JPH06322413A - Method for joining niti shape memory alloy - Google Patents

Abstract

PURPOSE:To join Ni and Ti shape memory alloy members without deterioration in the strength of the joint part by arranging a powder compressed body of a metal mixture or alloy consisting of Ni and Ti between both members and alloying and connecting the members by a combustion synthesis method at the time of joining the Ni and Ti shape memory alloy members. CONSTITUTION:The compressed body 1 consisting of <=100mum powder of the metal mixture or alloy of the compsn. which consists of 49 to 52atm.% Ni and the balance Ti or in which a part of the Ni and Ti are substd. within one kind or >=2 kinds among Fe, Cr, Al, V, Pd, Mn, Co, Nb and Cu in a 0.01 to 2atm.% range is arranged between two pieces of the Ni and Ti shape memory alloy members 2, 2 at the time of joining these members 2, 2. The combined bodies are held by copper blocks 3, 3 for water cooling from above and below. The powder metal compressed body 1 is ignited to melt by electrical heating with a resistance heating wire 4 for ignition in a vacuum or inert gaseous atmosphere of Ar, N, etc., and is simultaneously cooled by the copper blocks 3 for water cooling to prevent melting of the shape memory alloy members 2, 2, by which both shape memory alloy members 2, 2 are easily joined in the joint part without having the degradation in the strength.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to joining members made of NiTi type shape memory alloy and superelastic alloy.

[0002]

2. Description of the Related Art The shape memory effect and the superelastic effect of NiTi-based shape memory alloys both have a small transformation hysteresis.
This is due to the so-called thermoelastic martensitic transformation, and the shape memory effect is a phenomenon in which something deformed in the martensite temperature region returns to its original shape when heated above the martensite reverse transformation (austenite transformation) temperature. . On the other hand, the superelastic effect is a phenomenon in which a material deformed in the austenite temperature region elastically returns to its original deformation strain of 8% even without heating due to the stress-induced martensitic transformation accompanying deformation. Is. (Hereinafter, shape memory alloys and superelastic alloys are simply referred to as shape memory alloys).

Of the materials exhibiting such a shape memory effect and superelasticity effect, NiT is the most practically used material.
There are i-based alloys. Practical applications of this NiTi-based alloy that apply the shape memory effect include air outlets for air conditioners, pressure regulating valves for rice cookers, bone plates for medical use, and the like. In addition, there are orthodontic wires, brassieres wires, eyeglass frames, medical guide wires, etc. that have been put to practical use by applying the superelastic effect.

Furthermore, at the present time, peripheral technologies are being developed along with such practical use. One of them is Ni
There is a Ti-based alloy joining technology. One of the merits brought about by the establishment of the joining technology is that elements and members having complicated shapes can be manufactured with a high material yield. In particular, the NiTi-based shape memory alloy is not very good in machinability and is expensive, so that the merit is considered to be very large. In addition, if shape memory alloys having different operating temperatures can be joined together, the range of application of the present alloy will be further expanded.

[0005]

Conventionally, NiTi-based shape memory alloys can be joined by fusion welding such as laser welding, TIG welding, electron beam welding or pressure welding such as flash butt welding or friction welding. Is. However, in the fusion welding method, a weld metal having a cast structure of columnar crystals is produced, which causes a decrease in strength and a crack. In addition, the shape memory effect may be impaired by the precipitation of intermetallic compound phases other than the NiTi phase such as NiTi ₂ and Ni ₃ Ti and the inclusion of impurities from the atmosphere and the oxide scale of the base material. On the other hand, in the pressure welding method, almost no molten layer is generated, or even if it occurs, it is possible to extrude by pressure so that the molten layer does not remain at the bonding interface, so the decrease in the strength of the bonded portion can be reduced. . However, in the pressure welding method, the shapes of members and joints that can be joined are very limited, and it is not possible to fabricate elements or members having complicated shapes.

According to the present invention, as a result of studying the above problems,
This is a joint method developed by a simple method that can be applied to a joint member having a complicated shape with little decrease in the strength of the joint.

[0007]

According to the present invention, between a plurality of NiTi-based shape memory alloy members to be joined, two or more kinds of metals mainly containing Ni and Ti or an alloy containing Ni and Ti as main components, respectively. A mixed powder compressed body consisting of is arranged, alloyed by a combustion synthesis method, and joined together. A method for joining a NiTi-based shape memory alloy member according to claim 1, wherein the composition of the mixed powder compacted body is Is Ni49-5
2 at%, the balance consisting of Ti, or the above Ni
Or / and part of Ti is Fe, Cr, Al, V, P
The NiTi-based shape memory alloy member according to claim 1, which has a composition in which one or more of d, Mn, Co, Nb, and Cu are substituted in the range of 0.01 to 2 at%. The joining method is claim 2, and the particle size of the powder of the mixed powder compact is 100 μm or less. The joining method of the NiTi-based shape memory alloy member according to claim 1 is claim 3, and the combustion is performed. The method of synthesizing the NiTi-based shape memory alloy member according to claim 1, wherein the synthesizing is performed in a vacuum or in an atmosphere of an inert gas such as argon or nitrogen. The method for joining NiTi-based shape memory alloy members according to claim 1, wherein a cooling plate made of a material having a good thermal conductivity is brought into contact with and the joining is performed while cooling. is there.

