JPH05156423A - Al-cr composite diffusion coating treating agent for ti alloy and treatment using the agent - Google Patents

Abstract

PURPOSE:To execute the Al-Cr composite diffusion coating treatment of a Ti alloy and to improve its oxidation resistance by constituting the above treating agent of specific wt.% of aluminum powder, chromium powder, ammonium chloride and the balance sintering-preventive powder. CONSTITUTION:The Al-Cr composite diffusion coating treating agent for the Ti alloy is constituted, by weight %, of 10 to 30% aluminum powder, 10 to 30% chromium powder, 0.5 to 5% ammonium chloride and the balance the sintering-preventive powder. The Ti alloy is embedded into this treating agent and is heated at 1000 to 1300 deg.C in a nonoxidative atmosphere, by which the Al-Cr diffusion coating layer is formed on the surface of the Ti alloy. Al-Cr alloy powder is compounded in place of a part or the whole of the aluminum powder or chromium powder. As a result, a precision polishing stage is simplified or saved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an Al-Cr composite diffusion coating treatment agent for forming an oxidation resistant coating on the surface of a Ti-based alloy and a treatment method for a heat resistant Ti alloy using the treatment agent.

[0002]

2. Description of the Related Art Ti alloy is widely used as a lightweight structural material and as a corrosion resistant material because it has a small specific gravity, is lightweight, has high mechanical strength and good corrosion resistance.
In a high-temperature atmosphere, the surface of the Ti alloy is oxidized, its oxide layer easily grows, absorbs N and H, and becomes brittle, so the operating temperature is limited to 500 ° C or lower. So T
In order to impart the oxidation resistance of the i alloy, pure Ti or Ti-6A
Attempts have been made to form an Al coating layer on the surface of an l-4V alloy or the like to utilize the oxidation suppressing effect of the Al coating layer, and it has been recognized that this Al coating layer also reduces hydrogen embrittlement.

Further, in the conventional heat resistant Ti alloy,
There is a Ti-Al based alloy containing 35% Al, and the content is about 70.
It shows oxidation resistance that can be used in the atmosphere of 0 ° C. This alloy has suitable applications as a heat-resistant material for stator vane vanes of jet engine compressors, blades for gas turbines for power generation, turbine rotors for automobiles, etc., but since it has a low heat-resistant temperature, it contains powders containing aluminum powder. By embedding this alloy material in and heating it, A
Attempts have been made to improve the oxidation resistance by forming a 1 coating layer and using a TiAl ₃ layer (Japanese Patent Laid-Open No. 1111858).
issue).

[0004]

By coating a Ti-based alloy containing a high Al-Ti alloy with an Al coating layer, the oxidation resistance can be improved and the operating temperature can be raised.
In high temperature air above 00 ° C, the adhesion of the TiAl ₃ layer oxide film formed by the Al diffusion coating treatment is not sufficient.
Oxidation of the TiAl ₃ layer continues to proceed due to repeated peeling and regeneration, so it is not sufficient as a heat resistant material.

The Al coating layer on the surface of the Ti-based alloy is a diffusion coating treatment method in which a Ti-based alloy material is embedded in a treatment agent consisting of aluminum powder, alumina powder and ammonium chloride, and is heated and held at a high temperature for a long time. However, in this method, the surface of the coating layer is usually roughened, and the precision heat-resistant member requires a large amount of surface polishing to obtain a smooth surface. It was uneconomical because it was made thicker than necessary. Further, for parts having complicated shapes such as turbine rotors, it is very difficult to perform precise surface polishing, so that it is necessary to form a coating layer having a smooth surface.

The inventors of the present invention have already targeted heat-resistant steel,
We proposed a method of improving the conventional calorizing treatment by the powder method and performing the diffusion coating treatment with an Al diffusion coating treatment agent in which an aluminum powder and a chromium powder are mixed (Japanese Patent Application No.
99500). This method forms a smooth and uniform calorized layer by mixing chrome powder with aluminum powder.

The present invention has found that the above Al diffusion coating treatment agent containing Cr powder is applied to a Ti-Al alloy or other Ti-based alloy to improve the oxidation resistance and surface properties, and the oxidation resistance is improved. It is an object of the present invention to provide an Al-Cr composite diffusion coating treatment agent and a diffusion coating treatment method thereof for producing an excellent Al-Cr diffusion coating Ti-based alloy.

