JPS5913609A - Flaky nitride ceramics and its manufacture - Google Patents

Abstract

PURPOSE:To obtain flaky nitride ceramics with superior resistance to heat, thermal shock, corrosion, etc. by spraying a molten metallic or metalloid material on the surface of a cooling body, dropping the cooled thin chips before deposition, and nitriding them. CONSTITUTION:An element or a mixture of >=2 kinds of elements selected from Si, Ti, B, Al, W, Zr, Hf, Nb, Ta, La, Fe, Co, Ni, V, Cr and Mo is melted and sprayed on the surface of a cooling body moving at high speed. The sprayed and cooled flaky material is dropped before it deposits on the surface of the cooling body. The flaky material is then nitrided by contact with a heated nitriding gas. By this method flaky nitride ceramics with superior heat resistance, strength, hardness, wear resistance, etc. is obtd. The average diameter of the ceramic is >=10 times the thickness. The ceramics is suitable for use as a material for a machine, a structural material, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field to Which the Invention Pertains] The present invention relates to a metal or metal nitride having a flake-like shape and a method for producing the same.

Here, "flake-like" means that the average diameter is 1% of the thickness.
It refers to a thin plate-like shape that is 0 times or more. The shape does not necessarily have to be circular, but may be elliptical, rectangular, or other similar shapes, and the average diameter in this case is expressed as the geometric mean of the major axis and the minor axis.

The flaky nitride ceramic according to the present invention has this as a main component and has excellent heat resistance, thermal shock resistance, corrosion resistance, and wear resistance, and is suitable for various mechanical materials and structural materials having high strength and hardness. It can also be used as an additive in metal materials and plastic materials to produce composite effects.

[Description of prior art]

Traditionally, metal materials have been widely used as materials for gas pins and automobile engines, but metal materials have limitations when used at high temperatures1.In contrast, ceramics are attracting attention as materials for high temperatures. It started to be done. Ceramics generally withstand use at high temperatures and have excellent wear resistance, but a major drawback is that they are more brittle than metal materials.

However, in recent years, carbides, nitrides, sialon, etc. have been researched and developed as high-strength, high-temperature materials, and some of them have been put into practical use. Among these, nitrides such as silicon nitride, titanium nitride, and boron nitride are attracting attention because of their particularly excellent high-temperature strength, thermal shock resistance, and wear resistance.

In addition, these nitrides exhibit excellent characteristics as various additives. For example, by adding a small amount to carbon-containing refractories used in steel manufacturing, they provide oxidation resistance, corrosion resistance, and high hot strength, and are particularly effective in continuous The effect of adding it to casting nozzles etc. is great.

On the other hand, recently, fiber-reinforced glass and fiber-reinforced metal have been widely used in the engineering sector as composite materials reinforced with inorganic fibers such as glass fibers, ceramic fibers, and alumina fibers.

Empty materials may also be used for special purposes. It has been discovered that effects similar to or different from the reinforcement achieved by adding these inorganic fibers can be obtained using so-called two-dimensional additives in the form of plates or flakes. Reinforcement with fibrous materials is linear reinforcement, but reinforcement with plate-like or flake-like materials is planar reinforcement.
The mechanical properties are in-plane isotropic. Therefore, the most important feature is that physical anisotropy and warpage do not occur, as seen in mica-reinforced plastics, for example.

Furthermore, ceramics or refractories that are manufactured by sintering flake-like substances as a main component or mixtures of flake-like substances with other powder or granule materials are those that do not contain flake-like substances or that are made only in powder or granule form. It is known that the strength and thermal shock resistance are improved compared to those made of the same material.

Conventionally, as flaky ceramic materials, glass flakes, flaky mica, flaky graphite, 71/-
Silicon carbide in the form of silica, iron oxide in the form of flakes, and clay powder in the form of platelets are known. When these are used as sintered bodies for high-temperature materials, glass and mica are inferior to nitrides in heat resistance and strength, graphite in oxidation resistance, and silicon carbide in thermal shock resistance. However, even though nitride has excellent heat resistance, strength, oxidation resistance, and thermal shock resistance, its flake shape does not allow for the formation of a hole, and its characteristics are not fully utilized. .

[Purpose of the invention]

The object of the present invention is to obtain flaky nitride.

