JP6810939B2 - Cu-Sn-Si based superelastic alloy and its manufacturing method - Google Patents

Description

The present invention relates to a Cu—Sn—Si based superelastic alloy and a method for producing the same.

Conventionally, as alloys having shape memory characteristics, Ni—Ti alloys, Cu—Sn alloys, Cu—Zn—Al alloys, Cu—Zn—Sn alloys, Cu—Al—Ni alloys, Cu—Al Various alloys such as −Mn alloys are known (see, for example, Non-Patent Documents 1 and 2). Among them, Ni—Ti alloys show excellent shape memory effect (SME) and superelastic effect, and are also excellent in terms of repeat life, and are being put into practical use. However, Ni—Ti alloys have the problem of being expensive because they contain a large amount of Ti.

On the other hand, copper alloys such as Cu-Sn-based alloys, Cu-Zn-Al-based alloys, Cu-Zn-Sn-based alloys, Cu-Al-Ni-based alloys, and Cu-Al-Mn-based alloys should not contain Ti. It can be manufactured with inexpensive raw materials. These copper-based shape memory alloys have a matrix phase called a β phase (a phase having a crystal structure related to bcc) that is stable at high temperatures, and this matrix phase has a regular arrangement of alloying elements. There is. When this β phase is rapidly cooled to a metastable state near room temperature and further cooled, martensitic transformation occurs and the crystal structure changes instantly. The alloy exhibits a shape memory effect or a superelastic effect due to the martensitic transformation. However, although the raw materials of copper alloys as described above are inexpensive, the shape recovery rate is not as high as that of Ni—Ti alloys. For example, Cu—Sn-based alloys have a small recovery rate against deformation due to external force, low strength, and the transformation temperature changes significantly when left at a relatively low temperature near room temperature. No efforts have been made to put it into practical use other than research.

By the way, a copper alloy exhibiting stress-induced martensitic transformation, which undergoes reverse transformation in a high temperature range of about 500 to 700 ° C., has also been proposed. For example, in Patent Document 1 (International Publication No. 2017/16435), the basic alloy composition is Cu _{100- (x + y)} Sn _x Mn _y (8 ≦ x ≦ 16 and 2 ≦ y ≦ 10 in the formula). There is disclosed a copper alloy in which the βCuSn phase in which Mn is dissolved is the main phase, and the βCuSn phase is transformed into martensitic transformation by heat treatment or processing. Further, in Patent Document 2 is (WO 2017/164396), (wherein, a 8 ≦ x ≦ 12 and 8 ≦ y ≦ 9) basic alloy composition _{Cu 100- (x + y) Sn} x Al y There is disclosed a copper alloy having a βCuSn phase in which Al is dissolved as a main phase, and the βCuSn phase undergoing martensitic transformation by heat treatment or processing. These copper alloys show a high recovery rate in a high temperature range of 500 to 800 ° C. against deformation due to an external force.

International Publication No. 2017/1643495 International Publication No. 2017/1643496

Kazuhiko Tabei, "Material Properties and Applications of Copper Shape Memory Alloys", Journal of Textile Machinery Society, Vol.42, No.11 (1989), pp.587-593 C. M. Wayman, Translated by Tsuguo Yuiki, "Some Applications of Shape Memory Alloys", Bulletin of the Institute of Metals, 19 (1980), pp.323-332

However, the copper alloys disclosed in Patent Documents 1 and 2 are not intended to improve shape recovery at room temperature, and are used at room temperature for eyeglass frames, ingrown nail correction clips, valgus thumb correction devices, and the like. Not suitable for shape memory products. Therefore, a high-strength superelastic alloy that can be manufactured with an inexpensive raw material and exhibits high shape recovery at room temperature against deformation due to an external force is desired.

The present inventors have recently alloyed inexpensive raw materials Cu, Sn and Si with a predetermined composition to form a β-phase single phase, thereby exhibiting high shape recovery at room temperature against deformation due to an external force. We have obtained the finding that we can provide high-strength superelastic alloys.

Therefore, an object of the present invention is to provide a high-strength superelastic alloy that can be produced with an inexpensive raw material and exhibits high shape recovery at room temperature against deformation due to an external force.

According to one aspect of the present invention, it is composed of a β-phase single phase containing Sn: 9.0 to 15.0 at% and Si: 0.1 to 5.1 at%, and the balance is Cu and unavoidable impurities. Cu-Sn-Si based superelastic alloys are provided.