[0008]

Means for Solving the Problems A of the Ti-based alloy of the present invention
The l-Cr composite diffusion coating treatment agent is 10 to 30 wt% aluminum powder, 10 to 30 wt% chromium powder, and 0.5.
It is characterized by comprising ˜5 wt% ammonium chloride and the balance sintering inhibitor.

Further, according to the Al-Cr composite diffusion coating method of the Ti-based alloy of the present invention, aluminum powder of 10 to 30 wt%, chromium powder of 10 to 30 wt% and 0.5 to 5 wt% are used.
Al-comprising ammonium chloride and the balance sintering inhibitor
It is characterized in that a Ti-based alloy is embedded in a Cr composite diffusion coating treatment agent and heated at a temperature of 1000 to 1300 ° C. in a non-oxidizing atmosphere.

The aluminum powder and the chrome powder in the above Al-Cr composite diffusion coating treatment agent are partially or wholly Al-Cr.
It may be replaced with a Cr alloy. In this case, the Al-Cr
The Al amount and Cr amount in the alloy are added to the aluminum powder and the chromium powder, respectively, and adjusted so as to fall within the composition range in the treating agent.

[0011]

[Function] Al-Cr containing aluminum powder and chromium powder
When the diffusion coating treatment is performed on the surface of the Ti alloy with the composite diffusion coating treatment agent, at a temperature of 1000 to 1300 ° C., a part of the aluminum powder and the chromium powder are melted into Al-Cr synthetic financial droplets, and the rest is left. Al-Cr coexist as an alloy solid, Al-Cr and alloy melt droplet and Al-Cr alloy solid is reacted with ammonium chloride, AlCl ₃ gas and CrC
l ₂ is produced, and Al and Cr are deposited on the surface of the Ti alloy from these gases and diffused to form an Al—Cr diffusion coating layer. In the Al-Cr diffusion coating layer, the content of Cr in the treatment agent reduces the Al activity, thereby reducing the amount of Al deposited on the surface of the Ti alloy, and further by performing the high temperature treatment, the inside of the Ti alloy is reduced. The Al diffusion rate of
TiAl ₂ phase single phase coating layer containing Cr or TiAl
A two-phase coating layer is formed with the _three phases as the surface layer and the TiAl ₂ phase as the inner layer.

When chromium is not added to the treating agent, only a low melting point Al liquid phase is produced, and the vapor phase A having a high partial pressure is produced.
Since a large amount of lCl ₃ migrates to the alloy surface, the Ti
The crystal grains of the Al ₃ phase and the TiAl ₂ phase become coarse and the surface roughness becomes large.
The Al activity in the l-Cr melt and solid decreases and CrC
The formation of l ₂ reduces the partial pressure of AlCl ₃
l Crystal grains such as ₃ phase are refined to make the surface smooth. T
The Cr contained in the iAl ₃ phase may also be involved in the refinement.

Also, TiAl in the Al--Cr diffusion coating layer
Cr contained in a small amount in the ₃ phase significantly reduces the oxidation rate of the TiAl ₃ layer of the coating layer, and thus improves the oxidation resistance of the Ti-based alloy. However, when the Cr concentration in the coating layer becomes higher than about 8%, the oxidation resistance deteriorates. That is, the compounding of the chromium powder in the treating agent is performed by the Al--Cr alloy of the Ti alloy.
It has a function of homogenizing and smoothing the surface of the diffusion coating layer to prevent surface roughness and a function of diffusing and moving to the Al-Cr diffusion coating layer to increase the Cr concentration and improve the oxidation resistance.

The amount of aluminum powder in the Al-Cr composite diffusion coating treatment agent of the present invention must be 10 to 30%, but if the amount of aluminum powder is less than 10%, the Al-Cr diffusion coating layer is thin and has a surface. Oxidation resistance cannot be obtained due to variations in part thickness. Also, if it exceeds 30%, Al-C
The surface of the r diffusion coating layer is roughened and a smooth surface cannot be obtained.

