JPH1129848A - Chromium nitride coating film and its forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a CrN coating film at a low cost which has excellent adhesion property with a metal base and prevents peeling by thermal hysteresis without any limitation of the shape or dimension of a body to be treated, by plating the surface of a metallic material with Cr and nitriding the plating layer. SOLUTION: The CrN coating film is formed in the following processes. After a Cr-plated material to be treated is degreased and cleaned, the material is put in a heating furnace. The inside of the furnace is replaced by inert gas, and if necessary, heated to 400 deg.C. A reaction gas containing halogen compd. or halogen such as a mixture gas of Cl2 and N2 or a mixture gas of CIF2 and N2 is introduced into the furnace. Thereby, contamination remaining on the surface is removed and the gas is allowed to rapidly react with the oxide film or adsorbed oxygen on the plating surface to activate the surface. Then the halogen compd. or reactive gas remaining is replaced by an inert gas to form a CrN coating film. The coating film is formed preferably by heating and maintaining at 400 to 500 deg.C and introducing a nitriding atmosphere gas containing NH3 such as a mixture gas of NH2 and N2 .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for producing C
The present invention relates to a method for forming a CrN film for improving surface hardness, wear resistance, corrosion resistance and the like by forming an rN film.

[0002]

2. Description of the Related Art For the purpose of improving chemical and mechanical properties such as surface hardness, wear resistance, corrosion resistance, and fatigue strength of metal materials, Cr plating, nitriding, and the like have been generally performed. In any method, the surface hardness is 800
It only improves to about 1000 Hv. However,
A further high hardness recently to the metal material, the demand for high wear resistance strong, chromium nitride (CrN and Cr ₂ N) is noted with 1500~2400Hv as hardness. Therefore, the following method has been proposed as a method for forming a CrN coating for the purpose of improving surface hardness, wear resistance, and the like. Ion plating method Sputtering method Ion irradiation method

The ion plating method utilizes a vacuum arc discharge in a vacuum chamber to vaporize and ionize a metal chromium target and irradiates the target with a negative bias voltage. In this method, chromium nitride is formed by attracting ionized Cr ions and introducing nitrogen gas into a vacuum chamber. In the sputtering method, a glow discharge is generated by applying a high voltage between a target, which is a coating material, and a substrate in a vacuum chamber, and Ar ions generated by the discharge collide with the target surface to strike chromium atoms and strike the substrate. It is a method of depositing on the At this time, by introducing nitrogen into the chamber, a chromium film and a chromium nitride film in which nitrogen is dissolved in a supersaturated manner can be formed. Also,
The ion irradiation method combines vacuum deposition or sputtering with nitrogen ion irradiation (Japanese Patent Application Laid-Open No. 5-31139).
In 6), a CrN film can be formed at a low temperature.

However, gas-phase coating such as ion plating, sputtering, and ion irradiation requires a high vacuum atmosphere, so that the processing cost is higher than that of the conventional processing method, and the shape and size of the processed material are restricted. There are problems and to be more widely used industrially,
It is necessary to reduce the cost of process equipment and simplify the handling system.

[0005] In general, a disadvantage of CrN coating is that CN
Since the thermal expansion coefficient of rN is 1/6 smaller than that of Fe,
The problem is that thermal stress is easily applied, and the problem of thermal history peeling is likely to occur. In the case of low-temperature treatment, adhesion to a substrate is poor. Therefore, in order to improve the adhesion of the CrN film to the substrate, a Cr layer is formed by vacuum evaporation and then irradiated with nitrogen ions, and the composition ratio of Cr atoms and nitrogen atoms is gradually or gradiently applied to the chromium nitride film. Although a method of changing the thickness has been proposed (Japanese Patent Application Laid-Open No. Hei 7-109561), it has little effect on preventing thermal history peeling due to a difference in thermal expansion coefficient due to a small film thickness.

[0006]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a method for forming a CrN film on a surface of a metal material, which is inexpensive and economical in processing cost and is not restricted by the shape and size of the processed material. An object of the present invention is to provide a CrN coating film having excellent adhesion to a metal material base and preventing thermal history peeling, and a method for forming the same.

[0007]

In order to solve the above-mentioned problems, a CrN film and a method for forming the same according to the present invention have a laminated structure having a Cr plating layer of 1 to 50 μm between a metal material base and a CrN film. A method of forming a hard CrN film by reacting nitrogen after applying Cr plating on the surface of a metal material.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventors have developed a highly economical and versatile method for forming a rapid, uniform and strong CrN coating on a metal material surface. Intensive research has been conducted with the aim of providing a CrN coating film having excellent adhesion to a material substrate and little thermal history peeling.
As a result, it is effective to form a CrN coating by heating and holding in a nitriding atmosphere after applying Cr plating to the surface of the object to be treated, and by this method, a 1 to 50 μm gap between the metal material substrate and the CrN coating is obtained. By providing a Cr plating layer, it has been found that a CrN film excellent in adhesion to a metal material base and having little thermal history peeling can be obtained, and the present invention has been completed.

