JPH0693412A - Heat resistant ti-based alloy - Google Patents

Abstract

PURPOSE:To improve the oxidation resistance of an Al-Cr diffusion coating layer by forming the Al-Cr diffusion coating layer having a specified compsn. on the surface of a Ti-Al alloy. CONSTITUTION:An Al-Cr diffusion coating layer constituted of, by weight, 50 to 65% and 0.5 to 7% Cr, and the balance Ti is formed on the surface of a Ti-based alloy contg. about 14 to 36% Al. As for the formation for this Al diffusion coating layer, diffusion coating by a powdery method, a thermal spraying method, a build up welding, a PVD method, a CVD method, etc., can be adopted. The thickness of the coating layer is suitably regulated to about 15 to 300mum. Furthermore, in the case the Al-Cr alloy layer is formed on the surface layer of the Ti-based alloy base metal, the alloy layer is brought into a diffusion reaction in the using process in a high temp. oxidizing atmosphere to form the Al-Cr diffusion coating layer, by which oxidation resistance is manifested.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a Ti-based alloy having an Al-Cr composite diffusion coating layer on the surface and having excellent heat resistance and oxidation resistance.

[0002]

2. Description of the Related Art Titanium materials are light in weight and have excellent mechanical properties and corrosion resistance, so that they are used especially for industrial titanium and Ti.
-Al-based alloys such as 5Al-3Sn and 6Al-4V
Although system alloys are often used, generally, when they are used in a heat resistant manner, the upper limit of the operating temperature is about 500 ° C. When the Ti alloy is heated to a high temperature, the alloy reacts with air and moisture to form hydrogen compounds / nitrides in the alloy and embrittles, and forms an oxide layer on the surface. Since the oxide layer continues to grow, it cannot be used as an oxidation resistant material.

It is known that an Al coating treatment on the alloy surface is effective for improving the oxidation resistance of such a Ti-Al alloy, and by this treatment, the Al coating layer on the alloy surface becomes TiAl ₃ Even if a phase is formed and its surface is oxidized, the oxide layer does not grow and exhibits oxidation resistance. Also, T
Since iAl ₃ has a low hydrogen permeability, a Ti-based alloy having an Al coating layer is resistant to hydrogen embrittlement. These Ti-Al-based alloys that have been subjected to Al coating treatment can be used as heat-resistant materials although they are softened at a high temperature of 500 [deg.] C. or higher and their mechanical strength decreases.

In addition, Ti-based alloys with improved heat resistance include
There are 15-36% Al-Ti based alloys with increased Al content in the alloy. This alloy, with increasing Al content,
Improves high temperature strength and oxidation resistance, especially intermetallic compound TiA
The 34 to 36% Al-Ti alloy having the composition of 1 has a workability and ductility by adding a small amount of other components, and has heat resistance equivalent to Inconel 718. This TiAl alloy is drawing attention as a lightweight heat resistant member such as a stator vane of a jet engine compressor, a blade of a gas turbine, or a turbine rotor of an engine valve for automobiles or a turbocharger. Is about 700 ° C. from the viewpoint of oxidation resistance, and at a high temperature of 700 ° C. or higher, surface oxidation becomes remarkable and the life is shortened.

Such high Al-Ti alloy is subjected to aluminum permeation coating treatment to form a Ti-Al intermetallic compound layer of 60 to 70% Al on the surface thereof to suppress surface oxidation in a high temperature atmosphere. There is a known technology (Japanese Patent Application Laid-Open No. HEI-1)
-111858). In this case, the Al coating layer on the surface is T
It becomes iAl ₃ phase and becomes A even at high temperature of 700 ℃ or more.
l The oxidation resistance of the coating layer is improved by reducing the amount of oxidation.

[0006]

Even in the high Al-Ti alloy having the above Al coating layer formed on its surface, when it is used at a high temperature of 900 ° C. or higher, Ti in the Al coating layer on the surface is Oxidation still progresses insignificantly, the layer thickness of the Al coating layer decreases, and as a result, surface roughness and scale occur, resulting in size reduction. Therefore, sufficient oxidation resistance is required for precision heat-resistant parts. I can't say I have it. The present invention is
In view of the above problems, it is an object of the present invention to provide a high Al-Ti alloy and other heat resistant Ti-based alloys in which the oxidation resistance of the Al coating layer on the surface is improved.

