JPS59100263A - Plasma-sprayed piston ring - Google Patents

Abstract

PURPOSE:To improve the wear and scuffing resistances of the sliding surface of a piston ring and to reduce the wear of a cylinder opposite to the ring by plasma-spraying Fe alloy powder having a specified composition on the sliding surface of the ring. CONSTITUTION:Fe alloy powder is plasma-sprayed on the sliding surface of a piston ring for an internal-combustion engine, especially a car engine opposite to a cylinder to form a sprayed layer. A powdered mixture consisting of 40- 90wt% alloy powder consisting of 1-4% C, 10-30% Cr, 2-15% Ni, 10-30% Mo, 20-40% Co, 1-5% Nb and the balance Fe and 10-60wt% metallic powder with self-hardenability such as powder of high carbon steel or alloy steel contg. Cr, Mo, Ni, Mn, etc. is used as said Fe alloy powder.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal sprayed piston ring which has excellent wear resistance and scuff resistance and which causes less wear on a mating cylinder.

In recent years, due to advances in internal combustion engines, particularly automobile engines, the operating conditions for piston rings have become extremely severe. Conventionally, piston rings for automobiles have been made of hard C to provide friction resistance and scuff resistance, especially to the top ring.
R plating was applied to the sliding surfaces, but problems with scuff resistance started to appear, especially in diesel engines, and piston rings with high wear resistance and scuff resistance were developed as an alternative to conventional Cr plating. Demand is increasing.

It is well known that Mo sprayed rings have been developed and put into practical use in order to meet these demands. Thermal spray materials for this purpose are being researched and developed. However, these thermal spray materials are mainly composed of metal oxides, carbides, or intermetallic compounds. Generally, these thermal sprayed materials have high hardness, so the wear resistance and scuff resistance of the piston ring itself exceeds that of Cr plated or Mo thermal sprayed rings, showing good results. Cylinder wear occurs due to the high hardness of hard thermal spray materials such as, and in some cases, the cylinder wear is two to three times as much as when using a Cr-plated ring.

Therefore, the present invention proposes a thermal sprayed piston ring which has excellent wear resistance and scuff resistance, and which causes less wear on the mating cylinder. That is, the gist is that, in weight ratio, it consists of: C 1-4% Cr 10-30% Ni 2-15% Mo 10-30% Co 20-40% Nb 1-5% Fe (contains impurities) the balance A sprayed layer is formed on the ring sliding surface by plasma spraying a mixed powder of 40 to 90% by weight of special alloy powder and 10 to 60% by weight of self-hardening iron or iron alloy powder. The special alloy powder used in the present invention has the purpose of providing excellent wear resistance and scuff resistance as well as reducing wear of the mating cylinder, and is made by mixing alloying elements such as Cr, Ni, Mo, Co, and Nb with iron in a predetermined ratio. It is manufactured by mixing, melting, and pulverizing or atomizing the alloy.

Self-hardening iron or iron alloy powder refers to powder that has the property of hardening (self-hardening) when the sprayed particles are rapidly cooled when welding to the object to be thermally sprayed by plasma spraying, etc. Generally speaking, it refers to high carbon steel containing 0.6% or more of C or alloy steel containing elements such as Cr, Mo, Ni, Mn, etc., but when implementing it industrially, high carbon steel is preferable from the viewpoint of cost. .

Next, the reason for limiting each powder composition (weight ratio %) constituting the thermal spray coating of the present invention will be described.

First, regarding special alloy powder, C combines with Cr, Mo and Nb to form composite carbide,
If the amount is less than 1% (the same applies below weight %), the amount of precipitated carbide will be small, and if it exceeds 4%, the precipitated carbide will become extremely coarse, so the amount is set to 1 to 4%.

Cr and Mo form a composite carbide together with C and Nb as mentioned above, and contribute to improving wear resistance and heat resistance.Moreover, Mo has the effect of lowering the melting point of the alloy, so it is It melts well and has the effect of reducing the generation of pores. If the amount of Cr and Mo is less than 10%, the above effects cannot be fully exhibited, and if it exceeds 30%, not only will no further effect be recognized, but it will also be economically disadvantageous. are both 10~
The range shall be 30%.

Nb forms a special carbide by itself, and also forms a composite carbide with Cr, Mo, and C, and exhibits an excellent effect on the miniaturization of these carbides. If the amount is less than 1%, the above effects cannot be fully exhibited, and if the amount is less than 1%,
If it exceeds this, the Nb carbide becomes coarse, which is not preferable, so the content is set in the range of 1 to 5%.

Both Ni and Co improve the heat resistance and corrosion resistance of the sprayed layer. If Ni is less than 2% and Co is less than 20%, these effects cannot be fully exhibited, and if Ni exceeds 15% and Co exceeds 40%, it will be economically disadvantageous. The content of Co is in the range of 2 to 15%, and the content of Co is in the range of 20 to 40%. The hardness of the alloy powder obtained with the above component range is Hv750-1000, and as a thermal spray powder for piston rings, it has excellent properties in terms of wear resistance, scuff resistance, and corrosion resistance.

