JPS6024364A - Nickel-base thermal spraying material - Google Patents

Abstract

PURPOSE:To obtain a thermal spraying material giving a coating having superior corrosion resistance, wear resistance and lubricity in a highly corrosive atmosphere of combustion gas at high temp. by preparing particles each consisting of metallic Ni as a surface layer and Ni oxide as a core. CONSTITUTION:This thermal spraying material is obtd. by treating Ni oxide powder in a flow of a reducing gas such as H2 or CO. In the spraying material, the surface metallic Ni bonds firmly to the internal Ni oxide without using a binder. When the material is sprayed, both the components are sprayed at once, so a sprayed film having a uniform structure consisting of metallic Ni having high heat resistance and corrosion resistance even at high temp. and of Ni oxide having lubricity can be obtd.

Description

[Detailed Description of the Invention] The present invention is directed to a highly corrosive high-temperature combustion gas atmosphere.
This invention relates to thermal spray materials for obtaining coatings with excellent corrosion resistance, wear resistance, and lubricity.

Ni-based or Co-based alloys are generally used for parts exposed to high temperature and highly corrosive environments, such as cylinder liners of compressors and internal combustion engines. However, Ni
Base alloys and Co, 1 alloys are not only expensive, but also have the drawback of slightly inferior sliding properties. In order to overcome this difficulty, attempts have been made to use solid lubricants that are stable at high temperatures.

Generally known as solid lubricants that are stable at high temperatures, Irmo's Niha, calcium fluoride (CaF2), Kurafai (G), boron nitride (BN), and molybdenum disulfide (Mo
S2) etc. If these solid lubricants are always present on the sliding surface, frictional resistance is low and a good 714 sliding condition is maintained.

As a method of supplying a solid lubricant to a sliding surface, a method of dispersing the solid lubricant in an alloy mainly by powder metallurgy is known. However, in this method, since the entire member contains a solid lubricant, there are problems such as not only the solid lubricant being wasted but also the material strength of the member being inferior.

If the sliding surface of the member can be locally sealed with a solid lubricant, the above problem can be solved, and various methods including thermal spraying have been studied. However, BN, CaF2
, MoS2, etc. are exposed to high temperatures during the thermal spraying process and decompose, making it difficult to stick them onto the surface of a single member.

A material that can be thermally sprayed and has excellent lubricity is nickel graphite (Ni-G), but N1-G is expensive and the strength of the thermally sprayed coating is insufficient.

An object of the present invention is to provide an inexpensive thermal spray material for obtaining a thermal spray coating that has excellent heat resistance, corrosion resistance, cold resistance, and lubricity.

The present invention will be explained in detail below.

Metallic nickel is a metal with high heat resistance and corrosion resistance, and is widely used to form a sprayed coating layer on the surface of a member to improve local material properties.

On the other hand, nickel oxide is known as a lubricating substance. As a means of forming a thermal spray coating containing both of these,
A possible method is to use a thermal spray material that is a mixture of both.

However, with mixed type thermal spray materials, segregation of components occurs, and differences in range occur due to differences in specific gravity with particles, making it difficult to form a thermal spray coating with a uniform structure. A thermally sprayed coating with a non-uniform structure is fragile and cracks and easily peels off when subjected to thermal shock, which is undesirable. Another possible method is to use a solvent material in which nickel particles and nickel oxide particles are bonded together using a binder. However, thermal spray materials using binders have drawbacks such as impurities introduced from the binder that impair corrosion resistance. Furthermore, the binder decomposes during thermal spraying, making it impossible to obtain a uniform film.

The nickel-based thermal spray material according to the present invention firmly binds nickel and nickel oxide without using a binder,
By spraying both components at the same time, a sprayed coating with a uniform structure can be obtained.

The nickel-based thermal spray material of the present invention is composed of particles whose surface is made of metallic nickel and whose interior is made of nickel liquefied. Appropriate composition range is 10 to 80% nickel (less than % by weight)
, 20 to 90% nickel oxide, more preferably 40 to 60% nickel, and 40 to 60% nickel diluted. ” It has sufficient lubricity in the composition range other than those listed in 2.
Moreover, a thermal spray coating having strong adhesion to the base material cannot be obtained. It is important that the nickel oxide is uniformly dispersed within the sprayed coating layer and that the nickel oxide particles are strongly bonded with metallic nickel.

