JP2014034724A - Cermet powder for thermal spraying - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide cermet powder for thermal spraying which can have high deposition efficiency in use for a low-temperature thermal spraying process.SOLUTION: Cermet powder for thermal spraying has a thermal conductivity of 0.17 W/m K or less. The cermet powder for thermal spraying preferably consists of granulated-sintered cermet particles. The granulated-sintered cermet particles preferably have a mean primary particle size of 6 μm or less. Further, the granulated-sintered cermet particles preferably have porosity of 4.0% or less.

Description

  The present invention relates to a cermet powder for thermal spraying.

  Thermal spraying that forms a film on a substrate by spraying a powder such as metal or cermet onto the substrate using a combustion flame or a plasma jet as a heat source is widely known as a kind of surface modification technique. One of the performances required for the thermal spraying powder is that many of the sprayed toward the base material adhere and deposit on the base material to form a film, that is, high adhesion efficiency. However, in a low temperature spray process such as cold spray, it is not easy to achieve high deposition efficiency due to the low process temperature. This tendency is more remarkable when the thermal spraying powder is made of cermet.

JP 2011-17079 A

  Accordingly, an object of the present invention is to provide a cermet powder for thermal spraying capable of obtaining a high deposition efficiency in a low-temperature thermal spraying process application.

  In order to achieve the above object, in one embodiment of the present invention, a cermet powder for thermal spraying having a thermal conductivity of 0.17 W / m · K or less is provided. The thermal spray cermet powder is preferably composed of granulated and sintered particles. The average primary particle diameter of the granulated-sintered cermet particles is preferably 6 μm or less. The porosity of the granulated-sintered cermet particles is preferably 4.0% or more.

  ADVANTAGE OF THE INVENTION According to this invention, the cermet powder for thermal spraying which can obtain high adhesion efficiency in a low-temperature thermal spraying process use can be provided.

Hereinafter, an embodiment of the present invention will be described.
The cermet powder for thermal spraying according to the present embodiment is used for forming a cermet sprayed coating by various thermal spraying processes. Among these, it is particularly useful in applications where a cermet sprayed coating is formed by cold spray, warm spray, high-speed air fuel (HVAF) spraying, or high-speed oxygen fuel (HVOF) spraying. However, it is preferable that the cermet powder for thermal spraying of this embodiment is used for low-temperature thermal spraying process applications in which the process temperature is lower than the melting point of the metal component in the thermal spray cermet powder and lower than the reaction temperature of the ceramic component.

  In general, the cold spray is a thermal spraying process in which a thermal spray material is collided and adhered to a base material in a solid state by an accelerated low-temperature working gas. In general, a warm spray forms a relatively low-temperature combustion frame by mixing a cooling gas such as nitrogen gas, compressed air, or argon gas into a combustion flame obtained by using kerosene and oxygen as a combustion aid. Is a thermal spraying process in which the thermal spray material is heated and accelerated to collide and adhere to the substrate. HVOF thermal spraying is generally a thermal spraying process in which a thermal spray material is heated and accelerated by a combustion flame obtained using kerosene or hydrocarbon gas and oxygen as a combusting agent to collide and adhere to a substrate. In general, HVAF spraying uses air instead of oxygen as a combustor to form a combustion flame at a lower temperature than HVOF spraying, and this combustion flame heats and accelerates the sprayed material to impact and adhere to the substrate. It is a thermal spraying process.

  In order to obtain high adhesion efficiency in the low temperature spraying process application using the thermal spray cermet powder of the present embodiment, the thermal conductivity of the thermal spray cermet powder is preferably 0.17 W / m · K or less, and more preferably. Is 0.16 W / m · K or less, more preferably 0.15 W / m · K or less. When the thermal conductivity of the cermet powder for thermal spraying is 0.17 W / m · K or less, high adhesion efficiency is obtained because the lower the thermal conductivity of the cermet powder for thermal spraying, the higher the thermal spraying in the thermal spraying apparatus. The reason is that the temperature of the cermet powder for use in spraying is unlikely to decrease before the thermal spray cermet powder collides with the substrate. The thermal conductivity of the thermal spray cermet powder can be measured by, for example, a hot disk method.

