JPH0788674A - Method for joining ni-ti based shape memory alloy member - Google Patents

Abstract

PURPOSE:To prevent the degradation in the strength in a joint part by the simple method and enable the adaptation to intricate shapes by arranging a multilayered thin-film composite material consisting of >=2 kinds of metals mainly composed of Ni-Ti, etc., between plural Ni-Ti based shape memory alloy members to be joined and alloying and joining these members by a combustion synthesis method. CONSTITUTION:The multilayered thin-film composite material 1 mainly composed of Ni and TI is arranged between the Ni-Ti based shape memory alloy members 2 to be joined and these members to be joined are dissolved slightly and joined by the reaction heat generated by utilizing the combustion synthesis method, which is as follows: The Ni and the Ti induce a synthesis reaction and an Ni-TI intermetallic compd. is formed when the thin-film composite material 1 consisting essentially of Ni and Ti is stored between Ni-Ti based shape memory alloy members to be jointed and heat is inputted at one end of the multilayered thin-film composite material 1 from outside. The unreacted part is heated by the reaction heat generated by this synthesis reaction and the reactions propagate one after another until finally the entire part constitutes the Ni-Ti intermetallic compd. In addition, there is no more formation of different phases exclusive of the Ni-Ti and, therefore, the degradation in the strength of the joint part is lessened.

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 a material 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. Also, the shape of the bead, which is the joint, is 1
It is dimensional, and it is almost impossible to overlap the plates in a two-dimensional manner and join them over a large area by a method other than seam welding. 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. . Two-dimensional joining is also possible. 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 thin-film multi-layer composite material is placed, alloyed by a combustion synthesis method, and joined together. A method of joining a NiTi-based shape memory alloy member is defined in claim 1, wherein the thin-film multi-layer composite material is joined. Later composition is Ni
49 to 52 at%, the composition consisting of the balance Ti, or a part of the above Ni or / and Ti is Fe, Cr, A
2. The composition is adjusted so as to have a composition in which one or more of 1, V, Pd, Mn, Co, Nb, and Cu are substituted in the range of 0.01 to 2 at%. The method for joining NiTi-based shape memory alloy members according to claim 2, wherein the thickness of one thin film of the thin-film multilayer composite is 100.
NiT according to claim 1, wherein the NiT is less than or equal to μm.
The method for joining an i-based shape memory alloy member is claim 3, and the combustion synthesis method is performed in a vacuum or in an atmosphere of an inert gas such as argon or nitrogen.
A method of joining NiTi-based shape memory alloy members according to claim 4, wherein a cooling plate made of a material having good thermal conductivity is brought into contact with the plurality of NiTi-based shape memory alloy members to be joined, and the cooling plate is cooled. A method of joining NiTi-based shape memory alloy members according to claim 1 is characterized in that joining is performed.

[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 in the shape of members in joining, but in order to prevent the decrease in the strength of the joint, it occurs during fusion welding. It is necessary to minimize the molten layer and 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 thin-film multi-layer composite material made of the above-mentioned 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 structure can be made fine and two-dimensional bonding is possible.

According to the present invention, when a thin film multi-layer composite material mainly composed of Ni and Ti is arranged between NiTi type shape memory alloy members to be joined and heat is externally applied to one end of the thin film multi-layer composite material, 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 the minimum and the melted portion is suppressed. Is cooled rapidly and 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 and the seam welding method, the holding of the joining member at the time of joining work may be simply supported, which is similar to the conventional fusion welding method. Further, since the thin-film multi-layer composite material itself has a thin metal plate shape, it can be freely cut or bent according to the shape of the joint. In these respects, the joining method of the present invention has a large degree of freedom in the shape of the joining member, and it is easy to manufacture an element or member having a complicated shape. Further, the joining work itself can be performed very easily.

In the present invention, the composition of the thin film multi-layer composite material after bonding is adjusted to Ni 49 to 52 at%.
This is because the joint portion has the same composition as the composition of the usual NiTi-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 may be Fe, Cr, A
Substituting one or more of 1, V, Pd, Mn, Co, Nb, and Cu in the range of 0.01 to 2 at
Similar to the above, the usual NiTi-based shape memory alloys and superelastic alloys contain the above-mentioned third elements such as Fe and Cr as Ni.
This is because, by substituting Ti and Ti, the shape memory characteristics and mechanical properties are improved, and the same composition is used in the present invention.