The method of forming CrN of the present invention does not require a high vacuum system as compared with the prior art, so it is excellent in economy and has high versatility. Further, as one cause of the thermal history peeling, a thermal stress due to a difference in thermal expansion coefficient can be considered. For example, the coefficient of thermal expansion of Fe is 13.8 × 10 ⁻⁶ (/ deg), and other non-ferrous metals other than Cr also show a large value that is equal to or greater than that. However, the thermal expansion coefficient of CrN is 2.3 × 1.
Since it is as small as 0 ^-6 (/ deg), a situation is liable to occur in thermal stress. However, the thermal expansion coefficient of Cr is 8.4 × 10
⁻⁶ (/ deg), which is an intermediate value between the metal material and CrN. It is considered that thermal stress can be suppressed and dispersed by forming a Cr plating layer between the metal material base and the CrN coating.

Further, in the present invention, it is possible to carry out a pretreatment with a halogen compound or a reactive gas containing halogen before forming the CrN film. In this method, the object to be processed before the formation of the CrN film is heated and held in a halogen compound or a reaction gas atmosphere containing halogen. By this pretreatment, inorganic and organic contaminants adhering to the Cr plating surface layer are destroyed and removed to purify the surface, and furthermore, the oxide film and the O ₂ adsorption film present on the Cr plating surface layer are removed. , Cr plating surface is in an activated state. In forming the CrN film, the activated Cr-plated surface is easier to adsorb, permeate and diffuse nitrogen atoms than the untreated Cr-plated surface, and a quick and uniform CrN film is formed even at a lower temperature. The rapid formation of the CrN coating even at this low temperature is particularly effective when the object to be processed is desirably free from distortion and distortion.

Next, the present invention will be described in detail. The metal material used in the present invention is not particularly limited as long as it can be subjected to Cr plating, and for example, iron, steel, and non-ferrous metals can be used. Further, a combination with another plating process is also possible. Examples of the Cr plating used in the present invention include ordinary industrial Cr plating, high corrosion-resistant Cr plating without cracks, microporous Cr plating, and 2-4.
Special Cr such as amorphous Cr plating containing% carbon
Plating is available. Although the thickness of the Cr plating is not particularly limited, a thickness of 2 to 50 μm is preferably used. The shape and dimensions of the object to be treated are not particularly limited, but industrially, a mold for semiconductor sealing material, a mold for rubber molding, an injection molded part, a cylinder and a liner, a piston and a piston rod, a piston ring, a tool , Shafts and journals,
It can be used for rolls, mechanical parts, etc.

Examples of the halogen compound or the halogen-containing reaction gas used in the present invention include NaCl,
Salt baths such as KCl, CaCl ₂ , CaF ₂ , KF, and NaF, and those containing chlorine-based gases such as Cl ₂ , HCl, and CH ₃ Cl, F ₂ , HF, ClF ₃ , NF ₃ , BF ₃ , and CF
_4, those containing a fluorine-based gas such as SF ₆ can be used.
In particular, the halogen gas may be diluted with an inert gas such as N ₂ or argon, and the halogen concentration is 0.1 to 100.
%, A processing temperature of 20 to 400 ° C. and a processing time of 10 to 480 minutes are generally used. More specifically, among the above halogen compounds, the reactivity is high even at a low temperature, and the treatment at a lower concentration is possible.
lF ₃ is preferably used.

[0013] The method of the present invention will be described specifically.
After the object to be plated is degreased and cleaned, it is inserted into a heating furnace. The Cr-plated workpiece is desirably degreased and washed continuously after plating, and then inserted into a heating furnace. However, the method of the present invention does not interfere with the use of a stored product after a lapse of time. Next, the heating furnace is replaced with an inert gas such as N ₂ or argon. Further, if necessary, the temperature is raised to 400 ° C. or lower. In this case, the flow of the inert gas may be continued, or the flow of the inert gas may be stopped, and the heating furnace may be evacuated by a vacuum pump. This operation is intended to sufficiently remove and desorb moisture and oxygen which interfere with the subsequent halogen pretreatment and CrN film formation treatment. Thereafter, if necessary, the heating furnace is adjusted to a pretreatment temperature (20 to 400 ° C.), and then a halogen compound or a reaction gas containing halogen, for example, C 2
A mixed gas of l ₂ and N ₂ or a mixed gas of ClF ₃ and N ₂ is introduced. Cl ₂ or ClF ₃ is the active group C
Generates 1 and F, removes dirt remaining on the surface, and quickly reacts with an oxide film or adsorbed O ₂ existing on the Cr plating surface to form an activated surface. The pre-processed object is subjected to a CrN film forming process after replacing the remaining halogen compound and the reaction gas containing halogen with a non-oxidizing atmosphere of an inert gas atmosphere such as N ₂ or Ar. .

