JP2951108B2 - Thermal spray coating formation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a thermal sprayed coating, and more particularly to a method for forming a base material used in a severe environment such as a roll or a boiler tube, which is used in a severe environment such as high-temperature corrosion, a wear atmosphere, and a high load stress. The present invention relates to a spraying technique for protecting a sprayed material having high wear resistance by spraying the material on the surface thereof, thereby achieving high functionality and long life.

[0002]

2. Description of the Related Art In a conventional thermal spraying process, as shown in FIG. 6, thermal spray particles 2 melted by a plasma jet 1 are blown against a base material 3 to collide therewith and rapidly solidify. The solidification rate at this time was measured to be about 10 ⁵ k / sec, and it was found that solidification was instantaneous. For this reason, the thermal spray particles 2 do not sufficiently penetrate into the gaps between the laminated film particles 4, and the pores 5 are generated in the thermal spray film in principle. Further, since the thermal spray particles 2 are instantaneously solidified, atomic diffusion between the particles constituting the coating does not occur, and the bonding force is weak.

[0003] Due to these causes, the sprayed coating has poor ductility and poor strength, particularly poor bending strength.
Cracks (cracks), chipping, and peeling easily occur due to stresses and impacts in an actual use environment, resulting in low reliability.

[0004] As a method for improving the reliability of such a thermal spray coating, for example, Japanese Patent Application Laid-Open No. 2-294457 discloses a method of forming a thermal spray coating at an arbitrary temperature, and then setting the melting point of the thermal spray material to zero. Intermediate heat treatment is applied at a temperature of 0.6 times or more and 0.75 times or less, and finally, 2000 atm.
A method has been proposed in which hot water isostatic treatment is performed at 1150 ° C. for about 1 hour to eliminate pores present in the film.

[0005]

However, according to the above-mentioned conventional method, a process such as heat treatment for preventing peeling of the sprayed coating must be performed after the formation of the sprayed coating. In addition to lowering the yield, it is inevitable that equipment costs will increase. in addition,
Due to equipment limitations, the applicable range of the base material size that can be processed is narrowed. In addition, since this heat treatment is intended for the atomic diffusion effect of the sprayed particles, even if heat treatment is performed after spraying, the density of the sprayed coating itself before treatment and the degree of bonding between the coating constituent particles are reduced. Significantly affects heat treatment after thermal spraying. In other words, it is considered that a thermal sprayed film having excellent denseness and bonding degree in a state before the treatment has a greater treatment effect, a shorter treatment time, and a higher quality.

The present invention has been made in view of the problems of the prior art and the knowledge of the inventor. The main object of the present invention is to improve ductility and strength without special treatment after forming a thermal sprayed coating. An object of the present invention is to provide a method for forming a thermal spray coating capable of producing a rich thermal spray coating at low cost.

[0007]

SUMMARY OF THE INVENTION According to the present invention, when spraying a thermal spray material comprising at least one metal under a reduced-pressure inert atmosphere, the surface of the thermal spray base material to be sprayed is provided. Thermal spraying is performed by maintaining a temperature in the vicinity of 0.65 times or more and 0.9 times or less the absolute melting point of the material having the lowest melting point among the materials constituting the thermal spraying material. A transition type arc in which a base material is used as an anode between a base material and a nozzle of a plasma gun when spraying a sprayed material composed of one or more metals on a metal sprayed base material under a reduced pressure inert atmosphere. An electric current is applied, and the temperature in the vicinity of the surface of the portion to be sprayed on the sprayed base material is set to 0.65 of the melting point of the material having the lowest melting point among the materials constituting the sprayed material.
This is attained by providing a thermal spray coating forming method characterized in that thermal spraying is performed while maintaining the temperature at a temperature of at least twice and at most 0.9 times.

[0008]

The temperature of the base material during thermal spraying of the portion to be sprayed is 0.65 of the melting point expressed by the absolute temperature of the material having the lowest melting point among the thermal sprayed materials.
By keeping it more than twice, atom diffusion between the spray particles constituting the spray coating becomes active and the particles sinter, the pores generated during lamination gradually disappear and the bonding force between the particles is strong. As a result, the ductility and strength of the film are improved.

In the case where a base material having a large heat capacity is subjected to thermal spraying, it is necessary to maintain the base material temperature at 0.65 times or more the absolute melting point of the material having the lowest melting point among the sprayed materials during thermal spraying. However, a heating source other than the plasma jet is required.

In general, a contact-type heater, a high-frequency induction coil, or the like is considered as a heating source. However, since it can correspond to an arbitrary shape of the sprayed base material and does not physically block the sprayed particles sprayed to the base material spraying portion, It is easiest and most effective to heat the base material by passing a transfer type arc current having the base material as an anode between the base material and the nozzle of the plasma gun. By this transition type arc, it is possible to maintain the portion to be sprayed of the base material being sprayed at 0.65 times or more the melting point of the material having the lowest melting point among the sprayed materials expressed in absolute temperature.

[0011]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

[0012]

[Table 1]

As a thermal spraying material, a superalloy containing Co as a main component shown in Table 1 (melting point 1375 ° C.) was used.
As shown in (A), the SS400 base material 3 (dimensions: length 1
50T on the surface of 00mm x 30mm x 12mm)
Thermal spraying was performed under a reduced pressure air atmosphere of orr to form a thermal spray coating 8 having a thickness of about 2 mm. At this time, as shown in FIG. 1 (B), a thermocouple 9 was brought into contact with a position approximately 1 mm from the surface of the base material 3 to measure the temperature. By controlling between 200 A, the temperature of the base material 3 was kept constant. After the thermal spraying was completed, the thermal spray coating 8 cooled to room temperature was used to obtain L40 mm × W4 shown in FIG.
A test piece 10 of mm × T1 mm was cut out and subjected to a bending test (JIS R 1601) shown in FIG. The hardness of the test piece 10 was also measured.