  The thermal conductivity of the thermal spray cermet powder is affected by the structure, composition, physical properties, etc. of the particles in the thermal spray cermet powder. Therefore, the thermal conductivity of the thermal spray cermet powder can be appropriately adjusted by changing the structure, composition, and physical properties of the particles in the thermal spray cermet powder. For example, one effective means for obtaining a thermal spray cermet powder having a thermal conductivity of 0.17 W / m · K or less is to increase the porosity of the particles in the thermal spray cermet powder as much as possible. Specifically, the porosity of the particles in the cermet powder for thermal spraying is preferably 4.0% or more, more preferably 8.0% or more, and further preferably 15.0% or more. As the porosity of the particles in the thermal spray cermet powder increases, the thermal conductivity of each particle, and thus the thermal conductivity of the thermal spray cermet powder, tends to decrease. In addition, the measurement of the porosity of the particle | grains in the cermet powder for thermal spraying can be performed by the mercury intrusion method, for example.

  The thermal spray cermet powder is preferably composed of granulated-sintered cermet particles. The granulated-sintered cermet particles are composite particles obtained by agglomerating ceramic fine particles and metal fine particles, and are produced by granulating and sintering a mixture of ceramic fine particles and metal fine particles. According to such a granulation-sintering method, it is relatively easy to produce particles having a high porosity.

  Ceramic fine particles used for the production of granulated and sintered cermet particles include, for example, tungsten carbide, chromium carbide, vanadium carbide, niobium carbide, molybdenum carbide, tantalum carbide, titanium carbide, zirconium carbide, hafnium carbide, silicon carbide, Carbides such as boron, molybdenum boride, chromium boride, hafnium boride, zirconium boride, borides such as tantalum boride, titanium boride, nitrides such as titanium nitride, aluminum nitride, silicon nitride, silicides and oxidation It may be formed from an object. Among these, carbides, particularly tungsten carbide, chromium carbide, and vanadium carbide are preferable from the viewpoint of improving the wear resistance of the thermal spray coating formed from the cermet powder for thermal spraying. It is also possible to use a mixture of a plurality of types of ceramic fine particles having different compositions or characteristics.

  The fine metal particles used in the production of the granulated-sintered cermet particles are formed from, for example, a single metal or a metal alloy containing a metal such as nickel, iron, chromium, cobalt, titanium, aluminum, copper, silver, and molybdenum. It may be a thing. It is also possible to use a mixture of a plurality of types of metal fine particles having different compositions or characteristics.

  When the cermet powder for thermal spraying is composed of granulated-sintered cermet particles, the particle size of the ceramic particle part and the particle size of the metal particle part constituting the granulated-sintered cermet particle, that is, granulation-sintered Making the primary particle diameter of the sintered cermet particles as small as possible is also effective as a means for obtaining a cermet powder for thermal spraying having a thermal conductivity of 0.17 W / m · K or less. Specifically, the average primary particle diameter (constant tangential diameter) of the granulated / sintered cermet particles is preferably 6 μm or less, more preferably 1 μm or less, still more preferably 0.5 μm or less, and particularly preferably 0. .2 μm or less. As the average primary particle size of the granulated-sintered cermet particles decreases, the interface between the ceramic particle part and the metal particle part contained in the granulated-sintered cermet particle, the interface between the ceramic particle parts, and the metal particle part As the number of interfaces increases, the thermal conductivity of each granulated-sintered cermet particle, and thus the thermal conductivity of the thermal spray cermet powder, tends to decrease. The average primary particle diameter of the granulated-sintered cermet particles is determined from the cross-sectional image of the granulated-sintered cermet particles obtained by observing the cross-section of the granulated-sintered cermet particles using an electron microscope. Can do.

  The average primary particle size of the granulated-sintered cermet particles generally reflects the average primary particle size of the raw material ceramic fine particles and the raw material metal fine particles used in the production of the granulated-sintered cermet particles. However, since it is also affected by the sintering performed during the production of the granulated-sintered cermet particles, it differs from the average primary particle diameter of the raw material ceramic fine particles and the raw material metal fine particles.

