JPS6053109B2 - Heat treatment method for titanium alloys with high internal friction - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is applicable to, for example, the rotor blades of steam turbine blades, especially when the blades are large in size or high in speed. This invention relates to a heat treatment method for further improving properties.

Rotating blades such as steam turbine blades suffer from fatigue failure due to vibration.

Resonance prevention treatment and vibration damping treatment play an effective role in preventing fatigue failure. However, vibrations in steam turbine blades and the like are complex, and it is difficult to completely prevent resonance from a design point of view. Therefore, vibration damping becomes important.
Aerodynamic damping is a factor that dampens rotor blade vibration.
ng), route damping (RO()tdampin
g), mechanical, damping (Mechanica
ldamping), material damping (Ma
terial damping).

The total damping of these factors
Although there are various opinions regarding the contribution rate to mping), it is said that there are many cases in which material damping plays a large role. In fact, in many cases today, steam turbine blade materials are made of materials with high internal friction.
3Cr-Mo steel etc. are used. In general, titanium alloys have a high specific strength, so when the blade becomes faster or larger,
In order to reduce the load on the rotor, it can be used in rotary blades such as steam turbine blades, especially Ti-6A]
-4V alloy has the highest usage record among titanium alloys (approximately 7
0% or more), it can be considered for use in rotary blades such as steam turbine blades, and some examples have already been put into practical use. However, conventional practical Ti-6Al-4V alloys subjected to annealing treatment or quench aging treatment are not the same as those actually used as steam turbine blade materials, such as the above-mentioned 13Cr-Mo steel. In comparison, its internal friction is significantly lower, and no damping effect due to material damping can be expected.

Therefore, as a result of various researches, the inventors of the present invention found that (α
+β) It was discovered that internal friction can be significantly improved by rapidly cooling a titanium alloy from an appropriate temperature in the (α+β) phase region, and a patent application was filed in 1977-307. However, the (α+β) titanium alloy, for example a Ti-1-4V alloy, was thermally unstable as its internal friction decreased when heated and held at 100'C or higher.

Furthermore, since the higher the absolute value of internal friction is, the more advantageous it is to prevent fatigue failure, from this point of view as well, it has been desired to further increase the absolute value of internal friction. In view of these circumstances, the present invention was proposed for the purpose of providing a heat treatment method for improving the internal friction and thermal stability of titanium alloys.
Al5.5-6.75% by weight (hereinafter expressed as %), V1-
A heat treatment method characterized by heating and holding a titanium alloy consisting of 5%, MOl ~ 5%, but V+MO≧5% and the remainder being Ti and normal impurities at a temperature 125°C lower than the β transformation point and then rapidly cooling it. I will provide a.

The present invention will be described in detail below with reference to Examples.

First, the target alloy to be subjected to the method of the present invention will be explained. Titanium alloy with the composition shown in Table 1 was melted using the button melting method.
Melt 0gr and forge it to 20gr, and further (α+
β) 1−×15 for forging? It was formed into a corner and subjected to the following tests.

That is, each of these materials was rapidly cooled (water quenched) from each quenching temperature shown in Table 2, and the internal friction and mechanical properties were examined. The internal friction was measured using a transverse vibration type internal friction measuring device with a vibration damping capacity of 9-1. The shape of the test piece is 2T1$t
Thickness x 10W 1m width x 90m length. Table 2 also shows the measurement results of the internal friction of each material. According to the results, it can be seen that there is almost no effect of MO addition when comparing material B containing 0.64% MO with Ti-4V alloy (material A), which is a conventional standard alloy.

However, C, D, E, F, G, H to which MO is further added
It can be seen that the internal friction of material A is significantly improved compared to material A. This fact can be interpreted as follows.
The present inventors have previously discovered that internal friction can be increased by bringing the metastable β phase to room temperature in a titanium alloy by rapidly cooling it from a certain temperature range.
Is this effect due to allotropic transformation in titanium alloy? J stabilizing element (I
sOmOrphOusβ-Stabilzer) appears to play a major role. It was also confirmed that the internal friction of the Ti-J-4V alloy containing one of the β-stabilizing elements described above increases by rapid cooling from the temperature in the (α+β) phase region. Therefore, based on the conventional Ti-6A1-4V alloy, we investigated the case where MO, which is another allotropic transformation type β stabilizing element, was added, and as a result, the present invention was completed.

In other words, when comparing material D and material G in Table 2, both have ■+M
O+6.9, and the internal friction is almost the same. As mentioned above, V
, MO have been commonly used in titanium alloys because they have the same effect, and as a way to quantitatively assess the effect of combined addition, ■Equivalent (1 x V (%) + 1.3 x MO (
The concept of %)) has been proposed, but these things are
This almost agrees with the above test result that +MO=- constant and the internal friction is equal. Therefore, if V+MO=-constant, it can be considered that the effect of improving the internal friction of the titanium alloy is the same. Specifically, the composition range of ■ and MO is ■+MO=≧5
%, preferably ■+MO≧6%, it is clear from the test results shown in Table 2 that internal friction is significantly improved. Also, from the test results for Dou+B material, MO≧1
%, and in order for ■ and MO to be considered equivalent to each other both qualitatively and quantitatively, and for a synergistic effect of V<5M0 to be expected, ■≧1% must be satisfied. Next, the thermal stability of each material shown in Table 1 will be described.