FIG. 3 shows the results. Here, the relative temperature on the horizontal axis is the ratio of the coating temperature expressed in absolute temperature to the melting point of the coating material expressed in absolute temperature. When sprayed at a temperature not exceeding 0.6 relative temperature, cracks occurred during spraying, and test pieces could not be collected. In this temperature range,
Both the film strength and ductility are poor, and easily broken by thermal stress during thermal spraying.

When the relative temperature was from 0.6 to 0.65, there was no cracking or peeling of the film, and it was found that the strength increased.
The fracture of the sample was brittle. This region is called a brittle region.

When the relative temperature exceeded about 0.65, the sample exhibited a marked improvement in ductility without breaking. This region is called a ductile region.

When the relative temperature exceeds 0.9, thermal spraying is performed.
The erosion of the sprayed coating surface was observed by the heat input from the surface by the plasma and the transfer type arc current.

Based on these facts, in the present invention,
The lower limit of the temperature immediately below the surface to be sprayed during the thermal spraying was set to 0.65 in relative temperature, and the upper limit was set to 0.9 in relative temperature.

[0019]

[Table 2]

As a result of performing a bending test using the Ni-based alloy (melting point 1400 ° C.) shown in Table 2 as a thermal spraying material through the same procedure as described above, the relative temperature was again increased as shown in FIG. At 0.65 or more, it was found that the film entered the ductile range and the toughness was significantly improved. That is, although the material components are completely different, the same tendency as in the above-mentioned Co-based superalloy is shown in this case, and the relative temperature is set to 0.65.
It is shown that maintaining the above value greatly contributes to the thermal spray coating strength.

Next, when a sprayed material shown in Table 1 was sprayed on a surface of a stainless steel pipe (SUS304) having a diameter of 42 mm × length 850 mm (thickness 9 mm) in an argon gas atmosphere of 50 Torr, as shown in FIG. When the transition type arc current is 0 (A), that is, when only the plasma jet is heated, the base material temperature can be maintained at only about 700 ° C. and the relative temperature can be maintained at only about 0.59. At this temperature, as shown in FIG. Both the strength and ductility of the formed film were low, and the film was easily cracked. However, the base material temperature that can be held increases as the transfer type arc current amount increases, and 970 ° C. (relative temperature 0.75) at the maximum current amount 200 (A) of the equipment.
It was possible to raise and maintain the base material temperature up to this point, and it was possible to form a film having high ductility and high strength as shown in FIG.

As a result of subjecting this test material to a compression test in the axial direction, no peeling or cracking occurred even at a compression strain of 5% or more, and a remarkable improvement in ductility was shown. High-speed flame spraying in air (commonly referred to as HVOF) for reference
In the sample manufactured by the method described above, the peeling of the film was caused by the compression strain of 2%.

In this embodiment, the atmospheric pressure during thermal spraying is 50
Although it was set to Torr, there was no remarkable difference in the thermal spray coating structure when the pressure was between 20 and 100 Torr, and it was found that the same effect as in the above example was obtained. However, 100T
If it exceeds orr, the number of pores in the coating increases, and the effect of improving strength and ductility decreases. Also, 20To
Thermal spraying under reduced pressure below rr requires a large amount of equipment capacity and increases equipment costs, and is not suitable for the method of forming an inexpensive thermal spray coating which is the gist of the present invention.

[0024]

As described above, according to the method for forming a thermal spray coating according to the present invention, it is not necessary to perform post-processing after thermal spraying, and it is possible to remarkably improve both the strength and the ductility of the thermal spray coating. In addition, the use in a severe use environment, which could not be used conventionally, is expanded, and the reliability of the thermal spray coating is remarkably improved.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a procedure for manufacturing a test piece used in an example.

FIG. 2 is an explanatory view showing a film strength test method.

FIG. 3 is a graph showing a relationship between a film forming temperature and a sprayed film strength according to the present invention.

FIG. 4 is a graph similar to FIG. 3 for another thermal spray material.

FIG. 5 is a graph showing a relationship between a film forming temperature and a transition type arc current according to the present invention.

FIG. 6 is a schematic explanatory view showing a formation mechanism of a thermal spray coating.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plasma jet 2 Thermal spray particle 3 Base material 4 Pre-laminated coating particle 5 Particle 6 Unmelted particle 7 Plasma gun 8 Thermal spray coating 9 Thermocouple 10 Test piece

Claims (2)

(57) [Claims] When a thermal spray material made of one or more metals is thermally sprayed under a reduced-pressure inert atmosphere, the temperature of the thermal spray base material in the vicinity of the surface to be sprayed is adjusted to the most of the materials constituting the thermal spray material. The melting point of the material with a low melting point, expressed as an absolute temperature, of 0.
A method for forming a thermal spray coating, wherein the thermal spraying is performed while maintaining the temperature at 65 times or more and 0.9 times or less. 2. A transition type in which a sprayed material made of one or more metals is sprayed onto a metal sprayed base material under a reduced-pressure inert atmosphere and the base material is an anode between the base material and a nozzle of a plasma gun. An arc current is applied to set the temperature of the base material near the surface to be sprayed to 0.65 times or more of the absolute melting point of the material having the lowest melting point among the materials constituting the sprayed material. A method for forming a thermal spray coating, wherein the thermal spraying is performed while maintaining the temperature at 9 times or less.