tions of manufacture and the volumetric fraction employed, as well as the nature of the starting material.

   Some agglomeration of the silicon nitride particles and the press aid particles does occur, but, as already noted, one of the preferred embodiments of the invention is one in which most of the particles of silicon nitride and pressing aid are separated from the like particles .; by a certain amount of a continuous metal phase, which results in a homogeneous uniform dispersion of the distinct particles of silicon nitride and the pressing aid.



   We prefer \. in particular, that the homogeneity of the dispersion be such that the distribution of silicon nitride, of the pressing aid and of the metal in the refractory dispersion be varied on a scale of 100 microns.



   This means an etallographic examination or an examination or scanning of a photomicrograph under an electron microscope, which techniques are used. commonly in metallurgy to examine the structure of mountain pastures, reveals the presence of silicon nitride, pressing aid and metal in a square region not exceeding 32 microns per side and preferably not 10 microns per side. Additionally, in the preferred embodiment of the present invention, each 10 micron square region which is examined will exhibit substantially the same structural characteristics as the various other regions of the dispersion, in classic statistical distribution limits.



   The presence of a continuous phase of the metal in the preferred refractory dispersions according to the present invention can be determined, in a simple manner, by measuring the electrical resistivity of the dispersion. Since the

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 Silicon nitride is an excellent electrical insulator, when it is distributed in such a way as to interrupt the continuity of the metal, the electrical resistivity of the refractory dispersion is excessively high. On the other hand, if one of the metals is distributed so as to form a continuous phase in a refractory dispersion according to the present invention, the electrical resistivity of the dispersion is inversely proportional to the volumetric fraction and to the thickness of the dispersion. the continuous phase of the metal component.

   Appreciable continuity of the metallic phase in a refractory dispersion according to the present invention is indicated by a specific electrical resistivity of less than about 10,000 ohm cents, and in preferred refractory dispersions the specific electrical resistivity is lower. - re about 500 ohm centimeters.



   The refractory dispersions according to the present invention have a density greater than 90% of the theoretical density and, preferably, greater than 95% of the theoretical density. The refractory dispersions which are to be used for cutting tools should preferably have a density greater than 98% of the tea oric density and should be substantially free of boron when subjected to a high density. metallographic examination. Theoretical density is calculated, assuming the specific volumes of the individual constituents are added.



   The density of the reactive dispersions according to the present invention can be determined by any technique which permits simultaneous determination of the weight and volume of the composite material. In the simplest method, the weight can be determined using a sensitive analytical balance, while the volume can be determined by displacement of water or mercury.

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   Refractory products in the form of cutting tools or drill bits are particularly preferred embodiments of the invention. In these composite refractory products, distinct particles of silicon nitride, distinct particles of a pressing or compression aid and distinct particles of other possible refractory compounds, having an average size of less than 1 micron, are homogeneously dispersed in a vehicle or continuous phase of molybdenum, tungsten, chromium, rhenium, iron, cobalt, nickel or their alloys, so that the uniformity of the gauge extends to less than 100 square microns .

   The average size of the crystals of the metal in the composite product is less than 1 micron and the continuity of the metallic phase is such that the composite product has an electrical resistivity of less than 1 ohm-centimeter. The amount of silicon nitride and any other compounds is between 1.5 and 19 parts by volume per part of metal, when the metal is molybdenum, tungsten, chromium or rhenium, and between 3 and 50 parts by volume per part of metal when the metal is iron, cobalt or nickel, the amount of pressing aid is between 0.06 and 7 parts by volume per part of metal, and density of the composite product exceeds 99% of the theoretical density.

   Pressing aids or agents useful for compressing dispersions are, for such a composite material, magnesium nitride, lithium nitride and magnesium oxide nitride, the preferred metals being molybdenum, cobalt and tungsten.

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   The refractory dispersions according to the present invention are hard, strong and remarkably resistant to chemicals, thermal shock, corrosion, mechanical shock and high temperatures. They exhibit high thermal conductivity and electrical conductivity and show remarkable resistance to erosion. These properties make them particularly suitable for use in structural applications, for example in equipment used for carrying out chemical processes and having to resist corrosion and erosion, in the manufacture of high temperature electrodes, in the manufacture of dies or dies, in the manufacture of wire guides, in the manufacture of bearings or bushings and in the manufacture of seals.



   The refractory dispersions of the present invention are particularly suitable for use as bits or the like for cutting, grinding, shaping, perforating, and stamping very hard metals or metal alloys at high speeds. This is due to their high resistance to mechanical shock, high thermal conductivity and extraordinary resistance to thermal shock, wear, crater formation and welding.



   The following illustrative examples will make it possible to better understand the invention.



   EXAMPLE 1.



   200 grams of very finely divided metallic silicon are prepared by grinding, in a ball mill, powdered metallic silicon whose particles have an initial size of about 10 microns. The fine silicon powder is heated at 1360 C for 48 hours in a

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 alumina tube enclosed in an electric furnace, under an atmosphere of gaseous ammonia. The ammonia flow rate is maintained at about 1 liter per minute.



   X-ray identification, as well as surface measurements using nitrogen, indicate that the product obtained is a mixture of alpha and beta silicon nitrides with a surface area of 2.5 m2 / g., which corresponds to an average particle size of the product of about 75 millimicrons. Emission spectrographic analysis reveals that the main impurities are iron, aluminum, magnesium and calcium, with iron and aluminum present at about 1% each.



   The chemical analysis reveals that the oxygen content is 0.63%, the silicon content of 59.4%, the remainder of the composition being constituted by nitrogen (apart from the small amounts of iron, aluminum and other impurities previously reported).



   Electron microscopic photographs reveal the presence of very fine needle-like crystals which are agglomerated into bundles with a diameter of about 1 to 5 microns.



   31 grams of this finely divided powder of silicon nitride, 1.4 grams of powder with particles of less than 10 microns of magnesium nitride and 5.0 grams of finely divided powder of metal molybdenum in particles of less than 10 microns are charged into a rubber-lined steel ball mill with a capacity of 1.1 liters, which is filled to 40% of its volume with cylindrical pellets with a diameter of 6.35 mm and with a length of 6.35 mm of tungsten carbide containing 6% of

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 cobalt, and 350 cc of an ispparaffinic hydrocarbon oil having a flash point of 85 C.



   This composition is ground for 14 hours on rollers lined with rubber, rotating the mill at a speed of 60 revolutions per minute.



   After grinding, the intimate dispersion of metallic molybdenum and the powdered silicon nitride and magnesium nitride is separated by filtration, from the cylinders of tungsten carbide and cobalt used as grinding elements, and separated, by settling, most of the oil of the hydrocarbon type. The dispersion is then washed three times with hexane, each time using two liters of hexane, until it is free of residual oil, after which it is dried in a vacuum oven overnight. . The resulting dispersion is sieved through a sieve with a 0.21 mm mesh.