Next, the reasons for limiting the mixing ratio of special alloy powder and self-hardening iron or iron alloy powder (for example, high carbon steel) will be described.

If the content of the special alloy powder is less than 40%, the wear resistance and seizure resistance of the piston ring's sprayed layer itself will decrease, and if it exceeds 90%, the strength of the sprayed coating and its adhesion to the piston ring base material will decrease. Therefore, the special alloy powder should be in the range of 40 to 90%. In addition, self-hardening iron or iron alloy powder (for example, high carbon steel) is a material that stably disperses and holds special alloy powder in the sprayed layer, and due to its self-hardening property, this iron alloy part can be hardened. Hardness level (Hv
650-750).

For example, as mentioned above, when special alloy powder and high carbon steel powder are mixed in the above composition ratio and plasma sprayed at the same time, these powder particles are evenly layered and layered, forming a special alloy part and a iron alloy part. is evenly distributed, resulting in an overall homogeneous composition.

Moreover, both the special alloy powder and the carbon steel powder are well integrated during thermal spraying, and the spray particles of high carbon steel in particular are
Because it has sufficient thermoplasticity when colliding with the piston ring base material, the bond between each particle and the piston ring base material (cast iron or steel) is strengthened, preventing the thermal spray particles from flaking off. can do.

In addition, the thermal spray powder of the present invention has a homogeneous composition in which the special alloy part with excellent heat resistance and wear resistance and the iron alloy part with a level of quenching hardness are evenly distributed. Because of this, it has good workability during finishing processes such as lapping and grinding, and a smooth processed surface can be obtained, making it suitable for single thermal spraying of conventional metal carbides and metal oxides, or for mixed thermal spraying containing large amounts of them. In comparison, it has improved resistance to abrasion wear, reduces wear on the mating cylinder material, and has excellent wear resistance itself.

Therefore, the effect of extending the life of the sliding member can be obtained.

Next, the present invention will be explained based on examples.

The component ratios (wt%) of the thermal spray powder used in Examples (1) and (2) below are as shown in Table 1.

Example (1) After processing the outer peripheral surface, upper and lower surfaces of a piston ring base material made of spheroidal graphite cast iron with a nominal diameter of 90 mm, thickness of 3.8 mm, and width of 2.5 mm, a groove 1 as shown in Fig. 1 was formed on the outer peripheral surface. A special alloy powder with a grain size of -250 mesh and high carbon steel (0.8% C) with a particle size of -250 mesh were processed so that the ratio of the former to the latter was 90:10 and 70:3040:60, respectively. The prepared three types of mixed powders and the special alloy powder alone were plasma sprayed onto the outer peripheral surface of the ring, and then completed processing was performed so that the maximum thickness of the sprayed layer 2 was 0.2 mm. The main conditions for plasma spraying at this time are: Spraying machine: Metco 3MB Primary gas (argon) flow rate: 100PSI: 80S. C. F. H Secondary gas (hydrogen) flow rate 50PSI: 15S. C. F. H Plasma supply power 500A x 70V = 35KW Spraying distance 80mm.

The adhesion test results of the samples obtained in this way were
Shown in the table.

In order to measure the degree of adhesion to the piston ring base material 3 after thermal spraying, the piston ring 4 having the thermal sprayed layer 2 after the completed process shown in FIG. Apply a load P in the opposite direction to points A and B in the radial direction perpendicular to the surface, and expand the free mating gap until the piston ring base material is on the verge of breaking, as shown in Figure 2 (b). method was used. According to this method, maximum stress is applied to point C on the opposite side of the piston ring, and when the sprayed layer cannot withstand this stress, the adhesion with the piston ring base material is impaired and the sprayed layer peels off. Otherwise, cracks may occur within the sprayed layer, resulting in delamination within the sprayed layer.

Therefore, the increase amount ΔL of the free joint clearance at this time = (free joint clearance amount L during expansion) - (free joint clearance amount Lo before expansion) is an index indicating the degree of adhesion of the sprayed layer. It was used as That is, the larger ΔL is, the higher the degree of adhesion of the sprayed layer is.

As shown in Table 2, the free gap increase (ΔL) of the special alloy powder alone was 23 to 35 mm, but the ratio of the special alloy powder of the present invention and high carbon steel was 90:1.
0, 70:30, and 40:60, it can be seen that there is no peeling or cracking of the sprayed layer and the adhesion is excellent.

Example (2) Various thermal sprayed piston rings produced in the same manner as in Example (1) were assembled into a water-cooled inline 4-cylinder 2200cc diesel engine (maximum output 72PS/4200rpm) for 100 minutes.
A time bench test was conducted.