In order to adjust the composition of the above-mentioned thin film multi-layer composite material, Ni and Ti blanks are alternately laminated and compounded by rolling, or Ni or / and Ti are mixed with a third element such as Fe and Cu. Added Ni-Fe and Ti
The composition is adjusted by compounding using a base plate made of -Cu. In this case, the reaction is performed by the combustion synthesis method, but when a Ni-Ti alloy plate or a Ni-Ti alloy plate in which a third element is added to the base plate is used, the base plate itself has already been alloyed. Therefore, the reaction does not occur or the reaction becomes insufficient even by the combustion synthesis method, and good joining cannot be obtained. As a method for adjusting the composition, Ni and T
It is also possible to use the respective raw plates of i and the third element, and change the size and the number of the respective raw plates to form a composite. In this way, it is desirable that the thickness of the thin film of the thin film multilayer composite material that is rolled and composited is 100 μm or less. 100 μm
If the thickness exceeds the above range, the reactivity may be deteriorated and the composition after the reaction may be greatly varied to deteriorate the uniformity. 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, NiT
The i-based shape memory alloy includes a NiTi-based superelastic alloy.

[0016]

EXAMPLES An example of the present invention will be described below.
Ten Ti plates with a thickness of 0.81 mm and Ni with a thickness of 0.53 mm
Ten plates were alternately stacked and cold-rolled to a rolling reduction of 95% to produce a thin-film multilayer composite material having a thickness of 0.7 mm consisting of Ni of 51.0 at% and the balance of Ti. On the other hand, the composition was 51.0 at% N by ordinary melt casting and hot rolling.
A NiTi shape memory alloy plate of i was prepared and used as a base material. The oxide film on the surface of the base material plate was removed by polishing. Next, as shown in FIG. 1, L-shaped bent plates of the NiTi-based shape memory alloy base material 2 are put together, the thin-film multilayer composite material 1 of the same size is sandwiched between the seams, and water-cooled for cooling. It is a base material with copper block 3 and is sandwiched from both sides. This is 10 ^-5
In a vacuum of torr, one end of the thin-film multilayer composite material 1 was ignited by energizing and heating the resistance heating wire 4 for ignition to cause a reaction.
By igniting one end of the thin film multilayer composite material 1, the reaction heat was successively propagated by the heat of reaction and melted. The base material plate also melted slightly. These were immediately solidified by cooling with the water-cooled copper block 3. In this way, it was possible to join the two L-shaped plates. On the other hand, for comparison, an L-shaped NiTi-based shape memory alloy was similarly welded by the conventional seam welding method.

A schematic view of the metallographic structure of the cross section of these joints is shown in FIGS. 2 and 3. 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 or between the columnar crystals. In contrast,
According to the method of the present invention, as shown in FIG. 2, the entire joint has a fine and uniform structure, and no phase other than NiTi has occurred. Further, the deviation from the composition value of the composition was within 0.1 at%.

A peel test was conducted to examine the bonding strength. An outline of the peeling test method is shown in FIG. Bonding members having the same shape were produced by the method of the present invention and the conventional method, respectively, and a tensile load was applied in the direction of the arrow in FIG. With the method of the present invention, the fracture did not occur up to about 1.8 times the load of the method with the conventional method.

Further, the same Ni plate, Ti plate and F as described above are used.
The composition after joining the thin-film multilayer composite is Ni5 using the e-plate.
The thin-film multi-layer composite material was prepared by adjusting the number of blanks so that the content was 0.5 at%, Fe 0.2 at%, and the balance was Ti. Then, as a result of observing the structure of the joint portion and conducting a bending test in the same manner as described above, substantially the same result as in the case of the method of the present invention was shown.

[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 joints and to form a fine and uniform structure, and because the formation of heterogeneous phases other than NiTi is also eliminated, compared to the conventional fusion welding method. As a result, the decrease in the strength of the joint is reduced.
In addition, it is possible to easily perform two-dimensional overlapping and joining over a wide area. Further, unlike the pressure welding method and the seam welding method, the degree of freedom of the shape of the joining member is large, and moreover, heating can be performed only by electric heating of the resistance wire, so that the joining can be easily and easily performed.

[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 diagram showing a peeling test method according to an embodiment of the present invention.

[Explanation of symbols]

 1 Thin Film Multilayer Composite Material 2 NiTi Shape Memory Alloy Base Material 3 Water-Cooled Copper Block 4 Ignition Resistance Heating Wire 5 Joint

Claims (5)

[Claims] 1. A thin film multilayer 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 composed mainly of Ni and Ti respectively. A joining method for a NiTi-based shape memory alloy member, comprising arranging a composite material, alloying it by a combustion synthesis method, and performing joining. 2. The composition of the thin-film multi-layer composite material after bonding is Ni 49 to 52 at%, and the balance Ti.
Alternatively, a part of the above Ni or / and Ti may be Fe, C
1 of r, Al, V, Pd, Mn, Co, Nb and Cu
It adjusts so that it may become a composition which substituted in the range of 0.01-2at% by 1 type or 2 types or more.
A method for joining NiTi-based shape memory alloy members as described. 3. The method for joining NiTi-based shape memory alloy members according to claim 1, wherein the thin film of the thin film multilayer composite has a thickness of 100 μm or less. 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 cooling plate made of a material having good thermal conductivity is brought into contact with the plurality of NiTi-based shape memory alloy members to be bonded, and the bonding is performed while cooling. The method for joining NiTi-based shape memory alloy members of.