JPH04103750A - Formation of wear resistant coating layer - Google Patents

Abstract

PURPOSE:To reduce porosity in a coating layer and to improve its wear resistance by holding the temp. of the surface of a base metal to a specified one and plasma-spraying WC alloy powder mixed with Co, Cr, Ni or the like on the surface of the base metal under the reduced pressure. CONSTITUTION:The surface of a thermal spraying base metal is thermal-sprayed with alloy powder contg., by weight, 25 to 35% Co, 6 to 12% Cr, 5 to 10% Ni, 1.5 to 9% Si+B+C and the balance WC under the reduced pressure in the state where in the temp. of the surface of the above material is held to >=300 deg.C. By this thermal spraying, a spray coating layer having <=3% porosity is formed. Because the thermal spraying is executed under the reduced pressure, differently from thermal spraying in the air, the contamination of air does not occur and its porosity can be reduced. In this way, the formation of an excellent wear resistant coating layer is permitted, and the components to be added newly are general Ni, Cr, Si, B, C or the like which are inexpensive, so that the service life of a wear resistant member can remarkably be prolonged without raising the cost of the spray powder.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to sliding parts such as mechanical parts and parts that require wear resistance in relation to earth and sand. Regarding the method.

[Prior Art] Hard materials such as sintered ceramics and sintered carbide are generally used in parts that require wear resistance. In the case of sintered products, liquid-phase sintering basically forms a liquid phase of Go and solidifies it over time, so the hard particles (WC) of the structure and the matrix surrounding them The bonding with (Go) is reliable, and the matrix portion itself is also well-tightened. Micro-Vickers hardness, which is measured from the size of the indentation made by pressing a diamond needle into the material, usually has an excellent micro-Vickers hardness of about 1,600 to 1.800.

However, when using a hard material such as a sintered ceramic product or a sintered carbide product, it is technically difficult to manufacture a thin product for both, so a thickness greater than that required is required. That is, when used as a wear-resistant structural material, it usually requires about 5 to 1 Omm, and the powder itself is expensive, resulting in expensive parts. Further, in the case of a complicated shape other than a flat plate, cylinder, or cylindrical shape, a special mold or the like must be manufactured, resulting in a very high cost. Therefore, there are many cases in which the technology is not adopted because it is not cost-effective in practice. Furthermore, even when used as a profitable high-class component, there are major problems in the method of attaching it to materials made of steel, and there are many cases where it is difficult to use it.

In other words, even if holes are made in ceramics or sintered carbide crystals, etc. and sewn with bolts, etc., cracks will occur from the holes and breakage will occur during use, making it superior in terms of wear resistance. was also often impractical.

In contrast, thermal spraying of wear-resistant materials has recently become popular because it hardens only the necessary parts of the base material. Thermal spraying can easily be applied to any shape, and since it is only necessary to form a film with a required thickness, usually around 100 to 300 μm, less powder is required, and the manufacturing process is faster than the powder sintering method described above. In other words, since it is simple, it is extremely advantageous in terms of cost. In the case of thermal spraying, 12% Co or 17% Co cemented carbide powder, which has the same composition as sintered carbide, is currently most commonly used. 12% of the same composition as carbide
In the case of atmospheric pressure spraying of Co or 17% Co cemented carbide powder, particles with a size of about a few micrometers are usually used, and they are placed in a high temperature caused by plasma or gas combustion of acetylene + oxygen, etc., and instantly sprayed. Since the method involves melting and rapidly cooling and solidifying, the particles of the matrix portion (Co) are not sufficiently bonded to each other, and it cannot be said to be a completely integrated structure. In addition, unmelted particles and pores inevitably enter the structure and may cause defects in the sprayed film. Therefore, the above-mentioned throat hardness is only about 1,000 to 1,100 at most. Furthermore, in order to prevent the surface of the base material from being oxidized, the surface of the base material is usually cooled to about 150 to 200°C before thermal spraying, so the film quality itself is a rapidly solidified amount.
It also has poor toughness because it contains unmelted particles and pores. Furthermore, in the case of normal atmospheric spraying, after grid blasting, the temperature of the base material must be controlled to below about 150 to 200°C before spraying. This is to prevent oxidation of the surface of the base material.

That is, this is to prevent separation from the interface due to the production of oxides on the surface of the base material. For this reason, since the temperature of the surface of the base material is low, the sprayed particles are rapidly cooled, and the bonding between the sprayed particles does not take place sufficiently, nor does the chemical reaction in the components take place sufficiently.