Figure 1 shows materials A, D, and E in Table 1 at 100°C and 15°C.
The internal friction was measured at room temperature after heating and holding at 0° C. and 200° C. for 1 hour and air cooling, respectively. The results are shown below. In the figure, the horizontal axis indicates the temperature at which the temperature was maintained. As can be seen from the figure, alloys D and E, which are the target of the present invention, maintain a high internal friction value even at high temperatures and have better thermal stability than the conventional standard alloy Ti-6A1-4■ alloy (A material). It turns out that it is excellent. In particular, material E has a high absolute value of internal friction and a low rate of decline at high temperatures, making it extremely superior. As you can see from the above explanation, V<! :． M.O.
When a combination of titanium and titanium is added, the internal friction is improved more than expected from conventional considerations such as V equivalent, and a titanium alloy with excellent thermal and thermal stability is obtained. I understand that.

However, it is generally said that an excess of β-stabilizing elements increases density and lowers specific strength, but also lowers Young's modulus and reduces ductility and toughness. The amount must be kept within a composition range that increases internal friction without severely compromising Young's modulus and ductility/strength.

Table 3 shows the results of examining the mechanical properties of each material listed in Table 1. There's no big difference.

However, it can be seen that material F containing 5.41% MO had significantly lower elongation in the tensile test and 2 mV notched py impact value than the other test materials, and had lower ductility, patternability, and Young's modulus. Therefore, in order to increase internal friction without impairing Young's modulus, ductility, and patternability, MO needs to be 5% or less. Further, since V has the same effect as MO, its composition range is set to 5% or less. The amount of Al was set at 5.5 to 6.75%, as is well known, as it is necessary to prevent embrittlement and increase strength.

Next, the heat treatment conditions of the present invention will be explained.

Materials A, C, D, and H shown in Table 1 were rapidly cooled (water quenched) from arbitrary temperatures in the (α+β) and β phase regions, and the internal friction was measured. The measuring device and the shape of the test piece used were the same as those described above. Figure 2 shows A and C above.
, D, and H materials showing the relationship between quenching temperature and internal friction.

The internal friction of the conventional Ti-6A14V alloy (material A) reaches its maximum when the quenching temperature is approximately 180° C. lower than the β-transform point of the alloy. It has also been confirmed that when the quenching temperature exceeds the β transformation point, the internal friction becomes extremely small, and this is also described in the specification of Japanese Patent Application No. 1983-30. On the other hand, materials C, D, and H, which are alloys subjected to the method of the present invention, have a very high quenching temperature that is 100°C lower than the β-transformation point of the alloy, but the quenching temperature is 150°C lower than the β-transformation point. It can be seen from Figure 2 that the internal friction decreases as the temperature increases.

Next, FIG. 3 shows the measurement results of changes in internal friction due to heating aging after rapid cooling treatment for Materials A and D, that is, the results of a thermal stability test.

The horizontal axis indicates the heating holding temperature of the heat-treated material. The measurement was performed after the heat-treated material was held at the same temperature for 1 hour and then air-cooled. In the figure, RD material: (β transformation point - 50° C.) heat treated means that the RD material was rapidly cooled from a temperature 50° C. lower than its gradual φ transformation point. The following can be seen from Figure 3.

Even if the conventional alloy Ti-6A1-4 alloy (A material) is heat-treated at a temperature that is 180'C lower than the temperature at which the internal friction improves the most, that is, the β transformation point of A material, it is subsequently heated and held at 200°C. The internal friction decreases to 0.001 or less after quenching.On the other hand, the D material of the alloy treated with the method of the present invention is quenched at a temperature 100°C lower than the β transformation point of the alloy, that is, the quenching temperature Even if the value is low, the internal friction is 0.001
That's all. Furthermore, for those quenched at a temperature 50℃ lower than the β transformation point, that is, for those with a high quenching temperature, the temperature is 200℃.
There is almost no decrease in internal friction, and thermal stability is excellent. From the above results, if the alloy processed by the method of the present invention is rapidly cooled from a quenching temperature that is 125°C lower than the β-transformation point of the alloy, a very large internal friction can be obtained, and thermal stability can also be achieved. I can see that it is excellent.

Note that within this quenching temperature range, the higher the quenching temperature, the better the thermal stability of internal friction. As detailed above, the present invention provides a heat treatment method that further increases the internal friction and thermal stability of titanium alloys, which have large internal friction and excellent thermal stability, and which It is suitable for use in locations where vibration excitation is unavoidable, such as on blades.

[Brief explanation of the drawing]

Figures 1 and 3 are diagrams showing the thermal stability of the vibration damping ability of the alloy treated with the present invention and the conventional alloy, and Figure 2 is a diagram showing the thermal stability of the vibration damping capacity of the alloy treated with the present invention and the conventional alloy. There is a diagram showing the relationship with input temperature.

Claims (1)

[Claims] 1 Al5.5-6.75% by weight percent, V1-
Internal friction characterized by heating and holding a titanium alloy consisting of 5% Mo, 1 to 5% Mo, but V+Mo≧5% and the remainder being Ti and normal impurities at a temperature 125°C lower than the β transformation point and then rapidly cooling it. heat treatment method for large titanium alloys.