JPH0436455A - Formation of sprayed deposit - Google Patents

Abstract

PURPOSE:To form a dense hard film increased in binding force among grains by applying high frequency waves to a coil, wound round an insulating cylinder disposed in front of an anode nozzle, to produce a high frequency plasma and applying heating to a sprayed deposit. CONSTITUTION:A working gas is supplied into an anode nozzle 3, and non-load voltage is applied between the anode nozzle 3 and a cathode 2 from a D.C. power source 8. A high frequency wave generator 9 is operated and a plasma jet 14 is generated via the anode nozzle 3. A working gas is supplied into an insulating cylinder 10, and a high frequency oscillator 13 is operated and high frequency electric current is applied to an exterior coil 12 to produce a high frequency plasma 15. A powder of thermal spraying material supplied into the anode nozzle 3 is formed into thermally sprayed grains 16 heated and melted by the plasma jet 14 and are sprayed into the insulating cylinder 10. These grains 16 are allowed to fly while being further subjected to the acceleration of heating and melting by means of the high frequency plasma 15 and are allowed to collide against a subject 17 to be sprayed into flat form, which are then solidified and deposited. By this method, a dense sprayed deposit 18 can be formed.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for forming a thermal spray coating.

[Conventional technology]

In the conventional thermal spray coating formation method, linear or powdered thermal spray material supplied to a thermal spray gun is heated and melted by a combustion gas flame of a mixed gas of oxygen, acetylene, propane, or hydrogen, and the thermal spray particles are applied to the surface of the object to be sprayed. Spraying is achieved by the combustion heat spraying method that forms a thermal spray coating, or by flowing a working gas such as nitrogen or argon as a swirling flow around a direct current arc generated between a tungsten rod cathode and a copper anode nozzle in a thermal spray gun to turn it into plasma. A plasma spraying method is known in which a linear or powder spraying material is fed into the material, heated and melted, and the sprayed particles are carried in a plasma stream and sprayed onto the surface of the object to be sprayed to form a sprayed coating.

However, as shown in the cross-sectional view of Fig.
16 collides with the object to be sprayed 017 and becomes flat, which accumulates to form a sprayed coating 018. The overlap of the flattened sprayed particles 016 creates voids 019 at the grain boundaries, resulting in a porous coating as a whole. Become. Therefore, if such a thermal sprayed coating 018 is used as a corrosion-resistant coating, corrosive substances will penetrate into the porous coating and cause corrosion of the base material of the thermal sprayed object 017. Further, due to the presence of voids 019 in the grain boundaries, there are few contact areas between particles, and the adhesion force is small, so that the thermal sprayed coating 018 becomes a soft coating.

[Problem to be solved by the invention]

The present invention was proposed in view of these circumstances, and
It is a hard film that is dense with few voids in the grain boundaries of the sprayed particles and has a strong bonding force between particles. When applied as a corrosion-resistant film, it suppresses the penetration of corrosive substances and protects the base material of the sprayed object from corrosion. It is an object of the present invention to provide a method for forming a thermal spray coating that can prevent the formation of a thermal spray coating.

[Means to solve the problem]

To this end, the present invention generates a plasma jet by applying direct current between the cathode and anode nozzles of a plasma spray gun, and generates high-frequency plasma by applying a high frequency to a coil wound around the outer circumference of an insulated cylinder placed in front of the anode nozzle. let me,
The present invention is characterized in that a thermal spray material powder is supplied from the anode nozzle into the plasma die nozzle to form a thermal spray coating on the object to be thermally sprayed, and the thermal spray coating is heat-treated by the high frequency plasma.

[Effect]

In the thermal spray coating forming method of the present invention, the thermal spray material powder is heated and melted by the plasma jet generated by direct current application between the cathode and anode nozzle of the plasma spray gun, collides with the object to be sprayed, becomes flat particles, and is deposited. When a thermal sprayed coating is formed, it is exposed to the high temperature of high-frequency plasma, and the particles are first sintered by the heat of the high-frequency plasma, and then as the heating continues, the particles remelt, reducing the number of grain boundary voids. As a result, a dense thermal sprayed coating with strong interparticle adhesion and few voids is formed.

〔Example〕

An embodiment of the thermal spray coating forming method of the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal sectional view of a plasma spray gun for carrying out the method, and FIG. 2 is a sectional view of the thermal spray coating formed by the method.

In FIG. 1, a plasma spray gun 1 is composed of a cathode 2 made of a tungsten rod and an anode nozzle 3 made of copper. A cooling water passage 5 is bored in the latter nozzle wall.

Further, a thermal spray material powder supply port 6 is provided near the tip of the anode nozzle 3, and a working gas supply lower is provided in the insulator 4 at the base, and a DC power supply 8 and a high frequency Generators 9 are connected in parallel.

Further, in front of the anode nozzle 3, an insulating cylinder 10 made of, for example, a water-cooled quartz tube is arranged coaxially, and a working gas supply port 11 is bored at the base of the insulating cylinder 10, and a coil 12 is wound around the outer periphery. A high frequency oscillator 13 is connected to the coil 12.