In order to solve this problem, increasing the temperature at which the particles are melted in the thermal spray gun only causes the decomposition of the important component WC, which has the opposite effect. For this reason, normal atmospheric pressure spraying does not have a promising lifespan.

Therefore, using cemented carbide powder of 12% Co or 17% Co, an atmospheric pressure of 50 Torr and 300 t:
If low-pressure thermal spraying is performed at the above preheating temperature, a considerable improvement effect can be seen.

[Problems to be Solved by the Invention] According to the thermal spraying method, it is possible to manufacture wear-resistant parts easily and at low cost as described above. Since the mode of melting and solidification (solidification) is different from sintering, the quality cannot be compared to sintering. That is, current thermal spraying is inferior to sintered carbide in performance and has a short life as a wear-resistant component.

Therefore, in the current thermal spraying method for wear-resistant materials, which has the above-mentioned problems, the present invention takes advantage of the advantages of thermal spraying to produce a hard wear-resistant material that is low in cost and as close to sintered carbide in quality as possible. The purpose of this invention is to provide a practical method for producing thermal sprayed materials.

[Means for Solving the Problems] In order to achieve the above object, the method for forming a wear-resistant coating layer of the present invention includes applying a temperature of this material to the surface of a thermally sprayed base material at a temperature of 300°C.
25 to 35% by weight of Go and C while keeping the temperature above ℃
6 to 12% by weight of r, 5 to 10% by weight of Ni, 10B of Si
+ Contains 1.5 to 9% by weight of C, with the remainder being wC
It is characterized in that an alloy powder consisting of the following is plasma sprayed under reduced pressure to form a sprayed coating layer with a porosity of 3% or less.

[Operations and Examples] Wear resistance depends on the hardness of the hard particles, the hardness of the matrix portion, and the bonding force with the matrix portion that restrains the hard particles. Furthermore, the adhesion strength between the base material and the film has an effect on the longevity of the wear-resistant material from the viewpoint of preventing peeling during use.

The present inventors believe that the reason why thermal spraying is inferior to sintering is that in carbide thermal spray materials, the WC particles themselves are hard, but the Co that makes up the matrix is not sufficiently melted, and the bond between the particles is broken. It was thought that this had not yet been made strong enough, and it was also assumed that unmelted particles of the components, pores, etc. were mixed in and prevented sufficient bonding between the particles. In addition, the bonding force with the matrix portion that restrains the hard particles and the adhesion strength between the base material and the film become stronger as the temperature of the base material during vacuum spraying is higher.

If the temperature of the base material is below 300°C, diffusion at the adhesion interface will not occur properly, and the adhesion strength with the base material will be several kg/ID1.
112 or less, and the interparticle bonding force within the thermally sprayed coating layer also decreases, and there is a risk of peeling under strong abrasion conditions, making it impractical. For this reason, it is preferable to preheat the base material to 300°C or higher, more preferably 400°C or higher.

For this reason, the attached particles are not rapidly cooled either, allowing more time for the particles to become familiar with each other. This is only possible through low-pressure thermal spraying, which can be carried out in an atmosphere free of surrounding oxygen.

However, the upper limit temperature cannot be generalized because it is related to the melting point, coefficient of thermal expansion, size, etc. of the base material. That is,
For materials with a low melting point such as aluminum, the preheating temperature is naturally limited to 500° C. due to its melting point. It is also related to the coefficient of thermal expansion of the base material, and if it is made of stainless steel with a high coefficient of thermal expansion and is large in size,
The large shrinkage during the cooling process after thermal spraying can cause problems such as peeling of the film. However, in the case of castings with a small coefficient of thermal expansion, problems such as peeling are unlikely to occur even if the size of the base material is large. As mentioned above, it is necessary to understand the relationship between the melting point of the base material, its size, the maximum preheating temperature, the maximum temperature reached during thermal spraying, etc. in advance based on the actual shape.

Furthermore, since it is carried out by low pressure thermal spraying, unlike atmospheric thermal spraying, air is not involved and the porosity can be reduced.

Abrasion resistance also depends on the porosity of the sprayed coating layer, defined below.

Porosity (piece = (1 - (specific gravity of thermal spray coating layer / specific gravity of bulk material)) x 100 If there are many pores, for example, if the coating is applied to improve the abrasion resistance of a mold for molding fire-resistant ceramic bricks, etc. Ceramic particles that cause wear dig in and wear grows there, so a dense coating layer with few pores has excellent wear resistance.

The same applies to abrasion caused by earth and sand. Furthermore, in cases where erosion and wear are combined, or corrosion and wear are combined, the influence of the small porosity is particularly important. Attrition grows with the pores as the nucleus. In normal cases, the porosity tolerance is preferably 3% or less.

