JPH0778273B2 - Wing member surface treatment method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a surface treatment method for a blade member, and more particularly to a steam turbine blade for thermal, nuclear and geothermal power generation, various blower blades, various stirring propellers and screws, This is a proposal for an effective method for improving the erosion resistance of blade members such as various pump sleeves.

(Prior Art) Generally, blades, especially steam turbines are used in geothermal power plants including thermal power plants, nuclear power plants, and the like, but are required to have the following properties. That is, the rotor blade must be excellent in high-temperature strength such as creep rupture strength because it is subjected to bending stress and vibration stress due to centrifugal force and steam thrust during operation. When used in a relatively low temperature environment, it has excellent room temperature yield strength and toughness, fatigue strength, notch sensitivity, erosion resistance, etc., and is capable of forging and welding. Required.

On the other hand, the stationary blade is not subjected to centrifugal force but is subjected to high bending stress. Therefore, good high temperature strength and weldability are required.

Conventionally, for such moving blades and stationary blades, materials such as those shown in Table 1 (in addition to these, Ti alloys (Ti (residual) -6A1-4V) have been used recently) according to the operating temperature in response to the above requests.
Is also used) is used.

However, rotor blades and vanes made of these materials are
It has been found that the following problems occur due to long-term use.

(1) Various components contained in steam (eg Si
Since such _{O 2, Al 2 O 3,} Fe 2 O 3) collides with the blades, stationary blades of the turbine, part of the wing member, causes a so-called erosion, the performance of the animal and stationary blades decreases As a result, turbine efficiency is reduced.

(2) In a boiler that manufactures high-temperature, high-pressure steam, the scale produced by oxidation is mixed in the steam. Therefore, when this steam is supplied to the turbine unit, the oxide scale particles in the steam cause turbine movement and static electricity. Tsubasa receives erosion.

(3) As the steam passes through the turbine, its temperature and pressure drop, but as a result, part of the steam drops into water droplets and collides with the rotating rotor blades, resulting in
The wing member surface causes damage due to erosion. This damage phenomenon is generally called a drain attack, which is also one of the important problems to be solved in the steam turbine.

Several solutions have been proposed in the past for the above-mentioned problems of steam turbine blades. For example, as disclosed in Japanese Examined Patent Publication No. 61-6242, in order to prevent erosion due to solid water quality components in steam and oxide particles of boiler tube material, diffusion of boron on the blade surface, especially on the stationary blade There is a method of hardening by penetration.

(Problems to be Solved by the Invention) However, the following problems still remain in the above-described conventional techniques. That is, in the former "boron diffusion infiltration method", the wing member is immersed in a high-temperature molten salt containing boron for a long time, or is maintained in a powder containing boron or in a gas at a high temperature for a long time so that the boron is not dissolved. Since the surface of the blade member is hardened due to diffusion and penetration into the blade member, the mechanical properties of the blade member itself are deteriorated. In addition, the boron layer diffused and permeated in this manner has a drawback of being hard but very brittle, and has not been a sufficient countermeasure.

In addition, as a method for preventing drain attack, a method of lining a hard alloy plate (for example, Hastelloy alloy plate) to the relevant part, which has been performed for a long time, is a liquid mechanically limited position where the drain attack occurs. Because
This is a method in which a stellite alloy plate, which is harder than the blade member, is attached to the corresponding portion via silver solder. However, this method requires skill to attach the stellite alloy plate with silver brazing, so that it still depends on the manual work, and even if a skilled person works, the passing rate is still low, and the cost is increased. It had the drawback of poor reliability. Moreover, some of these silver waxes contain low melting point metal (Cd),
In addition to being harmful to the human body, many fatigue cracks due to minute defects in the silver braze itself occur during operation as an turbine blade, causing the stellite alloy plate to peel off from the surface of the blade members and cause serious damage to the turbine plant. May cause damage.

An object of the present invention is to propose a surface treatment method effective for producing a wing member excellent in erosion resistance, which is free from adverse effects such as deterioration of the wing member itself and deterioration of the lined stellite alloy plate.

(Means for Solving the Problems) In response to the above-mentioned demand, the present invention mainly uses an oxide-based thermal spray material in order to prevent a drain attack when manufacturing a steam turbine blade having excellent erosion resistance. Instead, it was decided to adopt a surface treatment method in which a non-oxide type hard carbide composite thermal spray material of a hard alloy and a carbide cermet material is subjected to thermal spray deposition in an oxygen-free atmosphere.