The particle size of the thermal spray material is 5 to 11007p, preferably 2
It is preferable that the powder has an excellent powder flowability between 5 and 44 pm.

Next, a method for manufacturing the thermal spray material of the present invention will be explained.

The solvent material of the present invention is obtained by treating nickel oxide powder in a reducing gas flow such as hydrogen or carbon monoxide.

As the nickel oxidize, those used as ordinary nickel additives for metallurgy can be used. Nickel oxide is 5~
It is advisable to adjust the size to a size suitable for a 100 gm thermal spray material. Nickel oxidized powder is heated to 700% in a reducing atmosphere.
When heated to a temperature higher than 'C', reduction of nickel oxide proceeds from the surface of the particles. Obtaining a 50% by weight metallic nickel film layer on the surface of the particles depends on the temperature, time, and amount of treatment; for example, in the case of 800'C, it can be obtained by treatment for about 1 hour. 1 at 900°C
If the reaction is held for too long, the reaction will proceed too much and the nickel component will increase. An ordinary box furnace is sufficient as the firing device.

Next, the present invention will be explained with reference to Examples.

Example 4 Nickel oxide classified into 4-5k was placed in a graphite boat and inserted into a box-type hydrogen furnace. The heating rate was approximately 200°C/H, and the temperature was raised to 800° while supplying 517ml of hydrogen gas.
It was held at C for 1 hour. Thereafter, it was cooled to 300°C in a hydrogen stream and taken out. When the removed nickel oxide was embedded in resin and the cross section of the particle was observed using EPMA, it was found that
It was confirmed that the surface of the particles was coated with metallic nickel.

Further, chemical analysis and X-ray diffraction peak analysis revealed that 50% of the nickel oxide was reduced to metallic nickel.

For the purpose of crushing the nickel oxide powder coated with metallic nickel obtained in this way, 44. Classify again with 4
4 liters or less was obtained as a thermal spray material. The powder spraying material having a particle size of 44 l or less obtained as described in Section 2 was sprayed onto the surface of a copper plate to a thickness of 0.3 mm by plasma spraying. The thermal spraying equipment used was a Plasma Dyne 5G100 type thermal spray gun, and the thermal spraying conditions were: argon gas flow rate of 35 1/min, plasma current of 750 A, plasma voltage of 30 V, and powder supply amount of 50 mm.
g/min ◇ Next, the properties of the obtained thermal sprayed coating were measured.

For comparison, the same structure as the thermal sprayed material according to the present invention (wt%
) with Ni-coated NiO powder and Ni
,! The same characteristic measurements were carried out using a mixed powder with =NiO and a graphite lr1 composite powder containing 75% Ni as the melting materials.

When the cross-sectional structure of the thermal spray coating 11 was observed under a microscope, it was found that when the thermal spray material according to the present invention was used, the structure had a uniform distribution of metal Ni and NiO.

On the other hand, when a mixed powder or coating powder material was used, a non-uniform structure in which metallic Ni aggregated was exhibited.

The peel strength of the sprayed coating was measured and was as shown in Table 1.

Table 1 As is clear from the results, the thermal sprayed coating using the thermal sprayed material according to the present invention was significantly stronger than the coating made from a conventionally known melting material.

This is considered to be because the uniformly distributed metallic Ni phase plays a strong role of 1ζIJ.

Corrosion resistance in heavy oil combustion gas is comparable to that of coating with powder coating, and is superior to coating with mixed powder.

Furthermore, the lubricity was superior to coatings using coating powder and mixed powder, and comparable to coatings using 75% Ni/graphite mixed powder. Furthermore, wear resistance has a good l/X correlation with peel strength.

Patent applicant: Showa Denko Co., Ltd. Representative Patent Attorney Sei Kikuchi

Claims (1)

[Claims] A nickel-based thermal spray material whose surface is made of metallic nickel and whose interior is made up of particles mainly composed of nickel oxide.