According to another aspect of the present invention, the method for producing a Cu—Sn—Si based superelastic alloy.
A step of obtaining a cast material by melting and casting a raw material containing Sn: 9.0 to 15.0 at% and Si: 0.1 to 5.1 at% and the balance being Cu and unavoidable impurities.
A step of homogenizing the cast material to form a β-phase single-phase,
A method for producing a Cu—Sn—Si based superelastic alloy including the above is provided.

It is a ternary phase equilibrium state diagram of the Cu-Sn-Si alloy obtained by the integrated thermodynamic calculation system (Thermo-Calc). It is a figure which shows the stress-strain curve of the Cu-12.6Sn-2.1Si alloy (Example 1) which was water-cooled after the homogenization treatment. It is a figure which shows the stress-strain curve of the Cu-12.6Sn-2.1Si alloy (Example 2) which was oil-cooled after the homogenization treatment. It is a figure which shows the stress-strain curve of the Cu-9.8Sn-4.5Si alloy (Example 3) which was water-cooled after the homogenization treatment. It is a figure which shows the stress-strain curve of the Cu-9.8Sn-4.5Si alloy (Example 4) which was oil-cooled after the homogenization treatment. It is a figure which shows the stress-strain curve of the Cu-8.8Sn-5.7Si alloy (Example 5) which was water-cooled after the homogenization treatment. It is a figure which shows the stress-strain curve of the Cu-8.8Sn-5.7Si alloy (Example 6) which was oil-cooled after the homogenization treatment. It is a figure which shows the stress-strain curve of the Cu-14.3 Sn alloy (Example 7) which was water-cooled after the homogenization treatment. Cu-12.6Sn-2.1Si alloy (Example 1), Cu-9.8Sn-4.5Si alloy (Example 3) and Cu-8.8Sn-5.7Si alloy (Example 5), which were water-cooled after the homogenization treatment. It is a figure which shows the XRD profile of). It is a figure which shows the XRD profile of the Cu-12.6Sn-2.1Si alloy (Example 1) which was water-cooled after the homogenization treatment, and the Cu-12.6Sn-2.1Si alloy (Example 2) which was oil-cooled after the homogenization treatment. ..

Cu-Sn-Si-based superelastic alloy The Cu-Sn-Si-based superelastic alloy of the present invention comprises a β-phase single phase. The β-phase single-phase contains Sn: 9.0 to 15.0 at% and Si: 0.1 to 5.1 at%, and the balance is Cu and unavoidable impurities. Stated differently, the alloy to β phase during _{Cu 100- (x + y) Sn} x Si y ( wherein the basic alloy composition except for the unavoidable impurities in atomic ratio, 9.0 ≦ x ≦ 15.0 And 0.1 ≦ y ≦ 5.1). By alloying Cu, Sn, and Si, which are inexpensive raw materials, with a predetermined composition to form a β-phase single phase, high-strength superelasticity that exhibits high shape recovery at room temperature against deformation due to external force. Alloys can be provided.

Si provides a function of suppressing plastic deformation in the Cu—Sn—Si-based superelastic alloy of the present invention. The Si content in the superelastic alloy of the present invention is 0.1 to 5.1 at%, preferably 0.1 to 4.1 at%, more preferably 1.1 to 3.1 at%, and particularly preferably 1.1 to 3.1 at%. It is 1.6 to 2.6 at%, for example 2.1 at%. With such a Si content, a β-phase single-phase is likely to be formed, and as a result, high shape recovery at room temperature is likely to be realized. In addition, since the amount of Cu as the balance increases, sufficient conductivity can be ensured.

Sn contributes to the shape memory effect by forming a βCuSn phase, which is a matrix phase, together with Cu. The Sn content in the superelastic alloy of the present invention is 9.0 to 15.0 at%, preferably 10.6 to 14.6 at%, more preferably 11.6 to 13.6 at%, and particularly preferably 11.6 to 13.6 at%. It is 12.1 to 13.1 at%, for example, 12.6 at%. With such a Sn content, a β-phase single-phase is likely to be formed, and as a result, high shape recovery at room temperature is likely to be realized. In addition, since the amount of Cu as the balance increases, sufficient conductivity can be ensured.

Therefore, the Cu—Sn—Si-based superelastic alloy of the present invention preferably has a Sn content of 12.6 at% and a Si content of 2.1 at%. That is, it is particularly preferable that the basic alloy composition excluding unavoidable impurities is Cu _85.3 Sn _12.6 Si _2.1 in terms of atomic number ratio.