   Chemical analysis reveals that this dispersion consists of approximately 21.9 parts by volume of silicon nitride, approximately 1.1 parts by volume of magnesium nitride and approximately 0.2 parts by volume of silicon carbide. tungsten per part by volume of a metal consisting of about 97.6% by volume of molybdenum and about 2.4% by volume of cobalt. The tungsten carbide and cobalt presumably arise from the attrition of the grinding rolls used as the grinding body during the grinding operation.



   15 grams of this material is loaded into a carbon mold with a diameter of 2.54 cm and / pressed, in an induction heated vacuum press, applying a press of 280 kg / cm2, which is first applied at a temperature of 10000C, the final temperature being high, while the pressure is maintained, at a value of 1850 C,

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 at which it is held for a further 5 minutes.



   The sample is cooled and the refractory dispersion according to the invention thus obtained is cut into strips of suitable size to enable their mechanical properties and their density to be determined. The transverse breaking strength of this refractory dispersion is 4207 kg / cm2 and its impact resistance is 4.056 kg-meter / cm2. Its density is 3.65 g / cc. Which corresponds substantially to the theoretical density of 1 which one would expect for this composition, assuming that the volumes of the various components add up.



   This refractory material is suitable for use as a structural material at high temperature, since it exhibits excellent resistance to oxidation and excellent mechanical strength, as well as high resistance to thermal shock, even in oxidizing atmospheres. , and this at temperatures up to 1200 to 1400 C.



   EXAMPLE 2.



   31 grams of silicon nitride from Example 1, 1.4 grams of magnesium nitride and 3.6 grams of finely divided powdered metallic chromium, the particles of which are less than 10 microns, are charged and ground in the manner described in Example 1, the durations of the grinding conditions, as well as the equipment and the grinding bodies being identical to those described in Example 1. The recovery of the intimate mixture of silicon nitride, nitride magnesium and chromium is carried out as described in Example 1.

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   Chemical analysis of this dispersion reveals that it contains about 18.6 parts by volume of silicon nitride, about 1.0 part by volume of magnesium nitride and about 0.3 part by volume of tungsten carbide per volume. part by volume of a metal consisting of about 95.8% by volume of chromium and about 4.2% by volume of cobalt.



   17 grams of this dispersion are compressed in an induction heated vacuum press, using the conditions described in Example 1, except that the maximum temperature is 17500C rather than 1850C.



   After cooling and cutting the refractory dispersion according to the invention obtained, into test pieces allowing its properties to be tested, the following values are obtained. Transverse tensile strength is 4413 kg / cm2, impact strength is 3.53 kg-meters / cm2, Rockwell A hardness is 90.2, and density is 3.50 g / cc , ie 99.5% of the theoretical density of the composition.



   This refractory material is suitable for forming a cutting tool for machining or treating steel and cast iron, this tool exhibiting relatively low lateral wear and only slightly giving rise to crater formation when used. uses at cutting speeds up to 102 surface meters per minute with cutting depths of 1.58mm.



   EXAMPLE 3.



   31 grams of silicon nitride from the example
1, 1,., Gram of magnesium nitride and 9.6 grams of powdered metallic tungsten are ground and recovered after grinding in the manner described in Example 1. Chemical analysis of the intimately mixed dispersion obtained

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 discloses that it consists of about 19.1 parts by volume of silicon nitride, about 1.0 part by volume of magnesium nitride and about 0.2 parts by volume of. tungsten carbide per part by volume and a metal consisting of about 97.9% by volume of tungsten and about 2.1% by volume of cobalt.



   16 grams of this dispersion are pressed or compressed in the manner described in Example 1 and the refractory dispersion obtained according to the invention exhibits the following properties: tensile strength 3822 kg / cm2; impact resistance: 1.14 kg-meter / cm2, Rockwell A hardness: 90.85. The density is 4.05 g / cc, which is roughly the theoretical density that would be expected for this composition.



   This refractory material is suitable for use in the manufacture of a cutting tool for processing cast iron, steel, copper, bronze and aluminum.



   EXAMPLE 4.



   31 grams of silicon nitride from Example 1, 1.4 g of finely divided magnesium nitride and 5.1 g of finely divided powdered metallic molybdenum are mixed and ground as described in Example 1, except that steel balls or balls with a diameter of 9.5 mm are used as grinding bodies, instead of the tungsten carbide and cobalt cylinders previously used.



   The extraction out of the mill, the purification and the drying are carried out as described in Example 1. Chemical analysis reveals that the powder obtained consists of approximately 12.4 parts by volume of sodium nitride. silicon and about 0.6 part by volume of magnesium nitride per part by volume of a metal consisting of approx.

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 ron 63.4% by volume of molybdenum and about 36.6% by volume of iron. 23 grams of this dispersion are hot pressed in the manner described in Example 1 and the refractory dispersion obtained is cut into test pieces used to characterize its mechanical properties.



   The transverse breaking strength of this refractory material is 4252 kg / cm2, its impact resistance is 3.43 kg / meter / cm2, and its Rockwell A hardness is 90.1. Its density is 3.61 g / cc, ie the theoretical density.



   EXAMPLE 5.



   31 grams of the silicon nitride of Example 1, 1.4 g of finely divided powdered magnesium nitride, and 3.6 g of finely divided metallic chromium are ground, purified and dried as described in the previous example. - cedent. Chemical analysis reveals that the obtained intimately mixed powder contains about 12.5 parts by volume of silicon nitride and about 0.6 parts by volume of magnesium per part by volume of a metal consisting of about 63%. 4 by volume of molybdenum and about 36.6% by volume of iron.



   This dispersion is compressed in the manner described in Example 2, and the refractory dispersion obtained according to the invention has the following mechanical properties and density:
The transverse breaking strength is 3069 kg / cm2, the impact strength is 3.84 kg-meter / cm2 and the Rockwell A hardness is 90.2. The density is 3.45 g / cc, that is 99.2% of the theoretical density expected for this composition.

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   EXAMPLE 6.



   31 grams of the silicon nitride of Example 1, 1.4 g of fine powdered magnesium nitride and 9.6 g of fine powdered metallic tungsten are mixed and ground as described in Example 4. The recovery , purification and drying are carried out in the manner described in the preceding examples.