Operating conditions: Full load 4800 rpm Test cylinder liner: FC30 equivalent material For piston rings, the amount of wear after 100 hours of operation is calculated using the amount of increase in gap clearance.
For the cylinder liner, the average value of the wear amount at the top dead center position of the top ring was used, and Hv 1100 was used as a comparison material.
High carbon ferrochrome powder (weight ratio 62
．． 8% Cr, 6.3% C, 1.7% Si, 0.02%
The amount of wear on the piston ring and cylinder liner when a piston ring sprayed with (P, 0.04% S, balance Fe) is assembled is (100), and special alloy powder alone and special alloy powder and high carbon steel powder are sprayed. FIG. 3 shows the amount of wear of the piston ring and cylinder liner in terms of wear index when piston rings sprayed with different blending ratios of the above are assembled.

(Figure 3 (a) High carbon ferrochrome (b) Special alloy single thermal spraying (c) Special alloy powder 70% and high carbon steel (0.8% C)
) 30% mixed and sprayed (d) Special alloy powder 4
(e) 30% special alloy powder and high carbon steel (0.8% C) mixed and sprayed.
C) 70% mixed and sprayed) Bench test results,
The following was found. A piston ring sprayed with special alloy powder alone has a slightly higher amount of wear compared to a piston ring sprayed with high carbon ferrochrome powder, but it has the advantage of being able to reduce the wear of the mating cylinder liner by about 1/3. have characteristics.

A material sprayed with a mixture of 70% special alloy powder and 30% high carbon steel (0.8% C) also has the same wear resistance as a material sprayed solely with the special alloy powder.

In addition, special alloy powder 40% and high carbon steel (0.8% C) 6
The amount of wear on the cylinder liner sprayed with a mixture of 0% is about 40% greater than that of the one sprayed with high carbon ferrochrome powder, but the amount of wear on the mating cylinder liner can be reduced to about 1/3. Has excellent properties. However,
30% special alloy powder and 70% high carbon steel (0.8%C)
Although the wear of the mating cylinder liner is reduced to about 1/2 of that of the high carbon ferrochrome sprayed ring, the wear of the sprayed coating itself increases by about 70% compared to the high carbon ferrochrome sprayed coating.

From the above test results, it can be seen that the thermal spray coating containing 40% or more of the special alloy powder has excellent wear resistance and causes much less wear on the mating cylinder liner than the high carbon ferrochrome thermal spray coating. Therefore, the improvement effect in terms of relative life is obvious.

Figure 4 is a cross section of the sprayed coating, taken at a magnification of 100x, and Figure 5 is the surface of the sprayed coating, taken at a magnification of 1.
This is a micrograph at 00x magnification.

Figure 4 (a): Thermal spray coating of the present invention (special alloy powder 70% + high carbon steel (0.8% C) 30%) ) Cross-sectional photograph (b): Cross-sectional photograph of the high carbon ferrochrome powder sprayed coating Figure 5 (a): Surface photograph of the invention thermal sprayed coating (70% special alloy powder + 30% high carbon steel (0.8%C)) (b): This is a surface photograph of a high carbon ferrochrome powder sprayed coating, where the reference numeral 2 in the photograph is the sprayed layer, 3 is the piston ring base material, and 5 is the hole.

As is clear from the above photo, the thermal spray coating of the present invention (70% special alloy powder + high carbon steel (0.8% C) 3
0%), it can be seen that fewer pores are generated compared to those sprayed with high carbon ferrochrome powder.

That is, the porosity (area ratio) of the sprayed layer formed by spraying high carbon ferrochrome powder is 18 to 28% (22.4% in the example photo), whereas the porosity of the sprayed layer of the present invention (special The porosity is 8 to 18% (13.2% in the example photo) of 70% alloy powder + 30% high carbon steel (0.8% C).

[Brief Description of the Drawings] Fig. 1 is a partial cross-sectional view of a piston ring having a sprayed layer on the sliding surface, Figs. 2 (a) and (b) are explanatory diagrams showing how to measure the degree of adhesion of the sprayed layer, Figure 3 shows the results of a bench test using a diesel engine. FIG. 4 is a cross section of the thermal sprayed coating, taken at a magnification of 100 times, and FIG. 5 is a micrograph of the surface of the sprayed coating, taken at a magnification of 100 times. And (a) in FIGS. 4 and 5,
Figure 4 (a): Cross-sectional photograph of the thermal spray coating of the present invention (70% special alloy powder + 30% high carbon steel (0.8% C)) (b): High carbon ferrochrome powder spray coating Cross-sectional photograph of Figure 5 (a): Thermal sprayed coating of the present invention (special alloy powder 70% +
Surface photograph (b) of high carbon steel (0.8% C) (30%): This is a surface photograph of the high carbon ferrochrome powder sprayed coating.

Claims (1)

[Claims] Special alloy powder consisting of C 1-4%, Cr 10-30%, Ni 2-15%, Mo 10-30%, Co 20-40%, Nb 1-5%, Fe (contains impurities), balance by weight ratio A thermal sprayed piston ring having a thermal sprayed layer formed on the sliding surface by plasma spraying a mixed powder of 40 to 90% by weight and 10 to 60% of self-hardening iron or iron alloy powder.