[0007]

The heat resistant Ti-A of the present invention
Al alloy has 50 to 65 wt% Al and C on the surface of the alloy.
Al-C consisting of r 0.5 to 6.5 wt% and the balance Ti
It is characterized in that an r diffusion coating layer is formed. In addition, the present invention provides Al90 on the surface of a Ti-based alloy.
A heat-resistant Ti-based alloy in which an Al-Cr alloy layer composed of ˜99.5 wt% and Cr0.5 to 10 wt% is formed, and the Al-Cr alloy layer is Al5 during the use process at high temperature.
A heat-resistant Ti-based alloy characterized by being formed in an Al-Cr diffusion coating layer consisting of 0 to 65 wt%, Cr 0.5 to 7 wt% and the balance Ti is included.

The Ti-based alloy of the present invention includes industrial pure titanium, Ti-based alloys such as Ti-6Al-4V-based alloy and Ti-8Al-Sn-based alloy, and heat-resistant Ti-14 to 36Al.
Targets are alloys.

For forming the Al-Cr diffusion coating layer, a diffusion coating method by a powder method of Al powder, a thermal spraying method, a build-up method, PVD.
A (physical vapor deposition) method or a CVD (chemical vapor deposition) method can be applied. In the powder method, Al powder, Cr powder and Al ₂
This is a method of embedding and holding a Ti alloy material in a pot obtained by mixing a small amount of ammonium chloride with O ₃ powder and heating it. In the holding process, Al and Cr deposited on the surface permeate inside and A Cr diffusion coating layer is formed.

In the thermal spraying method, a mixed powder of Al powder and Cr powder is sprayed on the surface of the alloy material by, for example, a plasma thermal spraying method using Ar gas to form an Al-Cr alloy layer. Then, before use, it is heated in a non-oxidizing high-temperature atmosphere to form a diffusion alloy with a material base material of a Ti alloy to form an Al-Cr diffusion coating layer.

The Al-Cr alloy layer in the present invention is formed by the above-mentioned thermal spraying method, and 90 to 99.5 wt% of Al and 0.5 to 10 wt% of Cr are formed on the surface of the Ti-based alloy.
% To prepare an alloy layer. Then, since the above diffusion alloying process is omitted and the product is used as it is, the Al—Cr alloy layer is formed in the Al—Cr diffusion coating layer having the above composition range in the use process under high temperature. is there.

The thickness of the Al-Cr diffusion coating layer is not less than 15 μm and not more than 300 μm for practical use, but preferably about 150 μm. Further, when the Al—Cr alloy layer is formed in advance, the thickness is similarly set to 15 to 300 μm.

[0013]

EXAMPLES Examples of the heat-resistant Ti-based alloy of the present invention are shown below. (Example 1) As a test material, a specimen of Ti-34% Al alloy having a diameter of 8 mm and a length of 10 mm was used.

The Al--Cr diffusion coating layer was molded by the powder method shown below. Diffusion and permeation treatment agents having various compositions of 10 to 30 wt% Al powder, 0 to 60 wt% Cr powder, 0.5 wt% ammonium chloride, and the balance alumina powder were prepared. This treatment agent was put in a heat resistant pot, the test piece was embedded, and the mixture was heated and held at a temperature of 700 ° C. to 1300 ° C. for 10 to 20 hours to perform an Al diffusion infiltration treatment and an Al—Cr composite diffusion infiltration treatment. .

In this diffusion permeation treatment, Al--Cr
So that the Al concentration in the diffusion coating layer is 50 to 65%,
The Al-Cr diffusion coating layer has a thickness of 50 μm and a thickness of 1 μm.
Aiming at stratification into two levels of a 50 μm thick film, at each level, the Cr concentration in the Al—Cr diffusion coating layer was 0-10.
Al powder and Cr in the treating agent so as to change to the range of wt%
The amount of powder blended was adjusted. After this treatment, each test piece was cut and polished, observed under a microscope to measure the thickness of the Al-Cr diffusion coating layer, and the concentration of Al and ACr in the Al-Cr diffusion coating layer was measured by EPMA analysis.