   Chemical analysis shows that the intimately mixed wines obtained contain about 11.4 parts by volume of silicon nitride and about 0.6 part by volume of magnesium nitride per part by volume of a metal consisting of about 58 , 4% by volume of tungsten and about 41.6% by volume of iron. 16 grams of this dispersion are pressed in the manner described in Example 1 and the refractory dispersion obtained has the following properties: transverse breaking strength: 2975 kg / cm2; impact: 2.28 kg-meter / cm2, Rockwell A density: 90.1, density: 4.03 g / cc, ie 99.8% of the theoretical density of this composition.



   EXAMPLE 7.



   11.77 grams of the silicon nitride of Example 1, 0.6 g of lithium nitride, 6.52 g of aluminum nitride, 52.11 g of metallic tungsten and 1.35 g of hydride of titanium are ground, using the equipment and conditions described in Example 1. Recovery, purification and drying are also carried out as described in Example 1. Chemical analysis reveals that the resulting fine powder dispersion contains about 1.23 part by volume of silicon nitride, about 0.1 part by volume of lithium nitride and about 0.67 part by volume of aluminum nitride per part by volume of 'a metal consisting of 90% by volume of tungsten and 10% by volume of titanium.

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   28 grams of this dispersion are hot pressed as described in Example 1, except that the maximum temperature is 1900 ° C. and the pressing time is 3 minutes. The refractory dispersion obtained according to the invention has a transverse rupture strength of 8400 kg / cm2, an impact resistance of 1.14 kg-meter / cm2 and a Rockwell A hardness of 88.7. Its density is 7.20 g / cc, ie 99.5% of the theoretical density which is 7.23 g / cc. This refractory material is ideally suited for use in making a cutting tool for processing steel and cast iron.



   EXAMPLE 8.



   15.58 g of the silicon nitride of Example 1, 0.29 g of magnesium orthoborate., 10.0 g of alumina, 24.99 g of finely divided metal molybdenum and 0.32 g of hydride zirconium are ground, using the conditions and equipment described in Example 1. The mixture obtained contains, as revealed by chemical analysis, about 1.96 parts by volume of silicon nitride. , 4 part by volume of magnesium orthobo-rate and 1.0 part by volume of alumina per part by volume of a metal consisting of 98% by volume of molybdenum and 2% by volume of zirconium.



   20 grams of this composition are hot pressed in the manner described in Example 1, except that the pressure used is 420 kg / cm2 and the duration of application of this pressure of 4 minutes, at the temperature. - ture of 1850 C.



   The dense body according to the invention thus obtained exhibits a transverse breaking strength of 5810 kg / cm2, an impact resistance of 9.36 kg-meter / cm2 and a Rockwell A hardness of 88.3. Its density is 4.71 g / cc, or 92.0% of the theoretical density which is 5.12 g / cc,

 <Desc / Clms Page number 26>

 of this composition.



   EXAMPLE 9.



   13.99 grams of the silicon nitride of Example 1, 2.15 g of fine powdered magnesium oxide, 16.2 g of fine powdered titanium nitride. 19.3 g of powdered metallic tungsten and 10.2 g of fine powdered metallic molybdenum are mixed. and ground as described in Example 1. Recovery of the ground product in the mill, purification and drying of this product is also carried out as described in Example 1.



   , Chemical analysis reveals that this composition contains 2.2 parts by volume of silicon nitride, 1.5 parts by volume of titanium nitride and 0.3 part by volume of magnesium nitride per part by volume of a metal consisting of 50% by volume of molybdenum and 50% by volume of tungsten.



   25 grams of this dispersion are compressed at a temperature of 1900 C, applying a pressure of 350 kg / cm2, for one minute.



   The refractory dispersion according to the invention thus obtained has a transverse breaking strength of 5670 kg / cm2, an impact strength of 6.24.
 EMI26.1
 kg-meter / cm2 and a hardness Rktl & ll A of 90.0e Its density is 6.19 g / cc, which corresponds to the theoretical density of this composition
EXAMPLE 10.



   19.08 grams of silicon nitride, 4.00 g of fine powdered almond powder with 300 millimicron particles, 7.29 g of finely divided titanium carbide and 10.65 g of finely divided chromium metal, are crushed ma-
 EMI26.2
 niere described in example 1 # cuper¯. , f:, ¯ ¯a ourifi- c and the drying is also carried out as described in Example 1. Chemical analysis reveals that the dispersal

 <Desc / Clms Page number 27>

 The finely divided fraction obtained contains 4.0 parts by volume of silicon nitride, 1.0 part by volume of titanium carbide and about 0.7 part by volume of alumina per part :; by volume of chromium.



   16 grams of this dispersion are hot pressed at a temperature of 1600 C by applying a press @ n of 420 kg / cm2, for 30 minutes.



   The refractory dispersion according to the invention thus obtained exhibits a transverse breaking strength of 4690 kg / cm2, an impact resistance of 5.2 kg-meter / cm2 and a Rockwell A hardness of 90.0. Its density is
3.90 g / cc, or 95% of the theoretical density of 4.11 g / cc of this composition.



   EXAMPLE 11.



   11.77 grams of the silicon nitride of Example 1, 2.88 g of fine powdered magnesium aluminate spinel, 17.65 g of fine powdered zirconium nitride,
40.53 g of fine powdered metallic tungsten and 18.9 g of fine powdered metallic rhenium are ground as described in Example 1.



   Recovery, purification and drying are also carried out as described in Example 1.



   Chemical analysis revealed that the dispersion contained about 1.23 part by volume of silicon nitride, about 0.83 part by volume of zirconium nitride, and about 0.27 part by volume of sodium aluminate. magnesium per part by volume of a metal consisting of 70% by volume of. tungsten and 30% by volume of rhenium.



   36 grams of this dispersion are pressed, applying a pressure of 35 kg / cm2 and a temperature of 1850 C, for 15 minutes.

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   The refractory dispersion according to the invention thus obtained has a transverse rupture strength of 875 kg / cm2, an impact resistance of 1.66 kg-meter / cm2 and a Rockwell A hardness of 88.7 .



  Its density is 9.17 g / cc, or 100% of the theoretical density which one should expect for this composition.



   EXAMPLE 12.



     1360 grams of particulate metal molybdenum 0.044 mm are placed in a steel ball mill with a capacity of 3.78 liters filled to 40% of its volume with steel balls and also containing 1800 that of a high boiling point hydrocarbon oil. It is crushed at a speed of 30 rpm for 3 days, after which the powdered molybdenum is separated from the hydrocarbon type oil and steelware, to be then washed vigorously with hexane to remove the powder. zero residual and finally be dried in a vacuum oven. This / powder is then treated with a mixture of 1 l of concentrated hydrochloric acid with 1.3 l of distilled water and heated for 1 hour at 90 C.