That is, the present invention, first, the blade member is preheated using a plasma arc in an oxygen-free atmosphere, and subsequently, in the same atmosphere, a carbide-based composite thermal spray material of a Co-based alloy and a carbide cermet is sprayed, and then obtained. The carbide system and the composite thermal spray coating are heated and melted by using a plasma arc with the supply of the thermal spray material stopped, and in some cases, the thermal spray material is re-sprayed after the heating and melting. Is the way to do it.

And by this method, on the so-called turbine blade surface,
It is possible to manufacture a blade member formed by forming a geothermal carbide-based thermal spray coating that does not contain any oxides and has no pores and is highly adhesive.

(Operation) The surface treatment method of the blade member according to the present invention will be specifically described below.

Generally, in the thermal spraying method, thermal spraying is carried out in the atmosphere, so that the thermal spraying material becomes an oxide with heating and melting. The thermal sprayed coating containing the oxide thus obtained is generally a deposited layer that is hard to plastically deform and is bonded via brittle oxide particles, and therefore, the minute spaces that are the main cause of the generation of pores between the particles. Is generated. As a result, even if the thermal sprayed layer is heated thereafter, the existence of the oxide particles interferes with the mutual fusion of the metal particles, and thus only a porous film can be formed. Moreover, the oxide surrounding the metal particles hinders the metallurgical bonding action with respect to the material to be treated (blade member), so that the thermal spray material components do not sufficiently diffuse and permeate the surface of the material to be treated, and are merely mechanical. Stop joining. In short, for this reason, the conventional film is easily peeled off.

On the other hand, even if the thermal sprayed layer is simply thickened under such a condition, internal stress is generated due to the difference in cooling rate between the front and back sides as the layer becomes thicker, and it is rather easy to peel off. Therefore, it is usually 0.5mm or less in atmospheric spraying, even if it is thick
No film is formed that exceeds 1.0 mm.

Therefore, in the present invention, a non-oxide material of a Co-based alloy and a carbide cermet, that is, a carbide-based composite material is used as the thermal spraying material, and the material to be treated is preheated in a low-pressure argon gas atmosphere with oxygen removed from the thermal spraying environment. And decided to perform thermal spraying. As a result, the resulting coating, that is, the dense carbide sprayed coating, contains no oxides at all, and particles easily fuse with each other to form a non-porous sprayed layer, and when the material to be treated is preheated in advance. Since the internal stress is thermally released, the above problem does not occur even if the film is thickened.

In particular, in the case of the present invention, since there is no opportunity for injection and formation of oxides including the processing atmosphere from the starting material for thermal spraying, a metallurgically strongly bonded coating is formed.

FIG. 1 shows an apparatus used for carrying out a method for surface treatment of a turbine blade member according to the present invention. In this figure, reference numeral 1 in the drawing is a chamber for defining a thermal spray atmosphere. An exhaust valve 2 and an intake valve 3 are provided in the chamber 1, and the chamber 1
A vacuum pump 4 for sucking the internal gas is connected via a multi-cyclone 5 and a filter 6 for removing dust in the atmospheric gas. Furthermore, this chamber 1
An argon gas supply pipe 7 for holding the internal pressure, an argon gas cooling pipe 8 for cooling the material to be processed, which is a blade member, and an argon gas cooling pipe 9 used for cooling the spray robot motor are attached to the.

A platform 10 is installed in the chamber 1, and a thermal spray robot is mounted on the platform 10.
11 and a turntable 12 are installed, and a material 13 to be treated is placed on the turntable 12. A thermocouple 14 for temperature measurement is attached to the material 13 to be processed, and a spray gun 15 is attached to the tip of the spray robot 11, so that both can be controlled from outside the chamber 1. Configured.
Gases such as argon, helium, hydrogen and nitrogen are used for the spray gun 15 as a plasma generating gas in consideration of atmosphere adjustment. The spray gun 15 and the material to be processed 13 are connected to the outside of the chamber, and the polarities of the two can be changed as necessary.

Next, a method for spray coating a hard material using the above apparatus will be specifically described.