FIG. 1 shows an Al-Cr diffusion coating layer thickness 150.
A micrograph of a cross section of the surface layer portion before the high temperature oxidation test is shown for the sample having a surface Cr concentration of 0.5 wt% and a clear Al—Cr diffusion coating layer is observed in the surface layer portion.

FIG. 2 shows the EPMA analysis results of the Al concentration and Cr concentration of the surface layer portion of the same sample. The first layer is about 63% Al inside the vicinity of the surface, and 53% Al is inside it.
Is recognized as a second layer, and a diffusion layer gradually decreasing to the Al concentration in the base material is further provided inside. TiAl for the first layer
_{The 3} phase and the second layer were identified as the TiAl ₂ phase. The Cr concentration gradually decreases from the surface toward the base material interface.

Next, each of the above-mentioned test pieces was heated and held in the atmosphere at a temperature of 1000 ° C. for 100 hours to conduct a high temperature oxidation test.
The oxidation increase was calculated from the weight change of the test piece, and the oxidation resistance was evaluated. The above results are summarized in Table 1.

[0019]

[Table 1]

From Table 1, the Al powder content in the treated material is 10
%, The thickness of the Al—Cr diffusion coating layer is 40 to
It is as thin as 90 μm and has an Al concentration of 60% or less and is a TiAl ₂ phase (Sample Nos. 3 to 9 in the table), but the Al powder content is 20 to
At 30%, the Al concentration increases to about 63% and Ti
It can be seen that an Al ₃ phase appears (sample numbers 10 to 1 in the table).
4).

FIG. 3 shows a photomicrograph of a cross section of the surface layer of the sample after heating and holding at a temperature of 1000 ° C. for 100 hours. FIG. 3A shows the sample of sample No. 9 in Table 1. Therefore, it is understood that oxide scale is generated on the surface of the Al—Cr diffusion coating layer. On the other hand, in the same figure (B), although the sample No. 7 is a test piece, almost no oxide layer is formed.

In FIG. 4, the thickness of the Al-Cr diffusion coating layer is set to 4
The thin film having a thickness of 0 to 90 μm and the thick film having a thickness of 140 to 150 μm are layered, and the Cr concentration of the Al—Cr diffusion coating layer and 1000 ° C.
It shows the relationship with the increased oxidation amount after heating for 100 hours. From this figure, it can be seen that the thicker the Al-Cr diffusion coating layer is, the smaller the increase in the amount of oxidation is as compared with the thin film.
When the concentration is 0.5% or more, the increase in oxidation is reduced, which is effective for imparting oxidation resistance. When the concentration is increased to about 8% or more, the increase in oxidation is increased. Cr concentration on the surface is 0.5-7.0%
It can be seen that the range of is good for oxidation resistance. Especially 3-5
At the concentration of% Cr, the oxidation resistance is most excellent without being affected by the layer thickness in the above range.

(Embodiment 2) Next, an embodiment of the TiAl ₃ alloy powder by the plasma spraying method will be described. Pure Ti shape 50 ×
97% TiAl ₃ powder on the surface of 100 × 5 mm substrate
The co-micronized with Cr powder 3% and were subjected to plasma spraying as the carrier gas Ar-H ₂ mixed gas. The thermal spraying conditions were carrier gas Ar 6.3 × 10 ⁻⁴ Nm ³ / sec and H ₂ 5.5 ×.
The supply rate of powder was 0.1 at a supply rate of 10 ^-5 Nm ³ / sec.
At 3 g / sec, the atmosphere pressure was 20.0 KP, and the moving speed of the substrate was 5 mm / sec. The thickness of the coating layer after thermal spraying is about 1
It was 50 μm.

Next, the thermal spray material is heated to 1200.degree.
It was annealed by heating for a period of time to perform a diffusion uniformization treatment on the coating layer. X
By line diffraction, the product of the coating layer was identified to obtain a substantially uniform T
An iAl ₃ phase Al—Cr diffusion coating layer was formed.
Further, the Cr concentration in the surface layer was 2.
It was 7%.

