JP2007029950A - Hvof spraying apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an HVOF spraying apparatus useful for a means capable of forming a dense coating film of metal titanium or a titanium alloy while restraining titanium from being oxidized. <P>SOLUTION: The HVOF spraying apparatus is provided with: a combustion chamber (1) arranged at one end of a conduit (2) for burning fuel gas and spouting a jet stream toward the other end of the conduit from a nozzle (4); and a particle mixing part (3) arranged in the middle of the conduit (2) for mixing a jetting particle in the jet stream. A mixing chamber (5) for mixing an inert gas is arranged on the side of the nozzle (4) in the combustion chamber (1). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to an HVOF thermal spraying apparatus used in a Ti film forming method for suppressing the oxidation of Ti by a thermal spraying method to form a dense Ti film having excellent corrosion resistance. More specifically, the present invention relates to a conduit (2). Is provided with a combustion chamber (1) that burns fuel gas and injects a jet stream from the nozzle (4) toward the other end, and injects particles for injection into the conduit (2). The present invention relates to an HVOF thermal spraying apparatus in which a particle mixing part (3) for mixing is provided.

Titanium is important as an anticorrosive material for offshore structures and plants because it has excellent corrosion resistance, and is not toxic to living organisms, and is also used as an implant material. In this case, an appropriate pore (100 microns or more) is said to be effective for bonding with bone.

Although a method for coating a titanium film having such characteristics by a thermal spraying method has been studied in the past, titanium is highly reactive with oxygen and nitrogen at a high temperature. As a result, there is a problem that most of oxides and nitrides can be formed only with a low-density film.

At present, low-pressure plasma spraying and cold spray are known as thermal spraying methods for coating titanium as a metal. In the low pressure plasma spraying, the inside of the chamber is set to an inert low pressure atmosphere, and the raw material titanium powder is melted by a plasma jet to form a film. This method is actually used to apply a porous titanium layer to a titanium alloy bioimplant. However, this low-pressure plasma spraying has a problem that the quality of the coating is high but the cost is very high.

On the other hand, in cold spray, an inert gas heated to about 500 ° C. with an electric heater is pressurized and ejected from a supersonic nozzle, and raw material powder is supplied into the nozzle and accelerated to form a film. According to this method, a dense film can be obtained with a soft metal such as Al or Cu. However, only a porous film can be obtained with titanium.

The present invention solves the problem of the conventional method of forming a Ti film by the thermal spraying method from the background as described above, and as a process that is more economical and productive in the atmosphere, a dense film is formed by the thermal spraying method. An object is to provide an HVOF thermal spraying device that can control a wide range of materials from porous to porous, and in particular, can form a dense metal Ti or Ti alloy film while suppressing oxidation of Ti. Yes.

In order to solve the above-mentioned problems, the present invention provides a mixing chamber (5) for mixing an inert gas on the nozzle (4) side in the combustion chamber (1) in the HVOF thermal spraying apparatus. It is characterized by.

By doing so, it is possible to perform supersonic injection below the melting temperature of particles, which has been difficult in the past, and to perform supersonic injection in a lower temperature range.
In other words, by controlling the amount of inert gas supplied, the amount of fuel supplied can also be controlled. If the amount of inert gas increases, the amount of fuel decreases. Conversely, if the amount of inert gas supplied decreases, the amount of fuel increases. As a result, the temperature could be controlled not only by diluting the combustion gas with an inert gas but also by increasing or decreasing the fuel.

The inventor experimentally verified the high-speed flame spraying (HVOF) method in which a powder such as metal or alloy is heated by a high-speed flame generated by burning a gas mixture of kerosene and oxygen and collides with the substrate surface at high speed. In detail, a patent has already been obtained for a method of passing a gas shroud portion for mixing an inert gas after supplying powder and a device therefor (Patent 3612568). From a detailed examination on the formation of Ti film based on such knowledge, as a means for suppressing the oxidation of Ti and forming a dense Ti film excellent in corrosion resistance, it is less than the melting temperature of particles. The supersonic injection is effective, and an apparatus for realizing it can be provided.

With this apparatus, a film of metal Ti (titanium) or Ti alloy useful as a corrosion-resistant structural material or a bio-related material is suppressed in oxidation of Ti, has excellent corrosion resistance, and has a dense structure, an oxygen content of 1 mass% or less, A film having a characteristic of porosity of 2 vol% or less can be formed.

It is also possible to obtain a coating film that can further significantly improve the corrosion resistance.

The present invention has the features as described above, and an embodiment thereof will be described below.

In the high-speed flame spraying (hereinafter referred to as “HVOF”) of the present invention, as its device means, for example, as illustrated in FIG. 1, a combustion chamber (Chamber) in which combustion is performed by mixing fuel such as kerosene and oxygen gas is performed. ) (1), a continuous conduit (2) via the nozzle (4) at its outlet, and in this conduit (2), powder of metal Ti or Ti alloy is supplied to the combustion gas. The basic structure is that which has a barrel portion heated and is cooled by cooling water as a whole. In the Ti film forming method using the apparatus having such a configuration, the oxygen concentration in the gas when supplying the powder is controlled to 5 vol%, and the gas temperature is controlled to 1500 ° C. or lower. In the present invention, this control is performed by mixing an inert gas into the combustion gas.

In the example of the apparatus configuration of FIG. 1, a gas mixing chamber (5) is provided in a combustion chamber (Chamber) (1), and an inert gas is supplied and mixed therein. It goes without saying that various aspects may be taken into consideration for the device configuration and the details thereof.

The gas temperature and oxygen concentration can be controlled by mixing the inert gas.

