JP2001240955A - Aluminum nitride material and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problems that no satisfactory hardness has been obtained so far by surface treatments of an aluminum material by the previous technology, such as positive formation of an oxide film on a basis material, impregnation of the film with resin and formation of a nitride (AlN) by melting of the surface, that improvement of adhesion is still required even in the case of a technology of deposition of a high-hardness nitride using PVD, and that, as for a technology of formation of a nitride layer by nitrogen diffusion using ion nitriding, improvements are still required because of, e.g. the lack of efficiency in a previous process for removal of alumina film and the incapability of forming a satisfactory nitrogen diffusion layer after once forming an AlN film on the surface. SOLUTION: In the aluminum nitride material, an aluminum nitride layer is formed on the surface of an aluminum basis material composed of aluminum material or aluminum-alloy material by holding the aluminum basis material at 200-400 deg.C, using gaseous ammonia and gaseous hydrogen, and applying glow discharge at 0.001 to 2.0 mA/cm2 to the surface of the metal member. In this aluminum nitride material, the aluminum nitride layer exists in 1-50 μm layer thickness in the inner part of the basis material and is formed into a thin layer where nitrogen density is reduced in the vicinity of the surface of the nitride layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an aluminum nitride material having excellent wear resistance and a method for producing the same.

[0002]

2. Description of the Related Art Aluminum or aluminum alloys have a low specific gravity and high electrical conductivity, thermal conductivity, reflectivity, etc. and have good corrosion resistance. Therefore, various applications in which these properties are required, for example, land, sea and air transportation equipment. , Electrical equipment,
It is used as a constituent member of household goods, optical equipment, and the like. However, in these applications, a portion that is subjected to friction such as sliding is inferior in wear resistance due to a low hardness of the base material. Various surface treatments have been developed or put to practical use in order to improve this. However, the aluminum material has a very high affinity for oxygen, like titanium or the like, and forms a strong oxide film. That is, the aluminum material left in the air reacts with oxygen in the air to form a dense thin alumina layer of about 100 angstroms. Due to the presence of the alumina layer, the surface treatment of the aluminum material was extremely difficult as compared with the iron-based material, and the surface treatment method was limited.

In general, for the surface treatment of aluminum materials, an anodic oxide film is formed by anodizing treatment in an electrolytic solution comprising oxalic acid, sulfuric acid, chromic acid or a mixed acid thereof for a long time. (JISH860
1). In recent years, as a method for improving the coefficient of friction and wear resistance, a process in which a fluororesin is fused into a porous layer of an anodic oxide film generated by an electrolyte capable of dissolving an oxide film is also used. (“Metal material”, Iei, 16 (1967) 50). All of these methods are based on the formation of an alumina coating, and the hardness of these coatings varies depending on the processing conditions, types, etc., but is not more than 800 HV, and is not necessarily sufficient for abrasion resistance. Does not have. Furthermore, these treatment methods are wet processes, requiring a great deal of time in the pre-treatment step, the main treatment and the post-treatment step, and requiring careful attention to waste liquid treatment, etc., which has generally increased the cost. .

On the other hand, the aluminum material has a strong affinity for nitrogen as in the case of oxygen, and easily reacts with nitrogen to form AlN.
Has high hardness and excellent wear resistance,
In terms of physical properties, the melting point is as high as 2000 ° C. or higher, the thermal conductivity is large, and the electrical insulation is excellent. Accordingly, various techniques for forming AlN on the surface of an aluminum material have been developed. For example, as described in JP-A-56-25966, a method of forming an AlN layer by holding an aluminum material in a molten state with an arc heat source in an atmosphere of an inert gas and nitrogen or ammonia gas (fused nitriding) Method), PVD (Physical Vapor)
Deposition method reactive sputtering or ARE method (activated reactive vapor deposition, Activated)
An AlN layer is formed by a method such as Reactive Evaporation. Although the fusion nitriding method can easily and quickly treat only the necessary parts of the treatment member, there is a possibility that thermal deformation or a change in surface roughness due to melting may occur. In addition, since the PVD method coats a film on the surface of the member to be processed, the adhesion between the member to be processed and the AlN film is low, and the value is greatly affected by the pretreatment or treatment temperature. There is also a problem that there is almost no turn around due to the straightness of the vapor deposition or sputtered particles, and it is difficult to uniformly process a complicated shape.

