JPS61210142A - Ni-ti alloy having superior shock resistance and its manufacture - Google Patents

Abstract

PURPOSE:To obtain an Ni-Ti alloy having superior shock resistance and contg. a very small amount of residual rare earth elements by adding rare earth elements to Ni melted in a vessel lined with a calcia-base material to deoxidize the molten Ni, adding Ti, and solidifying the resulting molten Ni-Ti alloy by cooling. CONSTITUTION:Ni is melted in a vessel lined with a calcia-base material in vacuum or in an Ar atmosphere. Y and other rare earth element such as Ce are added to the molten Ni by such an amount that 50-800ppm rare earth elements remain after solidification by cooling, and they are agitated to deoxidize the molten Ni. A desired amount of Ti is added to the deoxidized molten Ni and the resulting molten Ni-Ti alloy is solidified by cooling to obtain an Ni-Ti alloy contg. 50-800ppm Y and other rare earth element. This Ni-Ti alloy has low oxygen and carbon contents and superior shock resistance and is useful as a shape memory alloy.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a NiTi alloy with excellent impact resistance and a method for producing the same, and in particular to a NiTi alloy with excellent impact resistance useful as a NiTi shape memory alloy and its production method. Regarding the manufacturing method.

[Prior art] NiTi alloy contains 55% by weight of Ni and 45% by weight of Ti.
(±1 to 2% by weight) Alloys have attracted attention in recent years because they exhibit a shape memory effect.

Since Ti is extremely active in NiTi alloy,
A good alloy cannot be obtained by melting using a normal refractory container. Therefore, as a method for producing NiTi alloys, arc melting, high frequency melting using a graphite crucible, etc. have been conventionally used.

[Problems to be Solved by the Invention] However, among the above-mentioned conventional methods, the method using arc melting has the disadvantage that a homogeneous alloy cannot be obtained and, moreover, a casting cannot be obtained.

In addition, in the method using a graphite crucible, carbon (hereinafter abbreviated as C) is likely to be mixed into the alloy, and high-purity NiTi
The alloy was difficult to manufacture.

On the other hand, it has long been known that the mechanical properties and shape memory effect of NiTi alloys are significantly affected by the oxygen (hereinafter abbreviated as 0) content of the alloy. However, in any case, the conventional method cannot obtain a material with a low O content, that is, even if the conventional method uses high purity Ni and Ti raw materials with a low impurity content and melts them, The O content of the obtained alloy is 1100
It is difficult to maintain it below 0pp.

Among the above problems, the problem of C mixing in NiTi alloy can be solved by using a Cao crucible.
Although it has been reported that C contamination can be easily reduced, the problem of zero contamination has not been solved even when a calcia crucible is used.

Therefore, reducing the amount of 0 mixed in NiTi alloys has traditionally been considered an important improvement point for obtaining NiTi alloys with high properties, but at present, it is difficult to carefully examine raw materials and to No serious efforts have been made, and no satisfactory countermeasures have been proposed, with the exception of the selection of options.

[Means for Solving the Problems] The present invention solves the above-mentioned conventional problems and provides a NiTi alloy with an extremely low content of C and 0, and a method for manufacturing the same.

50-800pp of yttrium and/or rare earth elements
After melting Ni in a vacuum or argon atmosphere in a container whose inner surface is made of a NiTi alloy with excellent impact resistance characterized by containing m and a calcia furnace material, yttrium and/or rare earths are melted. A method of adding elements, deoxidizing treatment, and then adding Ti, which is characterized by adding yttrium and/or rare earth elements such that 50 to 800 ppm of rare earth elements remain after cooling and solidification. Excellent impact resistance. A method for producing a N i Ti alloy.

The present invention will be explained in detail below.

In addition, in this specification, "%" represents "weight %".

The composition ratio of Ni and Ti in the NiTi alloy of the present invention is not particularly limited, but in particular, the present invention has a composition ratio of Ni of 55% and Ti of 45%.
% (±1-2%) of N1Tt shape memory alloy.