  The metal particle portion in the granulated-sintered cermet particles preferably has a dispersibility value defined below of 0.4 or less, more preferably 0.3 or less, and even more preferably 0.25 or less. . The dispersibility value is a value obtained by dividing the number average diameter of the metal particle portions in the granulated-sintered cermet particles by the volume average diameter of the same metal particle portions. This dispersibility value is an index indicating the degree of dispersion of the metal particle portion in the granulated-sintered cermet particles, and the smaller the value, the more the metal particle portion in the granulated-sintered cermet particles. It shows that it is uniformly distributed. When the dispersibility value is 0.4 or less, more specifically, 0.3 or less or 0.25 or less, it is easy to obtain a cermet powder for thermal spraying having a thermal conductivity of 0.17 W / m · K or less. It becomes. The reason is that the number of interfaces between the ceramic particle portion and the metal particle portion and the number of interfaces between the metal particle portions included in the granulated-sintered cermet particles is increased.

  The average particle diameter (volume average diameter) of the cermet powder for thermal spraying, that is, when the cermet powder for thermal spraying is composed of granulated-sintered cermet particles, the average secondary particle diameter of the granulated-sintered cermet particles (volume average) The diameter is preferably 40 μm or less, more preferably 30 μm or less, still more preferably 20 μm or less, particularly preferably 10 μm or less, and most preferably 1 μm or less in order to improve the adhesion efficiency of the cermet powder for thermal spraying. is there. The reason is that as the average particle diameter of the thermal spray cermet powder becomes smaller, each particle in the thermal spray cermet powder is easily softened or melted when heated during thermal spraying. In addition, the measurement of the average particle diameter of the cermet powder for thermal spraying can be performed by, for example, a laser diffraction scattering method, a BET method, or a light scattering method.

  The compressive strength of the particles in the cermet powder for thermal spraying is preferably 500 MPa or less, more preferably 400 MPa or less, and further preferably 300 MPa or less. As the compressive strength of the particles in the cermet powder for thermal spraying decreases, each particle is likely to be deformed at the time of collision with the substrate, so that the adhesion efficiency of the cermet powder for thermal spraying is improved.

  The compressive strength of the particles in the cermet powder for thermal spraying is preferably 10 MPa or more, more preferably 25 MPa or more, and further preferably 50 MPa or more. As the compressive strength of the particles in the thermal spray cermet powder increases, the ceramic component is less likely to fall off from the thermal spray coating formed from the thermal spray cermet powder, so that the hardness and wear resistance of the thermal spray coating are improved. Also, as the compressive strength of the particles in the cermet powder for thermal spraying increases, it becomes difficult for the particles to collapse, so that spitting that may occur due to overmelting of the fine particles caused by the collapse of the particles in the cermet powder for thermal spraying It is possible to prevent adverse effects such as blocking of the thermal spray nozzle.

Next, the effect | action of the cermet powder for thermal spraying of this embodiment is demonstrated.
Thermal spraying of the thermal spraying powder is performed by heating the thermal spraying powder in a thermal spraying apparatus and then spraying the thermal spraying powder toward the substrate. The thermal spraying powder heated in the thermal spraying apparatus is cooled by the atmosphere after being blown from the thermal spraying apparatus toward the base material and before colliding with the base material. Further, even within the thermal spraying apparatus, the temperature of the thermal spraying powder may gradually decrease after being heated to the maximum temperature and before being blown out from the thermal spraying apparatus. In this respect, the cermet powder for thermal spraying of the present embodiment has a low thermal conductivity of 0.17 W / m · K or less, so that the temperature heated in the thermal spraying apparatus does not decrease so much and is relatively high. It can be considered that the particles in the cermet powder for thermal spraying are sufficiently plastically deformed at the time of collision with the base material. This is presumed to be the reason why high deposition efficiency can be obtained even when the cermet powder for thermal spraying of this embodiment is used for low temperature spraying process applications.

Therefore, the cermet powder for thermal spraying according to the present embodiment is particularly useful for low temperature spraying process applications.
The embodiment may be modified as follows.

  -The cermet powder for thermal spraying of the said embodiment may contain components other than granulation-sintered cermet particle. For example, it may contain free ceramic particles or metal particles.