   This treatment serves to dissolve the iron absorbed during grinding. The powder is then stirred with the mixture of hydrochloric acid and water overnight. The product is then centrifuged to recover the molybdenum and to separate it from the dissolved iron which has been removed by the acid treatment. The molybdenum powder is then washed with 0.1 N hydrochloric acid solution until the wash liquor no longer contains iron. This requires 5 washes. The powder is then washed with distilled water until it is free from chloride ions and the molybdenum powder is finally dried in a vacuum oven.

 <Desc / Clms Page number 29>

 



   The finely divided molybdenum powder thus obtained is in the form of particles with an average size of 100 to 200 millimicrons and contains only traces of iron as an impurity.



   64 grams of the silicon nitride of Example 1, 204 g of said metal molybiene powder, and 1.6 g of anhydrous powdered gamma-alumina in the form of p spherical particles of 20 millimicrons are mixed and ground in a mill. made of steel with a capacity of 3.78 liters, using molybdenum cylinders with a diameter of 6.35 mm as grinding bodies. The mill is filled to 40% of its volume with aluminum grinding bodies and a high boiling point hydrocarbon oil is introduced into it in an amount sufficient to cover the grinding elements of molybdenum, metal, nitride. silicon and alumina powder.



   After grinding for 48 hours, the finely divided powder dispersion according to the invention thus obtained is recovered as described above in other examples.



   40 grams of this dispersion are hot pressed at a temperature of 185uoC, under a pressure of
280 kg / cm2, applying these conditions for 5 minutes.



   The refractory dispersion according to the invention thus obtained consists of a dispersion of 1 part of colloidal silicon nitride and 0.02 part of colloidal alumina, in a continuous phase of one part of metallic molybdenum. The density corresponds to the theoretical density of 6.64 gram / cc. This refractory material constitutes an excellent high temperature structural material due to its good resistance to mechanical impact, high resistance to thermal shock and relatively good resistance to oxidation.

 <Desc / Clms Page number 30>

 



   Metallographic examination of this refractory composition reveals that it is an interdispersion of silicon nitride and alumina in metallic molybdenum. The average particle size of molybdenum crystals is between about 0.4 and 0.8 microns and the average size of silicon nitride alumina particles is about 0.5 microns.



   The metallographic examination of this dispersion reveals, moreover, that the silicon nitride, alumina and molybdenum are all present in a square region of 10 microns on side and that, among 10 regions of a surface of 100 square microns, 9 regions have the same structural characteristics.



   The electrical resistivity of this refractory dispersion is about 1 ohm-cn '. This low value of electrical resistivity indicates that the continuity of molybdenum in this dispersion is not interrupted by silicon nitride or alumina.



   EXAMPLE 13.



   A silicon metal powder in particles of less than 0.044 mm is nitrided as described in Example 1 and the silicon nitride obtained with a size of about 50 microns is mixed, in a proportion of 240 g of this silicon nitride powder, 40 g of the alumina described in the preceding example and 19.2 g of tungsten in particles of less than 0.044 mm. The product obtained is ground in the manner described in the preceding example, if not what. Cylindrical tungsten grinding bodies are used instead of cylindrical molybdenum grinding bodies.

 <Desc / Clms Page number 31>

 



   The purification, the drying and the hot compression are carried out in the same manner as in Example 12. The standard dispersion according to the invention thus obtained consists of 75 parts by volume of silicon nitride and 10 parts by volume. of alumina, per part in v @ - metallic tungsten. The density of this dispersion is 3.48 g per cc, which corresponds to the theoretical density of this composition. This refractory composition is very suitable for use as a cutting tool at surface speeds of up to 150 meters per minute, for the treatment of steel and cast iron.



   EXAMPLE 14.



   314.6 grams of silicon nitride from the previous example, 40 g of the alumina of example 12 and 19.2 g of metallic tungsten in particles of less than 0.044 mm are ground as described in *! 1 Example 12, except that cylindrical tungsten grinding bodies are used instead of cylindrical molybdenum grinding bodies. The hot pressing is carried out in the manner described in Examples 12 and 13. The dense composition obtained according to the invention consists of 98 parts of silicon nitride and 10 parts of alumina dispersed in a mixture. part of metallic tungsten. The density of this composition is 3.43 g / cc, which corresponds to the theoretical density of the composition.

   This refractory composition is also suitable for use as a cutting tool or as a high temperature refractory material. Examination of photographs under an electron microscope reveals the presence of very fine eye crystals which are agglomerated or united in bundles with a diameter of about 1 to 5 microns.

 <Desc / Clms Page number 32>

 



   EXAMPLE 15.



   29.7 grams of the silicon nitride of Example 1, 1.46 g of particles of 300 mm of magnesium nitru- re and 1.53 g of particles of 300 mm of powdered metal containing iron and metal boron in proportions by weight of 99 parts of iron to 1 part of boron, are charged into a rubber-coated steel ball mill with a capacity of 1.1 liters, which mill is filled up to 40% of its volume with Tungsten carbide pellets containing 6% cobalt with a diameter of 6.35 mm and a length of 6.35 mm. 350 cc of an isoparaffinic hydrocarbon oil having a flash point of 85 C. is also introduced into the mill.



     This composition is ground for 48 hours on rollers lined with rubber, rotating the mill at a speed of 60 revolutions per minute. After grinding, the intimate mixture of the powders of silicon nitride, of magnesium nitride, of iron and of boron is separated by filtration from the grinding bodies made of tungsten carbide and cobalt, said mixture then being separated by settling, most of the hydrocarbon oil.



  The resulting dispersion is then washed three times with hexane, each time using 2 liters of hexane, until it is free of residual oil, after which it is dried in an oven. empty until the next day. The powder obtained is then sieved through a t friends with a mesh of 0.21 mm.



   Chemical analysis reveals that it contains 46.7 parts by volume of silicon nitride and 2.3 parts by volume of magnesium nitride per part by volume of a metal consisting of 99% by weight of iron. and 1% by weight of boron.

 <Desc / Clms Page number 33>

 



   Chemical analysis reveals that it contains 46.7 parts by volume of silicon nitride and 2.3 parts by volume of magnesium nitride per part by volume of a metal consisting of 99% by weight of iron and 1% of boron weight.



   15 grams of this dispersion are placed in a cylindrical carbon mold with a diameter of 2.54 cm and are hot pressed, in a vacuum press heated by induction, applying a pressure of 280 kg / cm2, at a temperature maximum of 1900 C, these conditions being maintained for 1 minute. The squeezed sample is cooled, removed from the press and cut into test pieces used to determine its density and mechanical properties.



