JP2648822B2 - Manufacturing method of sintered Ti alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Object of the Invention (1) Industrial application field The present invention relates to a method for producing a sintered Ti alloy, and more particularly, to a method using a mixed powder of a Ti powder composed of titanium sponge and an alloy element powder. The present invention relates to a method for producing a sintered Ti alloy by subjecting a formed green compact to vacuum sintering including a heating step, a sintering temperature maintaining step, and a cooling step.

(2) Conventional technology Conventionally, the degree of vacuum in the entire process of the vacuum sintering process is as follows:
It is set to about 10 ^-3 Toor, and the heating process is performed at a constant heating rate.

(3) Process to be Solved by the Invention Ti powder composed of titanium sponge is generally obtained by reducing titanium tetrachloride with sodium under the application of the Hunter method. Contains chlorine.

Since this chlorine is not sufficiently removed from the green compact by the conventional vacuum degree and temperature raising method, a relatively large amount of pores are generated in the sintered Ti alloy due to residual chlorine, and as a result, the sintered Ti There is a problem that the fatigue strength of the alloy is reduced.

In view of the above, an object of the present invention is to provide a method for producing the sintered Ti alloy, which can remove chlorine more efficiently than a green compact.

B. Configuration of the Invention (1) Means for Solving the Problems The present invention provides a green compact formed by using a mixed powder of a titanium powder composed of titanium sponge and an alloy element powder, a heating process, and a sintering process. In producing a sintered Ti alloy by performing a vacuum sintering process including a temperature maintaining process and a cooling process, the vacuum degree in the entire process of the vacuum sintering process is set to a high vacuum degree of 10 ^-5 Torr or more. Further, the heating step includes a constant-temperature heating step of maintaining a temperature of 600 to 950 ° C. for 1 hour or more.

(2) Function When the degree of vacuum in the entire process of the vacuum sintering process is set to a high degree of vacuum as described above, chlorine is more efficiently removed from the green compact during the process. In particular, in the constant temperature heating step,
Since the sintering of the green compact has not yet started, and thus the pores of the green compact are in communication, the chlorine removal efficiency at this stage is the highest.

If the degree of vacuum is lower than 10 ^-5 Torr, chlorine is not sufficiently removed. Also, even when the degree of vacuum is 10 ⁻⁵ Torr or more, the chlorine removal efficiency is poor when the temperature in the constant temperature heating step is less than 600 ° C., whereas when it exceeds 950 ° C., the chlorine removal efficiency is good in the initial state, Since the sintering gradually starts to progress, the chlorine is easily trapped, and the removal action stops in a high concentration region of the residual chlorine. If the maintenance time is less than one hour, the chlorine removal amount is small regardless of the degree of vacuum and the temperature.

(3) Example [Example] 90% by weight of Ti powder composed of sponge titanium and having a particle size of 100 mesh or less, and 10% by weight of an alloy element powder composed of an Al-V alloy (Al: 60% by weight, V: 40% by weight) Was mixed to obtain a mixed powder.

Using this mixed powder, a rectangular parallelepiped green compact having a length of 10 mm, a width of 10 mm and a length of 80 mm was obtained under the conditions of a pressure of 60 kg / mm ² .

The compact was placed in a vacuum sintering furnace, and then the compact was subjected to vacuum sintering according to the heating pattern shown in FIG. 1 to produce a sintered Ti alloy.

In FIG. 1, A corresponds to a heating process, B corresponds to a sintering temperature maintaining process, and C corresponds to a cooling process. The whole process A ~
The degree of vacuum at C was set at 10 ^-5 Torr.

In the heating process A, the temperature is raised from room temperature to 850 ° C at a heating rate of 10 ° C / min.
Until the 1 TsugiNoboru temperature stage a ₁ to increase the temperature, the constant temperature heating stage a ₂ to maintain over the temperature of 850 ° C. for 4 hours, heating rate 10 ° C. / min
At and a 2 TsugiNoboru temperature stage a ₃ to increase the temperature from 850 ° to 1260 ° C..

