JPS63286565A - Plasma thermal spraying method at reduced pressure - Google Patents

Abstract

PURPOSE:To form a thermally-sprayed film having high density and high strength on the surface of a base material by providing a bored baffle plate between a nozzle and the surface of the base material, and making both the central axis of this bore and the central axis of a plasma jet nearly coaxial. CONSTITUTION:A baffle plate 4 having a bore is provided between the nozzle 2 of a plasma gun 1 and a bass material 8 in a reduced pressure tank 10, and both the central axis of this bore are the central axis of a plasma jet 5 are made nearly coaxial. In this state, the inside of the reduced pressure tank 10 is sufficiently exhausted and thereafter gaseous Ar is introduced to hold the pressure at about 20-100mmHg and powder is sent to the plasma gun 1 from a powder feeder 3. The powder 6 introduced into the high-temp. region of the center of the plasma jet 5 is sufficiently heated, melted and laminated on the base material 8 to form a thermally-sprayed film 9 but the powder 7 which is deviated from the center and insufficiently heated is laminated on the baffle plate 4 and substantially excepted from the thermally-sprayed film 9. Thereby only the sufficiently melted powder 6 is laminated on the surface of the base material and the thermally-sprayed film 9 having high density and high strength is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for forming a high-density, high-strength thermal spray coating.

(Prior Art) In a conventional low-pressure plasma spraying method, thermal spray powder is supplied by gas transport from a side direction with respect to a plasma jet axis. For this reason, unmelted powder that does not pass through the high-temperature region at the center of the plasma jet is mixed into the sprayed coating, causing deterioration in density and strength of the sprayed coating. FIG. 2 schematically shows a conventional low pressure plasma spraying method. In the figure, 1 is a plasma gun, 2 is a nozzle, and 3 is a powder supply device. Second
As shown in the figure, the powder 7 that has passed through the high-temperature area at the center of the plasma jet 5 and left the center, and the powder 7° that cannot enter the center of the plasma jet are cooled or
The heating will be insufficient. When the thermal spray gun is kept stationary and a thermal spray coating is formed on the flat plate 8, a thermal spray coating 9 as shown in the lower part of FIG. 2 is formed.
is obtained. In the center of the sprayed layer 9, the sufficiently melted powder 6 is stacked, so the sprayed powders adhere well to each other and become dense, but at the end portions 11 of the sprayed layer, unmelted sprayed powder is mixed in due to insufficient cooling or heating. Therefore, pores tend to increase,
In addition, the adhesion between the powder particles becomes weaker, so the strength of the sprayed coating also becomes weaker.

Generally, when performing thermal spraying, the plasma gun 1 is moved parallel to the surface of the material to be thermally sprayed (base material) to form a thermal spray coating over a wide area, so the edge of the thermal spray layer shown with diagonal lines in Figure 2 No. 11 is also incorporated into the sprayed coating. For this reason, the obtained thermal sprayed coating tends to contain pores, and the bonding force between particles is reduced, resulting in a decrease in the strength of the thermal sprayed coating.

(Problems to be Solved by the Invention) The present invention reduces unmelted thermal spray powder, which causes an increase in the porosity of the thermal spray coating and a decrease in the strength of the thermal spray coating, and provides a thermal spray coating with high density and high strength. It is intended to form a

(Means for Solving the Problems) The present invention provides a method for attaching a baffle plate with a hole between a nozzle and a base material surface so that the center axis of the hole is substantially coaxial with the center axis of the plasma jet. The unmelted particles contained in the periphery of the sprayed coating are blocked and only the sufficiently melted powder is layered on the substrate surface to form a high-density, high-strength thermal spray coating.

The present invention will be explained specifically and in detail below.

FIG. 1 shows an outline of one example of the present invention. plasma gun 1
, a nozzle 2 and a baffle plate 4 having a circular hole are attached so that the center axis of the hole and the center axis of the plasma jet are substantially coaxial. The baffle plate 4 and the plasma gun 1 are electrically insulated. Any baffle plate can be used as long as it is not eroded by the plasma jet, but graphite or water-cooled copper plates are usually used. The present invention is implemented within a vacuum tank 10. After the inside of the decompression tank IO is sufficiently evacuated, the slag is introduced to the pressure of a predetermined thermal spraying atmosphere, and thermal spraying is started. The pressure of the thermal spray atmosphere for effectively carrying out the present invention is in the range of 20 to 100 mm Hg. According to the method of the present invention, the powder 6 that enters the high temperature region at the center of the plasma jet is sufficiently heated and melted to form the base material 8.
A thermal spray coating 9 is formed by laminating on top. The underheated powder 7 that is off the center of the plasma jet is deposited on the baffle plate and is substantially removed from the sprayed coating.

The diameter of the hole in the baffle plate is set in consideration of the diameter of the plasma jet. The diameter of the plasma jet also changes depending on the pressure of the spraying atmosphere. For example, when the pressure of the spraying atmosphere is low, the diameter of the plasma jet expands and the diameter of the hole also increases, but when the pressure of the spraying atmosphere is high, the plasma jet expands. Since the diameter of the hole is narrowed down, the diameter of the hole must be made smaller.

Also, the diameter of the plasma jet increases as the distance between the nozzle tip and the baffle plate increases, so the diameter of the hole in the baffle plate should take this into consideration, and the diameter of the hole in the baffle plate should be smaller if the distance is short, and slightly larger if it is far away. .