[Features of the invention]

In view of these points, the inventors of the present application conducted repeated studies on their own, and as a result, succeeded in obtaining flaky nitride ceramics. This flaky nitride ceramic is a completely new old material that has never existed before, and by using it as a main component or adding it to other abrasives, it can improve heat resistance, thermal shock resistance, corrosion resistance, strength, hardness, A new ceramic body or refractory with excellent wear resistance etc. can be obtained. By using this flaky nitride ceramic, it is possible to obtain a product with improved filling properties and high strength and thermal shock resistance compared to the case where only conventional powder materials are used. By oriented and filling the molded composite material using this flaky nitride ceramic,
The physical and physicochemical properties of the in-plane method perpendicular to the molding direction can be obtained, and even higher smoothness can be obtained when the surface is polished, resulting in improved strength and wear resistance. Even better. Further, such flaky nitride ceramics can be used as a reinforcing material for plastic or d.
It can also be used for composite materials such as IJ socks made of metal materials, and unlike in the case of fiber reinforcement, materials with properties such as in-plane isotropic strength, abrasion resistance, and dimensional stability can be obtained. The method for producing flaky nitride ceramics according to the present invention involves spraying a metal or metalloid material onto the surface of a cooling body moving at high speed to form a flaky material, or by spraying two or more cooling bodies. A flake-like material is obtained by inserting it between rollers, and the material is nitrided in a nitriding gas atmosphere. A method of producing flaky or ribbon-like metal by melting a metal material and rapidly cooling it on the surface of a cooling body moving at high speed (ultra-quenching method) has recently attracted particular attention.

It is also well known that when a metal material is thermally sprayed, the molten metal droplets collide with the base material, are stretched thin, and then adhere or deposit on the surface of the base material in the form of flaky metal. ing. Furthermore, it is a well-known fact that metal nitrides can be obtained by heating metals at appropriate temperatures in a nitriding gas atmosphere.

The inventors of the present application focused on this knowledge and, as a result of intensive research, sprayed a metal or metalloid material onto the surface of a moving cooling body, cooled it, and solidified it to form a thin flake.
It has been found that when the flakes are separated from the surface of the cooling body, flaky flakes can be obtained. By heating and nitriding the thus obtained flakes in a nitriding gas atmosphere, they succeeded in obtaining flaky nitride ceramics, thereby completing the present invention.

Furthermore, Japanese Patent Application Laid-Open No. 56-154M40 discloses a method of obtaining a metal compound material by causing a direct production reaction of a metal compound with a reactive gas while plasma spraying a metal raw material, and then brushing off the deposited metal compound. is disclosed, but the metal compound obtained by this method is a deposit and is not a method for obtaining flake-like compounds.

There are also known methods to obtain flaky metal pieces, such as cutting out thin plates from whole lumps, or using ribbon-shaped metal obtained by ultra-quenching and crushing it, but there are also methods for cutting out thin plates. However, it is technically difficult to cut out a thin plate with a diameter of 300 μm or less, and even if it were possible, it would not be possible to manufacture it economically on an industrial scale. In addition, in any of the methods, it is not easy to obtain a predetermined shape and size by pulverization.

[Specific explanation of the manufacturing method of the present invention]

As the starting material used in the present invention, any metal material can be used, among which Si, T1, B, A
I, W, Zr, Hf, Nb, TaXLa, F
e.

If a metal or alloy consisting of one or more of Co, Ni, V, Or, MoO is used as a starting material, a particularly useful nitride ceramic can be obtained by subsequent nitriding treatment. The material used as a starting material may be in the form of a wire, rod, plate, or powder depending on the method of supplying the material to the thermal spraying apparatus.

As the thermal spraying method, any of explosive thermal spraying, flame spraying using acetylene-oxygen, etc., and plasma spraying using argon gas plasma, water plasma, etc. can be applied. melting point is 2
Thermal spraying of metal materials at temperatures below 000°C can also be carried out by flame spraying, but plasma spraying is preferred for spraying high-melting point metals whose melting points exceed 2000°C. In this plasma spraying, gas plasma using an inert gas such as nitrogen or argon as a working gas is most preferable in order to prevent oxidation of the metal during spraying.

The droplets of the molten raw material produced by thermal spraying the raw material collide with a cooling body, and are cooled and solidified to form a flake-like substance. Examples of the cooling body and cooling method used are as follows. Can be mentioned.

(1) Using a disk-shaped cooling body, spraying is performed from a direction almost parallel to the rotation axis while rotating at high speed, and droplets of the molten raw material collide on the plane of the disk, cooling and solidifying to form flakes. How to obtain the substance.

(2) Using a cylindrical roll as a cooling body, while rotating at a high speed relative to the cylinder axis, thermal spraying is performed from a direction approximately perpendicular to the rotation axis, causing droplets of molten raw material to collide on the cylindrical surface of the roll. , a method of cooling and solidifying to obtain a flaky substance.

(3) Using a pair of rolls as a cooling body, thermal spraying is performed toward the gap between the two rolls or the area where the two rolls touch while rotating at high speed, and the droplets of the molten raw material collide on the cylindrical surface of the rolls. At the same time, a method of obtaining flaky material by rolling, cooling and solidifying.