On the other hand, there is an ion nitriding method as one of the nitriding methods for steel materials and the like. This technology can process a large amount,
The member to be processed can be nitrided by controlling the glow discharge energy to an arbitrary processing temperature, and there is no need to melt the material to be processed. Further, the surface of the member to be processed is characterized by ion bombardment due to glow discharge and activation by hydrogen gas as a processing gas, thereby facilitating pre-processing and speeding up processing. Therefore, according to this treatment method, the surface nitriding treatment of stainless steel, which required a special treatment of the removal process due to the presence of a passivation film (oxide film) on the surface, is performed in the same manner as general steel materials by the above-mentioned effect. Is possible. Therefore, it has been studied to activate the alumina coating formed on the surface of the aluminum material by the effect of the above-described ion nitriding method to remove the alumina coating, nitride Al, and form AlN. However, alumina, which is a surface coating of aluminum, is smaller than the standard free energy of oxide formation, and in a general ion nitriding apparatus, it reacts again with oxygen in the residual gas, so that an active surface cannot be obtained. It was difficult.

Therefore, there is a method described in Japanese Patent Application Laid-Open No. Sho 60-211061 as a method of performing a nitriding treatment by removing an alumina film formed on the surface of an aluminum material by an ion nitriding method. In this processing method, a nitriding treatment is performed by performing a step of removing oxygen gas remaining in the closed vessel and an activation step of discharging the activation gas to activate the surface of the workpiece. According to this treatment method, oxygen gas can be removed by repeating gas introduction and decompression, then the alumina film can be removed by ion bombardment of a rare gas, and thereafter, hard AlN is formed on the surface by nitriding treatment. .
However, in this treatment method, a plurality of (two to three) gas (hydrogen) introductions and a reduced pressure (10 ^-3 To
rr, 0.0133 Pa), so that the processing steps become longer. Furthermore, since the removal of the alumina film in the activation step is performed only by sputter cleaning using ion bombardment of a rare gas, the activation is performed by sputter cleaning for 0.5 to 2 hours. It is long. In addition, since the sputter cleaning is heated to 500 ° C. after the temperature raising step, the standard free energy of oxide formation of alumina is extremely low due to the purity of the activating gas or the slight residual oxygen in the closed vessel. Therefore, there is a possibility that an alumina film is formed, and if an alumina film is formed, there is a possibility that AlN will not be formed even if nitriding is performed as described above.

[0007] In addition, in the ion nitriding, not a nitride of a base metal but a thick diffusion layer of a nitrogen element on a base material surface, and a hard nitride coating on the outermost layer, a combined effect of surface treatment, The strength of the layer was increased and the wear resistance was improved. However, when the base material is an aluminum material, it has been difficult to form a sufficient nitrogen diffusion layer even if an AlN film is formed on the surface by, for example, the above-described processing method. The reason is that, since AlN is an electrically insulating material, it is difficult to maintain a glow discharge for activating nitrogen ions after the formation of AlN on the surface.

[0008]

As described above, the surface treatment of an aluminum material according to the prior art includes a method in which an oxide film is positively formed on a substrate and a method in which a resin is penetrated into the film. Or melt the surface to nitride (Al
N) was formed, but the hardness was low. Further, even in the case where a nitride having high hardness is formed by the PVD method, there is a point to be improved in terms of adhesion.