The amount of chromium powder in the treating agent is 10 to 3
It requires 0%, but if it is less than 10%, the Al-Cr diffusion coating layer becomes porous and rough, and Cr does not diffuse and is not contained in the Al-Cr diffusion coating layer, which results in oxidation resistance. Is reduced. If the amount of chromium powder exceeds 30%, A
The Cr concentration in the l-Cr diffusion coating layer rises, the surface becomes rough, and the vicinity of the surface becomes porous, deteriorating the oxidation resistance.

The sintering inhibitor in the Al-Cr composite diffusion coating treatment agent uniformly disperses molten droplets and solid particles of the Al-Cr alloy, and appropriately disperses the embedded Ti alloy material. Acts as a carrier to carry. This sintering inhibitor is preferably alumina powder.

Ammonium chloride acts as a flux for melting and removing oxide deposits on the surface of the Ti alloy material, and as described above, as a transporter of Al and Cr to the surface of the Ti-based alloy. 0.5 to 5%. If it exceeds 5%, ammonium chloride will sublimate, resulting in loss.

The temperature of the Al-Cr composite diffusion coating process is 1
If the range of 000 ° C to 1300 ° C is appropriate and the treatment temperature is lower than 1000 ° C, the Ti alloy surface may be exposed to Al and Cr
Does not diffuse sufficiently and the formed Al—Cr composite diffusion coating layer becomes thin, so sufficient oxidation resistance cannot be obtained. Further, when the temperature exceeds 1300 ° C., Al—Cr alloy solid or powder of sintering inhibitor adheres to the Ti alloy surface to cause rough skin,
No smooth surface can be obtained.

[0019]

EXAMPLE Tests for forming an Al-Cr diffusion coating layer by performing Al-Cr composite diffusion coating treatment on a Ti-Al alloy by changing the blending amounts of aluminum powder and chromium powder of the Al-Cr composite diffusion coating treatment agent. I went.

The Al-Cr composite diffusion coating treatment agent was prepared by adjusting aluminum powder in the range of 5 to 40%, chromium powder in the range of 0 to 40%, and ammonium chloride at a constant composition of 0.5%, and baking the balance. Alumina powder was used as the anti-caking agent.

The test material is a Ti alloy containing Ti-for heat resistance.
Using 34wt% Al alloy, diameter 8mm, length 10m
It was processed into a cylindrical sample of m.

The Al-Cr composite diffusion coating treatment agent was placed in a steel container, and the test piece was embedded in the treatment agent.
The mixture was heated to a temperature of 900 ° C. to 1400 ° C. and kept in an argon atmosphere gas for 10 hours to perform Al—Cr composite diffusion coating treatment.

The surface properties of the sample after this treatment were observed, the thickness of the Al--Cr diffusion coating layer was measured by microscopic observation of the cross section, and the Al concentration and C on the surface were measured by EPMA.
The r concentration was measured.

The surface of the coating layer of the specimens after the Al-Cr composite diffusion coating treatment had rough skin-like rough surfaces and clean smooth surfaces. Therefore, the surface of the coating layer of the sample was observed with a scanning electron microscope (SEM). Figure 2
(A) is a SEM photograph of a sample having a rough surface (Sample No. 1), which has a coarse grain length of about 100 μ having a protrusion distribution on the surface.
m particles are observed. The sample (Sample No. 2) in FIG. 6B is an example in which the surface of the sample is roughened, but the surface particles are made fine. FIG. 6C is a SEM photograph of a sample (Sample No. 10) having a good surface quality without rough skin, and the surface particles are finely divided with a particle size of 2 μm or less.
From the SEM observation result, it was found that the finer the particles on the surface of the coating layer, the more dense and smooth the surface of the sample. That is, the surface quality after the Al-Cr composite diffusion coating treatment depends on the particle size of the surface granular material.

Next, the above-mentioned test piece subjected to the Al-Cr composite diffusion coating treatment was heated and held in the atmosphere at a temperature of 1000 ° C. for 100 hours to carry out an oxidation resistance test, and the weight difference of the test piece before and after heating. From this, the increase in oxidation was calculated to evaluate the oxidation resistance of the Al-Cr diffusion coating layer. The test results are summarized in Table 1.