(1) After closing the intake / exhaust valves 2 and 3 and the argon gas supply pipe 7 attached to the chamber 1, the vacuum pump 4 is operated to discharge the air in the chamber 1 to the outside of the system, Is 1 × 10 ^-2 to 10 ^-3 mbr (mbar).

(2) Next, the argon gas supply pipe 7 is opened, and a dilute argon gas atmosphere having an internal pressure of about 60 mbr is formed in the chamber 1.

(3) After that, the vacuum pump 4 is operated again to bring the argon gas pressure in the chamber 1 to 20 mbr, and then the spray gun 1
5 is operated to generate a plasma arc, and the tip of the arc is moved to the vicinity of the surface of the material to be processed, which is a blade member, to preheat the material to be processed.

(4) The preheating of the material to be processed is performed by sweeping the plasma arc on the surface of the material to be processed several times by connecting the external power source to the spray gun 15 as the cathode and the material to be processed 13 as the anode. By doing. By this treatment, the surface of the material 13 to be treated is cleaned, heated and heated, and the material 13 to be treated is preheated. The preheating temperature is usually 500 to 900 ° C. for Ni-based, Co-based, and Fe-based alloy materials, but can be arbitrarily selected as long as the mechanical properties of the materials are not adversely affected.

(5) During the processes of the above steps (3) and (4), the argon gas supply pipe 7 for cooling is opened so that the material 13 to be processed is not overheated while monitoring the temperature indicated by the thermocouple. Control. However, even if overheated, the atmosphere does not contain oxygen, so that the material 13 to be treated is not likely to be oxidized, but the above temperature control is necessary in order to reduce metallurgical changes in the substrate due to overheating. is there.

(6) When the surface of the material to be treated 13 is cleaned and preheating is completed, the argon gas supply pipe 7 is opened again and the pressure in the chamber 1 is set to 200 mbr.

(7) After that, the polarity of the spray gun 15 is switched from the cathode to the anode and the material 13 to be processed is switched from the anode to the cathode, and the hard spray material is sprayed onto the surface of the material 13 to a predetermined thickness.

The thermal sprayed coating thus formed contains almost no oxides because there is no oxygen in the atmosphere, exhibits a dense state with no pores, and seems to have deposited fine metal particles peculiar to the plasma thermal sprayed coating in the atmosphere. It is different from the organization. Moreover, since the thermal spray coating does not contain oxides, the material to be treated 13
The bond with the base is also tight, and the two can be metallurgically bonded by selecting the preheating temperature of the material to be treated 13 and the chemical composition of the hard spray material.

According to the present invention, after the treatment of the above (7), the following treatment is continuously performed to further secure the metallurgical bonding of the thermal spray coating to the material 13 to be treated and to achieve the densification.

That is, after the treatments of (8) and (7), the supply of the thermal spray material is stopped and only the plasma arc is generated, and the plasma arc is brought close to the thermal spraying surface again to heat and melt the generated thermal spray coating.

(9) To increase the thickness of the sprayed coating, the sprayed thickness may be increased by the treatment of (7), but it is also possible to repeat the treatments of (7) and (8).

(10) As another example of the process of the present invention, after the treatment of (8), the thermal spray treatment of (7) is repeated again to form a thermal spray coating.

(11) (7), (7) + (8) or (7) + (8) +
When the treatment of (10) is completed, the gas pressure in the chamber 1 is adjusted to 10 mbr by adjusting the vacuum pump 4 and the amount of argon gas supplied.
After adjusting the pressure to about 100 ° C., argon gas is introduced again into the chamber 1 to adjust the pressure to 100 mbr, and this state is left for 30 to 60 minutes.

During this process, the vacuum pump 4 is constantly operated and a new argon gas is supplied from the outside, so the temperature of the material 13 to be processed gradually decreases.

(12) After being left for 30 to 60 minutes, the argon gas supply amount is increased to about atmospheric pressure and the operation of the vacuum pump 4 is stopped. Next, the intake valve 3 and the exhaust valve 2
Is opened to confirm that there is no pressure difference between the atmosphere and the chamber 1, and then the lid of the chamber 1 is opened to take out the material 13 to be treated.

The dense carbide-based sprayed coating formed on the blade member surface through the respective steps in this manner is used between the particles and the matrix (blade member).
Since it has a very strong binding force with, even if it is a thick film of 1 to 2 mm, it does not peel off, and a hard spray material can be appropriately selected to form a coating on the turbine blade surface.