  The cermet powder for thermal spraying of the above embodiment may be composed of melt-ground cermet particles or sintered-ground cermet particles instead of granulated-sintered cermet particles, or melt-ground cermet. In addition to the particles or sintered-ground cermet particles, other components may be included. Alternatively, instead of granulation-sintered cermet particles, it may be composed of a mixture of ceramic particles and metal particles, or it may contain other components in addition to the mixture of ceramic particles and metal particles. There may be. However, granulated-sintered cermet particles are generally advantageous in that they are superior in adhesion efficiency and contain less impurities during production than melt-ground cermet particles and sintered-ground cermet particles. In addition, the granulated-sintered cermet particles are advantageous in that they have better fluidity than a mixture of ceramic particles and metal particles. The melt-pulverized cermet particles can be produced by melting and cooling and solidifying a mixture of ceramic fine particles and metal fine particles, followed by pulverization. Sintered-pulverized cermet particles can be produced by sintering and pulverizing a mixture of ceramic fine particles and metal fine particles.

Next, the present invention will be described more specifically with reference to examples and comparative examples.
(Examples 1-3 and Comparative Examples 1-5)
The cermet powders of Examples 1 to 3 and Comparative Examples 1 to 5 composed of the granulated and sintered cermet particles were prepared, and each cermet powder was cold sprayed under the conditions shown in Table 1. Table 2 shows the composition and characteristics of each cermet powder and the evaluation results of the coating obtained by thermal spraying each cermet powder.

(Examples 4-8 and Comparative Examples 6-10)
The cermet powders of Examples 4 to 8 and Comparative Examples 6 to 10 composed of granulated and sintered cermet particles were prepared, and each cermet powder was sprayed with HVOF under the conditions shown in Table 3. Table 4 shows the composition and characteristics of each cermet powder and the evaluation results of the coating obtained by thermal spraying each cermet powder.

In the “thermal conductivity” column of Tables 2 and 4, the results of measuring the thermal conductivity of each cermet powder are shown. The thermal conductivity was measured by a hot disk method using a thermophysical property measuring apparatus “TPS500” manufactured by Kyoto Electronics Industry Co., Ltd. More specifically, 30-40 g of cermet powder is placed in a powder container in a thermostatic chamber at 23 ° C., and the thermal conductivity is measured with a 2.2 kg weight placed on the cermet powder in the container. It was. As other measurement conditions, the sensor used was set to Φ7 mm, the applied power was set to 0.04 W, and the measurement time was set to 80 seconds.

  The “composition” column in Tables 2 and 4 shows the chemical composition of each cermet powder. In the same column, “WC-12Ni” represents a cermet composed of 12% by mass of nickel and the balance tungsten carbide, “WC-25Ni” represents a cermet composed of 25% by mass of nickel and the balance tungsten carbide, “WC-25 [Fe-18Cr-10Ni]” represents a cermet composed of 25% by mass of an iron-based alloy composed of 18% by mass of chromium, 10% by mass of nickel, and the balance of iron, and the balance of tungsten carbide. WC-25 [Fe-6Si-2.5Cr] "is a cermet comprising 25% by mass of an iron-based alloy composed of 6% by mass of silicon, 2.5% by mass of chromium and the balance of iron, and the balance of tungsten carbide. “WC-20CrC-7Ni” represents a cermet composed of 20% by mass of chromium carbide, 7% by mass of nickel, and the balance of tungsten carbide. "-20CrC-12Ni" represents a cermet consisting of 20 wt% chromium carbide, 12 wt% nickel and the balance tungsten carbide, and "WC-20VC-12Ni" represents 20 wt% vanadium carbide and 12 wt% nickel. And WC-12 [Fe-18Cr-10Ni] is an iron-based alloy consisting of 18% by mass of chromium, 10% by mass of nickel, and the balance of iron. It represents a cermet consisting of the remaining tungsten carbide. The chemical composition of each cermet powder was measured using a fluorescent X-ray analyzer “LAB CENTER XRF-1700” manufactured by Shimadzu Corporation.

  The “porosity” column in Tables 2 and 4 shows the results of measuring the porosity in the granulated-sintered cermet particles of each cermet powder. The porosity was measured by using a mercury intrusion porosimeter “AutoPore IV 9500” manufactured by micromeritics Co., Ltd., and the result of measurement under the conditions of a mercury contact angle of 130 ° and a surface tension of 485 dynes / cm (0.485 N / m). The result prescribed | regulated to the data above (0.034MPa) is shown.