On the other hand, in the method of diffusing nitrogen by ion nitriding to form a nitride layer, the pre-process of removing the alumina film is not efficient, and once the AlN film is formed on the surface, a sufficient nitrogen diffusion layer is formed. There was a point to be improved such as inability to form

[0010]

In order to solve the above-mentioned problems, the present inventors control the plasma used for the nitriding treatment to form the compound layer and the diffusion layer on the processing member. Radical nitridation that can be controlled (for example, JP-A-6-220606 or JP-A-7-220606)
It was considered that a nitride layer could be formed on an aluminum substrate by using the method described in -118826. When this radical nitriding treatment was applied to the aluminum base material, the alumina coating on the surface that was inconvenient for the formation of the nitride layer was not specifically removed as a pretreatment, and the formation of the alumina coating was suppressed even when the nitride layer was formed. However, they have obtained a study result that a nitrogen diffusion layer having a sufficient thickness can be formed.

The present invention has been made based on the above research results, and an object of the present invention is to maintain an aluminum substrate at a temperature of 200 to 400 ° C. in order to solve the above problems. In a radical nitriding method of performing a glow discharge at a current density of 0.001 to 2.0 mA / cm ^{2 on} the surface of the metal member using an ammonia gas and a hydrogen gas, and ion-nitriding the surface of the aluminum base material, The outermost surface of the aluminum substrate has a thin layer having a reduced nitrogen density, and an aluminum nitride layer having a thickness of 1
An object of the present invention is to provide an aluminum nitride material and an aluminum nitride method characterized by being present in a range of μm to 50 μm.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to diffuse a gaseous substance from a metal surface to the inside by an ion nitriding method and form a compound layer of a metal and a gaseous substance on a metal surface, gas concentration, reaction temperature and time are the main factors. Becomes However, before that, it is essential that the metal surface be in an active state so that the gaseous substance can easily penetrate and diffuse. However, as described above, an aluminum coating is formed on the aluminum material while it is left at room temperature, and the alumina of this oxide coating is stable and dense even though it is a thin coating (100 angstrom or less). Since it acts as a barrier to hinder the diffusion of gaseous substances, no nitrided layer is formed even if, for example, nitrogen gas is introduced. Therefore, in order to form a nitrided layer on the surface of the aluminum material, it is important to remove the alumina coating to obtain an active surface.

[0013] The method of removing the oxide film of the aluminum material includes (1) destruction of the film by chemical cleaning with an alkali solution or the like, (2) destruction of the film by a mechanical method such as wire brushing, and (3) destruction of the base metal. There are destruction of the coating by a metallurgical reaction such as eutectic reaction, and (4) destruction of the coating by an electric method such as ion bombardment. Considering the applicability of these methods as a pretreatment method for a member to be treated for ion nitriding, it is impossible to perform the treatments (1) and (2) in a furnace inside a vacuum vessel. If performed outside the furnace, the above-mentioned oxide film is formed and the purpose is not achieved. (3) is used for bonding with a metal and is not suitable for surface treatment. On the other hand, (4) is conventionally used for sputter cleaning by glow discharge, and there is also an ion beam sputtering method performed in a higher vacuum.

As described above, there is a point to be improved as a pre-process for removing the oxide film of the aluminum material by the ion nitriding method. However, according to the study of the present inventors, when radical nitriding is applied, the oxide film on the surface of the aluminum material is removed without performing the above pretreatment, and the oxidation during the formation of the nitride layer is performed. It has been found that the formation of a film can be suppressed and a nitrogen diffusion layer having a sufficient thickness can be formed.

Radical nitriding is disclosed in Japanese Patent Application Laid-Open No. 6-220606.
As disclosed in Japanese Unexamined Patent Application Publication No. Hei.
While maintaining the temperature at 0 ° C., using ammonia gas and hydrogen gas, the surface of the metal member is 0.001 to 2.0 mA.
Glow discharge at a current density of / cm ² and ion nitriding of the surface of the metal member. As a feature of the ion nitriding method, 0.0
The point is that ammonia gas and hydrogen gas are decomposed by glow discharge at a current density of 01 to 2.0 mA / cm ² . This is because the ratio of generated NH radicals is high, and the use of hydrogen as an auxiliary gas stably generates the NH radical species, so that a plasma having a high NH radical density is used for the nitriding reaction. The NH radical is a plasma species showing high reactivity in the nitridation reaction using plasma, and the ion nitridation reaction using the plasma having a high NH radical density forms a nitride layer more efficiently. It is possible to do.