   Cutting is performed with a thin diamond saw blade, using a pellet cutting machine for this purpose. The transverse breaking strength of this refractory dispersion is found to be 3591 kg / cm2, its Rockwell A hardness of 85.2 and its impact strength of 5.3 kg-meter / cm2. Its density is 3.24 g / cc, i.e. 99% of the theoretical density which is
3.27 g / cc, which can be calculated for this composition, assuming the volumes of the various constituents are active.



   A cutting tool insert is also machined from this refractory material and is found to be a remarkable cutting tool for processing steel and cast iron, this tool exhibiting relatively low wear and low tendency to weld or weld. to be combined with the workpieces, at cutting speeds of up to 1500 meters per minute on the surface.

 <Desc / Clms Page number 34>

 



   EXAMPLE 16.



   27.16 grams of the silicon nitride of Example 1, 1.46 g of powdered magnesium nitride, 7.8 grams of powdered tungsten carbide and 4.4 g of a mixture A finely divided powdered metal ge containing 99.5% by weight of cobalt and 0.5% by weight of metallic boron, are mixed and ground as described in Example 15.



   The recovery, purification and drying of this dispersion of intimately mixed powders are carried out as described in / Example 15. Analysis
Chemical analysis of this dispersion reveals that it contains approximately 17.1 parts by volume of silicon nitride, approximately 0.9 parts by volume of magnesium nitride and 1.0 part by volume of tungsten carbide per part by volume. the metal consisting of 99.5% by weight of cobalt and 0.5% by weight of boron.



   18 grams of this dispersion are made as described in Example 15, except that the temperature is 1800 C.



   The refractory dispersion according to the invention thus obtained has a density of 3.88 g / cc, ie 95% of the theoretical density which is 4.08 g / cc for this composition.



   The transverse breaking strength is
3409 kg / cm2, the Rockwell A hardness is 85.0 and the impact strength is 5.6 kg-meter / cm2. This refractory material is suitable for use as high temperature fabric material, exhibiting high oxidation resistance.



   EXAMPLE 17.



   27.3 grams of the silicon nitride of Example 1,
1.59 grams of finely divided magnesium nitride and 8.68 grams of a finely divided mixture of metals containing 99% by weight of nickel and 1% by weight of metallic boron are mixed. Grinding, recovery, purification and

 <Desc / Clms Page number 35>

 drying is carried out as described in Example 15. 17 grams of this dispersion are hot-compressed in the manner described in Example 15, except that the pressure used is 35 kg / cm2, the temperature is 1650 C and the duration of application of these conditions is 15 minutes.



   The refractory dispersion according to the invention thus obtained contains 8.5 parts by volume of silicon nitride and 0.5 part by volume of magnesium nitride per part by volume of a metal consisting of an alloy of nickel and boron. in weight proportions of 99 parts of nickel and 1 part of boron.



   The density of this refractory is found to be 3.58 g / cc, which represents 96% of the theoretical density of 3.73 g / cc. This refractory has a transverse tensile strength of 35.56 kg / cm2, an impact strength of 6.6 kg-meter / cm2 and a Rockwell A hardness of 82.0.



   EXAMPLE 18.



     25.57 grams of the silicon nitride of Example 1, 1.46 grams of dry magnesium nitride and 13.34 grams of a mixture of finely divided nickel and cob @ it are ground, extracted. from the mill, porif @ ed and dried as described in Example 15,
18 grams of the dispersio :: ob @ enue are hot pressed under the following conditions: pressure: 42U kg / cm2, temperature: 1300 C, time at. temperature: 30 minutes.



   The obtained standard dispersion contains, as revealed by analysis, about 0.4 parts by volume of silicon nitride and about 0.3% by volume of magnesium nitride per part by volume of a. 50-50 alloy of cobalt and nickel.

 <Desc / Clms Page number 36>

 



   The density of this refractory product is 3.76 g / cc, or 93% of the theoretical density of 4.04 g / cc.



   The transverse breaking strength of this refractory is 3388 kg / cm2, its impact strength is 6.86 kg-meter / cm2 and its Rockwell A hardness is 74.3.



   EXAMPLE 19.



   15.9 grams of the silicon nitride of Example 1; 4.0 g of alpha alumina in the form of 300 milli- micron particles, 4.89 grams of fine powdered alumina nitride, 9.85 grams of fine powdered iron, and 11.11 grams of co-balt The fine powdered metal is ground as described in Example 15. The powdered dispersion is recovered and purified as described in this same example.



   27 grams of this dispersion are compressed at a temperature of 1350 C, applying a pressure of 420 kg / cm2 and stirring under these conditions for 30 minutes.
 EMI36.1
 411dcaire dispersion securing the invention thus obtained consists of 2 parts by volume of silicon nitride, 0.4 part by volume of alumina and 0.6 part by volume of aluminum nitride per part by volume of a alloy with 50% by volume of iron, and 50% by volume of cobalt.



   The density of this refractory product is 4.30 g / cc, or 94% of the theoretical density of 4.57 g / cc.



   The transverse breaking strength of the refractory coproduct is 3701 kg / cm2, its Rockwell A hardness is 75.0 and its impact resistance is 8.9 kg-meter / cm2.



   EXAMPLE 20.



   16.06 grams of silicon nitride from Example 1, 1.43 grams of powdered magnesium nitride, 21.2 g of iron in particles of less than 10 microns and 16.0 g of metallic nickel in particles of less than 10 micron:

 <Desc / Clms Page number 37>

 are mixed and ground in the manner described: 1E Example 15. The recovery in purification is also carried out in the manner described in this example.
25 grams of the powder dispe @ ton: are pressed at room temperature, applying a pressure of 700 kg / cm2, in a hardened steel die, so as to form a raw billet.

   This billet is then sintered under vacuum at 1100 ° C. for 4 hours, resulting in a fairly solid billet having a density of about 65% of its theoretical density. This billet is enclosed in a stainless steel container containing 74% iron, 18% chromium and 8% nickel. This container is sealed and the billet enclosed in this container is quickly introduced into a press at high pressure, where it is first heated to about 1250 C. Immediately after being placed in the press, a pressure of 7000 kg / cm2 is applied and within 1 to 5 seconds the extrusion of this composition is complete.

   The die used is a hardened steel die with a reduction rate of diameter of 4: 1.



   The refractory dispersion obtained according to the invention consists of about 1.1 part by volume of silicon nitride and 0.1 part by volume of magnesium per part by volume of an alloy. 60% by volume iron and 40% by volume nickel.



   The density of this composition is 5.47 g / cc, ie the theoretical density.



   The refractory dispersion has a transverse breaking strength of 5600 kg / cm2, a Rockwell A hardness of 86.4 and an impact resistance of 15.3 g kg / n / cm2.