When the thermal sprayed layer is subsequently heated and melted, if the blade member to be processed is applied with a negative force,
Since the surface is further cleaned, it is possible to continue the thermal spraying work without elaborating the blast treatment which is an essential step during thermal spraying. Further, at the time of heating and melting the sprayed layer, a thermocouple is attached to the material to be treated, and the argon gas for cooling is supplied to the cooling pipe 8.
If you control its temperature by feeding through
There is no thermal adverse effect on the material of the material to be treated.

Further, according to the surface treatment method of the present invention, even if the carbide is sprayed, it does not change into an oxide, so that the high hardness can be maintained as it is. However, when using a cermet in which carbide and metal are mixed as a thermal spray material, it is necessary to keep the temperature at which only the metal melts during the plasma arc heating of the thermal spray coating in step (8).

The heat treatment of the material to be treated after the formation of the sprayed coating can be carried out by a conventional method, that is, by taking out the film-formed product from the chamber and performing it in a vacuum heat treatment furnace.

The steam turbine blade surface-treated by the method described above has a dense and highly adherent coating that is completely different from the conventional sprayed layer on the surface of the steam turbine blade, so it has excellent erosion resistance over a long period of time. It is possible to completely eliminate the drawbacks of the turbine blade mounted with the stellite alloy plate using the current silver solder.

(Example) Example-1 JIS G 4319, S of a steam turbine blade material as a material to be treated
Select US 403FB material, heat it to 1100-1200 ℃ in a heating furnace, take it out of the furnace and forge it, and after cooling, width 50 x length
It was processed into dimensions of 100 x 20 mm thick.

On the other hand, as the thermal spray material, the chemical components (A to
The one used in G) was used. That is, symbols A, B, and C are Co-based alloys, and D is a carbide-based composite thermal spray material obtained by carrying out the production method of the present invention.

The treatment for forming the sprayed coating was performed using the apparatus shown in FIG. 1 so that the thickness would be 1.0 mm. The results are shown as Test Nos. 1-1 to 1-4 in Table 3.

For comparison, a conventional stellite alloy plate (1.0 mm thick), which is commercially available for plasma spraying in the atmosphere, untreated material and steam turbine blades, is applied to the surface of the treated material with commercially available silver solder. The attached one is shown. The results are shown as Test Nos. 1-5 to 1-10 in Table 3.

Regarding the erosion resistance of the thermal spray coating, frequency: 18.7K
Using a magnetostrictive vibration type cavitation erosion tester equipped with a ferrite oscillator of Hz, a magnetostrictive test piece taken from the material to be treated with thermal spraying was attached to the tip, and this was immersed in tap water at 20 ° C. After being vibrated for 1 hour, it was taken out and the appearance of the test piece before and after the test and the weight reduction ratio were investigated. The cavitation erosion test device during magnetostriction vibration and the shapes of the test pieces are shown in FIGS. 2 and 3.

The device shown in FIG. 3 consists of a water tank system and a vibrator system.
The tap water 25 in 28 can be circulated by operating the pump 27 from the tank 24, and clean tap water is always supplied to the water tank. On the other hand, the vibrator 21 is provided with a phone 22, and a test piece 23 is attached to the tip thereof. A film is formed on the surface of the test piece 23.
29 is formed, and this part is immersed in tap water. When the ultrasonic generator 26 is turned on, the vibrator 21 vibrates, and the vibration is transmitted to the test piece 23 through the phone 22,
Repeats vertical movement. This vibration is so fast that the test piece 23
Since a cavitation phenomenon occurs on the surface on which the film 29 is formed, this effect is used to evaluate the erosion resistance of the film.

Table 3 shows the test results. As can be seen from Table 3, in the untreated material (No. 1-9), a pit was formed in the center of the test piece due to cavitation erosion.
On the other hand, the one with the current Stellite alloy plate attached (N
In o.1-10), although the pitting pit was small and erosion resistance was recognized, many problems in working as described in the section of the prior art were observed.

Also, plasma spray coating in the atmosphere (No.1-5 to 1-10)
In spite of the fact that the hardness shows almost the same value as that of the coating film of the present invention, it was found that all the test pieces were found to have large pitting pits and a decrease in weight, and the erosion resistance was extremely poor. . The cause of this is that even if a hard material is sprayed by the plasma spraying method in the atmosphere, the coating becomes porous containing oxides, so the interparticle bonding force is weak and the cavitation phenomenon caused by ultrasonic vibration is generated. It is thought that it was dropped by.