[0026]

[Table 1]

FIG. 1 shows the surface properties and the oxidation resistance in the relationship between the amount of aluminum powder and the amount of chromium powder in the Al-Cr composite diffusion coating treatment agent. In the figure, it was judged that the oxidation resistance was good when the oxidation increase was 5 mg / cm ² or less.

A range surrounded by a solid line in FIG. 1 is A of the present invention.
It is a compounding range of the 1-Cr composite diffusion coating treatment agent. 100
It can be seen that at a temperature of 0 to 1300 ° C., this range of the treating agent is preferable in terms of both surface properties and oxidation resistance.

Next, an example in which Al--Cr alloy powder is used instead of the total amount of aluminum powder and chromium powder will be shown. A
1-Cr alloy powder (Al content 75%, Cr content 25
%), Ammonium chloride 0.5%, and the balance alumina powder to prepare an Al-Cr composite diffusion coating treatment agent. This mixture of Al-Cr alloy powder is aluminum powder 3
Equivalent to 0% and 10% chromium powder.

This treating agent has a diameter of 8 mm and a length of 10 mm.
Of Ti-34 wt% Al alloy of
Perform Al-Cr composite diffusion coating treatment at 0 ° C x 10 hours,
Then, an oxidation resistance test was conducted at 1000 ° C. for 100 hours. The results are shown in Table 2. Both the surface properties and the oxidation resistance of the Al-Cr composite diffusion coating layer are good.

[0031]

[Table 2]

[0032]

EFFECT OF THE INVENTION Al-C blended with the chromium powder of the present invention.
r-composite diffusion coating treatment agent, Ti-based alloy Al-Cr
When the composite diffusion coating treatment is carried out, the oxidation resistance is improved by the Al-Cr diffusion coating layer containing Cr of the Ti-based alloy, and in the Ti-14 to 36% Al alloy, the maximum operating temperature is 1050 ° C. Can be increased up to.

At the same time, the surface of the Al-Cr diffusion coating layer can easily be made a smooth and unbroken surface. Therefore, for example, when it is used as a turbine blade, the turbine rotation efficiency can be improved without any surface polishing. It can be used without deteriorating, and even when performing precision polishing of the surface,
Since the shaving allowance can be made thin and the Al—Cr diffusion coating layer need not be made thicker than necessary, the diffusion coating treatment step can be simplified and the precision polishing step can be simplified or omitted.

[Brief description of drawings]

FIG. 1 shows the amount of aluminum powder and the amount of chromium powder in an Al-Cr composite diffusion coating agent, and the surface properties after the diffusion coating treatment,
The figure which shows the relationship of the oxidation weight increase of an oxidation resistance test.

2 (A), (B) and (C) are scanning electron microscopes of the surface of the diffusion coating layer of the test piece after the Al—Cr composite diffusion coating treatment for sample numbers 1, 2 and 10, respectively. Photographs of metal structures by (1) (magnification: 70).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masanobu Sueyasu 8 Oike-cho, Kosai-cho, Koga-gun, Shiga Japan Calorize Industry Co., Ltd.

Claims (3)

[Claims] 1. An Al-Cr composite diffusion coating treatment of a Ti-based alloy comprising 10 to 30 wt% aluminum powder, 10 to 30 wt% chromium powder, 0.5 to 5 wt% ammonium chloride and the balance sintering preventing powder. Agent. 2. An Al-C consisting of 10 to 30 wt% aluminum powder, 10 to 30 wt% chromium powder, 0.5 to 5 wt% ammonium chloride, and the balance sintering preventing powder.
Forming an Al-Cr diffusion coating layer on the surface of the Ti-based alloy by embedding a Ti-based alloy in the r composite diffusion coating treatment agent and heating at a temperature of 1000 to 1300 ° C in a non-oxidizing atmosphere. Ti-based alloy Al-Cr characterized by
Composite diffusion coating method. 3. The Al—Cr composite diffusion coating according to claim 1, wherein an Al—Cr alloy powder is mixed in the Al—Cr composite diffusion coating treatment agent in place of a part or all of the aluminum powder or the chromium powder. A treatment agent or an Al-Cr composite diffusion coating treatment method for a Ti-based alloy according to claim 2.