The NiTi alloy of the present invention contains yttrium and/or
Or 50 to 800 ppm of yttrium and/or rare earth elements in an alloy containing 50 to 800 ppm of rare earth elements.
PM-containing NiTi alloys have 0 mixed into the alloy due to the presence of yttrium and/or rare earth elements (hereinafter sometimes abbreviated as R).
Since it becomes an oxide of a rare earth element such as O2, the zero content is extremely reduced and its impact resistance is greatly improved.

(Yttrium and/or rare earth element oxides produced are absorbed by the slag and furnace wall refractory material.) When the yttrium and/or rare earth element content in the alloy is less than 50 ppm, sufficient O content reduction effect is exhibited. If the yttrium and/or rare earth element content exceeds 800 ppm, the yttrium and/or rare earth element will segregate at the grain boundaries of the alloy, resulting in an alloy with high impact resistance. becomes brittle, resulting in a decrease in impact resistance. A particularly preferred content of yttrium and/or rare earth elements is 100 to 700 ppm. More preferably, Zo.

~500 ppm.

Rare earth elements include Ce, Pr, and Nd.

Pm, Sm, En, Gd, Tb, Dy, Ha, Er,
Any of Tm, Yb, and Ln may be used, but Ce is usually used. These yttrium and/or rare earth elements may be used alone or in combination of two or more.

Next, a method for manufacturing the NiTi alloy of the present invention will be explained.

In the manufacturing method of the present invention, in a container whose inner surface is made of calcia furnace material, under vacuum or argon atmosphere,
First, after dissolving Ni, yttrium and/or rare earth elements are added and deoxidized. The amount of yttrium and/or rare earth elements added at this time is such that the residual amount when cooled and solidified after adding Ti in the subsequent process is 50%.
The amount is such that the amount is ~800 ppm. This addition amount is
For example, the yield of yttrium and/or rare earth elements to be used may be determined in advance through repeated experiments, and the determination may be made based on this.

The method of adding yttrium and/or the rare earth element is not particularly limited, and various methods conventionally used for inoculation etc. can be used.

Note that it is preferable to stir sufficiently after adding yttrium and/or rare earth elements.

Furthermore, in the method of the present invention, it is also useful to blow argon gas into the Ni molten metal to remove inclusions before adding yttrium and/or rare earth elements to the Ni molten metal.

After adding yttrium and/or rare earth elements, Ti is subsequently added to the molten metal.

It is preferable to use high-purity Ni and Ti raw materials, but in the present invention, the 0 content can be reduced by the deoxidizing effect of yttrium and/or rare earth elements added in a later process. Even relatively high raw materials can be used.

In the present invention, calcia furnace materials constituting the inner surface of the container used for melting the alloy include calcia (Cab), larnite (stabilized 2CaOesi02), merwinite (3Cao11MgO・2Si02), anorthite (cao・A1203e2sio2), and CaO. Examples include enriched dolomite.

Such calcia furnace material has a CaO content of 20
% or more, preferably 40% or more, calcia furnace material with a high CaO content easily reacts with oxides, and NiT
It can absorb oxides in the molten i-alloy, greatly reducing the amount of oxides present, and has high stability against Ti and the like, making it possible to melt at high temperatures.

[Function] By containing 50 to 800 ppm of yttrium and/or rare earth elements in the NiTi alloy, the zero mixed in one alloy is removed as yttrium and/or rare earth element oxides, reducing the zero content of the alloy. can be significantly reduced. Moreover, the yttrium and/or rare earth element in one alloy does not reduce the yttrium and/or rare earth element oxide, and the zero content is extremely reliably reduced.

In the present invention, it is possible to normally reduce the zero content of the obtained N i Ti alloy to 800 ppm or less.

[Example] The present invention will be explained in more detail with reference to Examples below.1
The present invention is not limited to the following examples unless it exceeds the gist thereof.

Example 1 Electrolytic nickel (nominal purity 99.9%) and sponge titanium (two types with oxygen content of 0.07% and 0.042%)
was used to produce a NfTi shape memory alloy containing 55% Ni and 45% Ti by blending so that the total amount was 0.8 kg per liter of melting.