   This refractory material is suitable for use as a copper wire drawing die, this die having

 <Desc / Clms Page number 38>

 relatively little tendency to wear, scratch or scratch, even at relatively high drawing speeds.



   EXAMPLE 21.



   19.72 grams of the silicon nitride of Example 1, 1.43 g of powdered magnesium nitride, 14.05 g of titanium monoxide in 10 micron particles, 2.66 g of finely divided metallic iron and 1.14 g of fine powdered metallic chromium are mixed. These products are ground as described in Example 15 and the powder is recovered and / purified also as described in this example.



   20 g of this powder are hot pressed in a cylindrical carbon mold with a diameter of 2.54 cm, at a temperature of 1900 ° C. and under a pressure of 280 kg / cm2, these conditions being maintained for 1 minute. The continuous refractory dispersion contains 12.4 parts by volume of silicon nitride, 0.9 parts by volume of magnesium nitride and 5.7 parts by volume of titanium monoxide per part by volume of an alloy to. 70% by weight of iron and 30% by weight of chromium.



   This refractory dispersion has a density of 3.82 g / cc, which represents 98% of the theoretical density of
3.90 g / cc.



   The transverse tensile strength of this composition is 3682 kg / cm2, its Rockwell A hardness is
89.0, its impact resistance is 6.03 kg-meter / cm2.



   This refractory material is an excellent cutting tool for both steel processing and cast iron processing, this refractory material exhibiting very low gage, as well as a very low tendency to crater or crater. to weld, even at relatively high cutting speeds.

 <Desc / Clms Page number 39>

 



   EXAMPLE 22.



   17.17 g of the silicon nitride of Example 1, 1.43 g of magnesium nitride and 17.1 g of titanium nitride in 1 micron particles, 6.76 g of fine powdered metallic nickel and 1.69 g of fine powdered metallic chromium are ground. Grinding, recovery, purification and drying are carried out as described in Example 15.



   20 g of this dispersion are compressed in a hardened steel mold with a diameter of 2.54 cm, by applying a pressure of 700 kg / cm2, to obtain a br @ e billet. This billet is sintered for 4 hours at a temperature. of 1300 C dan an alumina tube retained under a high vacuum.



   The refractory dispersion according to the invention thus obtained contains 3.4 parts by volume of silicon nitride, 0.45 part by volume of magnesium nitride and approximately 3.2 parts by volume of titanium nitride per part by volume of 'an alloy of 80% by weight of nickel and 20% by weight of chromium.



   The density of this composition is 5.38 9 / cc, or 99.5% of the theoretical density of 5.94 g / cc.



   The transverse breaking strength of this refractory is 4410 kg / cm2, its Rockwell A hardness is 65.7 and its impact resistance is 11.54 kg-meter / cm2.



   EXAMPLE 23.



   10.18 g of silicon nitride, 0.6 g of lithium nitride, 23.40 g of tungsten carbide, 30.8 g of fine powdered metallic nickel and 5.44 g of fine powdered metallic chromium are mixed, crushed, recovered, purified and dried as described in Example 15.



   30 g of this dispersion are hot pressed in a cylindrical carbon mold with a diameter of 2.54 cm, at a temperature of 14000C and under a pressure of 280 kg / cm2, these conditions being applied for 30 minutes. The dis-

 <Desc / Clms Page number 40>

 refractory persion according to the invention thus obtained consists of approximately 1.1 part by volume of silicon nitride, approximately 0.8 part by volume of lithium nitride and approximately 0.4 part by volume of tungsten carbide per part by volume of an alloy containing 85% by weight of nickel, and 15% by weight of molybdenum.



   The density of this refractory product is 6.62 g / cc, or 94% of the theoretical density of 7.04 g / cc.



   The transverse breaking strength is 4480 kg / cm2, the Rockwell A hardness is 68.3, and the impact strength is 11.64 kg-meter / cm2.



   EXAMPLE 24.



   12.08 g of the silicon nitride of Example 1, 0.3 g of powdered anhydrous magnesium orthoborate, 18.3 g of fine powdered zirconium nitride, 33.4 g of powdered metal cobalt and 5.9 g of fine powdered metallic tungsten are mixed, crushed, recovered and purified as described in the preceding examples.



   12 g of this dispersion are pressed into a hardened steel mold, applying a pressure of 700 kg / cm 2.



  The raw billet obtained is then placed in an aluminum tube in an electric furnace and heated to 1600 ° C. under a high vacuum, maintaining this temperature for 1 hour.



   The refractory dispersion according to the invention thus obtained consists of approximately 1.1 part by volume of silicon nitride, approximately 0.3 part by volume of magnesium borate and approximately 0.7 part by volume. of zirconium nitride per part by volume of cobalt-tungsten alloy containing 85% by weight of cobalt and 15% by weight of tungsten.

 <Desc / Clms Page number 41>

 



   The density of this refractory dispersion is 6.44 g / cc or 92% of * - theoretical density of 7.0 g / cc. Its transverse tensile strength is 3885 kg / cm2, its Rockwell A strain is 68.8 and its impact resistance is 10.4 kg / cm2.



   EXAMPLE 25.



   26.82 g of the silicon nitride of Example 1, 2.15 g of fine powdered magnesium oxide, 4.94 g of powdered colloidal thorium oxide in the form of particles of about 16 millimicrons, and. the following amounts of powdered metals: 3.04 g of cobalt, 0.87 g of chromium, 0.43 g of tungsten and 0.04 g of boron, are crushed and recovered, purified and dried, from as described in Example 15.



   18 g of the powdered dispersion obtained from the various metals and aluminum nitride as well as thorium oxide are hot pressed or compressed at a temperature of 17500C and under pressure of 280 kg / cm2, these conditions being maintained for 1 minute.



   The following refractory dispersion / The invention thus obtained contains approximately 16.9 parts by volume of silicon nitride, 1.2 parts by volume of magnesium oxide and approximately 0.9 parts by volume of thorium oxide per part in volume of a complex alloy containing 69% cobalt, 20% chromium, 10% tungsten and 1% boron by weight.



   The density of this refractory dispersion is 3.81 g / cc, ie 99.5% of the theoretical density of 3.83 9 / cc.



   The transverse breaking strength is 4900 kg / cm2, the Rockwell A density is 92.5, and the impact strength is 6.44 kg-meter / cm2. This refractory makes a good cutting tool for cast iron and steel, as well as bronze, copper, brass and aluminum.

 <Desc / Clms Page number 42>

 



   EXAMPLE 26.