The Cu-Sn-Si-based superelastic alloy of the present invention contains Cu and unavoidable impurities as a balance. That is, the superelastic alloy of the present invention is a Ti-free copper alloy, and therefore can be produced from a much cheaper raw material than a Ni—Ti alloy containing a large amount of expensive Ti. Examples of unavoidable impurities include Fe, Pb, Bi, Cd, Sb, S, As, Se and Te. The total amount of unavoidable impurities is preferably 0.5 at% or less, more preferably 0.2 at% or less, still more preferably 0.1 at% or less.

The Cu—Sn—Si-based superelastic alloy of the present invention comprises a β-phase single-phase. In this case, the β-phase single phase can be said to be the β-phase single phase of the Cu—Sn alloy in which Si is solid-solved. Therefore, it is desired that the Cu—Sn—Si based superelastic alloy of the present invention does not contain different phases such as α phase, δ phase and ε phase, or other components. The presence or absence of these different phases can be determined by whether or not peaks derived from different phases such as α phase, δ phase, and ε phase are detected in X-ray diffraction as described in Examples described later. However, a trace amount of different phase or other components may be contained to the extent that the characteristics derived from the β phase of the Cu—Sn—Si superelastic alloy according to the present invention are not deteriorated.

The Cu—Sn—Si-based superelastic alloy of the present invention can exhibit a superelastic effect at room temperature (also referred to as room temperature, for example, 25 ° C.). For example, in the three-point bending test described in Examples described later, when the residual strain shows a level of shape recovery of preferably 2.0% or less, more preferably 0.5% or less, it is considered to exhibit a superelastic effect. be able to.

Manufacturing Method The Cu—Sn—Si-based superelastic alloy of the present invention can be manufactured by sequentially performing a melt casting step and a homogenization step as described below.

(1) Melt-casting step First, a raw material giving the composition of the above-mentioned Cu—Sn—Si-based superelastic alloy is melt-cast to obtain a cast material. That is, as a raw material, a raw material containing Sn: 9.0 to 15.0 at% and Si: 0.1 to 5.1 at%, and the balance being Cu and unavoidable impurities, in other words, unavoidable impurities. (wherein, 9.0 ≦ x ≦ 15.0 and a 0.1 ≦ y ≦ 5.1) except the _{Cu 100- (x} + y) basic alloy composition in atomic ratio _Sn x Si _y raw material is It may be mixed and used. The raw material containing Cu, Sn and Si may contain at least one metal simple substance of Cu, Sn and Si, or may contain an alloy of two or more of these. The blending ratio of the raw materials may be adjusted according to the desired alloy composition. The dissolution method is not particularly limited, but the high-frequency dissolution method is preferable from the viewpoint of high efficiency. Further, as the dissolution method, it is preferable that oxidation is suppressed by a method that can be industrially used. For example, the casting step is preferably carried out in an inert atmosphere such as nitrogen, Ar, or vacuum in order to suppress oxidation of the casting material.

In melt casting, it is preferable to melt the raw material at a temperature of 800 to 1300 ° C. and then cool the raw material between 800 ° C. and 400 ° C. at a cooling rate of 50 to 500 ° C./sec. It is preferable that the cooling rate is as fast as possible within the above range in order to obtain a stable β phase. Examples of the cooling method include air cooling, oil cooling, water cooling and the like, and water cooling is preferable.

(2) Homogenization step Next, the cast material is homogenized to form a β-phase single phase. The homogenization treatment may be carried out by holding the cast material at a homogenization temperature capable of forming a β-phase single phase to obtain a homogenized material. The homogenization temperature is not particularly limited as long as it is a temperature at which the β-phase single phase is stably precipitated, but is typically 650 to 750 ° C., and more typically 680 to 720 ° C. The heating method is not particularly limited. The homogenization time is preferably 20 minutes to 48 hours, more preferably 30 minutes to 24 hours. The homogenization step is preferably carried out in an inert atmosphere such as nitrogen, Ar or vacuum in order to suppress the oxidation of the homogenizing material.