On the other hand, the film obtained by the surface treatment method of the present invention (N
Regarding o.1-4), there was no pickling, and even if pickling occurred, the degree was slight. Therefore,
It was found that the weight difference before and after the test was small and the erosion resistance was excellent.

Especially, regarding the weight reduction ratio, the film of the present invention (No1-
It can be seen that 4) is remarkably superior to the case where the Co alloy alone is sprayed. That is, since the carbide-based composite thermal spray coating according to the present invention is dense and does not contain any oxides, it has a strong particle bonding force, and the thermal spray environment is controlled, so that the carbides change to oxides. It seems that the result is that the high hardness of the material can be maintained as it is.

Example-2 A test piece having dimensions of width 50 × length 100 × thickness 20 mm, which is the same as in Example-1, was manufactured, blasted using alumina powder, and then sprayed by thermal spraying in the following manner ( No.2-1 ~ 2-
4).

(1) A film having a film thickness of 1.1 mm formed by a thermal spraying method (a film having a film thickness formed by stopping the step (7) described above) (2) The film of (1) was melted by a plasma arc (Through steps (7) and (8)) (3) Those in which a thermal sprayed coating was formed again on the coating of (2) (Same as above (8) and then passed through (7)) By the above thermal spray deposition, a thick film that cannot be obtained by the conventional plasma spraying method in the atmosphere was obtained, and particularly the film formed by the operation of (3) reached 1.4 mm.

As comparative examples (Nos. 2-1 to 2-3 and 2-5 to 2-11), a film thickness of 0.5 mm was obtained by a plasma spraying method in the atmosphere.
A 0.7 mm test piece was made and a thermal shock test was conducted by repeatedly heating it at 850 ° C for 15 minutes and putting it in water at c'20 ° C. The thermal shock resistance was determined by the number of times when the peeled area of the coating reached 10% of the total. The sex was evaluated.

Table 4 shows the results. The coating (No. 2-4) formed by the method of the present invention was (1) only the thermal spraying, (2) the coating was melted, (3) after the melting. All of the coatings on which the thermal spraying was applied again were subjected to the thermal shock test of 10 times or more, and none were peeled off.

That is, plasma sprayed coating in air (No. 2-5
In 2-11), the film peeled off after the number of thermal shocks of 1 to 3 times.
The reason for this is that in this type of thermal spraying method, it belongs to thick film 0.5-0.7
Since the thermal spraying up to mm, the internal stress increases,
This is because the bonding force with the base material has become small, which indicates that a conventional thermal spraying method cannot form a build-up coating.

The film obtained by the method of the present invention shows good results because, as described in Example-1, even if the test piece is preheated because it does not contain oxygen in the atmosphere, it does not appear to have oxide scale. This is because foreign matter that would interfere with the adhesiveness of the thermal spray coating was not formed, and a dense and excellent adhesiveness coating was formed. In addition, since the test piece is preheated, the stress of the film formed on it is directly thermally released, resulting in a film with a small internal stress, making it possible to form a thick film with good adhesion. It seems that it has become.

Example-3 As is clear from the results of Examples 1 and 2, it was revealed that the thermal spraying overlay obtained by the method of the present invention is excellent in cavitation erosion resistance and thermal shock resistance. Therefore, it was decided to apply the method of the present invention to a steam turbine rotor blade.

FIG. 4 (e) shows the appearance of the steam turbine blade, where part A is the part exposed to flowing water droplets (drain) of steam during operation as a turbine blade, and part B is the turbine. It is a figure of the part fitted in a disc.

In addition, the thermal sprayed overlay has the following (a),
Construction is performed in the manner as shown in (b) and (c).

(A) is the surface exposed to steam over the entire surface by thermal spraying (Fig. 4a), (b) is the tip and back of the rotor blade, and approximately 1 / th of the ventral surface, respectively.
Figure 2 (b) and (c) are thermal spray overlays on the area of 2 (Fig. 4b) and (c) are thermal spray overlays on and around the tail of the rotor blades (Figure 4c) Figure 4 (d). Is an example of a conventional commercially available stellite alloy plate attached with silver solder.