The CaO crucible (inner diameter 50 mm) used was made from CaO, a -grade reagent, and after pulverizing it into 20 meshes,
Place it in a crucible mold and harden it well.The hardened crucible is about 9
It was created by calcining in an electric resistance furnace at 00°C for 4 hours. The composition of the CaO crucible is shown in Table 1.

Table 1 Ni raw material was put into a CaO crucible, and this was put into an internal heating type induction furnace with an output of 10 KW and a frequency of 70 KHz.

Ni is first dissolved under a reduced pressure of 1O″″2Pa, then C
The content of e or Y in the cooled and solidified alloy is 0 to 110
A deoxidizing treatment was carried out by adding various amounts of chlorine to give a predetermined value between 0.00 pp and 0.00 pp. Subsequently, high purity argon gas was introduced to a pressure of 5×10 3 Pa, and Ti was added. Then, cast into a Calcia mold, 1 OmmX
I OmmX 1.60 mm square bar samples were cast.

A sample for 0 analysis was cut out from the obtained sample, and 0 was quantified by an inert gas transport dissolution-thermal conductivity method. FIG. 1 shows the relationship between the Ce and Y contents and the O content in the resulting alloy.

In addition, each of the square bar samples was cut into a length of 55 mm,
A Charpy impact test was conducted on the cast surface to determine the relationship between Ce and Y contents and impact resistance. The results are shown in Figure 2.

From Figure 2, the Ce and Y content in the NiTi alloy is 50pp.
It is recognized that impact resistance properties are significantly improved when it is more than m. As is clear from Figure 1, this is due to C in the alloy.
It is presumed that this is because when the e content is 50 ppm or more, the 0 content becomes extremely small. In addition, the Ce content is 80
If it exceeds 0 ppm, the impact resistance properties will decrease;
It is presumed that this is because the Ce component segregates at the grain boundaries of the alloy, making it brittle.

[Effect] As detailed above, the N i Ti alloy of the present invention contains 50 to 800 ppm of yttrium and/or rare earth elements.
Due to the zero absorption effect of yttrium and/or rare earth elements, the zero content in the alloy is significantly reduced, resulting in a low oxygen NiTi alloy. Therefore, the NiTi alloy of the present invention can be prepared using a container whose inner surface is made of calcia furnace material, and is heated under a vacuum or argon atmosphere.
After melting i, yttrium and/or rare earth elements are added and deoxidized, Ti is added and melted, and then cooled and solidified.

According to the present invention, (1) a TiNi alloy with low oxygen content and low carbon content can be easily obtained;

(2) Therefore, the resulting alloy has extremely good impact resistance.

■ An alloy with extremely homogeneous composition can be obtained.

■ Only one melting operation is required.

■ The raw material may have a high oxygen content and can be manufactured using inexpensive raw materials.

(2) The manufacturing cost of the alloy can be lowered by (2) and (2).

■ Can be cast as a casting.

Various effects such as these are achieved, and it is extremely advantageous industrially.

Therefore, the present invention is extremely advantageous in producing particularly excellent NiTi shape memory alloys.

[Brief explanation of the drawing]

Figures 1 and 2 are graphs showing the test results obtained in Example 1. Figure 1 shows the relationship between the Ce and Y contents and O content in the alloy, and Figure 2 shows the relationship between the Ce and Y contents and O content in the alloy. The relationship between the Ce and Y contents and the impact resistance properties is shown.

Claims (2)

[Claims] (1) 50 to 80 yttrium and/or rare earth elements
NiT with excellent impact resistance characterized by containing 0 ppm
i-alloy. (2) In a container whose inner surface is made of calcia furnace material,
This is a method in which Ni is dissolved in vacuum or in an argon atmosphere, then a rare earth element is added and deoxidized, and then Ti is added.
A method for producing a NiTi alloy with excellent impact resistance, characterized in that the NiTi alloy is added so that pm remains.