In the present invention, the collision speed of the heated particles on the substrate (Substrate) shown in FIG. 1 is set to 500 m / s or more.

When the oxygen concentration exceeds 5 vol%, when the gas temperature exceeds 1500 ° C., and when the collision speed is less than 500 m / s, the oxidation of Ti as described above is suppressed and a dense structure is obtained. Becomes difficult. On the other hand, the lower limit of the oxygen concentration is desirably as low as possible as the oxygen content ratio after the combustion reaction that generates the high-speed flame. The gas temperature affects the heating state of the Ti metal or its alloy particles and its flow rate. The lower limit varies depending on the scale of the apparatus, the powder supply, the type of powder, and the like, but in general, the lower limit is 900 ° C. or more.

In consideration of the above, in the actual operation, the supply amount and supply speed of the inert gas are determined by considering the apparatus scale and the like.

As for the kind of the inert gas, for example, a rare gas such as N ₂ (nitrogen gas), Ar (argon), or He (helium) is typically shown as a preferable one. Moreover, other things such as CO ₂ may be used depending on conditions.

Therefore, an example will be shown below and will be described in more detail. Of course, the invention is not limited by the following examples.

The HVOF thermal spraying apparatus using kerosene as a fuel is configured as shown in FIG. 1, a gas mixing chamber (5) is provided in the middle stage, a mixing chamber for mixing nitrogen is provided, and the gas temperature at the position where titanium powder is charged, The composition and flow rate can be controlled. As a result, the gas temperature at the titanium powder charging position can be controlled from 3000 ° C. to 800 ° C., and the oxygen concentration from 15% to 1%.

Using the above apparatus, a metal Ti film was formed on the surface of iron as a base material under the conditions shown in Table 1 below.

Table 2 exemplifies the calculated values of the gas temperature and the in-barrel flow rate during nitrogen mixing. At this time, the items in Table 3 are assumed.

FIG. 2 illustrates the relationship between the nitrogen gas flow rate and the mixed gas temperature. It can be seen that the introduction of nitrogen gas lowers the gas temperature, and the introduction of nitrogen gas allows the gas temperature to be controlled.

FIG. 3 shows the pore diameter and the porosity along with a photograph of the cross section of the formed Ti film when the N ₂ (nitrogen gas) flow rate (slm) and the spray distance (Spray distance) of FIG. 1 are changed. It is the figure which illustrated the relationship.

When the nitrogen gas flow rate is less than 500 slm, both the gas temperature and the oxygen concentration are high. Therefore, it can be seen that the boundaries of the titanium particles in the film are discolored by oxidation, but the oxidation is considerably suppressed at 1000 slm, and almost 1500 and 2000. unacceptable. On the other hand, when the nitrogen gas flow rate is 2000, the denseness of the film is significantly reduced. Therefore, it can be seen that when the spraying distance is about 180 mm in the vicinity of the nitrogen flow rate of 1000 to 1500 slm, there is little oxidation and a highly dense titanium film can be obtained.

For example, based on the above results, the relationship between the oxygen gas concentration in the gas, the gas temperature (Tg), and the oxygen content in the Ti film when supplying the Ti powder at the inlet of the Ti powder is shown. FIG. 4 illustrates the result of verification. FIG. 5 is a diagram illustrating the relationship between the collision speed of Ti particles to the substrate, the gas temperature (Tg), and the porosity. In addition, Tp has shown the surface temperature of Ti particle | grains measured with the two-color thermometer.

For example, from the above results, in order to suppress the oxidation of Ti and form a dense Ti film structure having excellent characteristics with an oxygen content of 1 mass% or less and a porosity of 2 vol% or less in the film, It was confirmed that it is desirable that the oxygen concentration is 5 vol% or less, the gas temperature is 1500 ° C. or less, and the particle collision speed to the substrate is 500 m / s or more.

In addition, when sprayed to a thickness of 800 microns under the most dense conditions and subjected to an immersion test in artificial sea water as it is, red rust generated from the base iron on the surface of the film in 3 days as shown in FIG. Appeared in. This is thought to be due to the presence of through pores in the film.

Therefore, this 800-micron film was polished to a thickness of 600 microns and immersed in artificial seawater for one month. As a result, as shown in FIG. 6, it was confirmed that no corrosion occurred. The corrosion resistance value measured by the AC impedance method also maintained a value of 10 ⁵ Ωcm ² or more.

It is the cross-sectional schematic diagram which illustrated the structure of the thermal spraying apparatus. It is the figure which illustrated the relationship between nitrogen gas flow volume and mixed gas temperature. It is the figure which illustrated the cross-sectional micrograph of a film | membrane, and the relationship between the pore diameter and cumulative porosity in a film | membrane. It is the figure which illustrated the relationship between the oxygen concentration in the gas at the time of Ti powder supply, the oxygen content in a membrane | film | coat, and gas temperature. It is the figure which illustrated the relationship between the velocity at the time of the collision of Ti particle | grains, a porosity, and gas temperature. It is the photograph which illustrated the result of the corrosion test of a film.

Explanation of symbols

(1) Combustion chamber (2) Conduit (3) Particle mixing section (4) Nozzle (5) Inert gas mixing chamber

Claims (1)

A combustion chamber (1) for combusting fuel gas and injecting a jet flow from the nozzle (4) toward the other end is provided at one end of the conduit (2), and particles for injection are provided in the middle of the conduit (2). Is a HVOF thermal spraying device provided with a particle mixing section (3) for mixing the gas with the jet flow, and mixing chamber (5) for mixing an inert gas on the nozzle (4) side in the combustion chamber (1). An HVOF thermal spraying apparatus characterized by comprising: