JPH1150282A - Surface treating method for and production of shape memory alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface treating method capable of sufficiently removing oxidized coating formed on the surface of a shape memory alloy and to provide a method for producing an alloy in which defects at the time of cold working caused by oxidized coating are suppressed and good in appearance. SOLUTION: This surface treating method for a shape memory alloy is the one in which a shape memory alloy composed of, by atom 0 to 49% Ni, 48 to 52% Ti, 3 to 52% Pd, and the balance impurities is pickled with mixed acid contg. 10 to 300/l HF and 400 to 900 g/l HNO3 . The method for producing the shape memory alloy is the one in which an ingod of a shape memory alloy is subjected to hot working and cold working, and, before, in the process of or after the cold working, pickling treatment is executed with mixed acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a NiTiPd-based alloy or TiPd having superelasticity or shape memory physical properties.
The present invention relates to a surface treatment method for a Ni-based alloy and a method for producing a NiTiPd-based alloy material or a TiPd-based alloy.

[0002]

2. Description of the Related Art An oxide film is usually present on a metal surface. This oxide film has the advantage that it plays a role of a lubricant during the manufacturing process such as hot working and cold working of the alloy material, but when its thickness increases, the wire drawing, during cold working such as rolling, It can cause cracking and breaking. Therefore,
It is often preferable to control the thickness of the oxide film to be appropriately thin. In addition, for applications such as medical treatment, decoration, and general living, there are cases where the alloy is exposed and used. In such a case, the surface of the alloy is required to be clean or beautiful. Therefore, in a final step of the production, a non-smooth oxide film containing a large amount of impurities formed during the production step is once removed to obtain a metallic luster.

As a treatment method for an oxide film formed on a metal surface, for example, a method of performing a pickling treatment of cleaning the surface with an acid can be mentioned. It is believed that the pickling treatment dissolves the matrix metal side of the oxide film / matrix metal interface and removes the oxide film. N
As a cleaning solution used in the surface treatment of the iTi alloy, a mixed acid obtained by mixing hydrofluoric acid, nitric acid, and water in appropriate amounts is generally used (Japanese Patent Application Laid-Open No. 3-295562). Also,
As a pre-plating treatment for shape memory alloys,
Hydrofluoric acid 5%, nitric acid 20%, residual water (volume%) (hydrofluoric acid 3
A mixed acid of 0 g / l and 170 g / l of nitric acid is used (JP-A-62-188701).

[0004]

In recent years, a NiTiPd-based alloy having a composition in which Pd is added to NiTi has been researched and developed for the purpose of shape memory characteristics of a high-temperature operation type and superelasticity of a small stress hysteresis type (D, Golberf, Ya Xu, Y.Murakam
i, K.Otsuka, T.Ueki, H.Horikawa, Mater.Letters22 (1995)
241. Mitose, Ueki, Asai, Horikawa: Abstracts of Autumn Meeting of the Japan Institute of Metals (1996) 171). However, this NiTiP
Since the d-based alloy contains Pd, the ductility of the alloy is lower than that of the NiTi alloy. When the oxide film grows and increases in thickness during the manufacturing process of the NiTiPd-based alloy material, the cold ductility of the alloy further decreases. Therefore, in the NiTiPd-based alloy material, the removal of the oxide film during the manufacturing process is indispensable. is there.

However, the above-mentioned hydrofluoric acid 5%, nitric acid 20
In the case of a mixed acid (% by volume) consisting of% and the balance of water, the oxide film cannot be completely removed, or Ni and Ti are selectively etched to leave the metal Pd and cover the alloy surface. This Pd layer cannot be removed even if the pickling treatment is continuously performed, and may cause cracking or breakage during cold working.

The present invention has been made to solve such a problem, and a surface treatment method capable of sufficiently removing an oxide film formed on a surface of a shape memory alloy such as a NiTiPd-based or TiPd-based alloy. It is another object of the present invention to provide a method for producing an alloy having a good appearance in which defects during cold working caused by an oxide film are suppressed.