Steam turbine blade using 12% Cr steel (length A of 28
5 mm, width 26 mm), and the blades were made of Ag, Cr and C ₃ C ₂ (80%)-Ni (16%)-Cr (4%) sprayed on Table ₂ with a thickness of 1.2 mm. The film of (a), (b),
It was formed as in (c). In addition, a commercially available stellite alloy plate 1.2 mm thick was pasted with silver brazing, and both were operated as actual turbine blades under the same conditions for about 1 year for comparison. The steam temperature during operation was 132 ° C. on average, and the rotation speed was 3600 rpm.

One year later, when the used turbine rotor blades were inspected, no abnormality was found in the rotor blades manufactured by the method of the present invention. On the other hand, in the case where the conventional method of adhering the stellite alloy plate was observed, the occurrence of erosion, although minute, was recognized, and many defects such as fatigue cracks were recognized in the silver brazing part.

Example-4 In this example, a rotor blade made of 6Al-4V-residual Ti and having the same dimensions as in Example 3 was manufactured, and the same thermal spray material was used to produce (a), (b) and (c) in FIG. As described above, the thermal spraying processing of the present invention was performed. However, the thickness of the sprayed coating is 0.5 mm.

This turbine rotor blade was attached to a steam turbine operating under the same conditions as in Example 3 and continuously operated for about one year, but no abnormality was recognized.

As described above, the method of the present invention is not limited to the iron-and-steel materials in the blade material as well as the thermal spraying materials having different chemical components, and an oxide film is easily formed in the high temperature atmosphere, and the conventional method is the thermal spraying processing. It was confirmed that the method can be sufficiently applied to a Ti alloy that is difficult to obtain and a film having high adhesion cannot be obtained.

(Effects of the Invention) As described above, the steam turbine blade manufactured by the method of the present invention can prevent the action of oxygen in the atmosphere in the manufacturing process, so that the film formed does not contain oxides, It has been revealed that it has excellent erosion resistance because of its excellent adhesion to the material. Moreover, the preheating temperature of the wing material. Since it can be increased, the residual stress in the film formed at high temperature is in a thermally released state, so it can be called a thick film that is not possible by the atmospheric spraying method, or an excellent thermal spray buildup. It is possible to form an erosion resistant film and it can be applied to a wide range of applications.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an apparatus used for carrying out the method of the present invention, FIG. 2 is a schematic diagram of a cavitation erosion test apparatus, FIG. 3 is a side view of a cavitation erosion test piece, and FIG. 4 is steam. The turbine rotor blade is shown, (a)-(d)
Is a sectional view and (e) is a partial perspective view. 1 ... Chamber, 2 ... Exhaust valve, 3 ... Intake valve, 4 ... Vacuum pump, 5 ... Multi cyclone,
6 ... Filter, 7 ... Argon gas supply pipe, 8 ...
Argon gas supply pipe for cooling the material to be treated, 9 …… Argon gas supply pipe for cooling the motor of the robot, 10 …… Platform, 11 …… Spraying robot, 12 …… Rotating table, 13 …… Treatment material, 14 …… Thermocouple for temperature measurement, 15 ... Thermal spray gun, 16 ...
… DC power supply, 17… Changeover switch.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-54-142220 (JP, A) JP-A-61-210171 (JP, A) JP-A-55-58360 (JP, A) JP-A-61- 159566 (JP, A) JP 61-288060 (JP, A) JP 52-54628 (JP, A) JP 56-32394 (JP, B2) JP 56-3001 (JP, B2)

Claims (2)

[Claims] 1. A pre-heated surface of a material to be treated is sprayed with a carbide-based composite thermal spray material of a Co-based alloy and a carbide cermet in a low-pressure argon gas atmosphere containing substantially no oxygen,
A method for surface treatment of a blade member, characterized in that the supply of the composite thermal spray material is subsequently stopped and only a plasma arc is generated to heat and melt the thermal spray coating for densification. 2. A preheated material surface to be treated is sprayed with a carbide-based composite thermal spray material of a Co-based alloy and a carbide cermet in a low-pressure argon gas atmosphere containing substantially no oxygen,
Subsequently, the supply of the composite spray material is stopped and only the plasma arc is generated to heat and melt the spray coating to densify it, and then the composite spray material is further applied onto the dense spray coating under an argon gas atmosphere. A surface treatment method for a blade member, comprising re-spraying to form a multilayer sprayed coating.