(4) Two flexible thin plates are used as cooling bodies, sandwiched between a pair of rolls, and the rolls are rotated at high speed to feed the two thin plates while spraying toward the part where they come into contact. A method of obtaining a flake-like material by impinging droplets of molten raw material on the surface of a thin plate, rolling, cooling, and solidifying at the same time.

Cooling body materials include copper, brass, cast iron, stainless steel,
Metal materials such as bearing steel and tool die steel are used. The roughness of the cooling surface is preferably thin, for example, the maximum height is RmaX≦±To/jm, and it is even more preferable that Rrnax≦±5 μm. However, when Ftmax > ±10 μm, it becomes difficult to peel off the flaky metal adhering to the cooling surface. Since the cooling body (disc or roll) is heated during thermal spraying, it is preferable to cool it from inside using a cooling medium such as water. The moving linear velocity of the cooling surface of the cooling body is 1
~200m 7 seconds is good.

If the linear velocity of the cooling surface of the cooling body is less than 110/sec, the supply speed of the droplets will be higher, so the molten droplets will overlap and collide with the cooling surface, resulting in stacked flakes or , tend to become a combination.

Furthermore, in normal thermal spraying, there is no need to increase the linear velocity of the cooling surface of the cooling body to 1200 m/sec or more, taking into account the entire flight velocity of the molten droplets. If the cooling body is rotating, such as a disc or a roll, if the surface roughness of the cooling surface is sufficiently small, the cooled and solidified 7 lakes will naturally separate from the cooling surface due to centrifugal force. Can be configured. If the flakes remain on the cooling surface without coming off, blow them off with compressed gas in the housing where the cold homogenizer rotates once, or scrape them off with a metal wire brush or knife, etc., to remove the flakes from the cooling surface. Prevent it from accumulating on the surface.

The flake-like material thus obtained is heated and nitrided at a predetermined temperature in a nitriding gas atmosphere to produce flake-like nitride ceramics. The nitriding gas atmosphere is 1, nitrogen gas, ammonia gas, or a mixture thereof.
j4A is preferred. In order to prevent the formation of oxides due to trace amounts of mixed oxygen, it is recommended to add hydrogen gas.
.

Generally, the nitriding reaction of metals is often accompanied by heat generation, and if the flakes condense due to this reaction heat, the nitriding reaction can be speeded up by performing the nitriding reaction under reduced pressure or by diluting it with a nitriding gas such as all-alcohol gas. can be lowered and the heat generation level can be adjusted.

It is most preferable to carry out the nitriding reaction under flowing conditions in order to reduce the force and condensation of the flakes without reducing the rate of the nitriding reaction. When the nitriding reaction is carried out under flowing conditions, the contact between the flakes and the nitriding gas is good, and the nitriding reaction rate is rather improved.Also, since the flakes are dispersed in the gas phase, it is possible to prevent the flakes from condensing. can.

The nitriding gas atmosphere and heating temperature conditions are appropriately selected depending on the material of the raw material, the type and microstructure of the intended nitride ceramic, and the like. In particular, in order to maintain the flaky shape as it is, it is necessary to convert the material into II at a temperature range where the raw material does not melt or soften.

According to the method according to the present invention yc, since the raw material droplets are rapidly cooled on the surface of the cooling body, their structure is often amorphous or metastable crystalline, and compared to the case of stable metal crystals, the nitridation Easy to do. The time required for nitriding is shortened due to the thinness of the single material, and furthermore, if nitriding is carried out under flowing conditions, the reaction efficiency is improved compared to the case of a fixed bed.

The larger the ratio of the average diameter to the thickness (aspect ratio) of the flake resin material, the more its characteristics will be exhibited when it is made into a ceramic sintered body or a composite with plastic or metal.

In the case of flaky nitride ceramics, the aspect ratio is also 10 or more. When this value is less than 10, flaky features are diminished. According to the method of the present invention, aspect ratios of 10 to 100 can be easily obtained, and 1oo(
Anything beyond f- is also possible. It was a long time ago.The thickness of the flakes was 3.
00 μm or less is preferable. This is because if it is thicker than 300 μm, mutual interference will occur and it will be difficult to orient when oriented as a sintered body or a composite material.

When the flaky raw material is nitrided under the appropriate conditions as described above, the flaky nitride ceramics obtained are:
Since it maintains the same shape and aspect ratio as the original flake material, by controlling the shape and dimensions of the initial flake material, the final product flake nitride ceramic can be made into any shape and size. It is possible to finish the product.