The distance between the nozzle tip and the baffle plate is also adjusted in consideration of the above-mentioned atmospheric pressure, etc., but it is usually effective to set it to about 120 mm to 300 mm in order to increase thermal spraying efficiency. In this way, the diameter of the hole in the baffle plate is determined by taking into account the diameter of the plasma jet, which changes depending on the pressure of the spraying atmosphere, the distance between the baffle plate and the nozzle tip, etc., and is designed to ensure that the powder entering the high-temperature area at the center of the plasma jet is Set the size so that it can pass through.

For example, in the case of a reduced pressure plasma with a plasma output of 40 to 120 kW and a spraying atmosphere pressure of 20 to 100 mm Hg, the diameter of the hole is about 15 to 40 mm.

Although it is easier to make the hole in the baffle plate circular, it may be polygonal as long as it can be approximated to a circular shape.

When installing the baffle plate, it is necessary to make the center axis of the hole in the baffle plate and the center axis of the plasma jet almost coaxial. If so, it is sufficient to install the baffle plate so that the center axis of the hole and the center axis of the nozzle are substantially coaxial.

According to the present invention, only sufficiently melted powder is laminated on the base material surface to form a sprayed coating, so that the adhesion between powder particles is strong, and a pore-free, high-density, high-strength coating can be obtained.

(Example-1) Length: 300 mm, Width: 30 mm, Thickness] 5US304 powder was sprayed by reduced pressure plasma spraying on a 5541 substrate of 0 mm by the method of the present invention. A water-cooled copper plate was used for the baffle plate. The water-cooled copper plate is fixed to the spray gun. In order to form a uniform thermal spray layer on the surface of the substrate, the thermal spraying was carried out while moving the thermal spray gun parallel to the substrate. Thermal spraying conditions were as follows: Ar-tie mixed gas was used, the plasma electric cuff was 0 kW, the pressure of the spraying atmosphere was 30 mm Hg, the hole diameter of the water-cooled copper plate was 30 mmφ, the distance between the nozzle and the water-cooled copper plate was j1300+nm, and the distance between the nozzle and the substrate was 400 mm. A thermal sprayed coating with a thickness of 31 Tl[I+ was uniformly formed on the surface of the C1 base material. The obtained thermal sprayed coating was processed to obtain a plate-shaped tensile test piece with a thickness of 1 mm, and the tensile strength at break was measured. The coating density was measured by the Archimedes method using a sample roughly cut out from the thermally sprayed coating part, and the density ratio was determined by setting the density of a commercially available rolled material determined in the same manner as 100.

Table 1 shows a comparison of the measurement results of thermal sprayed coatings obtained by the method of the present invention and by a conventional low-pressure plasma spraying method conducted under the same conditions without providing a baffle plate.

Table 1 (Example-2) Hastelloy C powder (Ni-Go0.
81%-Or 15.8%-Fe5.1! ni-Mo16
．． H-Mn 0.65 Kame-5i O,5! l;-W 4
．． 0196-V 0.31%;) was subjected to low pressure plasma spraying by the method of the present invention. A water-cooled copper plate was used for the baffle plate.

The water-cooled copper plate was sprayed while moving the spray gun parallel to the base material in order to form a spray gun. Thermal spraying conditions are Ar-He
Using a mixed gas, the plasma electric cuff was 2 kW, the pressure of the spraying atmosphere was 50 mm Hg, the hole diameter of the water-cooled copper plate was 20 mmφ, the distance between the nozzle and the water-cooled copper plate was 200 mm, and the distance between the nozzle and the substrate was 300 mm. 3mm thick
A sprayed coating was formed. The obtained thermal sprayed coating was processed to obtain a 1 mm thick plate-shaped tensile test piece, and the tensile strength at break was measured. The coating density was measured by the Archimedes method using a sample roughly cut out from the thermally sprayed coating, and the density ratio was determined by setting the density of a commercially available expanded material determined in the same manner as 100.

Table 2 shows a comparison of the measurement results of the sprayed coatings obtained by the method of the present invention and the conventional reduced pressure plasma spraying method conducted under the same conditions without providing a baffle plate.

Table 2 (Effects of the Invention) As is clear from the above results, the present invention has the following effects.

(1) A high-density sprayed coating with few pores can be obtained;
Superior corrosion resistance compared to conventional thermal spray coatings.

(2) Since the thermal spray powders are in close contact with each other, the mechanical properties of the film are excellent.

[Brief explanation of drawings]

FIG. 1 is a drawing schematically showing the outline of the method of the present invention,
Shows the state of thermal spraying on a steel plate. FIG. 2 is a drawing schematically showing the principle of conventional low pressure plasma spraying. DESCRIPTION OF SYMBOLS 1... Plasma gun, 2... Nozzle, 3... Powder supply device, 4... Baffle plate, 5... Plasma jet, 6° 7... Thermal spray powder particles, 8... Group Material, 9...
Thermal spray coating, 10...reduced pressure tank.

Claims (1)

[Claims] In the low pressure plasma spraying method, between the nozzle and the substrate surface,
A baffle plate with holes is provided so that the center axis of the hole in the baffle plate is substantially coaxial with the center axis of the plasma jet, and a high-density, high-strength thermal spray coating is formed on the substrate surface. Low pressure plasma spraying method.