     27.03 g of the silicon nitride of Example 1, 4.0 g of alpha-alumina in particles of 300 millimicrons, 3.67 g of fine powdered metallic iron, 0.4 g of carbon black in large surface area and 0.04 g of finely divided metallic boron are ground as described in the previous examples. After recovery, purification and drying as described above, 17 g of the obtained powder is compressed at a temperature of 1900 ° C., applying a pressure of 280 kg / cm2, for 5 minutes.
 EMI42.1
 The refractory dispersion according to the invention thus obtained contains 17.0 parts by volume of silicon nitride and 2.0 parts by volume of alumina per part by volume of an alloy containing 98% iron, 1% carbon and 1% boron. in weight.



   The density of this composition is 3.48 g / cc, which corresponds to the expected theoretical density.



   Its transverse breaking strength is 5600 kg / cm2, its Rockwell A hardness is 92, and its impact resistance is 7.28 kg-meter / cm2.



   EXAMPLE 27.



   26.08 g of the silicon nitride of Example 1, 2.88 g of powdered finely divided magnesium aluminate spinel, 7.6 g of metallic nickel divided into powder, and 0.4 g of flakes Divided aluminum foils are mixed, crushed, recovered, purified and dried, as described in Example 15.



   20 g of this dispersion are hot-compressed at a temperature of 1900 C. by applying a pressure of 2.80 kg / cm2 for 5 minutes.

 <Desc / Clms Page number 43>

 



    The refractory dispersion obtained contains 8 @ parts by volume of silicon nitride and 0.8 part @n volume of magnesium aluminate per part by volume of a nickel-aluminum alloy containing 95% nickel and 5% aluminum. minimum. The density of this composition is 3.70 g / @, which corresponds to the expected theoretical density.



   Its transverse tensile strength is 4830 kg / cm2, its Rockwell A hardness is 91.5 and its impact resistance is 7.8 kg-meter / cm2. This refractory material makes an excellent cutting tool for ferrous metals, aluminum, copper and bronze. It is very little, even at high working speeds. In particular, it withstands welding and crater formation very well.



   Metallographic examination of this refractory material reveals that it is an interdispersion of silicon nitride and magnesium aluminate in a nickel-aluminum alloy. The average particle size of the metal crystals is about 0.4-0.8 microns, and the average particle size of silicon nitride and mangesium aluminate is about 0.5 and 0.7 microns.



   Metallographic examination of this dispersion reveals, moreover, that the silicon nitride, the magnesium aluminate and the nickel-aluminum alloy are all present in a square region of 10 microns per side and that, among 10 regions with an area of 100 square microns examined, 9 regions show the same structural characteristics.



   The electrical resistivity of this refractory dispersion is about 1 ohm-centimeter. This low value of the electrical resistivity indicates that the continuity

 <Desc / Clms Page number 44>

 metal in this dispersion is not interrupted by silicon nitride or magnesium aluminate.



   EXAMPLE 28.



   Powdered metallic silicon the particles of which have a size less than 0.044 mm is nitrided in the manner described in Example 1 and the silicon nitride in particles of about 50 microns thus obtained is ground, in a ball mill, to that the particles have an average size of 10 microns. 64 g of this powdered silicon nitride are mixed with 1.6 g of commercial anhydrous gamma aluminum in spherical particles of 20 millimicrons, and with 178 g of nickel in particles of about 50 millimicrons in powder obtained by intensive grinding, in a ball mill, with nickel balls, of commercial nickel carbonyl powder with a size of about 1 micron.

   The resulting mixture was ground for 500 hours using nickel shot and grinding under high boiling point hydrocarbon oil. The grinding takes place in a steel mill with a capacity of 3.78 liters filled to 40% of its capacity with large nickel scales and containing sufficient high boiling point hydrocarbon oil, to coat the balls with nickel and powder. The powder is recovered, purified and dried as described in the previous examples.



   24 g of this powder are cold pressed, fried and extruded as described in Example 20.



  The dense body obtained consists of a dispersion of 1 part by volume of silicon nitride in 1 part by volume of a continuous phase of metallic nickel in which 0.02 part by volume is also dispersed, per part of metal, alumina serving as a pressing aid.

 <Desc / Clms Page number 45>

 



  The density of this composition is 6.03 g / cc.



   EXAMPLE 29.



   240 g of silicon nitride are prepared as described in Example 28, omitting the grinding in the ball mill. 40 g of the powdered alumina described in this example, 6.23 g of nickel in particles of less than 0.044 mm and 2.16 g of chromium in particles of less than 0.044 mm are ground with the nitride of silicon as described in Example 28. Purification, recovery and drying are also carried out as described in previous examples.



   24 g of this material are hot pressed at a temperature of 18500C in a carbon mold, applying a pressure of 420 kg / cm2. After cooling the furnace and extracting the product, it is found that this consists of a prohibition of 75 parts by volume of silicon nitride and 10 parts by volume of alumina, with 1 part by volume of a nickel-chromium alloy containing about 26% by weight of chromium and 74% by weight of nickel. The density is 3.35 g / cc, which corresponds to the expected theoretical density. This material is a structural material resistant to high temperature. It is also suitable for use as a cutting tool, for processing, at relatively high speeds, steel and cast iron.



   EXAMPLE 30.



   The procedure is as described in Example 29, using the same amounts of material, except that 305.8 g of silicon nitride in particles of 40 to 50 microns at a minimum are employed. instead of the 240 g cited in the previous example. The hot compression is carried out in the manner described above and the refractory dispersion according to the invention thus obtained consists of 99 parts by volume of silicon nitride and 10 parts by volume.

 <Desc / Clms Page number 46>

 of alumina per part by volume of binder metal. @e binder metal contains 26% by weight of chromium and 74% by weight of nickel. The density of the dispersion is 3.21 g / cc, which corresponds substantially to the theoretical density.



  This specimen exhibits good wear resistance when used as a cutting tool, especially at high speeds and in the case of light cuts.