In the "compressive strength" column of Tables 2 and 4, the results of measuring the compressive strength of the granulated-sintered cermet particles of each cermet powder are shown. Specifically, the average value of the compressive strength σ [unit MPa] of the granulated-sintered cermet particles calculated according to the formula: σ = 2.8 × L / π / d ² is shown. In the above formula, L represents the critical load [unit N], and d represents the average diameter [unit mm] of the granulated-sintered cermet particles. The critical load is the compression applied to the granulated-sintered cermet particles when the displacement of the indenter increases rapidly when a compressive load increasing at a constant speed is applied to the granulated-sintered cermet particles with the indenter. The magnitude of the load. For the measurement of the critical load, a micro compression test apparatus “MCTE-500” manufactured by Shimadzu Corporation was used.

  The “dispersibility” column in Tables 2 and 4 is obtained by dividing the number average diameter of the metal particle portions in the granulated-sintered cermet particles of each cermet powder by the volume average diameter of the same metal particle portions. Indicates the value. The number average diameter and volume average diameter of the metal particle portions are obtained by observing the cross section of the granulated-sintered cermet particles using a scanning electron microscope “S-3000N” manufactured by Hitachi High-Technologies Corporation. -It calculated | required from the cross-sectional image of sintered cermet particle | grains.

  In the “average particle diameter” column of Table 2 and Table 4, the average particle diameter (volume average diameter) of each cermet powder is measured using a laser diffraction / scattering particle size measuring instrument “LA-300” manufactured by Horiba, Ltd. The result measured using this is shown.

  The column “Adhesion efficiency” in Table 2 shows the results of evaluating the adhesion efficiency based on the thickness of the film formed per pass when each cermet powder is sprayed. Specifically, when the thickness of the sprayed coating formed per pass is 50 μm or more, it is good (◯), and when it is less than 50 μm (△), the sprayed coating cannot be formed. The case was evaluated as bad (x).

  In the "Adhesion efficiency" column of Table 4, the adhesion efficiency, which is a value (percentage) obtained by dividing the weight of the sprayed coating obtained by spraying each cermet powder by the weight of the sprayed cermet powder, is evaluated. The results are shown. Specifically, when the adhesion efficiency was 40% or more, it was evaluated as good (◯), and when it was less than 40%, it was evaluated as defective (×).

  The “film hardness” column of Table 2 shows the results of evaluating the hardness of each film based on the Vickers hardness of the film obtained by spraying each cermet powder. Specifically, when the Vickers hardness of the film measured using the microhardness measuring device HMV-1 manufactured by Shimadzu Corporation is 500 or more, it is good (◯), and when it is less than 500, it is bad (×). evaluated.

  The “Abrasion resistance” column of Table 4 shows the results of evaluating the abrasion resistance of the coating obtained by thermal spraying each cermet powder. Specifically, Examples 4 to 8 and Comparative Example 6 by a reciprocating wheel wear test according to JIS H8682-1 using a Suga abrasion tester NUS-ISO3 manufactured by Suga Test Instruments Co., Ltd. When the value obtained by dividing the wear volume of the thermal spray coating formed from each -10 cermet powder by the wear volume of the carbon steel SS400 by the same reciprocating plane wear test is less than 0.2. In the case of (◯) and 0.2 or more, it was evaluated as defective (×).

  As shown in Tables 2 and 4, in the case of the cermet powders of Examples 1 to 8, the evaluation of the adhesion efficiency was good. Moreover, the thermal spray coating obtained in Examples 1 to 8 also had good evaluation of coating hardness or abrasion resistance. On the other hand, in the case of the cermet powders of Comparative Examples 1 to 10 having a thermal conductivity of 0.17 W / m · K or less, high adhesion efficiency could not be obtained.

Finally, technical ideas other than those described in the claims that can be grasped from the above description will be described below.
The cermet powder for thermal spraying according to claim 1, wherein the porosity of the particles in the cermet powder for thermal spraying is 4.0% or more.

Claims (4)

  A cermet powder for thermal spraying having a thermal conductivity of 0.17 W / m · K or less.   The cermet powder for thermal spraying according to claim 1, comprising granulated-sintered cermet particles.   The cermet powder for thermal spraying according to claim 2, wherein the granulated-sintered cermet particles have an average primary particle diameter of 6 μm or less.   The cermet powder for thermal spraying according to claim 2 or 3, wherein the porosity of the granulated-sintered cermet particles is 4.0% or more.