JPS59200750A - Surface coating method - Google Patents

Abstract

PURPOSE:To form a surface film having superior wear resistance and sliding characteristics by forming a sprayed layer of a WC-(Ni-P) alloy on the surface of a member to be treated, heating the member in a nonoxidizing atmosphere to melt only the Ni-P phase, and solidifying the molten phase. CONSTITUTION:A WC-(Ni-P) alloy for forming a sprayed layer on the surface of a member to be treated is preferably prepd. by coating about 95-70% WC powder of about 20-60mum grain size with about 5-30% Ni-P contg. about 8-13% P by electroless plating. A sprayed layer of the WC-(Ni-P) alloy is formed on the surface of a member to be treated. The member is heated to about 950- 1,050 deg.C in a non-oxidizing atmosphere to melt only the Ni-P phase, and the molten phase is solidified. Ni-P is decomposed at about 400 deg.C, and Ni3P is precipitated, so the hardness of the entire film is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface coating method, and more particularly to a surface coating method capable of obtaining a surface coating having wear resistance and excellent sliding properties.

For example, the inner circumferential surface of the cylinder liner must have excellent scuffing resistance and wear resistance because the piston rings slide at high speed under high temperatures. Therefore, various plating treatments have been applied to the inner peripheral surface of the cylinder liner.
Chemical conversion treatment or nitriding treatment has been performed to increase the hardness of sliding surfaces. However, in recent years,
As engine performance improves, sliding conditions are also becoming more severe, and it is impossible to deal with such high-performance engines by the above-mentioned treatments.

Therefore, in order to withstand the harsh sliding conditions mentioned above,
It is conceivable to thermally spray a cemented carbide that can obtain relatively high hardness onto the inner circumferential surface of the cylinder liner. In this case, cemented carbide powder such as WC (tungsten carbide) alone has poor bonding properties, so co(
Cobalt) is added and thermally sprayed as an alloy powder of -C and Co.

By the way, the minimum surface pressure Pc when a crank occurs in the coating due to sliding is expressed as PC:=PO/(1+16.2 μ)3.

In the above equation, Pc represents the minimum surface pressure generated by the crank during sliding, Po represents the minimum surface pressure generated by the crank due to static load, and μ represents the coefficient of friction.

From the above equation, it is clear that as the coefficient of friction decreases, Pc increases exponentially and cracks are less likely to occur. In addition to having
Furthermore, the coefficient of friction is small, J='
It is 31S4.

However, CO, which has been used since Gfi to improve the bonding properties of 4000 powder, does not necessarily have a low coefficient of friction that meets the above requirements. Even by thermal spraying on the inner circumferential surface of the liner, it has not been possible to significantly improve scuffing resistance and wear resistance.

This invention has been made in view of the above, and its purpose is to provide high abrasion resistance by inscribing parts such as cylinder liners that are subject to sliding wear under high temperatures, and to provide smooth sliding resistance. It is an object of the present invention to provide a surface coating method that allows surface coating with dynamic characteristics to be applied without any process.

The surface coating method of the present invention, which achieves the above object, forms a sprayed layer of WC-(Ni-P) alloy on the surface of a member to be treated, and then heats it in a non-oxidizing atmosphere to coat NiP.
It is characterized by melting and solidifying only the phase.

As a result of the above, N1-P as a binder melts and fills the pores created by thermal spraying, resulting in a dense coating, and in addition to this, N1-P itself has a relatively high hardness) ■Coupled with the small cavity coefficient,
It becomes possible to form a surface coating that has wear resistance and excellent sliding properties. In addition, since N1-P, WC, and iron-based materials commonly used as base materials diffuse well into each other, the strength of the coating is good, and the adhesion to N and materials is also excellent. Furthermore, N1−P force g ;j4+,
After being melted, when cooled, N1-P decomposes and Ni3P precipitates at a temperature near 400°C (-1), but this phase has a hardness of jI (Vickers hardness Hν = 11
00), the hardness of the entire coating also increased.

In the above, the Ni-P alloy used for thermal spraying is
It is preferable to use a WC powder with a particle size of 20 to 60 microns electrolessly plated with N1-P, but a mixture of N1-P powder and a modified powder may also be used. In these cases, N
As 1-P, it is preferable to use one containing 8 to 13% P (phosphorus); however, when P is 8 to 13%,
Relatively low temperature (near the eutectic point), i.e. 880-95
This is because N1-P melts at 0°C. Therefore, in this invention, the temperature required to melt N1-P may be 880°C or higher;
Taking into account variations in the composition of -P, etc., the temperature is preferably 950°C or higher. On the other hand, considering the time required for heating, cost, thermal deformation of the material, etc., it is preferable that the heating temperature be 1050°C or less, and it is most preferable that the heating temperature be within the range of 950 to 1050°C.

In addition, in the above, the ratio between WC and N1-P is WC9
It is preferably in the range of 5-70% and N1-P5-30%. If N1-P is less than 5%, sufficient effect as a binder cannot be exhibited; on the other hand, if N1-P is 30%
This is because, if it exceeds this, the hardness of the coating will decrease. In addition, considering various errors in the manufacturing process, the most practically preferable one is about 90% WC and 10% Ni -■).

Next, specific embodiments of the present invention will be described in detail with reference to the drawings.

The amount of P is about 10% in the WC powder with a particle size of 30 to 60μ.
By electroless plating N1-P of
A composite powder (WC90%, N1-PIO%) was produced.

This composite powder was used as a cylinder liner (inner diameter 105 mm,
Plasma sprayed on the inner surface of abrasive FC25) to a thickness of 0.2
A film of 5μ was formed. As shown in FIG. 1, the plasma spraying was carried out using an extension gun 1 at a radiation angle of 65 degrees, and an air jet 2 was also used to minimize the amount of unmelted powder deposited.

Next, the cylinder liner was placed in a vacuum (10 Torr).
After heating to about 980° C. and holding it for about 30 minutes, it was cooled in a furnace.

A sample was cut out from the cylinder liner obtained above, and the hardness and adhesion strength of the coating were tested. The results are shown in FIG. 2, and it is clear that according to the method of the present invention, both the hardness and adhesion strength of the coating are increased compared to the conventional WC-18Go coated by plasma spraying.

Furthermore, a wear test was conducted using a reciprocating sliding tester using the above sample, and the amount of wear was the same as that of the conventional WC18c.

It was about 1/3 of that of plasma sprayed.

The surface coating method of the present invention has a two-legged structure. Therefore, according to the method of the present invention, high wear resistance can be achieved for members such as cylinder liners that are subject to sliding wear under high temperatures. It becomes possible to apply a surface coating that has excellent sliding properties.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an example of the plasma spraying method used to implement the method of the present invention, and FIG. 2 is a graph comparing the hardness and adhesion strength of coatings formed by the method of the present invention and the conventional method. . Patent applicant Komatsu Ltd. Han 1 Illustration 2-Diagram (W Koichi 111L*)

Claims (1)

[Claims] 1. A surface characterized by forming a sprayed layer of WC-(Ni-P) alloy on the surface of the member to be treated, and then heating in a non-oxidizing atmosphere to melt and solidify only the tJi-P phase. Coating method.