The CrN film forming process is performed at 350 to 700
° C., preferably heated to keep the treatment temperature of 400 to 500 ° C., nitriding atmosphere gas containing NH _3, and for example, NH ₃ and N ₂
Is carried out by introducing a mixed gas of In this case, it is also possible prior to CrN formation processing to form an efficient active Cr layer is treated with a reducing atmosphere gas containing H _2. Due to this, an active Cr layer is formed, so that nitrogen (N) in an active period generated by decomposition of NH ₃ is adsorbed and easily penetrates and diffuses into the metal. Then, a chromium nitride layer such as CrN, Cr ₂ N is formed. 2Cr + N → Cr ₂ N (1) Cr + N → CrN (2)

If the CrN film forming process is directly performed without the halogenation process after the Cr plating process, the activity of the Cr plating surface decreases due to the oxide film and the adsorbed contaminants existing on the Cr plating surface. Although the problem of elongation occurs, the CrN coating of the present invention can be formed. C
In the process of forming the rN film, Cr ₂ N is first formed, and N is further adsorbed and diffused to form CrN. Therefore, the ratio of Cr ₂ N is high in the deepest part, and the surface layer
The ratio of N is high. The CrN coating of the present invention is not limited to only CrN, but is a coating having a concentration gradient of CrN and Cr ₂ N. The thickness of the CrN and Cr ₂ N coatings is not particularly limited, but usually 1 to 20 μm is preferably used.

The thus obtained CrN of the present invention
The coating is between 1 and 50 μm between the metal material substrate and the CrN coating.
To have a laminated structure having a Cr plating layer. This structure
This has an effect of suppressing dispersion of thermal stress generated by a large difference between the coefficient of thermal expansion of the metal material and the coefficient of thermal expansion of CrN. However,
The effect is hardly seen in the case of a thin film having a Cr plating layer of 1 μm or less, and a film thickness of 50 μm or more is rather brittle, so that there is practically no effect. In addition, the laminated structure of this CrN coating not only improves the surface hardness and wear resistance, but also
It is also possible to improve the corrosion resistance of the plating.

[0017]

【Example】

(Example 1) Test piece of SKD61 (15 × 30 ×
2 mm) was subjected to 10 μm industrial chromium plating and degreased in acetone for 60 seconds by ultrasonic treatment. The degreased sample is placed in a reaction furnace (30 mmφ × 40
0 mm) and replaced with N ₂ gas twice, then at 50 ° C.
The temperature rose. Thereafter, 1% ClF ₃ diluted with N ₂ was introduced and kept for 1 hour. Next, the ClF ₃ gas containing remaining after replacing by flowing N _2, to introduce 40% NH ₃ gas diluted with N _2, the temperature was raised to 500 ° C.,
A CrN film formation treatment was performed at 500 ° C. for 24 hours. At this time, the NH ₃ gas was circulated using an NH ₃ decomposition catalyst so that the decomposition rate of the NH ₃ gas in the reaction furnace became 50%.

After the treatment, the sample was taken out by air cooling. The CrN and Cr ₂ N coatings of the obtained samples were uniform and 2 μm, and an 8 μm Cr plating layer was formed between the SKD61 substrate and the CrN coating. Hardness is base material SK
D61 is 500-600Hv, Cr plating is 900
1800 to 2000H
v. As a result of the reciprocating motion wear test, the Cr plating treatment was 820 ds / μm compared to 360 ds / μm. As a result of the liquid tank thermal shock test (100 cycles), no particular abnormality such as appearance was observed.

(Embodiment 2) As in Embodiment 1, SKD61
A sample obtained by subjecting a test piece (15 × 30 × 2 mm) to an industrial chrome plating of 10 μm was degreased in acetone by ultrasonic treatment for 60 seconds. The degreased sample is inserted into a reaction furnace (30 mmφ × 400 mm), and N ₂
After the gas was replaced twice, the temperature was raised to 50 ° C. Then N
Introducing 10% Cl _2, diluted with _2, and held for one hour. Then, the Cl ₂ containing gas remaining after replacing by flowing N _2, to introduce 40% NH ₃ gas diluted with N _2, the temperature was raised to 500 ° C., 24 h Cr at 500 ° C.
An N film forming process was performed. At this time, NH _{3 in the} reactor was
An NH ₃ gas was circulated using an NH ₃ decomposition catalyst so that the gas decomposition rate became 50%.