[0008]

It is clear that it is advantageous to use the fusion welding method or a method close to it in order to increase the degree of freedom of the member shape in the welding, but in order to prevent the decrease in the strength of the welding method, it is clear. It is necessary to minimize the molten layer produced during contact and to make the structure of the molten layer fine.

The present invention has been made on the basis of the above-mentioned idea, and when joining a NiTi type shape memory alloy and a superelastic alloy, two or more kinds mainly containing Ni and Ti are provided between the members to be joined. The mixed powder compression body made of the above metal or an alloy containing Ni and Ti as the main components is arranged, and alloyed and joined by the combustion synthesis method. Further, in order to reduce the penetration of the base material and to obtain a fine structure of the molten layer, a cooling plate made of a material having good thermal conductivity is brought into contact with the joint portion to cool it.
The present invention by such a method has a high degree of freedom in the shape of the joining member, which is a feature of the fusion welding method, and reduces the molten layer,
The tissue can be made fine.

According to the present invention, a mixed powder compact mainly composed of Ni and Ti is arranged between NiTi-based shape memory alloy members to be joined, and heat is applied to one end of the mixed powder compact from the outside. Ni and Ti undergo a synthetic reaction to form a NiTi intermetallic compound, the unreacted portion is heated by the reaction heat generated by this synthetic reaction, the reaction propagates one after another, and finally the whole becomes a NiTi intermetallic compound. By using the combustion synthesis method described above, the members to be joined can be slightly melted by the reaction heat generated at this time to join.

Further, according to the present invention, since the cooling plate made of a material having a good thermal conductivity is brought into contact with the joint portion to perform the joint while cooling, the melting of the joint member is suppressed to a minimum and the melted portion is Since it is cooled rapidly, it has a fine structure, and the decrease in strength of the joint due to the molten layer, which is a disadvantage of the conventional fusion welding method, is reduced.

In the conventional fusion welding method, the heat for melting the member must be supplied from the outside over the entire welded portion by means of an arc, an electron beam, etc. Therefore, the entire welded portion should be cooled by a cooling plate as in the present invention. Is impossible. Even if the cooling plate has a shape that can be used, the heat supplied is lost by using the cooling plate, and it becomes difficult to heat the joint portion.

In the present invention, the heat for melting the joint is generated internally from the synthesis reaction, and the amount of heat is very large. Therefore, it is easy to heat and melt the joint while cooling with the cooling plate. Further, in the joining method of the present invention, unlike the pressure welding method, the holding of the joining member at the time of joining work is simply supported, and since it is close to the conventional fusion welding method, the degree of freedom of the shape of the joining member is large and complicated. It is easy to fabricate elements and members of various shapes.

In the present invention, the composition of the above-mentioned compressed powder compact is set to 49 to 52 at% of Ni by the ordinary NiT.
This is because the composition is the same as that of the i-based shape memory alloy and the superelastic alloy, and the respective properties are not exhibited outside the range of this composition. Further, a part of the above Ni or / and Ti is Fe, Cr, Al, V, Pd, Mn, C.
One or more of o, Nb, and Cu is 0.01 to
Substitution within the range of 2 at is the same as in the case of ordinary Ni.
In Ti-based shape memory alloys and superelastic alloys, Ni and Ti are replaced by the above-mentioned third elements such as Fe and Cr to improve mechanical properties and corrosion resistance. This is because the composition is

Further, the particle size of the powder of the above-mentioned compressed powder mixture is set to 100 μm or less. When the size exceeds 100 μm, the reactivity is deteriorated, and the dispersion of the composition after the reaction is increased to deteriorate the uniformity. There is a risk. Further, in the above combustion synthesis method, it is desirable to carry out the bonding in a vacuum or in an atmosphere of an inert gas such as argon or nitrogen, whereby oxidation of the bonded portion is prevented and good bonding can be achieved. As described above, in the present invention, the NiTi-based shape memory alloy includes a NiTi-based superelastic alloy.