In the homogenization step, after the casting material is maintained at the homogenization temperature, the casting material is preferably rapidly cooled by water cooling, more preferably by ice water. Therefore, the cooling rate is desired to be fast enough to be achieved by water cooling (rather than oil cooling or air cooling), preferably 10 to 1000 ° C / sec, more preferably 100 to 1000 ° C / sec. By quenching in this way, a β-phase single-phase structure in which Si is solid-solved in the parent phase βCuSn single phase can be formed. By quenching with water cooling or a cooling rate equivalent to that as described above, it becomes easier to form a β phase single phase by avoiding the precipitation of α phase, δ phase or ε phase in the homogenizing material, and the homogenizing material becomes brittle. It becomes difficult to become difficult and workability is improved. Further, when casting an ingot having a size that can be used industrially, it is possible to avoid a heterogeneous structure due to a difference in cooling rate between the inside and the outside of the ingot.

The present invention will be described in more detail with reference to the following examples. In the following description, the composition notation of Cu-xSn-ySi (x and y are arbitrary numbers in the formula) means that each coefficient of Sn and Si means at% of each element, and Cu is the balance. means that it is, that is intended to mean the _{Cu 100-x-y Sn x} Si y a composition in terms of atomic ratio.

Example 1
A Cu—Sn—Si based alloy was prepared and evaluated by the following procedure.

(1) Determination of target composition Using an integrated thermodynamic calculation system (Thermo-Calc), a ternary phase equilibrium diagram of the Cu—Sn—Si alloy shown in FIG. 1 was computationally prepared. Thermo-Calc is a software that creates a phase equilibrium diagram by calculation based on the CALPHAD method, and by performing a regular solution approximation using the minimum experimental parameters on the database, the relationship between Gibbs energy, composition and temperature can be determined. It guides and draws a phase equilibrium diagram. With reference to the obtained phase equilibrium diagram, the target composition was Cu-12.6Sn-2.1Si, in which the constituent phase of the Cu-Sn-Si sample at 700 ° C. (973K) was a β-phase single phase.

(2) Sample preparation Pure Cu, pure Sn and Cu—Si mother alloy were weighed so as to have the target composition, and melt-cast while injecting Ar gas in a high-frequency melting furnace for the atmosphere. In melt casting, the raw material was melted at a temperature of 1000 to 1300 ° C., and then the raw material was cooled between 800 ° C. and 400 ° C. at a cooling rate of 50 to 500 ° C./sec. The sample thus obtained is vacuum-sealed in a quartz tube and held at 700 ° C. (973K) for 30 minutes using a muffle furnace to homogenize the sample by removing the cast structure of the sample by solidification. After the treatment), the sample was rapidly cooled (water-cooled) with ice water. The cooling rate of water cooling was estimated to be about 500 ° C./sec.

(3) Various evaluations The following evaluations were performed on the obtained alloy samples.

<X-ray diffraction (XRD)>
In order to identify the constituent phases of the alloy sample, an X-ray diffractometer (SmartLab, manufactured by Rigaku Co., Ltd.) was used to tube: Cu, tube voltage: 40 kV, tube current: 50 mA, measurement range: 10-90 °, sampling width. XRD analysis of the sample under the measurement conditions of 0.01 °, measurement speed: 40 ° / min, incident slit angle: 1/3 °, light receiving slit 1: 20.0 mm, and light receiving slit 2: 20.1 mm. The XRD profiles shown in FIGS. 9 and 10 were obtained. In the obtained XRD profile, a total of three peaks derived from the β phase are detected at the positions of 2θ = 42 °, 61 ° and 77 °, while peaks other than the above three peaks (for example, α phase, δ phase, etc.) are detected. Peaks derived from different phases such as ε phase) were not detected. From this, the alloy sample of this example was identified as β-phase single-phase as shown in Table 1.

<3-point bending test>
In order to evaluate the shape recovery (superelasticity) of the alloy sample at room temperature, a three-point bending test was performed at room temperature. First, a test piece having a length of 30 mm, a width of 5 mm, and a thickness of 0.3 mm was cut out from the alloy sample. The test piece was placed on two fulcrums (distance between fulcrums 20 mm) installed in the testing machine (manufactured by Shimadzu Corporation, AG-I). An indenter was applied to the center of the test piece (that is, the center between the fulcrums) to give a downward displacement at a load speed of 0.6 mm / min, and the direction was changed upward in the middle. During this time, the stress-strain curve was continuously recorded to obtain the stress-strain curve shown in FIG. When the obtained results were rated and evaluated according to the following criteria, it was judged to be evaluation A as shown in Table 1.
-Evaluation A: Excellent shape recovery and residual strain less than 1.0%-Evaluation B: Poor shape recovery and residual strain of 1.0% or more-Evaluation C: Sample during test Is broken

Example 2 (comparison)
After the homogenization treatment, samples were prepared and evaluated in the same manner as in Example 1 except that oil cooling was performed with silicon oil instead of water cooling. The cooling rate of oil cooling was estimated to be 2 ° C / sec. The results were as shown in Table 1, FIGS. 3 and 10.