[0007]

That is, in the present invention, Ni is 0 to 49 atomic%, Ti is 48 to 52 atomic%, P
The d3~52 atomic% and comprising a balance impurities shape memory alloy, HF10~300g / l, HNO ₃ 400~900
A surface treatment method for a shape memory alloy, wherein the surface treatment is performed by pickling with a mixed acid containing g / l. In addition, the ingot of the shape memory alloy is subjected to a hot working step and a cold working step, and before, during or after the cold working step, a pickling treatment with a mixed acid having the composition is performed to manufacture a shape memory alloy. Provide a way. Surface roughness R after pickling treatment performed before or during the cold working step
When a is 1 μm or less, cracking and breakage in the subsequent cold working can be suppressed, which is preferable. Pickling of the shape memory alloy after cold working or the shape memory treated material with the above mixed acid results in a surface having a metallic luster and a good appearance.

[0008]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, the composition of a shape memory alloy to be pickled is Ni0-49 at%, T
i is 48 to 52 atomic%, Pd is 3 to 52 atomic%, and the balance is impurities. Ni may be 0 atomic%. Ni, Ti,
An alloy having a Pd composition in this range has excellent workability, and exhibits superelasticity with small stress hysteresis due to the addition of Pd. In particular, when Pd is set to 20 to 52 atomic%, an alloy having a high-temperature operation type shape memory characteristic is obtained. Also,
Cr, Fe, Co, Mn,
Elements such as V, Cu, and B may be added in small amounts.

In the present invention, HF 10 to 300 g / l, HN
O ₃ using mixed acid containing 400~900g / l. A mixed acid having an acid concentration in this range can sufficiently remove an oxide film at an appropriate reaction rate, and is relatively easy to handle. If the HF concentration is less than 10 g / l, the removal of the oxide film becomes insufficient, and if the HF concentration exceeds 300 g / l, the reaction rate increases, the surface corrosion becomes severe, and the surface irregularities become too large. On the other hand, if the HNO ₃ concentration is less than 400 g / l, the removal of the oxide film becomes insufficient, and the HNO ₃ concentration becomes 9 g / l.
If it exceeds 00 g / l, the reaction rate increases, the surface corrosion becomes severe, and the surface irregularities become too large.

The mechanism of removing the oxide film formed on the surface of the NiTiPd-based shape memory alloy by the action of the mixed acid is as follows. First, the base metal is melted, and the gas generated by the reaction at the time becomes bubbles and the alloy surface is removed. It is presumed that the oxide film is mechanically peeled off from the alloy surface when leaving. NiT
Among the bases of the iPd-based alloy, Pd is more noble than Ni or Ti, so that Pd remains undissolved at a conventional acid concentration, resulting in insufficient removal of an oxide film or Pd.
It seems that the d metal remained and covered the alloy surface, but if a mixed acid having the acid concentration specified in the present invention was used, it would sufficiently act on Pd, so that an oxide film covering the surface would be removed. It can be sufficiently removed.

In general, in a method of manufacturing an alloy material having superelasticity and shape memory properties, a cold working process is performed and work hardening is performed, and a shape memory process is performed at a temperature and for a time that does not cause recrystallization. ing. In this case, it is assumed that sufficient cold working is performed, and in order to sufficiently perform cold working, an alloy having an oxide film formed thereon is processed as a lubricant. However, if the oxide film is too thick, the workability of the alloy is reduced, or cracks or fractures may be caused.Before the cold working process, the pickling process is performed with a mixed acid having the composition described above during the cold working process. Unnecessary oxide film should be removed. In the shape memory alloy to which Pd is added, when the oxide film grows during the manufacturing process and the thickness increases, the cold ductility of the alloy further decreases. Therefore, the removal process of the oxide film during the manufacturing process is indispensable. .

The surface roughness Ra after the pickling treatment before and during the cold working step is preferably 1 μm or less. When the thickness is 1 μm or less, defects caused by an oxide film such as breakage of a workpiece during cold working can be suppressed, and a product can be efficiently produced.

Further, if the surface treatment of the present invention is applied to the finished cold-worked material after the cold-working step or the shape-memory treated material subjected to the heat treatment after the cold-working, an alloy material having a beautiful metallic luster is produced. I can do it.

[0014]

【Example】

(Examples 1-12) Composition _{Ni 44 Ti 50 Pd 6, Ni} 40 T
Hot working and cold drawing were performed on an alloy ingot of i ₅₀ Pd ₁₀ , Ni ₂₆ Ti ₂₅ Pd ₄₉ and Ti ₅₁ Pd ₄₉ to produce a wire having a wire diameter of about 1 mmφ. A black or brown oxide film was present on the surface of the wire. Hydrofluoric acid (5
0% aqueous solution, specific gravity 1.155), nitric acid (61% aqueous solution,
Using water, water was used to adjust several tens of ml of the cleaning liquid having the composition shown in Table 1 (for preparing the cleaning liquid of Example 3,
Nitric acid (70% aqueous solution, specific gravity 1.42) was used. The above-mentioned wire (length 10 to 30 m) was added to the mixed acid kept at room temperature.
m) was immersed. Usually, the washing liquid is 30 to 7 depending on the reaction heat.
Although the temperature rises to 0 ° C, when the reaction is slow or the reaction does not start, the solution is heated to 50 ° C or more, and the liquid temperature is adjusted to 50 to 80 ° C. In the case of this example, heating was performed. In the pickling treatment step, it is sufficient that the oxide film on the surface can be removed. The pickling temperature depends on the amount of the cleaning liquid and the weight of the wire to be cleaned.
There is no particular problem in the vicinity of the range of 0 to 80 ° C. as long as the required effect can be obtained, so that it is not necessary to control strictly. After 10 minutes of immersion, the wire was taken out of the mixed acid, washed with water, and the surface condition was observed. If the surface had a uniform metallic luster, the result was ○. If the oxide film was insufficiently removed and the oxide film remained, or the metal Pd remained. Those were marked as x. Table 1 shows the observation results.

[0015]

[Table 1] ** Hydrofluoric acid 5, nitric acid 20, water 75 (vol%) (the same mixing ratio as in JP-A-62-188701)

As shown in Table 1, the acid concentration was HF10-3.
An unnecessary oxide film was removed from the surface of the wire treated with the cleaning liquids 2, 5, and 7 to 9 using a mixed acid of 00 g / l and 400 to 900 g / l of HNO ₃ , and exhibited a metallic luster. However, the cleaning liquids 1, 3, 4, 6, 10 to 10 out of the range of the acid concentration in either the hydrofluoric acid concentration or the nitric acid concentration.
The surface of the wire treated in Step 12 did not show any reaction by the cleaning liquid, and the oxide film was not removed, or even though the oxide film could be removed, the black Pd layer remained or the metallic luster was reduced. Even though it was present, it was over-corroded.

As a reference example, a wire obtained by subjecting an alloy of the composition Ni ₅₀ Ti ₅₀ to which Pd was not added to the same processing as above was immersed in cleaning liquids 1 to 12, and the wire surface was observed. As a result, the wire that had been pickled using the cleaning liquids 2 to 12 other than the cleaning liquid 1 containing no hydrofluoric acid had the oxide film removed and exhibited a metallic luster.

Example 2 Composition Ni _42.5 Ti _50.0 Pd
_7.5 NiTiPd-based alloy was subjected to high-frequency melting and subjected to casting, hot working, and optional annealing treatment to produce a wire having a wire diameter of 3.6 mmφ. The surface of the obtained wire was covered with a black oxide film. The wire was cut into four pieces to obtain wires A to D. Using the same concentration of hydrofluoric acid, nitric acid and water as in Example 1, a hydrofluoric acid concentration of 33 g / l and a nitric acid concentration of 539 g / l
Was prepared. With this cleaning solution, wire A
When the wire B was pickled for 5 minutes and the wire C was pickled for 3 minutes, the surfaces of the wires A to C exhibited metallic luster.
A test piece having a length of about 20 mm was cut out from each wire, and the surface roughness Ra was measured. as a result,
Wire A was 1 μm or less, wire B was 2 μm, and wire C was 3 μm.