In order to ensure high adhesion and interparticle bonding force of the thermal spray coating layer and reduce porosity to create a dense thermal spray coating layer, the pressure range when implementing the low pressure plasma spray method is 20 to 30℃.
0 Torr, more preferably 30 to
It is 100 torr.

When the pressure exceeds 300 torr, the effect of reduced pressure spraying decreases and approaches atmospheric spraying, that is, the film is formed by involving pores, so it is not a dense film. , wear resistance decreases.

Furthermore, if the pressure is lower than 20 Torr, the plasma flame will extend abnormally long, making thermal spraying work difficult with a normal low-pressure thermal spraying device, and the film quality will deteriorate, which is not preferable.

In the phenomenon of wear, first, the soft part of the matrix part is scraped off, and when the protrusion of hard WC particles becomes larger, it becomes difficult to hold the WC in the matrix part, and the part falls off. The part that fell off becomes a hole, and wear and erosion progresses around that part again.

In carrying out the present invention, the composition of the powder used is G
It is an alloy powder containing 25-35% by weight of O, 6-12% by weight of Cr, 5-10% by weight of Ni, 1.5-9% by weight of Si + B + C, and the raffinate part is made of We. However, the particle size of the powder is preferably 44 to 1 μm, more preferably 25 to 5 μm.

When the particle size of the alloy powder becomes coarse, the porosity increases and the bonding force between particles decreases, resulting in a decrease in wear resistance. Furthermore, if the particle size of the powder becomes too fine, the feeding of the powder into the plasma becomes unstable, making it difficult to form a dense and homogeneous coating layer.

In carrying out the present invention, the plasma scum used is A
Mixtures of He, Ar+N2, Ar+N2, etc. can be used, but it is preferable to use Ar+82.

As can be seen from FIG. 3, if Co is in the range of 25 to 35% by weight, it surpasses the wear resistance of conventional WC-17. Similarly, as is clear from Fig. 4, Cr is 6 to 1
2% by weight is optimal. On the other hand, as shown in Figure 5, Ni
is optimally in the range of 5 to 10% by weight.

Moreover, as shown in FIG. 6, the Sj+B+C component is 1.
A range of 5 to 9% by weight is preferred. silicide, boride,
It is effective in synthesizing carbides, etc., and hardening and strengthening the matrix. If the Si + B + C component exceeds 9% by weight, it will become brittle, and if it is less than 15% by weight, no effect will be seen. In practice, Si is 1 to 4% by weight and B is 0°5 to 3% by weight.
Weight %, C is 0. ] to 3.5% by weight is preferred.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

[Example] (Example-1) Alloy powders a, b, and c having the composition (wt%) and particle size (qm) shown in Table 1 were vacuum sprayed onto a mild steel surface under the spraying conditions shown in Table 2. Then, thermal spray coating layers A, B, and C were formed. The thickness of the thermal spray coating layer was 1 mm.

A wear test was conducted using a Suga sliding wear tester specified in JIS-88503. This is a numerically applied test method that measures the wear loss while rubbing SiC with Santo Vapor, and is representative of relatively many forms of actual sliding wear. be.

The test method of this example was also based on this method. A test piece with a thermally sprayed coating layer on the surface was prepared, and the degree of sliding wear damage was evaluated using a Suga type sliding wear tester. Test condition is load 3
00g, and #320, which is commonly used in terms of numbers, was used as the vapor. The vapor wrapped around the ring rotates 0.9 degrees per reciprocation, so a new vapor can be used for 400 reciprocations. Therefore, 40
The weight was precisely weighed and measured every 0 times, and the data was plotted.

As comparison materials, We-12Go, a conventional thermal spray material,
Using WC-17Co powder, power 87kW, pressure 50
Thor, spraying distance 400mm, preheating temperature 450"C
This figure shows a thermally sprayed coating layer that was sprayed under reduced pressure under these conditions. As can be seen from FIG. 1, the thermal spray coating layers A, B, and C of the present invention all exhibit higher wear resistance than conventional materials. Alloy powder a was thermally sprayed to form a thermal sprayed coating layer A, alloy powder A was thermally sprayed to form a thermal sprayed coating layer B, and alloy powder C was thermally sprayed to form a thermal sprayed coating layer C. The conditions for the thermal spray coating layer are shown in Table 2.