Example 3 (comparison)
Samples were prepared and evaluated in the same manner as in Example 1 (water cooling) except that the target composition was Cu-9.8Sn-4.5Si. The results were as shown in Table 1, FIGS. 4 and 9.

Example 4 (comparison)
Samples were prepared and evaluated in the same manner as in Example 2 (oil cooling) except that the target composition was Cu-9.8Sn-4.5Si. The results were as shown in Table 1 and FIG.

Example 5 (comparison)
Samples were prepared and evaluated in the same manner as in Example 1 (water cooling) except that the target composition was Cu-8.8Sn-5.7Si. The results were as shown in Table 1, FIGS. 6 and 9.

Example 6 (comparison)
Samples were prepared and evaluated in the same manner as in Example 2 (oil cooling) except that the target composition was Cu-8.8Sn-5.7Si. The results were as shown in Table 1 and FIG.

Example 7 (comparison)
Samples were prepared and evaluated in the same manner as in Example 1 (water cooling) except that the target composition was Cu-14.3 Sn. The results were as shown in Table 1 and FIG.

As can be seen from the results shown in Table 1, the alloy sample of Example 1 which is a water-cooled product of Cu-12.6 Sn-2.1Si is composed of β-phase single-phase and has excellent shape recovery at room temperature (superelastic effect). showed that. On the other hand, when the Si content is higher than the composition of Example 1 as in Examples 3 to 6, different phases such as α phase, δ phase, and ε phase are precipitated as shown as impurities in the XRD profile, and the β phase is single phase. As a result, it did not show excellent shape recovery (superelastic effect). Further, even if the composition is the same as in Example 1, if the cooling rate after the homogenization treatment is slow as in oil cooling as in Example 2, different phases such as α phase, δ phase, and ε phase are added to the β phase main phase alloy. Precipitated and became non-β phase single phase, the alloy was brittle and did not show excellent shape recovery (superelasticity). Therefore, in the cooling after the homogenization treatment, it can be said that a cooling rate as fast as water cooling (preferably water cooling with ice water) is preferable.

Further, the maximum stress value (about 800 MPa) in the stress-strain curve of the alloy sample of Example 1 shown in FIG. 2 (water-cooled product of Cu-12.6 Sn-2.1Si) is the alloy of Example 7 shown in FIG. Since it is considerably higher than the maximum stress value (about 300 MPa) in the stress-strain curve of the sample (water-cooled product of Cu-14.3 Sn alloy), the alloy of Example 1 which is a water-cooled product of Cu-12.6 Sn-2.1Si. It can be seen that the sample has much higher strength than the conventional Cu—Sn-based alloy. Further, from the comparison of FIGS. 2 and 8, it can be seen that the alloy sample of Example 1 is superior in shape recovery (superelasticity) to the alloy sample of Example 7.

Claims (5)

Sn: 12.1-13.1 at% and Si: 1.6-2.6 at%, the balance is Cu and unavoidable impurities, consisting of β-phase single phase, Cu-Sn-Si superelastic Elastic alloy. The Cu—Sn—Si-based superelastic alloy according to claim 1 , wherein the Sn content is 12.6 at% and the Si content is 2.1 at%. The method for producing a Cu—Sn—Si-based superelastic alloy according to claim 1 or 2 .
A process of obtaining a cast material by melting and casting a raw material containing Sn: 12.1-13.1 at% and Si: 1.6 to 2.6 at%, the balance of which is Cu and unavoidable impurities.
A step of homogenizing the cast material to form a β-phase single-phase,
Only including, the homogenization treatment is, after holding the cast material to a temperature of 650 to 750 ° C., which comprises rapidly cooling by water cooling the the casting material, manufacturing method of the Cu-Sn-Si-based super-elastic alloy. The claim comprises that the melting casting melts the raw material at a temperature of 800 to 1300 ° C. and then cools the raw material between 800 ° C. and 400 ° C. at a cooling rate of 50 to 500 ° C./sec. The method according to 3 . The method according to claim 3 or 4 , wherein the quenching is performed using ice water.