JPS64460B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for heat treating Ti-8Al-1Mo-1V alloy.

[Prior art] Ti-8Al-1Mo-1V alloy has poor hot workability, but it has the lowest density and high elastic modulus among titanium alloys, and is used for disks and blades in the compressor section of jet engines. .

The disks and blades in the compressor section of jet engines are exposed to high temperatures for long periods of time, so
Excellent functional properties are required, especially strength, creep resistance and toughness.

By the way, Ti-8Al-1Mo-1V alloy is often used as a solution aged material.

Conventionally, the heat treatment method for Ti-8Al-1Mo-1V alloy is to perform oil cooling (OQ) or water cooling (WQ) after solution treatment at 980℃~ (19℃ lower than β transformation point) for 1 hour, followed by aging. Method of treatment: Solution treatment at 980°C to 1010°C for 1 hour, followed by air cooling (AC) or faster cooling, followed by aging Treatment Method: Solution treatment at 899°C to 927°C for 1 hour, followed by oil or water cooling. These methods are specified by AMS (AMS4972C specifies bars, etc., and AMS4973C specifies forgings, etc.). ).

Materials heat-treated by this conventional method have the following creep characteristics.

Holding temperature 454℃ Creep load 28.1Kgf/ ^mm2 Holding time 28 hours Creep deformation 0.085% or more [Problems to be solved by the invention] In recent years, with the aim of increasing the output and thermal efficiency of jet engines, The gas temperature is increasing, and in order to withstand such high temperatures, Ti-8Al-1Mo-1V alloys are required to have higher creep resistance.

However, attempts to improve creep resistance lead to a decrease in other mechanical properties such as tensile properties and toughness.

Therefore, there has been a desire for a heat treatment method that can improve creep resistance without deteriorating other mechanical properties such as tensile properties and toughness.

[Means for solving the problem] The above problem is solved by using Ti-8Al-1Mo-1V alloy.
The problem is solved by a heat treatment method for a Ti-8Al-1Mo-1V alloy, which is characterized by solution treatment at a temperature 5 to 19° C. lower than the β transformation point, cooling, and then aging treatment.

In the present invention, the Ti-8Al-1Mo-1V alloy is, for example, one specified by AMS or the like.

For example, it has chemical components such as Al: 7.35 to 8.35, Mo: 0.75 to 1.25, V: 0.75 to 1.25, and Ti: the balance in weight percent. of course,
Those containing impurities or selectively added elements in the above-mentioned components are also covered.

Moreover, the processing method is not limited either. That is,
Forged products and cast products are also covered.

In the present invention, solution treatment is performed at a temperature 5 to 19° C. lower than the β transformation point.

Here, the β transformation point changes depending on the chemical composition,
For example, for an alloy with the above composition, 1030-1050℃
It is.

The reason why the solution treatment is carried out at a temperature 5 to 19° C. lower than the β transformation point is as follows.

First, if solution treatment is performed at a temperature 5° C. lower than the β-transform point or higher, the tensile properties will deteriorate, as shown in FIG. 2 (the right side of the shaded area in FIG. 2). In particular, yield strength (0.2%YS), area of area (RA), and elongation (El) decrease rapidly. Also,
If solution treatment is carried out at a temperature lower than 19°C below the β-transform point, the tensile properties will not deteriorate, but as shown in Figure 1 (the left side of the shaded area in Figure 1), the amount of creep deformation will be large. I get used to it.

There are no particular limitations on the retention time for solution treatment and the cooling rate after retention, but for example, AMS4972C,
Hold for 1 hour as specified in 4973C, air cooled (AMS4972C), water cooled or oil cooled (AMS4973C)
do it.

Incidentally, if the cooling is performed rapidly by oil cooling or water cooling, the creep resistance properties are further improved.

Conditions for aging treatment may be selected as appropriate. For example, as specified in AMS4972C, 4973C
What is necessary is just to maintain it at 565-595 degreeC for 8 hours or more, and to air-cool it.

[Function] When the solution temperature is set to a temperature 5 to 19° C. lower than the β transformation point, the amount of pro-eutectoid α decreases, and the microstructure after aging becomes an acicular region with good creep properties.

On the other hand, the tensile properties in the present invention are insensitive to the solution temperature below the β transformation point, and are 5°C below the β transformation point.
Increasing the solution temperature to lower temperatures has little effect.

[Example of the Invention] Rolled round bars of φ13 mm and φ22 m were manufactured using an 80 square billet made from a 1 ton ingot of φ480 mm.

The main chemical composition of this round bar is Ti−8Al−1Mo−
7.77% Al, 1.00% Mo, 1.12% V as 1V alloy,
0.093%Fe, 0.100%O, β transformation point is 1037℃
It was hot.

The samples thus prepared were solution treated at various solution treatment temperatures for 1 hour and then cooled with water. then
After holding at 593°C for 8 hours, aging treatment was performed by cooling in air.

The following characteristics of the sample thus prepared were tested.

(Creep resistance) Creep was conducted under the following test conditions.

Holding temperature: 454℃ Creep load: 28.1Kgf/mm ² Holding time: 23 hours The test results are shown in Figure 1. In FIG. 1, the shaded area is the range of the embodiment of the present invention, and the area to the left of the shaded area is the conventional example. Note that the dotted line indicates the β-transformation point.

While the conventional example shows a creep deformation amount of 0.085% or more, the example shows a good creep deformation amount of 0.05 to 0.08%.

(Tensile properties) Tensile properties were investigated by a tensile test at room temperature. The results are shown in FIG. The shaded area in FIG. 2 is the scope of the embodiment of the present invention,
The portion to the left of the diagonal line is the conventional example. Note that the dotted line indicates the β-transformation point.

It can be seen that the tensile properties of the examples are the same as those of the conventional examples.

However, the tensile properties rapidly decrease in a temperature range higher than 5° C. below the β-transform point.

(Fracture toughness) Fracture toughness was evaluated using the _K1 value according to the ASTM standard.

The K ₁ value in the example was almost the same as the K ₁ value in the conventional example.

[Effects of the Invention] As explained above, since the present invention is configured as described above, the creep resistance can be significantly improved without reducing mechanical properties such as tensile properties and fracture toughness.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the amount of creep deformation versus solution temperature. FIG. 2 is a graph showing tensile properties versus solution temperature.

[Claims]

1. When forming a thermal spray coating made of various components on the surface of a metal substrate, first pass an electric current through the metal substrate and raise the metal substrate to a predetermined temperature using the Joule heat, and then spray the thermal spray material. Characteristic thermal spraying treatment method for metal surfaces.