Further, according to the study of the present inventors, when radical nitriding is used for nitriding an aluminum material, the NH radical not only forms a nitrided layer but also has a reducing effect on an oxide film on the surface, and the removal of the oxide film It was also found to be effective in suppressing generation. The outermost surface of the aluminum substrate obtained in the present invention has a thin layer in which the density of nitrogen is reduced,
An aluminum nitride layer having a thickness of 1 μm
The structure having a thickness of about 50 μm is formed by the simultaneous occurrence of the reduction reaction and the nitridation reaction of the oxide film, and shows a characteristic of nitriding the aluminum material using radical nitridation. .

In the present invention, there are various aluminum materials such as pure aluminum, an aluminum alloy for casting, and an aluminum alloy for die casting.

[0018]

EXAMPLES Next, the aluminum nitride material of the present invention and a method for producing the same will be described in detail with reference to examples. First, as an aluminum substrate to be coated, an aluminum alloy for castings AC8A specified in JIS standard is prepared.
The sample was cut into a square with a square of 5 mm and a thickness of 5 mm.

Example 1 As Example 1, one of the manufactured samples was subjected to a radical nitriding treatment. After setting the sample in the nitriding furnace, the inside of the vacuum chamber was set to 10 ^-7 Torr (1.33 ×
It was evacuated to 10 ^-5 Pa).

Next, a voltage of -350 V was applied to the sample from a DC power supply to generate DC glow discharge plasma by hydrogen gas, and the inner wall of the vacuum chamber and the surface of the sample were cleaned for 30 minutes. Next, 1000 ml / min of hydrogen gas and 1000 ml / min of ammonia gas are introduced into the vacuum chamber,
The pressure is maintained at 1 Torr (133 Pa), and the applied voltage-
DC glow discharge plasma of hydrogen gas and ammonia gas was generated at 350 V to start ion nitriding. The value of the current flowing through the jig and the base material at which the current density was measured at this time was divided by the effective surface area of the base material and the jig, and calculated.
It was 5 mA / cm ² , which was confirmed to be the treatment condition for radical nitriding. The processing temperature was 200 ° C. After the nitriding treatment was continued for one hour, the plasma was stopped, gas supply and heating were stopped, and the temperature was cooled to room temperature.

(Example 2) In Example 2, the same aluminum alloy base material as in Example 1 was used, and the conditions for radical nitriding were a current density of 0.06 mA / cm ² ,
The treatment was performed at a temperature of 220 ° C. for a treatment time of 10 hours.

Example 3 In Example 3, the same aluminum alloy substrate as in Example was used, and the conditions for radical nitriding were a current density of 0.045 mA / cm ² ,
The test was performed at a temperature of 220 ° C. for a processing time.

Example 4 As Example 4, as an aluminum substrate to be coated, an aluminum alloy ADC12 for die casting as specified in JIS standard was prepared.
The sample was cut into a square with a square of 5 mm and a thickness of 5 mm. AD sample
A nitriding treatment was performed in the same manner as in Example 1 except that C12 was used. The processing conditions were a current density of 0.07 mA / cm ²
The temperature was 300 ° C. and the processing time was 1 hour.

(Comparative Example 1) As Comparative Example 1, Example 1
A similar aluminum substrate was prepared, and nitrided as in Example 1.
After setting the sample in the chemical treatment furnace,^-7Torr
(1.33 × 10 ^-FiveExhaust to Pa) and continue exhausting
And supply hydrogen gas at 1000 ml / min.
(133 Pa). At the same time sample with heater
Was heated to 380 ° C. for 1 hour. That
Then, under the same conditions except for setting the bias voltage to -600 V,
Treatment. This is the conventional ion nitriding condition.
The processing conditions are similar to.