In other words, the shape and dimensions of the flaky material obtained by thermal spraying depend on the material of the starting material, the particle size if the starting material is powder or granule, and the diameter and feeding speed if the starting material is a wire or bar. , further varies depending on the thermal spraying method, the material of the cooling body, the cooling method, the linear velocity of the cooling surface, etc. Particularly, when a powdery material is used as a starting material, the particle size has a large influence. The narrower the particle size distribution, the more uniform the shape and size of the resulting flaky material will be. In order to obtain flaky gold with a constant thickness, it is best to use a method using a pair of rolls, and by keeping the gap between the rolls or the pressing pressure of all the rolls constant, a flaky material with a uniform thickness can be obtained. It's a monkey. Of course, it is also possible to manufacture products that fit within a predetermined distribution range in terms of shape and size.

〔Effect of the invention〕

The flaky nitride ceramic of the present invention has a density, thermal conductivity, and coefficient of thermal expansion that are comparable to theoretical values,
Provides values close to theoretical values in strength, hardness, and elastic modulus,
Shows excellent heat resistance, thermal shock resistance, corrosion resistance and abrasion resistance. Because of these properties, the flaky nitride ceramic of the present invention can be used as a new material as a heat-resistant, high-strength material and mechanical parts in the fields of engineering ceramics, refractories, ceramic dispersion-strengthened metals, and composite materials as plastics. It can be used for etc. The substance of the present invention can be used as an additive for the above-mentioned mechanical parts and other structural materials, metal materials, and plastic materials.

[Description of Examples] Next, examples of the present invention will be explained. This example is an example of the present invention, and is not intended to limit the present invention.

(Example 1) Fine particulate metallic titanium with a particle size of 62 to 88 μm was sprayed between a pair of rolls having an internal water-cooled structure using an argon gas plasma spraying device, and was cooled and solidified to obtain flaky metallic titanium. . The roll is made of stainless steel (5US304
), and the surface roughness Rmax is ±1 μm. The circumferential speed of this roll is 17 m/sec.

The average diameter of the published titanium flakes is 150μ.
m, and the thickness was approximately 10 μm uniform. This flaky titanium metal was nitrided in a fluidized state at 1200° C. for 1 hour in a nitrogen gas atmosphere using a silicon nitride porous plate as a rectifying plate to obtain flaky titanium nitride (TiN).

The obtained flaky titanium nitride has almost the same shape as the original flaky titanium metal, and its aspect ratio is 10.
It was ~20.

The density of the obtained flaky titanium nitride was 543 g/er.
a. Vickers hardness was 2400. The product is T
It was confirmed by X-ray diffraction that it was iN.

The reaction rate is thought to be approximately 100%.

(Example 2) Fine-grained metallic silicon with a particle size of 56 to 105 μm was prepared in Example 1.
Flake-shaped silicon gold was obtained using the same equipment.

The peripheral speed of the roll in this case was 28 m/sec, and the obtained flaky silicon had a uniform diameter of 120 to 650 μm and a uniform thickness of approximately 5 μm. The obtained flaky silicon was placed in a nitrogen/ammonia mixed gas atmosphere (N2: NH
5=1000: i) Using a sintered silicon nitride porous plate as a current plate, distillation was carried out under flowing conditions at 1350°C for 40 minutes to obtain flaky silicon nitride (Si5N4).
See you again.

The oxidized silicon nitride flakes had a slightly increased diameter and thickness compared to the original silicon flakes, but their aspect ratios were between 20 and 70, which was similar to the original silicon flakes. Met.

The obtained flaky silicon nitride has a density of 3.18 g/cJ
The Vickers hardness was 2800. The product is Sj
3N4 was confirmed by X-ray diffraction. The reaction rate was almost 100%.

Patent applicant agent Patent attorney Naotaka Ide

Claims (6)

[Claims] (1) Si, T1, B, AI, W, Zr,
Hf, Nb, Ta. A nitride of one or more elements selected from TJa, F's, C01N1, ■, Or, and Mo, which has a thin plate shape and an average diameter relative to its thickness of 10
Flake-shaped nitride ceramics characterized by more than double the size. (2) The thickness is 300 μm or less (
The flaky nitride ceramic according to item 0. (3) fli%Ti, B, Al, W, Zr,
Hf, Nb, Ta. A process of thermally spraying a mixture of one or more elements of La, Fe, (3o, Ni%V, Or, Mo) onto the surface of a cooling body that moves at high speed, and flake-shaped flame sprayed by this process. A step of separating the substance from the surface of the cooling body before it is deposited on the surface of the cooling body, and a step of nitriding the flaky substance obtained by this step by contacting it with a heated nitriding gas. A method for producing flaky nitride ceramics. (4) The method for producing flaky nitride ceramics according to claim (3), wherein the surface roughness of the cooling body is 10 μm or less in maximum height. (5) The method for producing flaky nitride ceramics according to claim (3), wherein in the nitriding step, the nitriding gas and the flaky substance are in a fluid state. (6) The method for producing flaky nitride ceramics according to claim (3), wherein the thermal spraying step is plasma spraying.