With respect to the wire D not subjected to the pickling treatment, a test piece having a length of 20 mm was cut out, and the washing liquid was added for 3 minutes while confirming that only the oxide film was removed as much as possible so that the metal substrate was not strongly attacked. Dipped to the extent.

Subsequently, the wires A to D were drawn to a wire diameter of 1 mmφ while being subjected to an annealing treatment as needed. Wire A could be drawn without any breakage. Wires B and C are 5mm before the wire diameter becomes 1mmφ.
20 times (/ 1 km). Wire D has a wire diameter of 1
Many disconnections occurred before the diameter became mmφ, and the productivity was extremely poor. Table 2 summarizes the surface roughness measured before wire drawing and the degree of disconnection during wire drawing.

[0021]

[Table 2] * Measured after 3 minutes of pickling to remove oxide film.

As described above, the surface roughness Ra of the workpiece is determined by cold working, for example, by pickling prior to wire drawing.
Is set to 1 μm or less, the possibility of a decrease in work efficiency due to disconnection or the like can be greatly reduced.

After the completion of the drawing, a part of the wires A and D was pickled with the above-mentioned cleaning solution for 5 minutes. As a result, the surfaces of the wires A and D were all removed from the oxide film and exhibited metallic luster. Subsequently, the wires A and D were observed with a microscope and the surface roughness Ra was measured. The surface of the wire D had many longitudinal scratches formed along the wire longitudinal direction and a large number of lateral scratches having a length of 50 to 100 μm formed in the circumferential direction of the wire, and the surface roughness Ra was 5 μm. Wire A
Although a small number of shallow lateral scratches having a length of several tens of μm or less were observed on the surface of, the overall surface was smoother than the wire D. The surface roughness Ra was 1.5 μm. In addition,
When the wire A was further subjected to pickling treatment with the above-mentioned cleaning solution for 5 minutes, the shallow lateral wound completely disappeared, and an extremely smooth surface was obtained. When the surface roughness Ra was measured, it was 1 μm or less. A 200 mm piece is cut out from the wire A in the drawn state, and held in a straight line for 45 mm.
After performing a memory heat treatment at 0 ° C. for 1 hour, the resultant was subjected to pickling treatment with the above-mentioned cleaning solution, whereby an oxide film on the surface was removed.
It became a shape memory wire exhibiting metallic luster.

[0024]

According to the surface treatment method of the present invention, the oxide film formed on the surface of the shape memory alloy can be sufficiently removed. Further, according to the production method of the present invention, it is possible to suppress defects during cold working of the NiTiPd-based alloy, which is poor in workability and is easily affected by an oxide film, due to the oxide film, and even to an extremely fine wire. Can be processed. Others
According to the production method of the present invention, it is possible to obtain a cold worked material or a shape memory treated material having a beautiful appearance.

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Claims (4)

[Claims] 1. A shape memory alloy composed of 0 to 49 atomic% of Ni, 48 to 52 atomic% of Ti, 3 to 52 atomic% of Pd, and the balance of impurities is HF of 10 to 300 g / l, HNO ₃ 400
A method for surface-treating a shape memory alloy, which comprises pickling with a mixed acid containing up to 900 g / l. 2. A hot working step and a cold working step are performed on an ingot of a shape memory alloy comprising 0 to 49 atomic% of Ni, 48 to 52 atomic% of Ti, 3 to 52 atomic% of Pd, and the balance of impurities. The method for producing a shape memory alloy according to claim 1, wherein the acid is pickled with a mixed acid before, during, or after the hot working step. 3. The method for producing a shape memory alloy according to claim 2, wherein the surface roughness Ra after at least one of the pickling treatments performed before or during the cold working step is 1 μm or less. . 4. The mixed acid according to claim 1, wherein the material after cold working of a shape memory alloy comprising 0 to 49 atomic% of Ni, 48 to 52 atomic% of Ti, and 3 to 52 atomic% of Pd and an impurity is added to the mixed acid according to claim 1. Manufacturing method of shape memory alloy.