After the treatment, the sample was taken out by air cooling. The CrN and Cr ₂ N coatings of the obtained sample were uniform and 1.8 μm, and an 8.2 μm Cr plating layer was formed between the SKD61 substrate and the CrN coating. The hardness is
The base material SKD61 is 500-600 Hv, and the Cr plating process is 900-1000 Hv, whereas 1700-1
900 Hv. The result of the reciprocating motion wear test was Cr
800ds / μm against 360ds / μm plating
m. As a result of the liquid tank thermal shock test (100 cycles), no particular abnormality such as appearance was observed.

(Embodiment 3) SKD61 as in Embodiment 1
A sample obtained by subjecting a test piece (15 × 30 × 2 mm) to an industrial chrome plating of 10 μm was degreased in acetone by ultrasonic treatment for 60 seconds. The degreased sample is inserted into a reaction furnace (30 mmφ × 400 mm), and N ₂
After purging twice with gas, 40% NH ₃ diluted with N ₂
A gas was introduced, the temperature was raised to 500 ° C., and a CrN film forming treatment was performed at 500 ° C. for 24 hours. At this time, the NH ₃ gas was circulated using an NH ₃ decomposition catalyst so that the decomposition rate of the NH ₃ gas in the reaction furnace became 50%.

After the completion of the treatment, the sample was taken out by air cooling. The CrN and Cr2N coatings of the obtained sample were uniform and 1.5 μm, and a 8.5 μm Cr plating layer was formed between the SKD61 substrate and the CrN coating. The hardness is
The base material SKD61 is 500-600 Hv, and the Cr plating treatment is 900-1000 Hv, whereas 1600-1
800 Hv. The result of the reciprocating motion wear test was Cr
Plating treatment is 780ds / μm for 360ds / μm
m. As a result of the liquid tank thermal shock test (100 cycles), no particular abnormality such as appearance was observed.

(Comparative Example 1) SKD61 as in Example 1
Of a test piece (15 × 30 × 2 mm) coated with 2 μm of industrial chrome was subjected to ultrasonic treatment in acetone for 60 seconds to perform degreasing. Defatted sample,
It was inserted into a reaction furnace (30 mmφ × 400 mm), replaced with N ₂ gas twice, and then heated to 50 ° C. Thereafter, 1% ClF ₃ diluted with N ₂ was introduced and kept for 1 hour. Next, the ClF ₃ gas containing remaining after replacing by flowing N _2, to introduce 40% NH ₃ gas diluted with N _2, the temperature was raised to 500 ° C., 24 hours CrN film at 500 ° C. A forming process was performed. At this time, the NH ₃ gas was circulated so that the decomposition rate of the NH ₃ gas in the reaction furnace became 50%.

After the treatment, the sample was taken out by air cooling. CrN and Cr ₂ N coating of the resulting sample was 2μm uniform, Cr plating layer between the SKD61 matrix and CrN coating did not remain disappeared. Hardness is 0
６００600 Hv, 1600 to 1800 Hv. The result of the reciprocating motion wear test was 780 ds / μm. As a result of the liquid tank thermal shock test (100 cycles), peeling, cracks, swelling, and the like were observed in the appearance.

Comparative Example 2 A 2 μm CrN coating was applied to the surface of a test piece (15 × 30 × 2 mm) of SKD61 by ion plating. Hardness is 1600-1
800 Hv. The result of the reciprocating motion wear test was Cr
Plating treatment is 780ds / μm for 360ds / μm
m. As a result of the liquid tank thermal shock test (100 cycles), peeling, cracks, swelling, and the like were observed in the appearance.

[0026]

According to the present invention, it is possible to obtain a strong surface coating which has remarkably improved hardness and abrasion resistance and can withstand thermal shock.

Claims (6)

[Claims] 1. A CrN film comprising a metal plating and a Cr plating layer provided on a surface of the metal material substrate, wherein the surface of the Cr plating layer is nitrided. 2. After applying Cr plating on the surface of the metal material,
A method for forming a CrN film, wherein the metal material is heated in a nitriding atmosphere to nitride a part of the surface of the Cr plating layer. 3. After applying Cr plating on the surface of the metal material,
The metal material is heated in a halogen compound or a reactive gas containing halogen to purify and activate the Cr plating layer surface, and then heated in a nitriding atmosphere to nitride the Cr plating layer surface. A method for forming a CrN coating. 4. The method according to claim 3, wherein the halogen compound or the reactive gas containing halogen is a fluorine compound or a fluorine-containing gas. 5. The method for forming a CrN film according to claim 4, wherein the fluorine-containing reaction gas is a reaction gas containing ClF ₃ . 6. The method for forming a CrN film according to claim 2, wherein the heating is performed at a low temperature of 500 ° C. or less.