In addition, without mixing Cr powder, TiAl
A material obtained by subjecting only _three powders to plasma spraying and heat treatment under the same conditions as in the above-described examples was used as a comparative material. Diffusion coating layer is TiA
consists of l _3-phase, Cr was not detected.

The test material and the comparative material were tested at 1000 ° C. in air.
The sample was heated and held at 100 ° C. for 100 hours to observe the state of surface oxidation. The surface of the present test material was discolored to brown, while the scale of the comparative material had a thickness of about 100 μm and the scale was peeled off.

[0027]

[Operation and effect] Since the Al-Cr diffusion coating layer on the surface of the Ti-based alloy base material contains 50 to 65% of Al, TiAl ₃
Phase, or TiAl ₂ phase, Al is oxidized in a high temperature oxidizing atmosphere to form an oxide thin film of alumina phase containing Ti oxide. When a small amount of Cr is contained in the Al-Cr diffusion coating layer, TiAl _{3 is} converted from the alumina phase on the outermost surface even in an oxidizing high temperature atmosphere of 1000 ° C.
The diffusion and transfer of oxygen to the phase is prevented, the oxide layer of the alumina phase does not grow and is dense and stable, so that it does not peel off. A
When the Cr concentration in the l-Cr diffusion coating layer is increased to about 8% or more, the alumina-phase oxide layer grows and deteriorates the oxidation resistance. It is considered that this is because the surface is roughened and the vicinity of the surface becomes porous, so that a uniform alumina layer is not formed.

Further, Al-Cr is formed on the surface layer of the Ti-based alloy base material.
If the alloy layer is formed, the Al—Cr alloy layer causes a diffusion reaction with the alloy base material in the course of use in a high temperature oxidizing atmosphere and contains 50 to 65% of Al, so that the TiAl ₃ phase or TiAl ₂ phase is formed. An Al-Cr diffusion coating layer composed of a phase is formed to exhibit oxidation resistance.

When the heat-resistant Ti-based alloy of the present invention is carried out,
A heat resistant alloy excellent in oxidation resistance can be obtained. Especially Ti-1
When a 4-36% Al alloy is used as a base material, it can be used as a heat resistant material at a practical use temperature of about 1050 ° C.

[Brief description of drawings]

FIG. 1 Ti-Al having an Al-Cr diffusion coating layer formed thereon.
Optical micrograph showing the metal structure of the cross section of the alloy before the high temperature oxidation test (magnification: 100, corrosive liquid; hydrochloric acid 1.5 ml)
+ Nitric acid 2.5 ml + hydrofluoric acid 1 ml + water 95 ml).

FIG. 2 EPM of a base material adjacent to an Al-Cr diffusion coating layer
The concentration curve figure of Al and Cr by A analysis.

FIG. 3 Ti-Al on which Al-Cr diffusion coating layer is formed
An optical micrograph showing the cross-sectional metallographic structure of the alloy after the high temperature oxidation test (magnification: 100, corrosive solution; mixed solution similar to FIG. 1).

FIG. 4 is a diagram showing the relationship between the amount of increased oxidation and the Cr concentration after heat treatment.

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

Claims (3)

[Claims] 1. A surface of a Ti-based alloy is 50 to 65 wt% Al.
%, Cr 0.5 to 7 wt% and balance Ti Al-
A heat resistant Ti-based alloy having a Cr diffusion coating layer formed thereon. 2. Al90-99.5 on the surface of the Ti-based alloy.
Al-Cr consisting of wt% and Cr 0.5 to 10 wt%
A heat-resistant Ti-based alloy having an alloy layer formed thereon, the Al-Cr alloy layer having an Al content of 50 to 65 w during use at high temperature.
Al consisting of t%, Cr 0.5 to 7 wt% and the balance Ti
-A heat-resistant Ti-based alloy characterized by being formed in a Cr diffusion coating layer. 3. The Ti-based alloy is 14 to 36 wt% Al.
The heat-resistant Ti alloy according to claim 1 or 2, further comprising: