JPS5983736A - Method for melting titanium base alloy - Google Patents

Abstract

PURPOSE:To stably obtain a low oxygen and low carbon Ti-base alloy, by such a melting method wherein the inner surface layer of a crucible is formed of Al2O3, MgO or ZrO2 and the temp. of the molten alloy is held below a critical temp. at which temp., the molten alloy and the crucible inner surface layer are reacted. CONSTITUTION:In an induction heating furnace for melting a Ti-Ni alloy, at least the inner surface layer of a crucible is formed of one or more of Al2O3, MgO and ZrO2. In addition, said alloy is melted while the temp. of the molten alloy is held below a critical temp. at which temp., the molten alloy and the crucible inner surface layer are reacted. For example, when the Ti-base alloy is a Ti-Ni alloy, the temp. of the molten alloy is adjusted to about 1,320- 1,350 deg.C. By this method, the Ti-base alloy low in oxygen and carbon contents and having stable characteristics can be prepared even if the melting method due to induction heating is used.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates in particular to a method for manufacturing titanium-based alloys, such as titanium-nickel (Ti-Ni) alloys.

It is related to its dissolution method.

A typical example of a titanium-based alloy is a +Ti-Ni alloy or some of its constituent elements are other elements (Cu, Fe, etc.)
The alloy formed by substituting with
28518), is a useful alloy.

Ti-based alloys are generally produced by a melting method, but
The melting method described in the above-mentioned US Pat. No. 3.1.74.851 is an argon arc melting method, which is shown to have been carried out on an experimental scale. On the other hand, the above-mentioned Japanese Patent Application Laid-Open No. 1983
-28518 discloses a melting method by induction heating using a graphite crucible.

The reason for using a graphite crucible in the induction heating method is as follows. That is, since the standard free energy of formation of Ti with oxygen is small, + Ti is extremely likely to react with oxygen.

Therefore, when a normal silica (S 102 )-based crucible is used, the reaction occurs through alternating reactions between Ti and SiO2.

This resulted in oxygen being mixed into the molten metal.

Therefore, until now, it was thought that ordinary oxide crucibles could not be used.

As mentioned above, by using a graphite crucible.

Although it becomes possible to melt Ti-Ni alloys by induction heating, it has the drawback that carbon contamination from the graphite crucible into the molten metal is unavoidable, and it is difficult to control the amount of contamination, making it impossible to produce a stable alloy. . That is, as shown in Table 1, the carbon content varied greatly depending on the lot, making it impossible to obtain products of the same type.

Furthermore, Ti was produced using an induction heating melting method using a graphite crucible.
In the -Ni alloy, the martensitic transformation starting point (M
The relationship between the s point) and the N1 concentration is as shown in Figure 1.The correlation between the two is extremely weak compared to that in the Ti-Ni alloy produced by the argon arc melting method, and therefore it is difficult to form the desired shape. It is not easy to produce memory effects.

The inventors thought that such a low correlation was due to the inclusion of carbon, and calculated the corrected amount of nickel using a second-order correction formula.

Corrected nickel concentration (atomic %) - Ni atomic coefficient + C atomic coefficient When the relationship between this corrected nickel atomic coefficient and the Ms point was investigated, as shown in Figure 2, it was extremely high, similar to that by the arc melting method. A correlation was obtained.

Therefore, in the +Tj-Ni alloy, it is necessary to keep not only the oxygen content but also the carbon content low.

In view of the above points, it is an object of the present invention to provide a method for manufacturing a Ti-based alloy containing low oxygen and low carbon.

The present invention provides a method for producing a titanium-based alloy by a melting method, in which the crucible has an inner surface layer of At203.
The method is characterized in that a crucible made of at least one of MgO and Z r O2 is used, and the temperature of the molten metal is kept below a critical temperature at which the molten metal reacts with the inner surface layer of the crucible.

Note that when the titanium-based alloy is a Ti-Ni alloy, the temperature of the molten metal may be approximately 1320°C to 1350°C.

According to the present invention, while using a melting method by induction heating,
Since a low carbon and low oxygen Ti--Ni alloy can be produced, an alloy with desired stable properties can be easily obtained.

An embodiment of the present invention will be described below.

The raw material with TI and N1 adjusted to the required blending ratio is melted using the argon mark method, the resulting seed alloy is charged into the crucible of an induction heating furnace, melting is started at a temperature just above the melting point, and the temperature of the molten metal is lowered to the crucible. The Ni and T1 raw materials were gradually charged while maintaining the temperature at which they would not react with each other (approximately 1320 to 1350°C) to obtain alloy 2. The oxygen content and carbon content of the obtained alloys were measured when a magnesia crucible, an alumina crucible, and a zirconia crucible were used as crucibles.

The results are shown in Table-2. In addition, Table 2-2.

For comparison, argon arc melting and induction heating using a silica crucible are also shown.

In Table 2, the reason why oxygen is mixed into the argon gas product is that Ti is extremely active with oxygen, so all the residual oxygen in the vacuum and the oxygen contained in the argon gas cannot be absorbed into the molten metal. .

As is clear from Table 2, the magnesia crucible.

When using aluminum alumina and zirconia alumina.

The amount of reaction carbon is the same as or less than that of the argon arc melting method, and the amount of reaction oxygen is also extremely reduced compared to when a silica crucible is used, and is close to that of the argon arc melting method. Therefore.

The Ti-Ni alloy obtained by the method of the present invention has a martensitic transformation initiation temperature similar to that of the argon arc melted product.
It has a high correlation with concentration, small variations in memory effect characteristics, and high reliability.

In addition, a graphite crucible becomes unusable after a few heat cycles, but crucibles made of magnesia, alumina, zirconia, etc. can be used more than twice as long, so production costs can be reduced.

In addition, although the +Tl-N+gold alloy was shown in the example, the present invention can also be applied to general Ti-based alloys, which has the industrial advantage of being able to melt a large amount by induction heating.

[Brief explanation of drawings]

Figure 1 shows 'p' produced by the induction heating melting method using a graphite crucible.
The starting point of martensitic transformation of i-Ni alloy and Ni! 1
FIG. 2 is a graph showing the relationship between the corrected nickel content and the martensitic transformation start point of the same alloy.

Claims (1)

[Claims] ], a method for producing a titanium-based alloy by a melting method, in which at least the inner surface layer of the crucible is At203. M
A titanium-based alloy characterized in that it is melted using a crucible made of at least one of gO and ZrO2, and maintaining the temperature of the molten metal below a critical temperature at which the molten metal reacts with the inner surface layer of the crucible. Dissolution method.