[0016]

EXAMPLES An example of the present invention will be described below.
An atomic ratio of Ti powder and Ni powder having an average particle diameter of 30 μm is 4
Formulated to be 9.0: 51.0 (51.0 at%
Ni), which was mixed with a ball mill. About 10 g of this mixed powder was molded by cold pressing to prepare a rectangular rod-shaped compressed powder compact. On the other hand, a plate of a NiTi shape memory alloy having a composition of 51.0 at% Ni was produced by ordinary melt casting and hot rolling, and was used as a joining member. The oxide film on the surface of the member was removed by polishing. Next, as shown in FIG.
With the mixed powder compact 1 sandwiched between the two NiT
The plates of the i-based shape memory alloy member 2 are butted, and sandwiched from both sides with a water-cooled copper block 3 for cooling. This is 10 ^-5 torr
In the vacuum of r, one end of the mixed powder compact was ignited by energizing and heating the resistance heating wire 4 for ignition to cause a reaction. By igniting one end of the mixed powder compact, reactions were successively propagated by the heat of reaction and melted. The member plate also melted slightly. These solidified immediately upon cooling with a water-cooled copper block. In this way, the two plates could be easily joined.

2 and 3 are schematic diagrams of the metal structure of the cross section of the joint after the reaction. FIG. 2 shows the joint by the method of the present invention, and FIG. 3 shows the joint by the conventional fusion welding method. In the conventional fusion welding method of FIG. 3, solidification proceeds as coarse columnar crystals upward along the direction of heat flow, and in particular, the elongation in the direction perpendicular to the columnar crystals and the impact value decrease. Further, a heterogeneous phase such as Ni ₃ Ti is likely to occur at the tips and gaps of the columnar crystals. On the other hand, in the method of the present invention, as shown in FIG. 2, the entire joint had a fine and uniform structure, and no phase other than NiTi was generated. Further, the deviation from the composition value of the composition was within 0.1 at%.

In order to examine the tensile strength of the joint, a dumbbell-shaped tensile test piece was cut out from the sample and a tensile test was conducted. The shape of the test piece is shown in FIG. All fractures occurred at the joint, but the tensile strength of the joint was 50% to 60% of the tensile strength of the member by the conventional method, whereas about 80% of the member by the method of the present invention was used. Rose to.

Further, using the same powder as described above, Ni50.
5 at%, Fe 0.2 at%, and remaining Ti were compounded, a mixed powder compact was prepared in the same manner as above, and the structure of the joint was observed and the tensile test was conducted in the same manner as described above. The result is almost the same as that of the method of the present invention.

[0020]

As described above, according to the present invention,
When joining NiTi-based shape memory alloys, it is possible to suppress the formation of columnar crystals in the joint to form a fine and uniform structure, and to eliminate the formation of different phases other than NiTi. As a result, the decrease in the strength of the joint is reduced.
Also, unlike the pressure welding method, the degree of freedom of the shape of the joining member is great,
In addition, since heating can be performed only by conducting heating of the resistance wire, there is an effect that joining can be performed easily and easily.

[Brief description of drawings]

FIG. 1 is a schematic view of a method for joining NiTi-based shape memory alloy members according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of a metallographic structure of a cross section of a joint portion of a NiTi-based shape memory alloy member joined by the joining method of the present invention.

FIG. 3 is a schematic diagram of a metal structure of a cross section of a joint portion of a NiTi-based shape memory alloy member joined by a conventional joining method.

FIG. 4 is a schematic view showing the shape of a tensile test piece according to an example of the present invention.

[Explanation of symbols]

 1 Compressed Powder Mixture 2 NiTi Shape Memory Alloy Member 3 Water-Cooled Copper Block 4 Resistance Heating Wire for Ignition 5 Joint

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location B23K 103: 08

Claims (5)

[Claims] 1. A mixed powder comprising a plurality of NiTi-based shape memory alloy members to be joined and made of two or more kinds of metals mainly composed of Ni and Ti or an alloy mainly composed of Ni and Ti respectively. A method of joining a NiTi-based shape memory alloy member, comprising arranging a compressed body, alloying by a combustion synthesis method, and joining. 2. The composition of the mixed powder compact is Ni4
9 to 52 at%, the balance consisting of Ti, or a part of the above Ni or / and Ti is Fe, Cr, Al,
One or two of V, Pd, Mn, Co, Nb and Cu
The method for joining NiTi-based shape memory alloy members according to claim 1, wherein the composition is a composition in which at least one species is substituted in the range of 0.01 to 2 at%. 3. The particle size of the powder of the compressed powder mixture is 1
The N according to claim 1, which is less than 00 μm.
A method for joining iTi-based shape memory alloy members. 4. The method for joining NiTi-based shape memory alloy members according to claim 1, wherein the combustion synthesis method is performed in vacuum or in an atmosphere of an inert gas such as argon or nitrogen. 5. The joining of NiTi-based shape memory alloy members according to claim 1, wherein a cooling plate made of a material having a good thermal conductivity is brought into contact with the joining portion and the joining is performed while cooling. Method.