In the figure, 14 is a plasma jet generated by applying a direct current between the cathode 2 and anode nozzle 3, 15 is a high-frequency plasma generated by applying a high frequency to the coil 12, 16 is a flying sprayed particle, and 17 is a The object to be thermally sprayed 18 placed opposite the plasma spray gun 1 is a thermal spray coating formed on the surface of the object to be thermally sprayed 17 .

To explain how to form the thermal spray coating 18 using such a plasma spray gun 1, Ar5j! /+++in is supplied, a no-load voltage of several 40 cm is applied between the cooled anode nozzle 3 and the cathode 2 from the DC power supply 8 with an output of kW, and the high frequency generator 9 is turned on. As a result, a plasma jet 14 is generated.

In addition, a working gas of Ar501/ll1n is supplied from the working gas supply port 11 into the insulating cylinder 10, and the frequency of 4MHz, 20kW is
When the high frequency oscillator 13 is activated to apply a high frequency current to the coil 12, an alternating magnetic field is generated within the insulating cylinder 10 and high frequency plasma 15 is generated. Then, adjust the gas flow rate and output to the set thermal spray conditions.

Next, Intoria (Y2 o2) bone stabilized zirconia (Zr0
2) is supplied into the anode nozzle 3 from the thermal spray material powder supply port 6 at a rate of 10 g/sin using Ar gas from a powder supply device (not shown).

Then, the thermal spray material powder becomes thermal spray particles 16 that are heated and melted by the plasma jet 14, are accelerated together with the plasma jet 14, and are sent from the anode nozzle 3 to the insulating cylinder 10.
It is ejected inward, heated and melted by the high-frequency plasma 15, and flies toward the object 17 to be thermally sprayed. The flying thermal spray particles 16 then collide with the surface of the object 17 to be thermally sprayed, become flattened, and solidify. The flat particles are deposited to form a thermal spray coating 18.

This thermal sprayed coating 18 is heated as it continues to be exposed to the high frequency plasma 15 as the thermal sprayed particles 16 accumulate and the coating thickness increases, and heat treatment is applied to the thermal sprayed coating 18 by appropriately controlling the heat capacity given to the thermal sprayed coating 18. The heat capacity can be controlled by changing the distance between the object to be sprayed 17 and the tip of the insulating cylinder 10.

In other words, if the heat capacity imparted to the thermal spray coating 18 is lower than the melting point of the thermal spray material, the sintering action will proceed at the grain boundaries of the flat particles constituting the thermal spray coating 18, the bonding force between the particles will be strengthened, and the heat capacity imparted will be lower than that of the powder material. When the temperature rises above the melting point, the flat grains remelt and the grain boundaries disappear, the bonding force between the grains further increases, and the voids formed at the grain boundaries decrease, forming a dense film.

For example, the distance between the object to be sprayed 17 and the tip of the insulating cylinder 10 is set to 4.
A cross-sectional view of the thermal sprayed coating 18 in the case of 5 fl is as shown in FIG. 2, and the thermal sprayed coating 11 has no grain boundaries and few voids 19! i! 18' is formed.

〔Effect of the invention〕

In short, according to the present invention, a direct current is applied between the cathode and anode nozzles of a plasma spray gun to generate a plasma jet, and a high frequency is applied to the outer circumferentially wound coil of an insulated cylinder placed in front of the anode nozzle to generate high frequency plasma. By supplying thermal spray material powder from the anode nozzle into the plasma jet to form a thermal spray coating on the object to be thermally sprayed, and heat-treating the thermal spray coating using the high-frequency plasma, the voids in the grain boundaries of the thermal spray particles are removed. It is a hard coating that is dense and has a strong bonding force between particles, and if it is used as a corrosion-resistant coating, it will suppress the penetration of corrosive substances, and in turn, it will prevent the base material of the sprayed object from corroding. The present invention is industrially extremely useful because it provides a method for forming a thermal spray coating that can be formed.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of a plasma spray gun for carrying out the method in one embodiment of the method for forming a thermal spray coating of the present invention, and FIG. 2 is a sectional view of the thermal spray coating formed by the method. FIG. 3 is a sectional view of a thermally sprayed coating obtained by a conventional method. DESCRIPTION OF SYMBOLS 1... Plasma spray gun, 2... Cathode, 3... Anode nozzle, 4... Insulator, 5... Cooling water passage, 6...
...Thermal spray material powder supply port, 7...Working gas supply port, 8
... DC power supply, 9 ... High frequency generator, 10 ... Insulating cylinder, 11 ... Working gas supply port, 12 ... Coil, 13 ... High frequency oscillator, 14 ... Plasma jet , 15... High frequency plasma, 16... Thermal spray particles,
17...Thermal spraying object, 18.18'...Thermal spray coating, 1
9...Void. Agent: Patent Attorney Masa Tsukamoto Figure 3 Figure 3

Claims (1)

[Claims] Direct current is applied between the cathode and anode nozzle of a plasma spray gun to generate a plasma jet, and high frequency is applied to an insulated cylindrical outer circumferentially wound coil placed in front of the anode nozzle to generate high frequency plasma. A method for forming a thermal sprayed coating, comprising: supplying thermal spraying material powder from the anode nozzle into the plasma jet to form a thermal sprayed coating on the object to be thermally sprayed, and heat-treating the thermal sprayed coating using the high-frequency plasma.