The sintering temperature maintaining process was performed at 1260 ° C. for 4 hours.

The cooling process is furnace cooling, and the cooling rate is about 5
° C / min.

[Comparative Example I]

A sintered Ti alloy was manufactured under the same conditions as in the above example except that the degree of vacuum was set to 10 ⁻³ Torr.

(Comparative Example II)

As shown in FIG. ₂ , except for the constant temperature heating step a2 in the above embodiment, a heating process of increasing the temperature from room temperature to 1260 ° C. at a heating rate of 10 ° C./min was adopted, A sintered Ti alloy was manufactured under the same conditions as described above.

Rotating bending fatigue test pieces and tensile test pieces were prepared from the sintered Ti alloys of the examples and comparative examples I and II, and each test was performed on them. The pores were observed with a scanning electron microscope, and the residual chlorine amount was measured with an electron probe microanalyzer.

 The following table shows the results of each test.

As is apparent from the above table, the sintered Ti alloy manufactured according to the present invention has almost no chlorine and very few pores, and as a result, has excellent fatigue strength.

This is the the maintenance of high vacuum, such as, due to the adoption and constant temperature heating step a _2.

Figure 3 shows the temperature and holding time of the thermostatic heating stage a ₂ in vacuum of 10 ^-5 Torr, the relationship between the residual chlorine content of the sintered Ti alloy. In the figure, the line x ₁ temperature 400 ° C., the line x ₂ temperature 600 ° C.
In, a line x ₃ temperatures 850 ° C. (corresponding to the embodiment), the line x ₄ is the temperature 950 ° C., the line x ₅ correspond respectively to the temperature of 1000 ° C..

As is clear from the lines x _{2 to} x ₄ , the residual chlorine amount is greatly reduced by setting the temperature to 600 to 950 ° C. and the maintenance time to 1 hour or more at a vacuum degree of 10 ⁻⁵ Torr, respectively. I understand.

On the other hand, even the degree of vacuum 10 ^-5 Torr, the efficiency of removal of chlorine at a temperature 400 ° C. As the line x ₁ is poor, also to set the temperature so that the line x ₅ to 1000 ° C., chlorine in the initial stage Although the removal efficiency is good, sintering gradually starts to progress, so that chlorine is easily contained and the removal action stops in a high concentration region of residual chlorine. If the maintenance time is less than one hour, the chlorine removal amount is small regardless of the degree of vacuum and the temperature.

FIG. 4 shows the relationship between the residual chlorine content and the fatigue limit in the sintered Ti alloy. It can be seen from FIG. 4 that the fatigue limit decreases as the residual chlorine content increases.

C. Effects of the Invention According to the present invention, the degree of vacuum in the vacuum sintering process is specified as described above, and a specific isothermal heating step is adopted.
By employing such a relatively simple method, a sintered Ti alloy having excellent fatigue strength can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the relationship between the temperature and time of the vacuum sintering process in one embodiment of the present invention, and FIG. 2 is a graph showing the relationship between the temperature and the time of the same process in a comparative example. FIG. 3 is a graph showing the relationship between the residual chlorine amount and the temperature and the maintenance time in the constant temperature heating stage, and FIG. 4 is a graph showing the relationship between the residual chlorine amount and the fatigue limit.

Claims (1)

(57) [Claims] 1. A green compact formed using a mixed powder of a titanium powder composed of titanium sponge and an alloy element powder is subjected to a vacuum sintering process including a temperature increasing process, a sintering temperature maintaining process and a cooling process. In producing a sintered Ti alloy, the degree of vacuum in the whole process of the vacuum sintering process is set to a high degree of vacuum of 10 ^-5 Torr or more, and the temperature is raised to a temperature of 600 to 950 ° C. Characterized by including a constant-temperature heating step of maintaining the temperature for 1 hour or more.