 

Claims (1)

CLAIMS. 1.- Refractory dispersion, characterized in that it comprises a metal selected from molybdenum, tungsten, chromium, rhenium, iron, cobalt, nickel and their alloys, in which metal is dispersed silicon nitride , as well as a pressing aid selected from among magnesium nitride, lithium nitride, aluminum oxide, magnesium oxide, silica, boric oxide and spinels of the oxide type. 'a divalent oxide selected from magnesium oxide, iron oxide, cobalt oxide, and nickel oxide in combination with a trivalent oxide selected from aluminum oxide, iron oxide and chromic oxide, provided that the divalent and trivalent oxides are oxides of different metals. 2. A dispersion according to claim 1, characterized in that it comprises 1 part to 98 parts by volume of silicon nitride in separate particles per part by volume of metal. 3.- Dispersion according to either of claims 1 and 2, characterized in that it comprises 0.02 part to 10 parts by volume of pressing aid per part by volume of metal, 4.- Dispersion according to one or other of claims 1 to 3, characterized in that it comprises 0.06 part to 7 parts by volume of pressing aid per part by volume of metal. 5. - Dispersion followed one or the other of claims 1 to 4, characterized in that it comprises 3.0 parts to 50 parts by volume of distinct particles of silicon dioxide per part by volume of iron, cobalt or nickel. <Desc / Clms Page number 48> 6.- Dispersion according to one or the other of claims 1 to 4, characterized in that it comprises 1.5 parts to 19 parts by volume of distinct particles of silicon nitride per part by volume of molybdenum, of tungsten, chromium or rhenium. 7. - Dispersion according to one or the other of claims 1 to 6, characterized in that the metal is molybdenum. 8.- Dispersion according to one or the other of claims 1 to 6, characterized in that the metal is cobalt. 9. - Dispersion according to any one of claims 1 to 6, characterized in that the metal is tungsten 10.- Dispersion according to one or other of claims 1 to 6, characterized in that the metal is an alloy of nickel and 155 by weight of molybdenum, relative to the total weight of the metal. 11.- Dispersion according to one or the other of claims 1 to 10 in the form of a refractory dispersion having a density greater than 98% of its theoretical density. 12.- Dispersion according to either of claims 1 to 11, in the form of a refractory dispersion having a density of more than 95% of the theoretical density. 13. - Dispersion according to one or other of claims 1 to 12, in the form of a refractory dispersion having a density greater than 90% of its theoretical density. 14.- Dispersion according to any one of claims 1 to 13, characterized in that the silicon nitride is replaced, in proportions of less than 5% by volume, by a compound in the form of particles. chosen among the <Desc / Clms Page number 49> nitrides of hafnium, titanium, zirconium, aluminum, tantalum, thorium, uranium, cerium, carbides of molybdenum, tungsten, hafnium, chromium, tanta., le, de niobium, titanium, zirconium, silicides and disilicides of chromium, tungsten, molybdenum and their mixtures. 15. - Process for obtaining a refractory dispersion, characterized in that a composition comprising a metal chosen from molybdenum, tungsten, chromium, rhenium, iron, cobalt, nickel and their alloys. , in which are dispersed silicon nitride and a pressing aid selected from magnesium nitride, lithium ni tride, aluminum oxide, magnesium oxide, silica, boric oxide and spinels of the oxide type of a divalent oxide chosen from magnesium oxide, iron oxide, cobalt oxide and nickel oxide in combination with a trivalent oxide chosen from oxide of aluminum, iron oxide and nickel oxide, the trivalent oxide and the divalent oxide being oxides of different metals, in the form of fine particles, is thoroughly mixed, so as to obtain a homogeneous dispersion, after which the mixture is compressed in a mold under a pressure greater than 35 kg / cm2 and heated to a temperature of 1000 C to 1900 C 16. A process according to claim 15, characterized in that the pressure is 35 to 420 kg / cm2. 17. A process according to claim 15, characterized in that the metallic component is iron, cobalt or nickel, the heating temperature is 1000 C, and the heating takes place for a period of time up to dre 4 hours. <Desc / Clms Page number 50> 18.- The method of claim 15, characterized in that the metal component is molybdenum, tungsten or chromium, the heating temperature is from 1600 C to 1850 C and the chauffase continues for a period of time which reach 4 hours. 19. A method according to either of claims 15 to 18, characterized in that the particles of the constituents have a size of less than 50 microns. 20. - A method according to one or the other of claims 15 to 19, characterized in that the particles of the constituents have a size of less than 10 microns. 21. - A method according to either of claims 15 to 20, characterized in that the particles of the constituents have a size of less than 1 micron. 22.- Composition, characterized in that it comprises a metal selected from molybdenum, tungsten, chromium, iron, cobalt, nickel and their alloys, in which are dispersed silicon nitride and a pressing aid selected from magnesium nitride, lithium nitride, aluminum oxide, magnesium oxide, silica, boric oxide and spinels of the oxide type of a divalent oxide chosen from magnesium oxide, iron oxide, cobalt oxide and nickel oxide, in combination with a trivalent oxide chosen from aluminum oxide, iron oxide and oxide nickel, it being understood that the divalent and trivalent oxides are oxides of dissimilar metals. 23. A composition according to claim 22, charac- terized in that it comprises 1 part to 98 parts by volume of distinct particles of silicon nitride per part by volume of metal. <Desc / Clms Page number 51> 24. Composition according to either of Claims 22 and 23, characterized in that it comprises 0.02 part to 10 parts by volume of pressing aid per part by volume of metal. 25. - Composition according to / either of claims 22 to 24, characterized in that it comprises 0.06 part to 7 parts by volume of pressing aid per part by volume of metal. 26. - Composition according to one or the other of claims 22 to 25, characterized in that it comprises 3.0 parts to 50 parts by volume of distinct particles of silicon nitride per part by volume of iron, cobalt or nickel. 27.- Composition according to one or the other of compositions 22 to 26, characterized in that it comprises 1.5 parts to 19 parts by volume of separate particles silicon nitride per part by volume of molybdenum, of tungsten , chromium or rhenium. 28.- Composition according to either of Claims 22 to 27, characterized in that the particles of the pressing aid, of the silicon nitride and of the metal have an average size of less than 50 microns. 29.- Composition according to one or the other of claims 22 to 28, characterized in that the particles of the pressing aid, of the silicon nitride and of the metal have an average size of less than 10 microns. . 30 - Position according to either of Claims 22 to 29, characterized in that the particles of the pressing aid, of the silicon nitride and of the metal have an average size of less than 1 micron. <Desc / Clms Page number 52> 31. - Composition according to either of claims 22 to 30, characterized in that the metal is molybdenum. 32.- Composition according to either of claims 22 to 30, characterized in that the metal is cobalt. 33.- Composition according to either of claims 22 to 30, characterized in that the metal is cobalt. 34. - Composition according to either of claims 22 to 30, characterized in that le'métal is an alloy of nickel with 15% by weight of molybdenum, relative to the total weight of metal. 35. - Composition according to either of claims 22 to 34, characterized in that the silicon nitride is replaced, in proportions of less than 50% by volume, by a compound in the form of particles, chosen from among nitrides of hafnium, titanium, zirconia, aluminum, tantalum, thorium, uranium, cerium, carbides of molybdenum, tungsten, hafnium, chromium, tantalum, niobium , titanium, zirconium, silicides and distilicides of chromium, tungsten, molybdenum and their mixtures. 36.- Refractory dispersion according to one or the other of claims 1 to 14, characterized in that it constitutes a component part of a cutting tool.