As a result of confirming the surface condition of each sample after the nitriding treatment by an optical microscope, the sample of Comparative Example 1
The surface roughness was remarkable, suggesting the formation of a compound. on the other hand,
The sample subjected to the radical nitriding treatment of the present invention showed almost no surface roughness in appearance.

Next, GDS (G
low Discharge Spectroscop
y: glow discharge spectroscopy) analysis. FIG. 1 shows a GDS spectrum of the sample of Example 2. In the sample of Comparative Example 1, the presence of nitrogen was recognized on the surface, but the presence of nitrogen atoms could not be confirmed inside. In contrast, in the sample subjected to the nitriding treatment of the present invention, the presence of nitrogen was reduced at a depth of 2 μm from the surface, but a nitrided layer having a width of about 7 μm with a peak at a depth of 3 μm was observed.

The same analysis was also performed on the samples of the examples and the examples in which the treatment time was changed. As a result, the nitrided layers were 30 μm and 50 μm, respectively. In each of the samples, the structure of the surface layer was such that the presence of nitrogen was reduced as in Example 2.

Next, the surface hardness of the sample of Example 2 was measured. The hardness before and after the treatment was measured by micro Vickers hardness with a load of 0.05 N, and the hardness was 132 HV before the nitriding treatment, but was 159 HV or more after the treatment.

Next, in order to evaluate the wear resistance of the aluminum nitride material manufactured according to the present invention, a ball-on-disk wear test was performed. As a comparative example, an untreated aluminum alloy sample was used. Using a ball of cemented carbide with a diameter of 6 mm as the ball material, with a load of 10 N and a wear distance of 1000
A 0 m test was performed.

For an untreated aluminum material, approximately 55
At 00 m, an increase in the coefficient of friction which was considered to be due to welding of aluminum was observed. On the other hand, any of the samples subjected to the nitriding treatment of the present invention did not show any particular signs of welding even at the end of 10,000 m, and showed a good abrasion state. This is presumably because the hardness was increased by the surface nitride layer.

[0031]

As described above in detail, according to the present invention, the nitridation of an aluminum base material which conventionally required a special surface oxide removing step is performed by the radical nitridation treatment of the present invention. Accordingly, the nitride layer can be formed without performing the oxide removing step, and an aluminum nitride material having excellent wear resistance can be formed.

[Brief description of the drawings]

FIG. 1 is a glow discharge spectroscopy (GDS) measurement spectrum of a sample of Example 1 according to the present invention.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Matsufumi Takatani 2-17-1 Tsudanuma, Narashino-shi, Chiba Chiba Institute of Technology (72) Inventor Yukihiro Sakamoto 2-17-1 Tsudanuma, Narashino-shi, Chiba Chiba Institute of Technology (72) Inventor Atsushi Kawana 3860 Shimotsuruma, Yamato-shi, Kanagawa Japan Coating Center Co., Ltd. (72) Inventor Yoshiro Ishii 3-18-5, Chugoku, Ichikawa-shi, Chiba Sumitomo Metal Mining Co., Ltd. (Reference) 4K028 AA02 AB02 AC08

Claims (2)

[Claims] 1. An aluminum nitride material having an aluminum nitride layer formed on the surface of an aluminum substrate made of an aluminum material or an aluminum alloy material, wherein the aluminum nitride layer has a thickness of 1 μm or more inside the substrate.
An aluminum nitride material having a thickness of not more than μm and a thin layer near the surface of the nitride layer, the density of nitrogen being reduced. 2. An aluminum substrate is maintained at a temperature of 200 to 400 ° C., and an ammonia gas and a hydrogen gas are used, and the surface of the metal member is 0.001 to 2.0 mA / cm ^2.
A glow discharge at a current density of 1 to form an aluminum nitride material on the surface layer of the base material.
A method for producing an aluminum nitride material, comprising: a thin layer having a thickness of not less than μm and not more than 50 μm and having a nitrogen density decreasing near a surface of the nitrided layer.