(Example-2) Using alloy powder C shown in Table 1, the surface of mild steel was sprayed under reduced pressure under the spraying conditions shown in Table 3 to form thermal spray coating layers with different porosity, E, F, and G. was prepared, and the degree of wear resistance and damage was evaluated in the same manner as in Example-1. FIG. 2 shows the relationship between the porosity of each sprayed coating layer and the amount of weight loss after 4,000 reciprocating sliding abrasion tests.

The thickness of each thermal spray coating layer was 1 .mu.m. From thermal spray coating layer I
A sample for specific gravity measurement of OX IOX 1.5 mm was cut out, and the specific gravity was measured by the submerged weighing method specified in JIS Z8807.

In addition, the specific gravity of the bulk material can be determined by cutting out a sample similar to the above from a sample plasma-melted in a water-cooled crucible in a water-cooled crucible in the atmosphere of A. Ta.

From the results shown in Figure 2, it is clear that if the porosity is approximately 3% or less, the thermal spray coating layer formed by the method of the present invention can be formed using conventional wear-resistant materials (1
Using cemented carbide powder of 2% Go and 17% Co, at an atmospheric pressure of 50 Torr and a temperature of 300°C or higher,
The wear resistance can exceed the wear resistance of those that have been sprayed under reduced pressure. Since thermal spraying is carried out at a high temperature, the reaction of forming borides, silicides, carbides, etc. of B in the components proceeds well, resulting in improvements in the strength and hardness of the matrix.

If the powder supply speed and gun movement speed for thermal spraying are appropriately set in advance and the number of urns formed per thermal spraying pass is known, it is easy to obtain a film thickness that meets the design requirements. Generally, according to this method, it is possible to freely achieve a thickness between 10 and several hundred micrometers. Of course, for special purposes, 1mm
It is also possible to obtain a film with a membrane pressure of more than a certain degree.

In this way, it is possible to easily obtain a wear-resistant coating layer. In Tables 1, 3, and 5 below, the particle size is u
rn, composition indicates weight %.

In addition, the breakdown of Si, B, and C in Table 1 is, for example, in the case of powder a, specifically 1.9% by weight and 1.1% by weight, respectively.
% by weight and 2.9% by weight, and for powder S and c, S
The ratios of i, B, and C were the same.

Table 1 Table 2 (Example-3) Thermal spraying conditions were unified to those shown in Table 4 below, and various components were changed to produce a thermal sprayed film, and the film was used to conduct a sliding wear test. The optimal ranges of various components were determined. Note that, due to the nature of the experiment, the composition ratios of the thermal spray alloy powders in Table 5 were rounded to the nearest whole number, and only four representative points were shown for each component. The results of the sliding wear test are shown in FIGS. 3 to 6. Figure 3 shows the Go component ratio, Figure 4 shows the Cr component ratio, Figure 5 shows the Ni component ratio, and Figure 6 shows the Si + B + C component ratio. ,000 times of the reciprocating sliding abrasion test. In this case, the composition ratio of Si:B:C is ! , 5:1:2.5, and this ratio was kept constant.

In addition, the beams in the figure are thermally sprayed with powders i, j,...
The formed films were indicated by H, 1, J, . . . .

Table 4 Table 5 [Effects of the Invention] As explained above, according to the present invention, the conventional wear-resistant coating, that is, wc-12Co, which is commonly used,
It is possible to form a wear-resistant coating layer that is superior to the WC-]7Co thermal spray coating layer, and the newly added components are numerically Ni, Cr, Si, B, C, etc., and are inexpensive. Therefore, the present invention has great practical effects, such as not increasing the cost of the thermal spray powder and greatly extending the life of the wear-resistant member.

[Brief explanation of drawings]

FIG. 1 shows the results of a wear resistance comparison test using a Suga sliding wear tester. Figure 2 shows the porosity and 4
．． The relationship between weight loss after 000 reciprocating sliding abrasion tests is shown. Figure 3 shows the component ratio of co, Figure 4 shows the component ratio of C, Figure 5 shows the ratio of Ni, and Figure 6 shows the ratio of Sj+.
By changing the component ratio of B + C, 4,0
The relationship with the amount of weight loss after 00 times reciprocating sliding abrasion test is shown.

Claims (1)

[Claims] 1. 25 to 35% by weight of Co and 6% by weight of Cr are added to the surface of the sprayed base material while maintaining the temperature of this material at 300°C or higher.
An alloy powder containing ~12% by weight, 5~10% by weight of Ni, 1.5~9% by weight of Si+B+C, and the remainder WC was plasma sprayed in a reduced pressure of 20~300 Torr to obtain a porosity of 3. A method for forming a wear-resistant coating layer, the method comprising forming a thermally sprayed coating layer of % or less.